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About The Sub Zone: Testing Methodology and Environment

13702 Views 36 Replies 13 Participants Last post by  AudiocRaver, 
Dale Rasco
Welcome to The Sub Zone​

The Sub Zone is the place to get accurate, data driven test results on how the many subwoofer models compare to the manufacturer's specifications. Additionally a majority, if not all, of the tests will be coupled with a subjective listening review and impressions, which we hope will give the reader a much more complete picture of a particular subwoofer.

The Sub Zone Testing Methodology

This particular thread is to serve as the single source for all questions with regard to The Sub Zone testing methodology. This is the information I refer to before and during my testing. If there are any changes to the environment or methodology, it will be reflected here as well as in the results thread in which a change occurred.

Testing Environment

Tests for The Sub Zone subwoofer testing forum will be conducted outside in an open area with the nearest reflection point being no closer than 35 feet away. I will be measuring frequencies down to 0 Hz and up to 200 Hz. This obviously falls outside of all manufacturer specifications, however, it creates a level playing field for measuring against all manufacturer specifications and will provide more consistent results. This is not a ‘shootout’ or any other competition between subwoofer manufacturers. I will do my best to provide the data that directly compares a subwoofer’s results with the stated manufacturer specs.

This is The Sub Zone​
​

There are obviously many concerns when performing these tests outside such as ambient and random background noise, trains, planes and yes automobiles. Weather can also play a large factor when testing subwoofers outside. Wind, temperature and barometric pressure are all things that must be taken into account when setting up these tests and pre-test checks are absolutely critical to getting consistently accurate results.

A majority the subs being tested will be accompanied with a subjective listening review in order to paint a complete picture of a given subwoofers potential. The Sub Zone tests will not include any of the information in those reviews however, the reviews will include a section for measured results both outside and in-room.

Equipment

I will be using the following equipment to conduct all tests. As I update or replace equipment, I will re-visit this thread to update those changes.

Computer: Dell Latitude 6400 Running Windows 7 64-bit Operating System.



Soundcard: Creative X-Fi 5.1 External/USB

X-Fi Specifications
Playback
  • USB 2.0: Stereo/Surround: Up to 24-bit/96kHz
  • USB 1.1: Stereo: 24-bit/96kHz Surround: 16-bit/48kHz

Record
  • Up to 24-bit/96kHz

Control
  • Volume Control

Connectivity
  • Mic In/Line In
  • Headphone/Front Left & Right Speaker Output
  • Center/Sub Output
  • Rear Left & Right Speaker Output
  • Optical Digital Output
  • USB


Microphone: IBF-Akustik EMM-8
The IBF-EMM8 electret microphone utilizes a small, accurate omni directional capsule housed in an aluminum body. The EMM8 connects to the MP-r1 using a 50’ shielded digital coaxial cable, which provides bias power to the EMM8 with a minimum current of 0.5 mA.



EMM8 Specifications
  • On Axis Frequency Response - 20 - 20.000 Hz +- 2dB
  • Polar Pattern (Directivity) - omnidirectional
  • Sensitivity - 6mV/Pa/[email protected] 2.5V,2.2k Ohm
  • Power Requirements - 1.5 - 10V / approx. 0.5 mA
>120dBSPL

  • Output Connector - RF phono jack

  • Noise - S/N ratio >58 dB
  • Dimensions - probe dia : approx. 5/16", 8 mm length : 12 3/8" , 315 mm
max dia : 25/32" , 20 mm
  • Weight - 1 1/2 oz, 42 grams (without clamp)
  • Calibration - individually calibrated. The calibration microphone and preamp for this is the Bruel & Kjaer
 condensor B&K 4133 (1/2" free-field) and B&K 2639 preamp.

Pre-Amp: IBF-Akustik MP-1r
The IBF-MP1r is a portable microphone preamplifier that uses bias supply voltage for electret microphones. The unit was designed for 20Hz to 20kHz audio bandwidth operation and specifically for speaker and room acoustic measurements.



