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Old 03-25-2008, 01:56 AM   #1
Big Daddy Big Daddy is offline
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Default A Guide to Subwoofers (Part I): Characteristics, Placement, & Adjustments

A GUIDE TO SUBWOOFERS

Prepared by Big Daddy


For multiple subwoofers, check A Guide to Subwoofers (Part II): Standing Waves & Room Modes and A Guide to Bass Management. For subwoofer problems, read DIY Subwoofers Building & Repairing thread.

Subwoofers are becoming more important to the home theater experience. They are designed for reproducing the lowest audio frequencies around 120Hz and lower. Not only are these low frequencies heard, but also they are felt.

Components of a Subwoofer Driver
The following diagram exhibits the cross-section of a subwoofer drive unit,
(http://www.ht-audio.com/pages/SpeakerBasics.html).



Subwoofers for home audio systems come in two basic types: powered (active) and unpowered (passive).

Active (Powered) Subwoofers
Powered subwoofers are by far the most popular, and generally the best option for most Home Theater applications. An active subwoofer is generally much more flexible. However, they do not necessarily sound the best. The simplest type of an active subwoofer would contain an amplifier, a crossover frequency control, a phase control, and some type of input connections. Since it contains an internal power amplifier, it will also need to be plugged into the wall power outlet.

The crossover frequency control allows you to set the range of frequencies that the subwoofer will reproduce and the frequencies it will filter out. The phase switch allows you to better integrate the subwoofer with the rest of the speakers in the system. It allows you to reverse the phase of the subwoofer’s audio signal. To set it properly, you’ll probably have to listen to it in both positions (0 and 180) to see which position creates the deepest bass in your home theater room. Finally, a powered subwoofer needs a line output from a receiver (or preamplifier).

Passive (Unpowered) Subwoofers
Passive subwoofers are designed to be powered by an external amplifier. The amplifier may be a dedicated amplifier (best option) or from the speaker terminals of the receiver. The important thing is that since a subwoofer needs more power to reproduce low frequency sound, the amplifier must be sufficiently powerful. In addition, if the subwoofer does not have a crossover frequency control, the signal to the subwoofer must be filtered by the receiver before it gets to the subwoofer. If the subwoofer has a a crossover network to filter out sound, it may also have output speaker terminals for the main or surround speakers.

For advantages and disadvantages bewteen active and passive subwoofers, check here.

Additional Subwoofer Characteristics
Auto on/off: This option allows the subwoofer to turn on when an input signal from the receiver or pre-amp is detected. The subwoofer will turn off in a few seconds or minutes (depending on the manufacturer) after there is no input.

Servo Feedback: Some advanced subwoofers may use a feedback signal from a device mounted on the speaker’s cone. The servo control unit compares the subwoofer’s output to the input signal and attempts to compensate for the driver’s output errors in order to smooth out distortion level. Unfortunately, this feedback circuit, no matter how quickly it works, cannot make the correction until after the error has occurred. As a result, the correction is always arriving at the subwoofer’s output with the next signal. Therefore, the correction is made on the wrong signal and it may compress the subwoofer’s transient response and remove its impact.

Down Firing: This type of subwoofer has the woofer installed in the bottom so that it fires toward the floor. Down-Firing subwoofers look like a piece of furniture (do not need a grill) and may be more efficient. It is important that these types of subwoofers are not placed in a corner too close to the walls as they may sound boomy.

Front Firing: This type of subwoofer has the woofer installed on the side and fires its output signal parallel to the floor. Front-Firing subwoofers need a grill to cover the woofer and look more like a speaker.

Sealed Enclosure: Originally this design was pioneered by companies like Acoustic Research. It consists of a driver mounted on one side of a sealed box. The air tight enclosure completely isolates the back wave of the driver from the front.

The sealed enclosure system is characterized by excellent transient response, excellent power handling at low frequencies, easy to design and build, smaller box size, and lower sensitivity to misaligned parameters when compared to port enclosure. However, sealed designs have a higher cutoff point and lower sensitivity than ported systems.

Because of excellent transient response (i.e., no boomy sound), when designed and build properly, some audiophiles prefer these type of subwoofers. There are others who completely dispute that sealed boxes have better transient response. They claim that the perception of transient is really a function of perceived sound quality and not the type of enclosure. According to these critics, what does improve transient response (or perceived quality) is usually more headroom, more drivers, larger boxes (depending on the driver), better efficiency, and very low distortion.

Ported Design: Some subwoofer enclosures may add an additional open port (sometimes called duct, vent, or tunnel) which allows the passage of air in and out of the box. At low frequencies, the port contributes up to +3dB to the output and makes the system more efficient and thus increases the bass response. A ported enclosure system consists of a driver mounted on one side of a box that has an open port (duct, vent, tunnel).



The ported subwoofers are characterized by lower distortion and higher power handling in the operating range, and lower cutoff frequency than a sealed enclosure system using the same driver. Distortion rapidly increases below the cutoff frequency however as the driver unloads and loses damping. Due to this, ported enclosures require a low frequency filter. The transient response of a ported enclosure is usually worse than a sealed enclosure system using the same driver. Ported enclosure systems are much more sensitive to misaligned parameters than sealed enclosure systems, which makes their construction more difficult.

Passive Radiator: Another type of subwoofer enclosure may add a passive radiator, instead of a port, to increase the efficiency of the sub. Passive radiators are sometimes drivers with the voice coil and magnet removed, or like a flat diaphragm. The radiator must usually be at least as large (or larger) than the driver in the enclosure.



Advantages of the passive radiator include the absence of port noise, and some audiophiles claim the radiator provides a better sounding bass than a ported enclosure. However, the cutoff (-3dB) frequency is slightly higher than ported design using the same driver.

Other Disadvantages include difficulty in tuning passive radiator designs as they have much higher mass than an equivalent port. In a port, the moving mass is comprised of the air in the port and the driver. The mass of the passive radiator, however, is high because it is the mass of the usually larger moving radiator plus the active driver. It is possible that when the powered subwoofer cone stops, the passive radiator's cone continues to move for a short period of time and may cause the powered driver cone itself to move after the signal has stopped. This so called "ping-pong" effect can cause distortion.

4th Order (Single Reflex) and 6th order (Dual Reflex) Bandpass Design: In a 4th Order Design the driver is completely buried in the enclosure and is mounted in a sealed chamber. It fires into a second ported chamber with the sound emanating from one or more ports.

These designs are very efficient within the operating bandwidth, with superior power handling, but generally can be very difficult to design and build. Companies like KEF helped pioneer this design.



The 6th Order Design was engineered and patented by Bose with their original AM-5 Acoustimass home speaker system.

This design is even more efficient than a single reflex bandpass, but with a compromise. Power handling within its frequency bandwidth is excellent, enabling these enclosures to play very loud. Transient response, however, is relatively poor, making them one of the most difficult enclosures to build and tune.

