Frequency Response of Speakers/Subwoofers

[Big Daddy]

Please post the frequency response of your speakers and subwoofers in this thread. Thank you.

FREQUENCY RESPONSE OF SPEAKERS/SUBWOOFERS

If you made a recording of all the frequency test tones at the same volume and played that recording through a speaker, you would want all the tones to come out at the same volume. That is how we measure frequency response of speakers. We run a wide range of test tones through the speaker in a room with no reflections (anechoic chamber). A calibrated microphone is placed in front of the speaker and feeds the speaker's output into a machine that plots the amplitude (dB) versus frequency (Hz). It is desirable that the speaker can play the various frequencies with no variation in intensity. A perfect speaker is one with a perfectly flat frequency response with zero variation in loudness or intensity of various frequencies. For example, 20Hz to 20,000Hz with zero variation.

Since the middle frequencies are usually the best behaved, a frequency of 1000Hz (1kHz) is usually taken as the reference point, and the maximum deviation from that level is measured. In fact, speakers' sensitivities are measured by feeding 1 watt of a 1,000Hz frequency tone into a speaker and measuring its response at one meter.

But speakers are not perfect. Some tones may play softer or louder than others. These variations in a speaker's output is measured in decibels. Decibel is a measure of sound level. A 1dB difference in output is barely noticeable. A difference of 3dB is a lot more noticeable. We perceive a difference of 10dB as "twice as loud," or "half as loud". A frequency response that has a ±3dB associated with it means that the level never varies by more than 3 decibels above or below that at 1kHz.

Frequency Response: 56.5 Hz - 12.5k Hz (+/- 3dB)



Frequency Response: 40.0 Hz - 16.5k Hz (+/- 6dB)

In practice, we do not live in an anechoic chamber. We can equalize the frequency response of a speaker/subwoofer in our HT room to get a flat curve. Lowering a peak is much easier than increasing the level of a dip. That is why we are more concerned with -3dB.

Please remember that the +/-3dB measures the flatness of the frequency response and does not tell us anything about the quality of the sound that we hear. Two speakers with exactly the same +/-3dB response do not sound the same.

Generally speaking, loudspeakers have a much more difficult time to reproduce bass frequencies in an anechoic chamber. The intensity of these frequencies may drop by -6dB or more. Furthermore, our ears are less sensitive to bass frequencies as they are to midrange sounds and we will not be able to hear these dropped bass frequencies. That is the reason manufacturers report the frequencies of their speakers in the +/- 3dB range.

The frequency response of a speaker changes in a home theater room and in particular the bass frequencies are helped quite a bit by "room gain". That is why we need equalization.

INTERPRETATION OF FREQUENCY RESPONSE

The sound quality of a speaker cannot completely be quantified. Frequency response, sensitivity, timbre, type of drivers, type of cabinet, cabinet damping, etc. etc., etc. play a role. Although we can make two speakers sound alike in an anechoic chamber, in a home theater room, it is not unusual for the right front speaker and the left front speaker to sound differently depending on their position in the room.

Look at these three speakers. All three have relatively the same frequency response of 20Hz-20kHz +/-3dB, but they don't sound the same.

Speaker C will have the so-called one-note bass and will make the voices and some musical instruments a bit unnatural. Speaker D has smoother amplitude variations and sounds a bit more natural. Speaker C has the rapid changes in amplitude and experience has shown that these types of speakers are less pleasing and more fatiguing. Based on frequency response, speaker D is preferred to speaker C.

Speaker E also has relatively large amplitude variation, but it demonstrates a much smoother response curve. It will sound more natural and pleasing even though the bandwith of frequency variation is large (+6dB). Speaker E will have rich bass, good treble, and relatively laid-back midrange. Despite its inadequacies, some people may prefer speaker E.

THE EFFECT OF SCALE ON THE SMOOTHNESS OF THE FREQUENCY RESPONSE CRUVE

It is important to note that the scale chosen for the Y axis can have a significant effect on the shape of the curve and can easily mislead the casual observer. The following 3 diagrams represent exactly the same frequency response. However, the scale of the Y axis has been changed. The first diagram gives the impression that the frequency curve is very volatile. The second diagram, on the other hand, gives the opposite impression and the third diagram is the intermediate case. In most cases, a 30 to 40 dB difference from top to bottom on the Y axis as in diagram 3 should be used so as not to mislead people.