MP-1r Specification
  • Number of preamplifier channels - 1 Mic
  • 
Connectors - RF phono jacks for both inputs and outputs
  • Input - unbalanced, capacitor coupled, input impedance >2kOhm

  • Output - unbalanced, capacitor coupled, min load 2kOhm, short circuit protected, guaranteed output level without clipping +3dBV (full battery) Note: 0dBV=1Vrms
  • Power output – 3.5mm connector, low impedance drive capability (ideal for driving long cables and head/earphone), reduced output level -5dB

  • Gain Range - up to 52 dB input to output

  • Frequency Response - 20 Hz - 20 kHz, +-0.2 dB (relative to 1 kHz)

  • Output Clipping Level - 4Vpp (2 k• load)

  • Clipping indicator LED - Red indicates clipping short attack time, long release time. Bipolar detection

  • THD < 0,02%
  • THD & Noise < 0.04%
  • SNR > 70 dB Bias Supply - typ. 2.5V coupled via 2.7kOhm resistor
  • Power - 1x 9V battery, plug-in power supply connector
  • Power LED - Green indicates power ON, blinking LED indicates low batt. (Vbatt < 7V)

  • Acoustic REF LED - 94dB acoustic reference LED (off / bright / weak indicates < = > 94__1 dBspl)

  • -10 dBV LED – Consumer Level reference LED (off / bright / weak indicates < = > 10__2 dBV)

  • Polarity - Mic input to line output is non-inverting.
  • Operating Temperature Range - 
0 to 40 degrees Celsius (32 to 104 degrees F)
  • Power up delay – approx. 10 sec

  • Dimensions
 - 34 mm x 68 mm x 120 mm (h x w x d) (1 11/32" x 2 11/16" x 4 23/32")

  • Weight - 120 grams (4 1/8 oz). Battery removed

Calibrator: IBF-Akustik SC-1
The SC-1 is a single frequency dual amplitude, self-contained field calibrator. The unit generates a 1kHz reference tone at 94 and 110 dB SPL.



SC-1 Specifications
  • Output Frequency - 1kHz ± 0.2% (crystal stabilized)
  • Output Amplitude - selectable 94dB / 110dB
  • Accuracy - ± 0.5dB @ 155oF and 760mm Hg
  • Temperature - 90oF to 230oF operating,14oF to 
266oF storage (battery removed)
  • Temperature drift Coefficient of SPL - 0 to -0.012 
dB/oF
  • Temperature Correction - Sound-Pressure-Level of 
the Calibrator decreases about 0.1dB per +8oF temperature change. e.g.: at 203oF SPL is about 109.4dB (93.4dB) at 138oF SPL is about 110.2dB (94.2dB)
  • Humidity - 5 to 95% relative humidity
  • Power supply - 9V standard transistor battery 
(Low Batt control)
  • Construction - Solid state integrated circuitry in 
aluminum/plastic housing
  • Size and Weight - dia 1.57", length 5.24", 5 3/4oz (without battery)

Software: REW


Methodology​


Frequency Response (FR)
Frequency response is measured utilizing a 512K (11.9s) sine sweep from 0 Hz to 200 Hz via REW (Room Equalization Wizard). The microphone is placed on the ground at a 2 meter distance measured from the center of the subwoofer driver. In the event a particular subwoofer requires a deviation from this it will be noted within that particular set of measurements. For example, if a ported/vented sub with multiple drivers requires different mic placement in order to capture accurate results, it will be spelled out within that particular subwoofer test.

A measure of how accurately a system reproduces different frequencies. In the case of audio in a home theater system, it is desirable for the frequency response of a whole system, including speakers and subwoofer, to be from 10 Hertz to 20,000 Hertz ±3dB. This performance requires a very expensive system indeed and, in practice, very few systems will produce bass down to anything like that bottom limit. Manufacturers who claim a frequency response for speakers of, say, 20 to 20,000 Hertz without specifying decibel boundaries are telling you nothing. A tinny two inch transistor radio speaker can reproduce that range, although you won't actually hear it at either extreme because its output will be so low. Even subtle variations of less than half a decibel across the audio band can be quite audible, especially if they're spread over a fairly wide band of frequencies, and can thus change the character of the sound. Indeed, with speakers the single measure most closely related to their sound is the frequency response. (Home Theater Shack Glossary)​

Max Output Before Compression
Max output before compression is measured using a 2M (23.8 second) sine sweep from 0 Hz to 200 Hz. The first sweep is taken after level matching 50Hz at 90db. The level is then raised by 5 db for each successive sweep until the output level is clearly compressed. The graph reflects the last sweep 'Before' compression is audible.