Size of the Driver: Subwoofers use the largest drivers (woofers) because they are responsible for moving the most air to create the lowest frequencies. Dropping down an octave in response requires four times as much output to maintain the same level. In general, the lower a speaker's resonance frequency, the lower the frequency reproducible by the speaker at a given level of distortion. Resonance frequency (denoted by Fs) is determined by a combination of the mass of the moving parts of the speaker (the cone, dust cap, voice coil, and former) and the compliance (i.e., flexibility) of the cone suspension (surround and spiders). Under normal conditions, we need a more powerful amplifier to drive a subwoofer. However, it is important to remember that you always want enough amplifier power to prevent clipping, but your main goal should be only to play the subwoofer at a level that blends with the rest of the system at any level.

The most popular sizes for subwoofers are 8", 10", 12", 15", or 18". Although an 18" subwoofer is capable of producing the lowest frequency bass at the highest volumes, a large driver is not necessarily the best option for optimum bass reproduction. Larger drivers are more difficult to control and tune. There are 10” subs on the market now that move as much air as some of the old 15” units. This is because the cone has a very large peak to peak excursion specification. It is important that the driver is designed correctly so that it stays in its linear range when moving this far. These subwoofers generally need a high power digital amplifier to make a long-throw woofer produce good performance in a small box.

Recommended Minimum Power for Subwoofers:
8" 50 watts
10" 75 watts
12" 100 watts
15" 150 watts
18" 250 watts

Room Size: For a smaller room, you can use subwoofers with smaller drivers. However, for bigger rooms, since there is more air volume for the subwoofer to pressurize, a 12" or 15" subwoofer is recommended. One of the biggest problems in home theater rooms is caused by standing waves. These are created when the wavelengths (or ½ or ¼ wavelengths) of certain frequencies coincide with one or more room dimensions. Standing waves cause certain frequencies to be reinforced and cancelled at different locations throughout the room. The effect of standing waves is to have areas of the room where bass is very boomy and others where there is no bass at all. An equalizer will do nothing to fix these problems. These problem frequencies are known as room modes.

Ideally, two or more subwoofers may be a better option than a super large one, and since low-frequency sounds are non-directional, a subwoofer can be placed anywhere in the room. Please refer to the subwoofer placement section below.

Magnetic Shielding: Most modern speakers are magnetically shielded. Unshielded speakers can distort the picture and shift the colors. If an unshielded speaker must be placed close to a TV because of room-size or furniture considerations, it is recommended that you put two sheets of solid galvanized steel, cut to size, between the speaker and the TV to block the harmful electro-magnetic fields. Please note that magnetic fields are a major problem for CRT (tube) TVs. However, LCD and Plasma TVs are not affected by them.

Port Plugs: Port foam plugs allow customizing the subwoofer to suit your taste and room. They give the option that favor either maximum SPL output, or lower frequency bass extension depending on source material and preference. With port plug removed and the Port Mode switch set for "maximum output," output levels increase to room shaking levels. When the port plugs are installed, and the Port Mode switch is set to "maximum extension," the subwoofer is re-tuned for linear response to lower frequencies at a slightly reduced maximum output.

With home theater systems, ports are left open. This tuning provides an increase in bass output which is more ideal for movies where explosions and other action sounds need greater impact. For music applications, one or more of the ports is/are blocked. This tunes the subwoofer for a flatter response with extended low frequency response. It will produce lower frequencies and do so more accurately.

Speaker Impedance and Sensitivity
Read Impedance & Sensitivity of a Speaker.

SUBWOOFER INSTALLATION AND ADJUSTMENT

Connecting the Subwoofer
If your receiver has a Subwoofer or LFE Output, run a standard RCA cable (RG6 cable is preferred) from the LFE Output on the receiver to the powered subwoofer’s LFE (Sub-In) input.

If your receiver does not have a Subwoofer or LFE Output, you can run two speaker wires from your receiver’s main speaker outputs to the subwoofer’s speaker inputs. Set the front speakers to Large and subwoofer to NO.

If your receiver does not have a Subwoofer or LFE output, but has an extra Pre-Outs, you can use a set of stereo RCA cables from the Pre-Outs of the receiver to the Left and Right Inputs on the powered subwoofer. In the receiver's menu, set the speakers corresponding to the Pre-Outs to Large.

Subwoofer Adjustment
Everyone wants the kind of bass they can feel, but what many people get is either weak or boomy bass. In some cases, they will have good bass at one seat location and little or no bass at other locations. Sometimes they try to crank up the subwoofer level to compensate for these deficiencies. Usually that makes the bass even more bloated and boomy. Sometimes it makes the amplifier clip or the subwoofer starts bottoming out.

A well-integrated subwoofer should not sound boomy. It should produce a deep and tight bass that blends with the main speakers. You should not be able to tell that the bass sound is coming from the subwoofer. This is particularly more important with music than movies.

Adjusting the Subwoofer Level
It is highly recommended that you use an SPL (Sound Pressure Level) meter to adjust the subwoofer level. If you do not have an SPL meter, use the built-in calibration program of your receiver or trust your ears. Read the Calibrating Your Audio with an SPL Meter thread.

Make sure you adjust the subwoofer channel level until you read the same number on the SPL meter (or hear the same level) as the main speakers. Because the low frequency sounds are very much room dependent, you should move around the listening area to get an average value.

For the most precise integration with your main speakers, go through test tones with an SPL meter. Setting the level using test tones by ear may result in misconfiguration. When you use the pink noise from your receiver to adjust the subwoofer level, you will not get accurate results. The main reason is that your calibration program or the SPL meter (if you are using one) measure the peak frequency generated by the sub at that listening position and all other frequencies are obscured. This is why it is best to use test tones and an SPL meter for a subwoofer calibration.

Using a test tone disc, adjust the volume so that the SPL meter reads 75dB with a 50Hz tone at the listening position. Do not play the test tones too loud as this may damage your speakers. Take measurements of four different tones 1/3 octave above 50Hz and four different tones 1/3 octave below the 50Hz. Average together each set of four measurements and adjust the subwoofer’s volume level to match the other speakers. Using the receiver's test tones is less accurate as they are not in one-third octave increments. Check the Using Test Tones thread.

Subwoofer Placement
Room acoustics and furniture have an enormous impact on the sound of speakers. A well placed subwoofer’s bass integrates with the sound of the main speakers and produces a natural reproduction of music. A few guidelines for subwoofer placement are listed below.

Corner placement: This is the advice that is given most often. Although corner placement will yield loud bass, it may make the music sound boomy. You should place your subwoofer in a corner only if it is not capable of producing deep bass. It is also important to note that corner placement will not always make the subwoofer boom. In most cases, it depends highly on the geometry of the room. According to some experts, you should always place a sub in a corner, and use equalization to deal with audible peaks of the subwoofer's frequency response at that position.

You should not sit against the wall: Your movies and music will sound heavy and tiring when you are sitting against a wall. If you must sit against the wall because of the room’s layout, turn down the volume of the subwoofer to compensate.

Do not place the subwoofer in a symmetrical position in the room: Avoid putting a subwoofer in a location that is the same distance from the walls. Subwoofers sound better if they are placed in a location where their distances to the front, side, and rear walls are different.

Put the subwoofer close to the main speakers: Even though bass sounds are not directional, you will get a better blending between the main speakers and the subwoofer if they are on the same side of the room.

Use
.

