A Guide to Subwoofers (Part II): Standing Waves & Room Modes

[Fors*]

Originally Posted by Big Daddy

And your wife hasn't forced you to sleep in the living room yet?

Where the set-up is located is in our family room(basement) and we have no living room, its a rancher and we converted the living room into a master bedroom, so we could have 3 bedrooms (one for each of the kids and our own.) Sending me to the "living room" would be sending me back down to the scene of the crime......so no suck "luck" being forced to sleep in the "living room".

[elninoloco7]

In the first posted pics of Good, Very Good, and Best subwoofer placement, i have tried all of those ways and more alternative ways, the BEST way for my roomsetup is....

However, i guess it all depends how ones room is set-up. My room is 22' wide and 19' long and my Projector screen (or viewing direction) is wide. Its a dedicated Theater Room so there are four walls inclosed into a rectangle.

However this is a darn good post Big-Daddy

[Big Daddy]

Originally Posted by elninoloco7

In the first posted pics of Good, Very Good, and Best subwoofer placement, i have tried all of those ways and more alternative ways, the BEST way for my roomsetup is....

However, i guess it all depends how ones room is set-up. My room is 22' wide and 19' long and my Projector screen (or viewing direction) is wide. Its a dedicated Theater Room so there are four walls inclosed into a rectangle.

However this is a darn good post Big-Daddy

Thank you for the compliment. A lot of work went into this thread. I am glad you found the optimal positioning in your room. Many people do not realize that placement is probably the most important factor in getting good bass sound in a small home theater room.

[Driver_King]

Originally Posted by Big Daddy

For maximum output, some experts suggest that you put a single subwoofer in a corner for maximum output and place a second one in a less reflective area to smooth out the response. You can use the “crawl around the room” technique as described above for determining the location of the second subwoofer, except in this case, look for the minimum amount of bass output.

Dr. Toole suggests that in a rectangular room you should put one subwoofer close to the front wall in the middle, and another subwoofer at the back of the room in the same relative position. THX recommends placing them in the middle of the left and right walls. Dr. Toole also recommends some equalization to flatten the bass response so that all the seats in the primary listening area hear solid and even bass.

Currently, I have my Elemental Designs A2-300 subwoofer near the middle of the front wall about 6" or so away from the wall. Similarly on the rear wall, I have my DIY subwoofer squeezed between a dresser and my nightstand about 3" away from the wall. The DIY sub is not completely aligned with the sub near the front wall. After reading the quoted section above, I saw some experts suggest that having one subwoofer along a less reflective area (the middle of the front wall for me) and then another subwoofer elsewhere in a corner would be the best. I can move my DIY subwoofer the the back right corner of my room beneath the right back surround speaker. Would I be better off moving the DIY subwoofer to the corner or leaving it in its current spot, which is also an ideal spot?

[Big Daddy]

Originally Posted by Driver_King

Currently, I have my Elemental Designs A2-300 subwoofer near the middle of the front wall about 6" or so away from the wall. Similarly on the rear wall, I have my DIY subwoofer squeezed between a dresser and my nightstand about 3" away from the wall. The DIY sub is not completely aligned with the sub near the front wall. After reading the quoted section above, I saw some experts suggest that having one subwoofer along a less reflective area (the middle of the front wall for me) and then another subwoofer elsewhere in a corner would be the best. I can move my DIY subwoofer the the back right corner of my room beneath the right back surround speaker. Would I be better off moving the DIY subwoofer to the corner or leaving it in its current spot, which is also an ideal spot?

Most experts believe the middle of the side walls or the middle of the front and rear walls are the best positions. However, rooms and the boundaries are different and your listening position also affects the performance of the subs. You can move the DIY sub to a corner and see what kind of results you will get. The corner is not exactly a less reflective area.

I have my two Hsu subwoofers in the middle of the side walls, the DIY subwoofer in the middle of the rear wall and the AA sub in the rear corner. I prefer to move it to the middle of the front wall, but there is absolutely no room. The results are very good and the bass is fairly even, but there is always the possibility of phase cancellations. Your next item on the agenda should be an equalizer like the Velodyne SMS-1.

Did I tell you that ED is building me a big box for my 15" DIY subwoofer?

[Driver_King]

Recently, I re-ran Audyssey do to some older settings that bottomed out the DIY's driver too fast since the settings were very old and were made when I calibrated the old DIY's subwoofer driver and old amplifier (which has since been replaced with a significantly better driver and amplifier). I found that to get results that are even remotely close to what they used to be, I've had to go through loads of settings and controls to try to get it back to where it was before. Before, I had extreme low end impact (10-30hz range used to be much more audible). Although I have much more headroom and a much more even frequency response, I think that the corner with the much improved settings and modifications will yield even lower frequency response and possibly better frequency response in the corner. I will try this. Will I need to make any settings modifications like phase if I move the sub to the corner?

[Driver_King]

Originally Posted by Big Daddy

Most experts believe the middle of the side walls or the middle of the front and rear walls are the best positions. However, rooms and the boundaries are different and your listening position also affects the performance of the subs. You can move the DIY sub to a corner and see what kind of results you will get. The corner is not exactly a less reflective area.