Group Delay
Group delay is a good indicator as to whether a subwoofer provides tight bass or a sloppier/looser type of bass. Higher numbers equals 'looser' sound.

Spectrogram

The spectrogram takes a lot of complex information and presents it in an easy to read 'pretty picture'. For our purposes, we will be using it to determine how much additional response that a cabinet lends to the measurement. In other words, we are looking to see how much a particular cabinet 'colors' the sound or response of the driver by measuring the intensity of the vibration once the signal has stopped being generated. Keep in mind that this is measured in milliseconds and for our tests we will use 500 milliseconds as a baseline/expected response.

To illustrate what I am talking about, let's look at the measurement below. Given the information presented,you can see that this particular sub suffers from about a 300 millisecond decay at 63Hz when the signal goes from 93db to 53db. As a reference, 300 milliseconds is about as long as it takes to blink your eyes.



Waterfall
The waterfall measurement will be taken from the frequency response measurement and will reflect 70db to 105db. This will eliminate the chances of floor noise which can be had starting at 45db from the wind.

Harmonic Distortion
Harmonic distortion, in very simplistic terms, is the addition of undesirable harmonically related tones to the fundamental frequency. Harmonic distortion by component is measured using different frequency intervals and correspond to the max output level sweeps. The frequency intervals measured are 32 Hz, 40 Hz, 50 Hz, 63 Hz and 80 Hz. Harmonic distortion should be as low as possible across all frequencies.
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E
acoustat6 said:
Thats great, we have to show consistency and that is why you should start measuring at 75db. That is what everyone else is holding to at REW forum, unless there is a house curve or for measuring for compression.
Click to expand...
Why 75dB? I think it's more important to start somewhere where compression becomes a legitimate concern. If the driver is moderately efficient (mid 80's), compression isn't of concern until you're at least there. So, to me, 75dB testing is moot.

acoustat6 said:
"While 75db is the default for REW it is hardly a standard per se. There has been a lot of emphasis over the years on 75db being a standard of some sort but it is really just a reference guideline for level setting speakers. "

Right, so stick with it! If you started at 75db then you could go up in 10 db increments and have this reapeatable for all of your measurements. Would this not make sense from a sciencetific/reference standard.

Looking at your graphs of the 5 woofers that you measured there are no target lines. If you are not measuring at 75db you then need to state the target level for the measurenent taken. IE: on the graph for the Emotiva where would you place the target level? And in the graph for the SVS is the target level 116db? If so you missed it by 20db!
Click to expand...
I have a very fundamental issue with the talk around compression testing here. What's catching me off guard here is people saying to test compression by increasing the output to achieve 10dB steps. This is flawed. Compression shouldn't be solely focused on the FR. Compression is a measurement of input vs output. It is not a measurement of response as you increase the output itself. For example, if you increase the input voltage at a speaker's terminals then you should get that same relational value in dB output by the DUT. Anything less is due to the effect of compression.

Yes, you are looking to see how the response changes but what's the point if a driver is so inefficient at higher output that you're having to feed it twice as much as you should for the same output?

Consider this: What happens if you're increasing SPL by 10dB but your voltage ratio from your previous input voltage of 4v to your new voltage input, which should be 12.6 volts, is actually 14.6v? All you've done is increase the output but you've failed to acknowledge the 2v loss in your test, which equates to about 14watts or 6dB! Yikes! So, yea, the curve at the reference frequency increased by 10dB, but it's not illustrating the fact that you just had to make up more than 6dB by turning the amp gain up higher and higher.

This is what compression testing should tell you. Again, voltage in vs SPL out vs what should be there. Then you get the FR curve, but most importantly, you get to see how efficiently the driver is able to use the power provided to it.

Hope that makes sense. Maybe my assumption on how this kind of testing is being performed is wrong so please correct me if so.