Two or more subwoofers are better than one: According to some experts, the way multiple subwoofers interact with the room is the single biggest factor in being able to get great bass in every seat of your home theater. Depending on your budget, you should use either two or four subwoofers. There is not much benefit from using more than four. Multiple subwoofers can reinforce each other’s bass response and will yield a smoother and more dynamic sound. If using multiple subwoofers, you must use identical subwoofers. Different models, even from the same manufacturer, may cause uneven response.

When using two subs, they can be placed in the front corners of the room close to the main speakers or one can be placed in the front and the other one in the rear. For even better bass and smoother frequency response throughout your home theater, use four subwoofers. As a starting point, put the four subs at the midpoints of each wall.



It is possible that you may still get some peak points, but they can be taken care of with a good parametric (not graphic) equalizer. The problem with graphic equalizers is that most of them do not have better than 1/3 octave resolution. Although they can be quite expensive, parametric equalizers can give you much better results.

Setting the Low Pass Crossover Frequency
It is helpful to read A Guide to Crossover Networks for a better understanding of how crossover filters work.

You need to set the crossover on the receiver’s menu and not the subwoofer. If your main front speakers are full-size with good bass response, set the low pass filter to 80Hz. If your main speakers are small, bookshelf, satellite, or in-wall, set the low pass filter in the 100 to 120Hz range. According to the Recording Academy recommendations, selecting a frequency between 80 and 100Hz will produce the best results.

Run the test tone generator for intervals between 30Hz to 200HZ and listen to the output level or measure it with an SPL meter. If different output levels are heard or read by the SPL meter for different frequencies, it is quite normal as different frequencies interact differently with the room acoustics. Increase or decrease the low-pass frequency to achieve the smoothest response. Decrease the crossover frequency if there is too much output around the crossover point, increase it if you notice a drop in the response.

In general, if the main speakers are large and capable of creating low frequency sound, it will be easier to match them with a subwoofer as opposed to the smaller speakers that most people own. However, it is not always best to set the crossover frequency at the lowest possible frequency to avoid the sonic signature of the subwoofer. If the crossover is set as low as possible, the subwoofer cannot stimulate the main speaker drivers near their resonance frequency, leaving only the main speakers as the dominant resonance contributor. If the crossover is set slightly higher, the bass from the subwoofer and the main speakers can reinforce one another resulting in a smoother and more pleasing bass.

Setting the Subwoofer’s Phase (Polarity)
When the woofer on the sub and the woofers of the front speakers move in and out in sync with each other, the system is said to be in phase. When the speakers and the subwoofer are moving out of sync with each other, the subwoofer and the front speakers’ bass overlap and cancel each other. In this case the system is said to be out of phase, resulting in less bass.

Unfortunately, there may be another problem between the main speakers and the subwoofer. If the main speakers are producing bass at the same time as the subwoofer, at some points the bass will reinforce each other. At other points the bass will cancel each other. The solution is to allow only the subwoofer to reproduce bass by setting the front speakers to small in the receiver’s setup menu. This can yield a smoother bass response throughout the entire room.

To get the best bass response, you should set the phase (polarity) of the subwoofer(s) to deliver the highest output at the listening position. This can be achieved with the help of a test signal at the crossover frequency and an SPL meter. You should run this test several times by changing the polarity of the subwoofer and measuring the bass response on the SPL meter. Select the phase option that results in the highest bass response. If you don’t have an SPL meter, you will have to trust your ears.

Fortunately, most subwoofers have a switch to change their polarity. If the subwoofer does not have a phase switch, you can change the polarity of the main speakers by switching the positive with the negative speaker wires (the black wire goes to the red terminal and the red wire to the black terminal). Some subwoofers have a “variable phase control”. This control can be set continuously between 0 and 180 and allows for a more precise phase control of the subwoofer.

When setting the subwoofer phase by ear, play some music (not a movie) that has a repetitive bass line. Switch the polarity several times and choose whichever setting sounds “faster” or “fuller”. If you do not hear any difference, leave the phase switch at “0" or “normal”.

If you are using two subwoofers, you have to position them properly and run the experiment mentioned above by adjusting the phase of one subwoofer and observing the result on the SPL meter. You may possibly have to set the phase of one of the subwoofers to 180.

Importance of Polarity (Phase)
The animation in the following shows two waves traveling in the same direction. The phase difference between the two waves varies with time so that we see constructive interference when maximum points are aligned (peak) and destructive interference when minimum and maximum points are aligned (null). This illustrates why it is important to adjust the subwoofer’s phase control with respect to the main speakers so that we obtain maximum output.


How to Check the Polarity of Speakers: Take the grill off a speaker. Apply a wire from the (-) terminal on the speaker to the (-) end of a AA battery. Then touch a wire from the (+) terminal on the speaker to the (+) end of the battery and look at the cone of the speaker. The speaker cone should move forward. If the cone moves backward, the speaker is wired out of phase. In some instances midrange drivers are intentionally wired out of phase with their woofers.

Repeat Everything Several Times
All the speaker adjustments are inter-dependent. Once you change something like polarity, you may have to go back and check the low-pass crossover frequency. Getting the optimum bass response from a subwoofer is a tricky business. There are no easy solutions. Don’t be afraid to experiment. If you hear differently than the SPL meter, trust your ears and not the meter. After all, we are not bats or dogs! To read about the hearing range differences between animals and humans, read the following: http://en.wikipedia.org/wiki/Hearing_range .


FREE TEST TONES

http://www.realtraps.com/test-cd.htm
http://www.cleansofts.com/softdownlo...Generator.html
http://www.nch.com.au/tonegen/index_b.html

MOVIES TO TEST SUBWOOFERS AND SPEAKERS

Check the following sites for a list of movies with good bass sound to test your subwoofer.
http://www.svsound.com/questions-faqs.cfm
http://www.avsforum.com/avs-vb/showthread.php?t=755493
http://forum.hsuresearch.com/archive...php/t-653.html
http://www.stealthsettings.com/woofe...fer-sound-test
http://www.realmofexcursion.com/downloads.htm
http://www.demo-world.eu/trailers/hi...n-trailers.php

SUBWOOFER REVIEWS

http://www.hometheatermag.com/subwoofers/
http://www.hifi-directory.com/new/on...-reviews/14083
http://reviews.cnet.com/4566-11312_7-0.html?tag=pm
http://hometheater.about.com/od/loud...er_Reviews.htm
http://www.audioholics.com/reviews/speakers/subwoofers
http://www.hometheaterhifi.com/subwoofers.html
http://www.audiovideoreview.com.au/S...subwoofers.htm
http://www.ultimateavmag.com/subwoofers/
http://home.comcast.net/~frank_carter/Nousaine.htm
http://www.hometheatershack.com/foru...rer-model.html
http://www.tweakcityaudio.com/forum/showthread.php?t=11
http://www.calibex.com/Home-Audio--z...x2zB7z5---html
http://www.avtalk.co.uk/forum/index....t=0&rid=0&SQ=0