WATERFALL GRAPHS AND THEIR MEANING

http://www.realtraps.com/art_etf.htm
http://www.hometheatershack.com/foru...aterfalls.html


FREQUENCY RESPONSE OF SUBWOOFERS

As far as subwoofers are concerned, they are expected to play the lower octaves relatively well. Furthermore, human ears are imperfect. We are much better at hearing upper bass frequencies than lower bass frequencies. We can only feel lower bass frequencies. That is why car subwoofers sound so loud even though most of them may not go below 25H-35Hz.

If you are concerned about the frequency response of a subwoofer, you can use 50Hz as a good starting point and that frequency can be used as a reference frequency. If you look at the following table, you will notice that 50Hz falls in the middle of the 1/3 octave frequencies that a subwoofer is expected to play. If you want to use test tones to calibrate a subwoofer with an SPL meter, you should play a 50Hz tone until you read 75dB on the SPL meter. Then play four 1/3 octaves above 50Hz and four 1/3 octaves below 50Hz and take SPL meter readings. Average the 8 numbers until you get 75dB.

REFERENCES

http://www.mcsquared.com/nsca98.htm
http://www.audioholics.com/education...o-measurements
http://www.bcae1.com/spboxad1.htm
http://www.axiomaudio.com/frequencyresponse.html
http://www.absoluteastronomy.com/top...er_measurement
http://forum.ecoustics.com/bbs/messa...79/131062.html
http://shibatch.sourceforge.net/eq/
http://www.crutchfield.com/S-AM1gGHt...rs.html?page=5
http://www.ishtek.com/spkr_basics.htm
http://www.ishtek.com/spkr_app.htm
http://www.ht-audio.com/pages/SpeakerBasics.html
http://qscaudio.com/support/library/...hite_paper.pdf
http://www.superlux.us/frequency_response.html
http://svconline.com/mag/avinstall_a...ency_response/
http://www.audioholics.com/education...uency-response
http://home.comcast.net/~thomasw-2/S...ndEQpage4.html
http://home.comcast.net/~thomasw-2/S...andEQpage.html

[Big Daddy]

USING A SOFTWARE PROGRAM TO MEASURE FREQUENCY RESPONSE

Using a software program such as the Room Equalization Wizard (REW) to make measurements requires a computer with a full duplex sound card (these can both record and playback at the same time). If you're using a laptop that only has a microphone input, you need a USB soundcard.

You need several components to do an accurate frequency response (both subwoofer and full-range speaker response).

1. Behringer ECM8000 Measurement Condenser Microphone:
   
   http://www.behringer.com/EN/Products/ECM8000.aspx
   http://www.amazon.com/Behringer-ECM8.../dp/B000HT4RSA
   http://www.parts-express.com/pe/show...number=248-625
   
   
   
   
   
   
   • Omnidirectional Measurement Condenser MicrophoneUltra-linear condenser microphone for measurement and recording application
   • Exceptionally flat frequency response and ultra-high sound resolution
   • Evenly weighted, true omnidirectional pattern
   • Perfectly suited for room equalization application and high-resolution recordings such as acoustic instruments, overhead, piano, etc.
   • Works with phantom power from +15 to +48 V
   • Perfect for use with the BEHRINGER ULTRACURVE or any other analyzer
   • Ultra-low noise transformerless FET input eliminates low-frequency distortion
   • Gold-plated, 3-pin XLR output connector for perfect signal transmission
   • Swivel stand mount and transport case included
   • High-quality components and exceptionally rugged
   
   If you plan to do only low frequency (subwoofer) calibration, an SPL meter may be adequeate. If you plan to do full-range sweeps and calibrate or measure frequency responses of the other speakers, you will need a calibrated microphone. If you plan to use an SPL meter, a better quality SPL meter such as the Galaxy CM140 is recommended.
   