- Erin


Below I've attached a picture of compression testing I did on a Seas w18nx driver. This is the 20-110hz band. As long as the lines are stacked on top of each other, what you're seeing is what is expected; no loss in output vs voltage input. Where the lines deviate, is an indication of how much output (in dB) is lost with the input vs the initial voltage vs frequency. As you go higher in frequency in the chart, you can see a loss of about 0.4dB from 1v to 8v input.






This is the same thing but from 400hz to 6khz. You can see a loss of about 0.8dB at 3800hz. Likely due to inductance issues (yet to verify).
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Dale Rasco
acoustat6 said:
Thats great, we have to show consistency and that is why you should start measuring at 75db. That is what everyone else is holding to at REW forum, unless there is a house curve or for measuring for compression.
Click to expand...
Bob, I understand what your preference would be however; I have clearly outlined what the methodology is and how I will go about taking the measurements. If I were to cater to everyone's preference I would never get anything done. The purpose here is to compare my measurements to the measurements posted, published, etc by the manufacturer. 75db is not a standard. I do not know how else to explain that. Additionally this is not REW forum discussion, The Sub Zone is it's own forum and the fact that I happen to use REW is irrelevant to this discussion outside of the defined methodology. The consistency comes from the measurements listed and outlined below taken directly from the methodology.

Frequency Response (FR)
Frequency response is measured utilizing a 512K (11.9s) sine sweep from 0 Hz to 200 Hz via REW (Room Equalization Wizard). The microphone is placed on the ground at a 2 meter distance measured from the center of the subwoofer driver. In the event a particular subwoofer requires a deviation from this it will be noted within that particular set of measurements. For example, if a ported/vented sub with multiple drivers requires different mic placement in order to capture accurate results, it will be spelled out within that particular subwoofer test.

Long Term Output
Maximum long-term output is measured using a 1M (23.8 second) sine sweep from 0 Hz to 200 Hz. The first sweep is taken after level matching 50Hz at 90db. The level is then raised by 5 db for each successive sweep until the output level is clearly compressed. Compression measurements are taken at the same time as the max output. The compression graph reflects the relative compression to the original 90 db sine sweep.

acoustat6 said:
Right, so stick with it! If you started at 75db then you could go up in 10 db increments and have this reapeatable for all of your measurements. Would this not make sense from a sciencetific/reference standard.
Click to expand...
You have just made my point. I could start using 75db, but it is irrelevant to the tests that I perform. Saying it repeatedly does not make it true. You are more than welcome to start your own forum and start all of your measurements at 75db or whatever number you would like. Starting at 75db and moving it up 10db per sweep is no more scientific than starting at 90db and raising it by 5db as I have outlined in the methodology.

acoustat6 said:
Looking at your graphs of the 5 woofers that you measured there are no target lines. If you are not measuring at 75db you then need to state the target level for the measurenent taken. IE: on the graph for the Emotiva where would you place the target level? And in the graph for the SVS is the target level 116db? If so you missed it by 20db!
Click to expand...
Uhm.. What? I did state the target. 'From 0 Hz to 200 Hz starting at 90db and raising it 5db until the signal compressed. Please let me know what part of this is unclear to you.

acoustat6 said:
Of course it would, you are describing what you hear in your room, we need to see the actual in room freq resp to correlate what is measured with what is heard.
Click to expand...
One has absolutely nothing to do with the other. You cannot correlate a subjective opinion to a sine sweep. The best you could hope for is to correlate it to a given part of a song or film that I happen to capture that I also commented on. Subjective, emotional responses to audio are not measurable.
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robbo266317
OK, You have my attention. Nice work Dale. :T
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Dale Rasco
Thanks Bill, I have some cool stuff headed to the Sub Zone so stay tuned!
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Dale Rasco
Erin H said:
Why 75dB? I think it's more important to start somewhere where compression becomes a legitimate concern. If the driver is moderately efficient (mid 80's), compression isn't of concern until you're at least there. So, to me, 75dB testing is moot.