ADDITIONAL INFORMATION AND REFERENCES

http://hometheater.about.com/cs/loud...subwoofera.htm
http://en.wikipedia.org/wiki/Subwoofer
http://www.bcae1.com/subwoofr.htm
http://www.polkaudio.com/homeaudio/p...al/subwoofers/
http://www.danmarx.org/audioinnovation/theories.html
http://www.aes.org/technical/documents/AESTD1001.pdf
http://www.bigpicturebigsound.com/article_560.shtml
http://www.ehow.com/how_2002139_trou....html?ref=fuel
http://www.ohmspeakers.com/speakerbasics.cfm
http://www.djsociety.org/Speaker_1.htm
http://www.grammy.com/PDFs/Recording...rs/5_1_Rec.pdf
http://www.ht-audio.com/pages/SpeakerBasics.html
http://www.diysubwoofers.org/
http://www.nolaspeakers.com/products/thunderbolt_b.php
http://www.audiopulse.com/know-how/s...ut-subwoofers/
http://www.soundstage.com/maxdb/maxdb200101.htm
http://www.tbisound.com/dsp_faqs.asp#myths
http://www.audioholics.com/tweaks/ge...udio-test-cd-2
http://www.hsuresearch.com/products/stf.pdf
http://ezinearticles.com/?How-to-Get...ater&id=114553
http://www.soundstage.com/entry11.htm
http://www.caraudiobook.com/car_audi...fer_system.htm
http://www.sunfire.com/pdf/Sunfire_S...Whitepaper.pdf

Last edited by Big Daddy; 02-06-2013 at 07:24 AM.
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Old 03-25-2008, 06:08 PM   #2
Deckard_9732 Deckard_9732 is offline
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Post Dual Powered Sub Setup

Thanks for the help! I should have my new sound meter & DVE blu-ray this Friday. I beleive my issue is with the my old analog meter and the DV lfe signal. As I mentioned the difference between VE & DVE (2dB) and Analog Meter (4dB) = 6dB which may account for my current sub settings. Again as I mentioned that my sub setup is as descibed in your sticky and is not boomy but just overpowering loud.
I will let you know what I find with my new Galaxy CM140 SPL & the new Digital Video Essentials - Blu-Ray.
Deckard_9732.....Blade Runner
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Old 03-25-2008, 06:21 PM   #3
un4gvn94538 un4gvn94538 is offline
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good informations. your on a roll!
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Old 03-25-2008, 07:08 PM   #4
dobyblue dobyblue is offline
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No subwoofer thread would be complete without the AV Talk tests!


http://www.avtalk.co.uk/forum/index....t=0&rid=0&SQ=0
The first thing I try to communicate to my crew is that there will be no shaky-cam and no rack zooms, because those techniques are only used to hide the fact that there is no energy. When you eliminate those gimmicks you’re confronted with the reality of the shot you have in front of you, and nine times out of 10 you say to yourself: “This just isn’t working.”
~Christopher McQuarrie (Director, Mission: Impossible - Rogue Nation)
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Old 03-25-2008, 07:38 PM   #5
Johk Johk is offline
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Well done!

Thank you for this user-friendly guide!
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Old 03-25-2008, 08:38 PM   #6
Big Daddy Big Daddy is offline
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Quote:
Originally Posted by dobyblue View Post
No subwoofer thread would be complete without the AV Talk tests!


http://www.avtalk.co.uk/forum/index....t=0&rid=0&SQ=0
Thank you. I will add your suggestion to the subwoofer reviews.
HT Room: Panasonic PT-AE8000, Epson 1080UB Proj., Mitsubishi 65" Diamond Series HD TV, Yamaha-RX-A3010 Rec., CinePro 6-Ch. Amp. (350 W/Ch, 8 Ohm), Proton D1200 Amp., Behringer EP4000 & EPX3000 Amps., Oppo BDP-83, Sony BDP-S790, Audio Technica Tuntable, Mitsubishi S-VHS, 2 Def. Tech. Super Towers w 15" subs, 1 Def. Tech. Center & 1 Martin-Logan Center, 2 Def. Tech. Surr. & 2 PSB Surr., 2 Cadence Presence, 2 Bose 901 Rears, 2 Modified HSU 12" Subs, 1 ED DIY 12" Sub, 1 ED DIY 15" Sub, Velodyne SMS-1 Subwoofer Equalizer, DirecTV HD, Monster HTS 5000 & APC H15 Power Conditioners.
Two-Channel Room: XiangSheng Tube Preamp., Carver TFM-45 Amp. (375 W/Ch), Behringer EPX4000 Amp., Onkyo CD player, Denon Turntable, Yamaha Tuner, 2 Vintage Polk RTA-15TL Speakers, 2 LCY 100 Super Tweeters, 2 DIY Folded Horn Super Towers with 15" Sub., 1 Modified AA HD-SUB12
Family Room: Mitsubishi 73" Diamond Series TV, Yamaha DSP-A3090 Rec., DirecTV HD-DVR, PS3, Zvox Speaker, 1 DIY 12" Sub.
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Old 03-25-2008, 08:54 PM   #7
hoogoosedmoose41 hoogoosedmoose41 is offline
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are plasma and LCD tvs affected by magnetic fields? that might be a worthwhile addition to your guide.

unfortunatly I have to use a less than ideal subplacement in my living room.
the only place I could put the sub in a corner is in the rear near my surround speakers. ( right now i have it up against the wall about midroom.
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Old 03-25-2008, 07:47 PM   #8
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Quote:
Corner placement: This is the advice that is given most often. Although corner placement will yield loud bass, it tends to make the music sound boomy. You should place your subwoofer in a corner only if it is not capable of producing deep bass. Putting a down-firing subwoofer in a corner is not a good idea.
I think this guide is excellent, but I do have an issue with just this one point. Corner placement will not always guarantee the sub will boom, it really depends highely on the geometry of the room itself, and where you are placed within it. It is quite likely you could place a sub in a corner, sit yourself in a low pressure zone like the middle of the room, and never hear a single resonant frequency from the sub. Corner placement will make a sub boom because it is exciting a room mode just like wind excites a resonant point when you blow over a bottle top. Corner placement excites all of your rooms modes, but it also supports low frequency output which is very important for keeping cone travel, and therefor distortion down. Corner placement will not make subwoofers that are deep bass deficent suddenly able to produce deep bass. All it will do is reinforce what bass it can produce.

According to Floyd Toole's research you should always place a sub in a corner, and use equalization to deal with audible peaks in the subs frequency response at that position. His theory is to place the sub where it performs the best, and equalize out the problems this placement causes. It doesn't make any difference whether the sub fires downward or outward, at the frequencies the sub covers, the wavelengths are so long it makes absolutely no difference what side the driver is on. Corner placement gives you additional output without any penalty on the subwoofer amp. Its free power that you can use to decrease distortion to both your driver and your sub amp directly.
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Old 03-25-2008, 08:21 PM   #9
helfdene helfdene is offline
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Which is the best woofer setting, LFE+Main or LFE?

I've got my crossover frequency set at 80Hz with LFE+Main enabled. After reading the above information, it seems that I may be getting some bass cancellation or reinforcement between 80Hz and 120Hz?

Should I switch to LFE only?

Thanks
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Old 03-25-2008, 08:37 PM   #10
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Quote:
Originally Posted by helfdene View Post
Which is the best woofer setting, LFE+Main or LFE?

I've got my crossover frequency set at 80Hz with LFE+Main enabled. After reading the above information, it seems that I may be getting some bass cancellation or reinforcement between 80Hz and 120Hz?

Should I switch to LFE only?