I have my two Hsu subwoofers in the middle of the side walls, the DIY subwoofer in the middle of the rear wall and the AA sub in the rear corner. I prefer to move it to the middle of the front wall, but there is absolutely no room. The results are very good and the bass is fairly even, but there is always the possibility of phase cancellations. Your next item on the agenda should be an equalizer like the Velodyne SMS-1.

Did I tell you that ED is building me a big box for my 15" DIY subwoofer?

Yeah, I saw that! Are they doing anything special for a coat or finish? Maybe you should have Elemental Designs send the enclosure to Brent for a special Mozambique finish first. I think you may $hit yourself once you drop that Titanic driver into the enclosure for the first time. An equalizer like the Velodyne or SVS would be awesome though.

[Big Daddy]

Originally Posted by Driver_King

Yeah, I saw that! Are they doing anything special for a coat or finish? Maybe you should have Elemental Designs send the enclosure to Brent for a special Mozambique finish first. I think you may $hit yourself once you drop that Titanic driver into the enclosure for the first time. An equalizer like the Velodyne or SVS would be awesome though.

The finish will be the standard matte finish, the corners will be rounded, and it will have rubber legs. The 28" depth scares the hell out of me. I am already thinking about building a riser with 5" casters and locks. I don't think I am in the mood to carry a big monster around. I already placed an order for the casters. I got them real cheap from a manufacturer in Massachusetts.

[Driver_King]

Originally Posted by Big Daddy

The 28" depth scares the hell out of me.

[Big Daddy]

Originally Posted by Driver_King

Recently, I re-ran Audyssey do to some older settings that bottomed out the DIY's driver too fast since the settings were very old and were made when I calibrated the old DIY's subwoofer driver and old amplifier (which has since been replaced with a significantly better driver and amplifier). I found that to get results that are even remotely close to what they used to be, I've had to go through loads of settings and controls to try to get it back to where it was before. Before, I had extreme low end impact (10-30hz range used to be much more audible). Although I have much more headroom and a much more even frequency response, I think that the corner with the much improved settings and modifications will yield even lower frequency response and possibly better frequency response in the corner. I will try this. Will I need to make any settings modifications like phase if I move the sub to the corner?

You will definitely need to adjust each sub separately. If you have an SPL meter, adjust the amp level of each sub first by turning off the other one so that each subwoofer gives you approximately the same level. You don't want one subwoofer to overpower the other one.

Next, you need to adjust the phase of either subwoofer to get the maximum output at your listening pposition.

After that, run Audyssey for multiple positions and tweak a little with an SPL meter.

[Driver_King]

Oh my god. Big Daddy, you are the man. I put the subwoofer in the corner and went to adjust some tone levels and settings to turn it the hell down! I was playing some Frequency Sweeps and started to sweat when it went down to the 10hz range!! I think the tuning of the DIY subwoofer is probably 16 or 17 hz with all of the Poly-fill in it. I can't believe what I'm hearing. I am truly terrified of the subwoofers now. Before, the bass was drowning out the other speakers and it was just too high for my tastes. Now I need to make sure to turn that volume down! I have been listening to music at well over 0dB on my system and going that high now will hurt your ears! Huge difference! I checked my SPL meter and I'm still averaging 75dB on the receiver test tone. I'm worried about tweaking any more right now because it might get better! I feel like Chevy Chase in National Lampoon's Christmas Vacation right now where he's on a rant about his boss.

[sterryo]

Question for B I G D A D D Y,
have you had a chance to read the followig article currently being linked from AVS Forum
http://www.hometoys.com/ezine/09.10/atlantic/index.htm

their take on sub placement is directly opposite of the research I've done (which supports the great data in this thread)

i was wondering what the master's take on this is?

[Big Daddy]

Originally Posted by sterryo

Question for B I G D A D D Y,
have you had a chance to read the followig article currently being linked from AVS Forum
http://www.hometoys.com/ezine/09.10/atlantic/index.htm

their take on sub placement is directly opposite of the research I've done (which supports the great data in this thread)

i was wondering what the master's take on this is?

There are some good points in that article that I agree with. For example, performance is room dependent and you need to experiment. Also, I agree with the fact that asymmetrically positioning a subwoofer may be a good idea. For example, in a rectangular or square room, the center of the room is the worst position for a subwoofer. Usually a corner is a good starting position. For most rectangular rooms, the subwoofer should be located at least 25 percent away from the corner walls to best avoid stimulating any of its first three harmonics.

I also agree that two subwoofers are much preferred to one subwoofer to even out the bass across the room for all listening positions.

Unfortunately, the article becomes a bit confusing and erratic when it starts dealing with positioning of two subwoofers. There are simple formulas in the original post that demonstrate how to calculate the axial (horizontal & vertical) room modes. Extensive research at the National Research Council of Canada and at Harmon International have recommended that the best position for two subwoofers is in the middle of side walls or the the middle of the front and rear walls.