I have a very fundamental issue with the talk around compression testing here. What's catching me off guard here is people saying to test compression by increasing the output to achieve 10dB steps. This is flawed. Compression shouldn't be solely focused on the FR. Compression is a measurement of input vs output. It is not a measurement of response as you increase the output itself. For example, if you increase the input voltage at a speaker's terminals then you should get that same relational value in dB output by the DUT. Anything less is due to the effect of compression.

Yes, you are looking to see how the response changes but what's the point if a driver is so inefficient at higher output that you're having to feed it twice as much as you should for the same output?

Consider this: What happens if you're increasing SPL by 10dB but your voltage ratio from your previous input voltage of 4v to your new voltage input, which should be 12.6 volts, is actually 14.6v? All you've done is increase the output but you've failed to acknowledge the 2v loss in your test, which equates to about 14watts or 6dB! Yikes! So, yea, the curve at the reference frequency increased by 10dB, but it's not illustrating the fact that you just had to make up more than 6dB by turning the amp gain up higher and higher.

This is what compression testing should tell you. Again, voltage in vs SPL out vs what should be there. Then you get the FR curve, but most importantly, you get to see how efficiently the driver is able to use the power provided to it.

Hope that makes sense. Maybe my assumption on how this kind of testing is being performed is wrong so please correct me if so.

- Erin


Below I've attached a picture of compression testing I did on a Seas w18nx driver. This is the 20-110hz band. As long as the lines are stacked on top of each other, what you're seeing is what is expected; no loss in output vs voltage input. Where the lines deviate, is an indication of how much output (in dB) is lost with the input vs the initial voltage vs frequency. As you go higher in frequency in the chart, you can see a loss of about 0.4dB from 1v to 8v input.






This is the same thing but from 400hz to 6khz. You can see a loss of about 0.8dB at 3800hz. Likely due to inductance issues (yet to verify).
Click to expand...
Wow Erin, that is a great example! Thank you for contributing your knowledge to the conversation!
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A
Hi Dale, I will give you that what you are measuring, the reason why and your methodology is different form mine. As this is your forum, so be it.

Though, I have no idea why you would bother measuring speakers like this, but thats OK, I am a little behind the obvious learning curve. Does it not matter most what the speaker is doing in your room, rather than out in your driveway? But that is your methodology, and I will respect it.

But when you measure your system as you listen to it in your room, and give SUBJECTIVE reports to how it sounds then I am sure you will go by the standard REW specifications.

You have not answered my question as to which SPL meter you use, .... so please do.

Dale said, "Uhm.. What? I did state the target. 'From 0 Hz to 200 Hz starting at 90db and raising it 5db until the signal compressed. Please let me know what part of this is unclear to you.

Uhm....Yes that is correct, you have to state a target level as you are the one measuring. Otherwise I can infer any level I want to on your graph if you don't state what is the actual level. So you say that in all of your graphs, the first measurement is 90db going up in 5db increments, is that correct? Then looking at the following graphs:
the Axiom your initial reading of 90db is 4db too high.
the Chase is so wrong I dont know what to say
the Emotiva is 5db to high
the power soud is about correct is about correct but we need to see it overall freq response since it is clearly not a "subwoofer"
the svs graph clearly shows that you did not correlate 90db with you intended target.

Dale said, "One has absolutely nothing to do with the other. You cannot correlate a subjective opinion to a sine sweep. The best you could hope for is to correlate it to a given part of a song or film that I happen to capture that I also commented on. Subjective, emotional responses to audio are not measurable."

I say, really? Then why are you measuring? If measured freq response has no correlation with what you are hearing, why bother measuring?


Bob
"Make more progress, less excuses"
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Sonnie
acoustat6 said:
Though, I have no idea why you would bother measuring speakers like this, but thats OK, I am a little behind the obvious learning curve. Does it not matter most what the speaker is doing in your room, rather than out in your driveway? But that is your methodology, and I will respect it.
Click to expand...
I can answer this one...

Take a look at our Subwoofer Tests - Archived forum.

That forum has more views than any other forum on our site with as few threads as it has. 10's of thousands of views for most of the threads... most likely over a million views total. Obviously there are quite a few viewers who appreciate this type of testing. We are indeed going one step farther with subjective reviews on many of these we will be testing. We will try to do them all if we can. However, the purpose of our testing has been thoroughly explained.
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Dale Rasco
acoustat6 said:
Hi Dale, I will give you that what you are measuring, the reason why and your methodology is different form mine. As this is your forum, so be it.