Thanks
Yes, normally you should set the speakers to small and and the LFE to LFE only (unless your speakers can handle low frequency and you have set the system properly so there is no cancellation)
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Old 03-25-2008, 08:23 PM   #11
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I have found that placing the subwoofor behind your seating position will work if you have tower speakers up front that have an extended low range. For example, I have a Hsu Research subwoofor 3 feet in front of the rear wall about 4 feet from the left side of the room. I have a pair of Klipsch Reference towers up front that already produce deep lows and are set to full range. Sound and Vision magazine put out a Sub Woofer annual issue back a few years ago and in it were a number of different set ups. I kept trying them till I found one that worked for me.
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Old 03-25-2008, 08:53 PM   #12
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Originally Posted by Snowgod View Post
I have found that placing the subwoofor behind your seating position will work if you have tower speakers up front that have an extended low range. For example, I have a Hsu Research subwoofor 3 feet in front of the rear wall about 4 feet from the left side of the room. I have a pair of Klipsch Reference towers up front that already produce deep lows and are set to full range. Sound and Vision magazine put out a Sub Woofer annual issue back a few years ago and in it were a number of different set ups. I kept trying them till I found one that worked for me.
There is no "one size fits all" solution for subwoofer placement. If you are getting good results, you are in good shape.
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Old 03-25-2008, 08:50 PM   #13
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Quote:
Originally Posted by Sir Terrence View Post
I think this guide is excellent, but I do have an issue with just this one point. Corner placement will not always guarantee the sub will boom, it really depends highely on the geometry of the room itself, and where you are placed within it. It is quite likely you could place a sub in a corner, sit yourself in a low pressure zone like the middle of the room, and never hear a single resonant frequency from the sub. Corner placement will make a sub boom because it is exciting a room mode just like wind excites a resonant point when you blow over a bottle top. Corner placement excites all of your rooms modes, but it also supports low frequency output which is very important for keeping cone travel, and therefor distortion down. Corner placement will not make subwoofers that are deep bass deficent suddenly able to produce deep bass. All it will do is reinforce what bass it can produce.

According to Floyd Toole's research you should always place a sub in a corner, and use equalization to deal with audible peaks in the subs frequency response at that position. His theory is to place the sub where it performs the best, and equalize out the problems this placement causes. It doesn't make any difference whether the sub fires downward or outward, at the frequencies the sub covers, the wavelengths are so long it makes absolutely no difference what side the driver is on. Corner placement gives you additional output without any penalty on the subwoofer amp. Its free power that you can use to decrease distortion to both your driver and your sub amp directly.
Thank you for your comments. I cannot disagree with you. I will try to modify the paragraph by adding a few additional clarifying statements. I would also like to state that in my experience, corner placement of large subwoofers in several different rooms have worked well with movies, but when I listen to high quality music, it tends to make the music a bit boomy and when I move it away from the walls, it works better. That is the reason why I said in my conclusion that "Getting the optimum bass response from a subwoofer is a tricky business. There are no easy solutions. Don’t be afraid to experiment".
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Old 03-25-2008, 09:00 PM   #14
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Quote:
Originally Posted by Big Daddy View Post
Thank you for your comments. I cannot disagree with you. I will try to modify the paragraph by adding a few additional clarifying statements. I would also like to state that in my experience, corner placement of large subwoofers in several different rooms have worked well with movies, but when I listen to high quality music, it tends to make the music a bit boomy and when I move it away from the walls, it works better. That is the reason why I said in my conclusion that "Getting the optimum bass response from a subwoofer is a tricky business. There are no easy solutions. Don’t be afraid to experiment".
Your last statement couldn't be more true. I be willing to bet the subwoofer that you moved into the corner and got a boomy sound from music was probably a ported subwoofer.
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Old 03-25-2008, 08:20 PM   #15
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Room Size: For a smaller room, you can use subwoofers with smaller drivers. However, for bigger rooms, since there is more air volume for the subwoofer to pressurize, a 12" or 15" subwoofer is recommended. Ideally, two subwoofers may be a better option than a super large one, and since low-frequency sounds are non-directional, a subwoofer can be placed anywhere in the room.


How do you connect two subwoofers to one LFE output. Is it as simple as using a Y cable? Does that degrade the signal any?
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Old 03-25-2008, 09:03 PM   #16
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Quote:
Originally Posted by NotMe View Post
Room Size: For a smaller room, you can use subwoofers with smaller drivers. However, for bigger rooms, since there is more air volume for the subwoofer to pressurize, a 12" or 15" subwoofer is recommended. Ideally, two subwoofers may be a better option than a super large one, and since low-frequency sounds are non-directional, a subwoofer can be placed anywhere in the room.


How do you connect two subwoofers to one LFE output. Is it as simple as using a Y cable? Does that degrade the signal any?
Yes, you can use a Y connection. Signal degrading for low frequency signal is insignificant. The benefit of two subs far outweighs any minimal signal degrading.

A few receivers have two output connections for subwoofers. I remember my old Yamaha receiver had that. For some passive older subwoofers, there were only speaker wire input connections. You had no choice but to connect them to the speaker output of the receiver (amplifier) just like your main speakers.
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Old 03-26-2008, 06:47 PM   #17
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Quote:
Originally Posted by Big Daddy View Post
Size of the Driver:

The most popular sizes for subwoofers are 8", 10", 12", or 15". Although a 15" subwoofer is capable of producing the lowest frequency bass at the highest volumes, a large driver is not necessarily the best option for optimum bass reproduction. The larger the driver, the slower the response to changes in bass frequencies. Large subwoofers create more boom for home theater applications, but they may not be able produce the tight bass needed for high-end music applications.
Likewise, I'd have to disagree with certain aspects of this too, again seeing point #8.
The first thing I try to communicate to my crew is that there will be no shaky-cam and no rack zooms, because those techniques are only used to hide the fact that there is no energy. When you eliminate those gimmicks you’re confronted with the reality of the shot you have in front of you, and nine times out of 10 you say to yourself: “This just isn’t working.”
~Christopher McQuarrie (Director, Mission: Impossible - Rogue Nation)

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Old 03-26-2008, 06:51 PM   #18
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Originally Posted by dobyblue View Post
Likewise, I'd have to disagree with certain aspects of this too, again seeing point #8.
For me, just the second part. The first part is cool.
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Old 03-26-2008, 06:57 PM   #19
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This is the full article from Audioquest, if their site comes back up, I'll remove the text and replace it with a link.

TOP SUBWOOFER MYTHS

Quote:
There are so many myths about subwoofers and their behavior that we decided to make a formal list to clarify what really goes on. With 15 years of practical design and engineering experience we have literally built everything in the high end audio book, so here are the facts from the fiction as we see it.