2. M Audio MobilePre USB Powered Preamp and Audio Interface:
   
   http://www.m-audio.com/products/en_us/MobilePreUSB.html
   http://www.amazon.com/M-Audio-Mobile.../dp/B0000TP57E
   http://www.zzounds.com/item--MDOMOBILEPRE
   http://www.americanmusical.com/Item-...MOBILEPRE-LIST
   
   
   
   MobilePre_front.jpg
   
   
   MobilePre_back.jpg
   
   
   • Includes phatom power for condenser microphones
   • 2 x 2 16-bit/48kHz analog I/O
   • 2 microphone inputs (XLR balanced) with 48v phantom power
   • stereo microphone input (1/8”)
   • 2 high-impedance instrument/line inputs (balanced/unbalanced 1/4” TRS)
   • 2 mono line outputs (1/4” @ -10dBV)
   • stereo line output (1/8”)
   • stereo headphone output with level control knob
   • gain control knob for each input channel (+40 dB max)
   • zero-latency hardware direct monitoring (mono/stereo) with software level control
   • USB-powered for total mobility
   
   
3. SPL Meter
   
   https://forum.blu-ray.com/receivers/...spl-meter.html
   
   Radio Shack Digital SPL Meter ($49.99)
   
   
   
   
   
   Radio Shack Analog SPL Meter ($44.99)
   
   
   
   
   
   Better SPL Meters:
   http://www.amazon.com/s/?ie=UTF8&key...l_275mc11tsf_b
   http://www.musiciansfriend.com/navigation?q=SPL+meters
   
   
4. Microphone Stand
   
   http://www.americanmusical.com/Item--i-MUS-DS7200B-LIST
   
   
5. Room Equalization Wizard (REW) or TrueRTA
   
   http://www.hometheatershack.com/roomeq/
   http://trueaudio.com/rta_selection_guide.htm
   
   
6. Behringer Feedback Destroyer DSP1124P for Equalizing a Subwoofer:
   http://www.behringer.com/EN/Products/DSP1124P.aspx
   http://www.behringer.com/EN/download...P0124_M_EN.pdf
   http://www.behringer.com/EN/download...P0124_S_EN.pdf
   http://www.zzounds.com/item--BEHDSP1124P
   http://www.americanmusical.com/Item-...-DSP1124P-LIST
   
   
   
   
   
   
   
   
   
   
7. REW and BFD Guides:
   http://www.hometheatershack.com/roomeq/
   http://www.hometheatershack.com/forums/bfdguide/
   http://www.hometheatershack.com/foru...n-calibration/
   
   
8. Cables: Several XLR, TSR (microphone), XLR to TSR, TSR to RCA, and USB cables from Monoprice.
   
   http://www.monoprice.com/products/su...02&cp_id=10244

This is the frequency response of the 4 main external subwoofers in my HT room as measured by REW from the main listening position:

4 Subs Overlay.jpg

This is the frequency response of the 15" built-in subwoofer (300 watt amplifier) inside my Definitive Technology BP2000 speakers with no external equalization. The measurement is made about 3 feet away with an SPL meter and 1/3 octave test tones burnt on a CD. In general, subwoofers do not behave very well in a small home theater room and interact with the room boundaries. As long as the frequencies are not below -3dB, the peaks can easily be smoothed out with an equalizer.

DefTechSubwoofer.jpg

This is the frequency response of the external subwoofers in my HT room using the Velodune SMS-1 Equalizer/Analyzer.

FourEqAudyssey.jpg

[Big Daddy]

Over the past several months, too many people have sent me private messages and asked me the same questions about the frequency response of a speaker/subwoofer. I decided to create this thread so that I won't have to repeat myself like a parrot.

[crazyBLUE]

Originally Posted by Big Daddy

Over the past several months, too many people have sent me private messages and asked me the same questions about the frequency response of a speaker/subwoofer. I decided to create this thread so that I won't have to repeat myself like a parrot.

I gave it A run through & will read it 4 more times before the end of next week

Nice Sticky Big Daddy

[Big Daddy]

Originally Posted by crazyBLUE

I gave it A run through & will read it 4 more times before the end of next week

Nice Sticky Big Daddy

Thanks. Don't forget that there will be a quiz.

[Big Daddy]

I created and added a few more helpful diagrams to post #1.