Though, I have no idea why you would bother measuring speakers like this, but thats OK, I am a little behind the obvious learning curve. Does it not matter most what the speaker is doing in your room, rather than out in your driveway? But that is your methodology, and I will respect it.

But when you measure your system as you listen to it in your room, and give SUBJECTIVE reports to how it sounds then I am sure you will go by the standard REW specifications.

You have not answered my question as to which SPL meter you use, .... so please do.

Dale said, "Uhm.. What? I did state the target. 'From 0 Hz to 200 Hz starting at 90db and raising it 5db until the signal compressed. Please let me know what part of this is unclear to you.

Uhm....Yes that is correct, you have to state a target level as you are the one measuring. Otherwise I can infer any level I want to on your graph if you don't state what is the actual level. So you say that in all of your graphs, the first measurement is 90db going up in 5db increments, is that correct? Then looking at the following graphs:
the Axiom your initial reading of 90db is 4db too high.
the Chase is so wrong I dont know what to say
the Emotiva is 5db to high
the power soud is about correct is about correct but we need to see it overall freq response since it is clearly not a "subwoofer"
the svs graph clearly shows that you did not correlate 90db with you intended target.

Dale said, "One has absolutely nothing to do with the other. You cannot correlate a subjective opinion to a sine sweep. The best you could hope for is to correlate it to a given part of a song or film that I happen to capture that I also commented on. Subjective, emotional responses to audio are not measurable."

I say, really? Then why are you measuring? If measured freq response has no correlation with what you are hearing, why bother measuring?


Bob
"Make more progress, less excuses"
Click to expand...
I keep forgetting the SPL, it is a Galaxy CM140. For measuring I am using the IBF.

acoustat6 said:
the first measurement is 90db going up in 5db increments, is that correct?
Click to expand...
No, what I stated was that the volume is level set at to 90db AT 50Hz and then I will begin the sweeps and raise the volume by 5db.

acoustat6 said:
the Chase is so wrong I dont know what to say
Click to expand...
If you would actually read the words instead of just looking at the pictures you would have seen at the top of the Chase test that I stated:

"Before we start I would like to say that the tests that I did back in February on the Chase VS-18.1 were performed before any methodology was written for The Sub Zone and as a result the measurements for max output were based on maintaining <10% THD. This is different than other tests that have been performed on this beast utilizing the CEA 2010 standard."​

acoustat6 said:
I say, really? Then why are you measuring?
Click to expand...
To show an estimated room gain benefit.

Bob, I am done trying to help you grasp this as it seems you only really want someone to argue with.
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Dale Rasco
ironglen said:
I guess no spl capability will be tested since that would be a very long power run; even at low current it will require a decent gauge cord.

Cool idea
Click to expand...
Hey Glen, sorry I missed this one. I have been working out the SPL thing. I actually think it will be possible but probably will not be added until next Spring.
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E
Dale,
I really do implore you to consider what I wrote above regarding the fundamental purpose of compression testing. Raising the output by 5dB doesn't really tell us anything about compression other than how the curve changes. That's fine... but that's only one (small) part of compression. We need a way to gauge input voltage for each step vs output SPL. You can do this pretty easily with online calculators. Just figure what each voltage input will be, in steps, and that should tell you what your output should be. Make a table with 6-7 stepped voltages, then the theoretical (what you should get, if compression were not inherent in design), and the real result. Then you'll see how much output in SPL is lost due to inefficiency at your reference frequcney of 50hz and you can still provide your FR curves so we can see how the overall curve is affected. It's not quite as pretty as the examples I gave above, but it'll suffice. Once I get set up, I will be providing the compression testing the same way as I did above. Flying in the face of apparent standard REW convention. lol.