# 1 Subwoofers have an RMS rating
Speakers actually have a very complex thermal compression relationship and certainly can not be quantified by just one or two numbers typically called RMS and Program or Peak. Because voice coils in traditional drivers are inherently resistors, any amount of voltage generates some amount of heat which then adversely changes the resistance and properties of the speaker. This is the principle of thermal compression: As the voice coil heats up, the resistance changes and the efficiency and performance of the driver decrease until the point of maximum thermal compression. There are some unique types of materials that have a close to zero temperature coefficient and of course there is also superconducting metals that operate at subzero temperatures with no indications of any sort of resistance. In theory, only these types of materials would have no thermal compression, but they are not employed or very practical yet. Copper and Aluminum are still the two most widely used materials for voice coils. Both copper and aluminum heat up considerably and the resistance changes as a function temperature, and there lies the problem, therefore a discrete RMS scalar value is entirely inappropriate.
Under heavy use, the TSP parameters can shift as much as 35% and in a generally un-favored direction. (higher Qts, lower sensitivity). The common ultra high RMS ratings we see of large and expensive subwoofers are at best marketing ploys to make the driver seem far more worthy than it is, or in fact they are really intended to give the customer an idea of what type of amplifier to buy. The fact is, even the highest “RMS” rated subwoofers in the world in excess of 5 digit figures will begin to compress with far less power than you would ever image, try only a few hundred watts! (no joke!). Now this doesn’t mean you still don’t need lots of power to reach the maximum potential of the driver. As a rule of thumb, the amplifier should be much more capable than what the driver needs on average. For example, quick short bursts will produce huge SPL’s and the voice coil will not have time to heat up as much, but longer term high power use will result in considerable performance regression if not failure from glues giving way due to heat or differences in the thermal expansion of materials around the glues. Under heavy use thermal compression limits begin to play a large part in SPL but most people are oblivious to this concept. It is true that woofers can be used well into their thermal compression state, and typically that is what occurs. As the power increases linearity, the SPL does not increase linearly. This is some form of compression, usually thermally related unless the woofer is beyond or close to xmax. In an ideal non-compression circumstance of either power, BL or otherwise, you can expect a 3dB increase every time the power is doubled. Rarely does this ever occur, in extremely compressed and dangerous states it can be less than 1dB!
As a woofers reaches its very limits, unless failure occurs there will become a point where the resistance of the voice coil is rising faster than the power going into the subwoofer. When the resistance doubles as the power doubles then absolute thermal compression has set in. In practice you can’t actually increase the power from the amplifier because most amplifiers start to produce less power as the resistance increases because almost every car, home and pro audio amplifier is a constant voltage source rather than a constant current source. So in a way this phenomenon is a self limited occurrence that accidentally works to protect the driver. However, running the driver at or near the maximum thermal compression limit will likely result in rapid failure. Ultimately, thermal compression is a very large but unavoidable shortcoming of mass controlled transducers. Likely, compliance controlled transducers, or rather subsonic transducers are not limited by their thermal properties as much, but rather their compliance or linear limits (xmax). It is believed by a few experts in the field that thermal compression plays a much greater role in linearity and distortion than we know of, but it’s rarely discussed.

# 2 More xmax means more SPL
Subwoofer drivers really can be broken down in two categories: “Mass” controlled drivers and “compliance” controlled drivers. Mass controlled drivers tend to have low xmax and high sensitivity. These tend to be punchy and very loud and mostly used in live concerts for sound reinforcement or even car SPL competitions. Compliance controlled subwoofers which tend to be the majority of car audio subwoofers have high xmax, more weight, lower sensitivity, but more SPL in the lower frequency spectrum. Then there are of course hybrid drivers which are basically mixes of the two. Any driver in these categories can sound good or bad, but more important is being able to use the woofer where it performs the best. Using a low xmax woofer for subsonic content is probably not wise, likewise using a high xmax low sensitivity driver for sound reinforcement is not going to be very effective. In truth, there is no best driver and most drivers can overlap these zones with good results. We are not really used to the idea of a two way subwoofer, but as we demand more and more SPL and deeper bass, we may some day find that two different types of subwoofers used together are required to get the full reference SPL effect we all hunger for!
So yes, more specified xmax does mean more SPL but only for lower frequencies. Generally speaking, during lower frequencies, the driver tends to run out of usable throw (beyond xmax) before high thermal compression states occur and mechanical failure is a greater risk. 0-40Hz is primarily mechanical, 40-60 is in between) 60 and up is going to be more thermally limited. 0-20Hz is the subsonic content and in fact there are more efficient methods of producing bass in this spectrum rather than a regular piston based transducer. Surprisingly, even the largest drivers with high xmax and big voice coils can be bottomed out or run past a safe mechanical state with only a few hundred watts if the frequencies are low enough. Without a high pass (subsonic) filter, or in a low tuned system, bottoming out or breaking a driver could be a very real possibility without careful modeling and testing. The difference in displacement from 40Hz to 20Hz or rather half the frequency, or one octave, is quadruple! In the simple large sealed box example, that means if your woofer displacement is 1” peak to peak at 40Hz, you’ll bottom out just about anything in existence by the time you dip below 20Hz without protection.
Often times when people want more SPL, they really need higher sensitivity in the form of higher BL product or less moving mass, rather than more xmax because 50-60Hz is really what they are after. This is a very sensual frequency range for humans and much of the bass in music content exists in that frequency domain.

# 3 Subwoofers are fast / slow
More appropriately labeled Damping or Ringing, these concepts are really reciprocals of one another have nothing to do with speed, tightness, “boomieness” or any other misused and inappropriate term for subwoofers. Subwoofers, or rather bass drivers, all move at the same frequency when instructed to via an input single. The difference is really about the Q alignment of the system. There are many famous Q alignments which produce various frequency responses, but beyond the complex mathematics is a fundamental principal of force and acceleration and the driver will respond to a sinusoidal wave at various accelerations depending on the moving mass and force that the voice coil and motor generate on the cone. Therefore any driver can be faster or slower depending simply on the voltage! It makes little sense to call any driver faster or slower.
Damping or Ringing is really what we’re after and the amount of either is really a function of system volume along with the electro-mechanical damping factor of the driver. For example, in a sealed box system, as the volume of the cabinet becomes small, the internal pressures increase when the driver pushes in and out. This pressure is a force which, not nearly as strong as the electromotive damping force, works in the opposite direction. Contrary to intuition, higher internal pressure (which we tend to associate with tightness or stiffness) decreases damping and promotes ringing at one particular frequency (Fc in the case of a sealed box). The pressure from the air inside the box works against the driver’s natural damping factor of 1/(Qts). When the pressure becomes large relative to the motor’s damping factor, the driver will ring more and cause a peak in SPL at the given resonate frequency (Fc). This tends to be somewhere around 40-60Hz in a given sealed box, but could be outside that range under abnormal circumstances. This peak is ill desired and is accountable to the proclaimed “boomy” sounding subwoofers which tend to lack clarity, good transit response and dynamics. However some people prefer some ringing because it provides a natural boost in a very audible frequency band. Likewise, in a larger box, the Q will decrease and the ringing and SPL around that frequency will too, but the low end will open up and you’ll have more deep bass. This tends to sound better and more controlled.
On the flip side, over dampened drivers tend to have poor low frequency response and require equalization to boost the low frequencies. They tend to work better in vented boxes where their larger motor force factor (BL^2/Re) is put to good use with a resonator which then makes the low end much more efficient with its increased displacement. Likewise, drivers with high Qts will work better in sealed boxes and should be exempt from being used in a ported system without careful consideration. When high Q drivers are used in a vented system they will ring at the tuning frequency of the box (Fb in this case) and the “boomy” problem is considerably worse.