[NoNic2]

Hello

I really like this article but can you explain how exactly do you mesure sub placemant relative to distance calculated. Most good subs are really large so for example my room lenght is 21ft so min (25% distance from first resonant mode) is 5.25ft. Now if my sub is 1.5 feet lenght front-fireing woofer do i calculate this 5.25ft min. from front wall to end of sub or actually to where woofer is as this is point where frenquencies are created? So in the end it wouldent be 5.25ft from wall but end of woofer would be 3.5ft from front wall. Soo is it to end box of sub or to woofer location ?

[JediFonger]

this post is just a work of art

i've read bits and pieces of all these information... but never one so concisely put together w/evidence and actual primary research! =).

you don't write for an AV magazine do u =P. you SHOULD!!! =). this is an easy article in HT or Widescreen or any of those mags =0.

[Big Daddy]

Originally Posted by JediFonger

this post is just a work of art

i've read bits and pieces of all these information... but never one so concisely put together w/evidence and actual primary research! =).

you don't write for an AV magazine do u =P. you SHOULD!!! =). this is an easy article in HT or Widescreen or any of those mags =0.

Thank you for your compliments. A lot of work went into post #1. I spent about two months writing it with all the documentations and diagrams.

I don't write for any AV magazines, but if you are offering me a job, I would consider it.

[MADNOD]

Dear BD,

happy new year,

i've been reading recently about some subs, (polk micro pro 4000), and some people are mentioning that they are "Quick" Subs and are musical and HT subs,

what does Quick mean when subscribing subs,

and what is the pre-requisit for a sub to be musical rather for HT or vice versa.

thanks in advance.

[Big Daddy]

Originally Posted by MADNOD

Dear BD,

happy new year,

i've been reading recently about some subs, (polk micro pro 4000), and some people are mentioning that they are "Quick" Subs and are musical and HT subs,

what does Quick mean when subscribing subs,

and what is the pre-requisit for a sub to be musical rather for HT or vice versa.

thanks in advance.

Happy new year to you.

Generally speaking, most people assume that smaller drivers are faster and larger drivers are slower. Furthermore, they assume that a sealed subwoofer is more musical than a ported subwoofer. Unfortunately, there are more myths than facts in the above assumptions. A good subwoofer can be effective in both music and HT applications at the same time.

What makes a subwoofer fast or slow (tight or loose) has to do with how quickly it starts and stops or its transient response. A 15" driver in a sealed cabinet will probably have a better transient response than a 10" in a ported cabinet. That is because the air behind the driver pushes the driver back in a sealed cabinet.

Another issue that deals with slow or fast bass has to do with the phase setting between the subwoofer and the rest of the speakers. If there is a lag at the crossover region, the bass will sound slow and out of step with the rest of the music. A lot of what is perceived as fast or slow is actually good or poor integration with the other speakers in your system.

An important factor that affects a driver's performance is the Q of the driver.

Qes: Electrical Q of the driver at Fs. Qes is a measure of the driver's tendency to resonate at Fs, based on its electrical characteristics, e.g. magnet strength, magnetic circuit characteristics, etc.). The driver's overall resonance characteristics are usually dominated by Qes.

Qms: Mechanical Q of the driver at Fs. Qms is a measure of the driver's tendency to resonate at Fs, based on its mechanical characteristics, e.g. surround compliance, the compliance of the spider, weight of the cone, etc.

Qts: Total Q of the driver at Fs. Qts is a measure of the driver's tendency to resonate at Fs, based on its overall characteristics. Qts can be calculated using the equation:

Qts= Qms*Qes/(Qms+Qes)

Qms, Qes, and Qts are measurements related to the control of a driver's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch each other as this would damage the driver. The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act as a shock absorber.

As a general rule, a driver with:

• Qts <= 0.4 is appropriate for a vented enclosure.
• 0.4 < Qts < 0.7 is recommended for a sealed enclosure.
• Qts >= 0.7 is usually used for infinite baffle applications.

There are some exceptions and some drivers such as the Eminence Kilomax 18 with a Qts of 0.56 can work well in a vented enclosure.

The total combined driver plus enclosure Q is dependent on the Theile/Small parameters of driver, volume of enclosure, and stuffing or deadening of the inside walls of the cabinet. A lower system Q can result in better system damping and transients. This can be achieved by either making the enclosure larger or by adding stuffing/damping material such as polyfill.

It is generally accepted that a speaker should be tuned so that its frequency response is as smooth and as extended as possible without any peaks and early roll-off. This in turn implies a Q of around 0.5 to 0.7 for the combined speaker and the enclosure.

When a driver is placed in a cabinet, the Q is raised. A small box raises the Q more, and a large box raises the Q less. For example, if a driver has a very low Q, a small box is more desirable to obtain an overall Q of 0.5.


Subwoofer Myths:
http://www.audiopulse.com/know-how/s...ut-subwoofers/

# 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.

[MADNOD]

thanks for the excellent and quick responce.

[Fors*]

BD, I tried a bunch of the links in the first post and also other links in other sticky's and couldn't find this really good article about the # of subwoofers and their locations from Todd Weiti of Harman International Industries, Inc. It is called Subwoofers: Optimum Number and Locations. I have a hard time believing that you haven't linked this somewhere, but I can't seem to find it. I am going to link it here, but if it is in this sticky or another, please let me know, thanks.