# 4 Ported boxes don’t sound as good as sealed
In most cases this is strictly a result of linear response vs non-linear response and it could go both ways. 4th order systems or “vented” boxes tend to be far more particular to volume, port size and length and the driver TPS’s rather than sealed systems. Misalignments are therefore amplified and greatly affect the frequency response. Often times in car audio, ported boxes are not tuned low enough, or the volume is too large and there is a large peak in the frequency response from literately too much sensitivity or SPL at a very narrow frequency band. The other issue is if the driver does not have enough BL or has too high of a Qts and becomes under damped at resonance. This again leads to drastic peaks at the resonating frequency; however in this case, the driver will be peaky there regardless of content and it will sound ultimately less dynamic and very bottom heavy. However, a well designed vented box may have considerably lower distortion and higher dynamics than a sealed box because of the added SPL gained from the port without increasing the active driver displacement requirements. Sealed systems evoke the most non-linear driver behavior to reach any given SPL, so in fact, they could be the worst sounding system if your SPL demands are considerable. It is important to model a ported design or ask the manufacture for a recommendation. It is also critical to include a high pass filter on the active driver in a ported box for protection.

# 5 Subwoofers care what they play
Your subwoofer driver does not have a conscience, and it does not perform better with one type of music over another. It’s just a driver. Good subwoofer systems will play all types of music or movie material very well. A bad subwoofer system may have a null or peak in the frequency response that may benefit some material over others but essentially this non-linear behavior is not ideal. It is true that movies have lower frequency content and perhaps more dynamic bass than music, especially with the recent compressed CD’s of the last 10 or so years, but a good system can be used for movies and music alike if it is indeed a “good” system.
It is also true that it tends to be more important to emphasize subsonic frequencies in the home theater environment versus the music environment where there is simply less emphasis on subsonic inaudible material. As a tradeoff, you can align a system to be more efficient above 30Hz or so. This trade off reduces the bandwidth but increases the SPL. Careful consideration should be taken to insure linear response is still maintained. It is very easy to have peaky bass with low Q drivers in high tuned ported systems. This is approaching the concept of basic SPL vehicles which use low Q, highly sensitive drivers tuned very high for very narrow but ferociously peaky response. Such systems are not very ideal for listing to music material of any kind. If you want your system louder, then it is better to add a second driver, more volume and more amplification, rather than tuning higher. It is important to understand that getting more SPL without compromise is never very cheap!

# 6 Sealed box can take more power than ported
There is some truth to this, and some myth, but as far as the thermal limits of the driver are concerned, it can’t take more power one way or another. However, in a sealed box the driver will require more power to reach the same SPL as the frequency range lowers. A ported system is simply more efficient so it wont need as much power to reach the same SPL. Based on the mechanical limits of a driver, different frequencies can take different power loads. At higher frequencies, driver can be pushed hard and won’t necessarily be in a mechanical-risk state. However the driver tends to be in a higher thermal compression state and could be thermally at risk. This is true for both ported and sealed boxes. However, for lower frequencies, the sealed box also acts as a filter in a way because the internal air pressure prevents the driver from over excursion. In a sealed box, the compliance of the suspension system almost always forgoes that of the air spring system unless the box is very large. In a vented box, there is no pressure to protect the driver and furthermore, when the system unloads below resonance, the active driver’s excursion increases exponentially and a high pass (subsonic) filter is critical to prevent mechanical failure.

# 7 Sensitivity does not matter for subwoofers
Sensitivity is indeed very important for subwoofers. Not all frequencies are limited by xmax. In fact, most of the bass frequencies for music are really limited by sensitivity or more accurately BL product and moving mass, but not by maximum driver displacement. Higher sensitivity means more SPL and ultimately better performance especially for upper bass punch or kick such as a “kick drum” which resonates at 63Hz. In fact, all good SPL competition drivers need to have high sensitivity not xmax!
There are several standards for sensitivity. SPL at 2.83 volts or SPL at one watt. The SPL at one watt is the more accurate number as 2.83 volts could correlate to more than 1 watt which would not be relatively appropriate to go by. Also sensitivity is a function of, in part, the driver’s cone area which is never quite explicit and could be exaggerated slightly. Ultimately as engineers, we do strive for high sensitivity because not all bass resides in subsonic domain and many good sounding subwoofers are in fact good because they have great sensitivity and not necessarily high xmax.

# 9 I can compare two drivers using the same box
What you will find is primarily how different TSP’s work in different boxes. And the differences usually observed are of course differences in TPS’s with a given system, rather than performance. The best way to compare two drivers is to make two different systems based on the driver itself and ensure that the frequency responses are linear to the range you desire, and then compare those two systems in terms of dynamic headroom, SPL and distortion. Simply saying one system is “louder” or “deeper” in the same box is inappropriate. In one case it could be a something as simple as an under dampened driver ringing a lot more than an over dampened one at resonance causing a larger peak in low frequencies throughout. It does not mean it’s louder or deeper or better outright, it is simply non-linear, and all bets are off. Proper enclosure deigns and/or EQ should be used for any system.

#10 cone material affects the sound
For low frequencies, the cone on a driver makes no difference in the sound whatsoever. The only possible affect it could have is in the case of a metal cone or very stiff composite cone that resonates at a high frequencies and buzzes. However this frequency would be up around 1000 to 2000Hz: Well beyond a bass driver’s usable limits.
Various cone materials are used for various purposes. Some cones, such as composite core with fiberglass or carbon fiber skins are extremely light and very stiff, especially when pressed with epoxy. Other cones such as aluminum provide excellent thermal cooling to decrease voice coil operating temperatures when the heat is conducted though the (if possible) conductive former. The cones job is to push air, not break, and ideally not be too heavy (easier said that done). But they don’t change the tone, pitch or timbre of a subwoofer system whatsoever. Anyone who tells you otherwise is probably hearing differences in the motor distortion, likely related to BL, compliance or other non-linear distortions not relating to the cone.

#11 bigger magnet means more magnetic force
The motor is essentially the steel and magnets on the bottom of the driver. Its job to create a magnetic circuit that has an air gap where flux lines cross in one direction so that a coil can rest in this field and carry current which then produces a force up and down and moves the piston to create SPL. The force that this motor creates is dependent on the amount of power or rather current inside the conductor F = B*L*I. So we need a more intuitive understanding of how a motor affects a driver’s performance without considering how much current it receives. This is the simple concept of “force factor”. Larger motors will ideally have higher force factors, but this number not only affected by the motor, its affected by the voice coil size, length, distance to the motor (gap) and conductive martial used too. The end result is in fact the BL squared divided by Re (resistance of the vc). This is literally Newtons squared per watt and is called the force factor. The higher the number, the more efficient the motor voice coil combination is and the more performance you get out of the motor.
BL, one of the many TS parameters you are probably somewhat familiar with. It is literally the magnetic field “B” crossed with the conductor length “L.” L does not in fact depend on the number of turns on the voice coil, but rather the actual cross section area of the coil itself which is inside the gap. While force factor is entirely important for any high performance driver, one should also consider the moving mass. A 600 horse power engine in a semi truck is pretty typical, but in a sports car it’s certainly something to gloat about. Together, the force factor, moving mass and the piston area account for sensitivity. This number is very important even for subwoofers, especially for frequencies above ~60Hz.

#12 Double bass kick, only good sounding drivers can do it
We have all heard that only good “SQ” drivers can do double bass kick because they have good transient response or something to that extent. This is really nothing more than linear frequency response and lack of ring. If high Q subwoofers are in small boxes or if low Q subwoofers are in large ported boxes, the frequency response of the system will likely be greatly non-linear. This non-linear response compromises relative SPL and can drown out certain sounds and frequencies. Room acoustics can also do the same thing. The same subwoofer may sound completely different in another room simply because there could be poor coupling and non-linear frequency response as a result of standing waves and peaks in the response curve. A peak at 80Hz may make for a rather anemic 60Hz response, and while 60Hz appears to be the problem, it’s actually from the nonlinear response else where! The bottom line is “double bass kicks” are usually not a function of the driver or driver’s performance but rather the system design, linear frequency and room equalization.
Often times people associate double bass as something to do with speed and only good drivers are fast. Believe it or not, even the largest and heaviest drivers, have no problem producing low frequencies, even 300Hz is a relatively slow long wavelength with a slow impulse time. Subwoofers are in fact MUCH faster than you would expect. Bottom line is, the lack of double bass, within the working limits of a driver, is not a problem with the driver so much as it is probably a problem with the system design, room and/or EQ settings.

#13 Transient response is better with sealed boxes
The fact is “transient response” is truly misleading and probably entirely unimportant at least for low frequency response. What people hear is really a function of the linear frequency response and distortion. It is often accepted that transient is a function of timing, but our ability to hear differences of a few milliseconds of low frequencies is quite negligible which is why the low frequency group delay of a 4th order system is quite unimportant next to the sensitivity advantages provided. Transient does not exclusively depend on sealed or ported designs, high Q, low Q, in fact, even drivers with high inductance don’t outright suffer from “transient response” insofar as we can physically distinguish certain sporadic behaviors because within their working range, they may be very efficient and dynamic. The fact is, what makes bass indeed bass, are long wavelengths that take considerable time to pass our ears. The perception of transient is really a function of perceived sound quality and there is really not appropriate example for good “transient response”. We as humans hear two things, distortion and SPL, and in the end that’s really want matters. What does improve “transient” response or perceived quality is usually more headroom, more drivers (usually larger boxes depending on the Qts of the driver), better efficiency and ultra low distortion within the prescribed limits of the system or drivers within the system. Sealed systems in fact don’t offer better transient response no more than ported even with their lower group delay tendencies, at least to human ears!

#14 It’s a bigger driver, then I need a bigger amp
Often times larger drivers require less amplification, that’s sort of the idea. The concept of bigger woofers need more power is not always true and plays right into the ever progressing misconception of car audio. What you should consider is the efficiency of the subwoofer. Efficiency will literally tell you how much acoustic output you will get given an amount of power (assuming linear limits of course). If the driver is bigger, has a larger motor and has a higher sensitivity, there is no mystery about it, you are going to get more SPL with the same amplifier provided the impedance is similar and the amplifier can produce high voltage at impedance peaks when the driver naturally draws very little current for a narrow range. If a driver is more efficient and has a larger voice coil, well you just got your cake and you can now eat it. Not only will it be louder, but it will have less thermal compression and ultimately more sound provided all else is equal (but such is not usually not the case). It’s often difficult to make voice coils larger and increase sensitivity too. This usually requires very large motors and expense. Sensitivity is most easily achieved by weight reduction usually from the cone surround and voice coil. Sensitivity is often a trade off of xmax and thermal compression limits.
However there are many larger drivers that don’t have ultra high sensitivity. A good pro audio subwoofer may have 6 to 10dB higher sensitivity over an average high excursion car audio subwoofer. That advantage makes them very capable with quite a bit less power at least for their frequency range which is usually above 40Hz. Likewise, SPL drivers ironically enough don’t need much power either! Let me repeat. True SPL drivers ironically enough don’t need much power! That’s because they are used in the higher frequency domain not limited by displacement and generally have great sensitivity numbers. They need this in order to get the excursion and ultimately SPL they need to win contests. High sensitivity and lots of power means lots of SPL provided the driver is still reasonably linear and does not physically break of course. Note: Strictly for SPL contest, drivers are normally burped at Fc (system resonance) which is the point of maximum current draw and minimum active driver displacement which is why excessive power must be used. Do not confuse that requirement with the much lower power requirements for sound reproduction outside that single SPL frequency. It’s important you know the TSP’s of the driver you buy, otherwise it could be the wrong driver for you! Who buys a car without knowing the horsepower? Just because a driver big and the manufacture claims pie in the sky RMS numbers doesn’t mean a thing!

#15 Neodymium will lose its strength with heat
Of course it will, and so will ceramic motors too, but the fact is, under even extreme operating conditions, it’s not likely the motor will ever reach these temperatures. There is just too much steel to absorb the heat from the voice coil in almost any practical case. In practice, gradual demagnetization due to use simply does not occur. We have been making high power neodymium based drivers for many years now and we have never once measured a discernible number from heat.
While Neodymium is nearly 10 times as strong as a similar sized ceramic magnets, it can cost up to 50 times too which is almost exclusively why it is not used often. Also, traditional overhung motors, which account for more than 95% of all car audio designs, can get everything they need out of a ceramic magnet assembly and stronger neodymium would be perhaps unnecessary. If we could use neo more, we would, but because it’s a patented martial, it’s just not economically practical for most designs. Furthermore, in order the magnetize neodymium, A magnetizer with over twice as much power and energy needs to be used. Many manufactures lack the capabilities of even magnetizing neodymium, so it becomes impractical to not only use it, but to manufacture.

#16 Its all about maximum displacement
A DIY’er favorite statistic, displacement / dollars. If you’re considering any bass above 40Hz then throw it out the door right now. Often times people assume that simply because one or more drivers have more maximum displacement over another type of woofer, than they will ultimately be the better performer(s). In many cases this is true, but it’s not true in general. Displacement alone does not guarantee SPL. In fact, SPL depends on not only displacement, but frequency range, sensitivity, box size, and BL product too. This is simply a matter of converting energy into acoustic sound pressure level and different devices work more efficiently than others for different frequency ranges. For subwoofers, it is generally accepted that BL product is the dominate factor that accounts for much of the performance or rather system efficiency, especially in a bass reflex or more complex system where there is a lot of air mass to displace. But keep in mind, depending on the type of system, size, frequency range, power and thermal limits, there may be even more critical and dependent variables that determine the overall performance of a system. None the less, high displacement is usually a good indicator that the subwoofer can excel in deep bass SPL. Of course there are other factors to consider depending on the system of system.
The first thing I try to communicate to my crew is that there will be no shaky-cam and no rack zooms, because those techniques are only used to hide the fact that there is no energy. When you eliminate those gimmicks you’re confronted with the reality of the shot you have in front of you, and nine times out of 10 you say to yourself: “This just isn’t working.”
~Christopher McQuarrie (Director, Mission: Impossible - Rogue Nation)

Last edited by dobyblue; 03-26-2008 at 07:09 PM.
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Old 03-27-2008, 09:15 PM   #20
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I added more content and made some changes to the original post (#1). More to come soon.
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