Playing devil's advocate: As far as subjective vs objective, I actually agree. I'm more of a 'let the data talk' kind of guy. I stay away from subjective thoughts regarding sound; I freely talk subjectively on my likes/dislikes with a product interface, usability, etc. I do agree that when a subjective review is given, objective data should be provided to help the both the reviewer and the viewers (possibly) understand why your subjective analysis came out the way it did. Subwoofers are especially prone to placement and as we know placement will dictate response at the seated position. A simple 6 point spatial average of frequency response would suffice in objective/subjective correlation.


Just my $.02....

- Erin
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Dale Rasco
Erin H said:
Dale,
I really do implore you to consider what I wrote above regarding the fundamental purpose of compression testing. Raising the output by 5dB doesn't really tell us anything about compression other than how the curve changes. That's fine... but that's only one (small) part of compression. We need a way to gauge input voltage for each step vs output SPL. You can do this pretty easily with online calculators. Just figure what each voltage input will be, in steps, and that should tell you what your output should be. Make a table with 6-7 stepped voltages, then the theoretical (what you should get, if compression were not inherent in design), and the real result. Then you'll see how much output in SPL is lost due to inefficiency at your reference frequcney of 50hz and you can still provide your FR curves so we can see how the overall curve is affected. It's not quite as pretty as the examples I gave above, but it'll suffice. Once I get set up, I will be providing the compression testing the same way as I did above. Flying in the face of apparent standard REW convention. lol.


Playing devil's advocate: As far as subjective vs objective, I actually agree. I'm more of a 'let the data talk' kind of guy. I stay away from subjective thoughts regarding sound; I freely talk subjectively on my likes/dislikes with a product interface, usability, etc. I do agree that when a subjective review is given, objective data should be provided to help the both the reviewer and the viewers (possibly) understand why your subjective analysis came out the way it did. Subwoofers are especially prone to placement and as we know placement will dictate response at the seated position. A simple 6 point spatial average of frequency response would suffice in objective/subjective correlation.


Just my $.02....

- Erin
Click to expand...
Thank you Erin and I would like to discuss this in more detail when you have time for me to call. I understand all about letting the data talk however; there are other elements outside of hard numbers that need to be told as well. I do plan to do in room measurements, moving forward but am not yet committed to a methodology around it.

Thanks for the input, I sincerely appreciate it.
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no worries. shoot me a PM and let me know when is best to call you and when/if I get a chance tonight I'll give you a shout. :)
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E
I take back what I said about doing a spatial average for the subwoofer subjective analysis. If you're only concerned about the low end response, there's no reason to do a spatial average here... not unless the listening room is haunted by ghosts. the response is not going to vary here within a few inch window. If you're measuring multiple seats, it's a different story.

anyway, one simple FR capture with a LONG window (enough to allow fine resolution of resonance/modes) and a good CSD (waterfall) should help with your subjective to objective correlation if you choose to go this route. Personally, I'd say do the subjective, post the data of the driver in the 'ideal' situation as your baseline and then post the listening position response.
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AudiocRaver
Dale,

I am in catch-up mode here, have read through the thread, and clearly have soooooooo much to learn about subs and sub testing. What an amazing resource you are providing.

Two questions, and beg pardon if they were covered and I missed them, or if they totally miss the mark somehow:

1. It would seem that there should be a direct relationship between the compression measurements and harmonic distortion, i.e. as the measurement level reaches onset of compression, harmonic distortion would also be going through the roof. Does this appear to be the case? If so, is there any value in correlating the two as a measurements sanity check of some sort? If there is no such correlation, what am I missing?

2. As I see it, your measurements are half-space measurements, due to obvious physical limitations. How does that compare to typical manufacturer's measurement methods and specifications for subs? It is clearly a restatement of the obvious that whole space versus half space versus quarter space versus corner loading would have a big effect on frequency response measurements for a sub. Is there any industry-standard for how manufacturers approach this, and what is your feeling for how it affects your ability to correlate your measurements with manufacturers specs and measurements?

Thanks again, appreciate your work and feedback.
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Dale Rasco
AudiocRaver said:
1. It would seem that there should be a direct relationship between the compression measurements and harmonic distortion, i.e. as the measurement level reaches onset of compression, harmonic distortion would also be going through the roof. Does this appear to be the case? If so, is there any value in correlating the two as a measurements sanity check of some sort? If there is no such correlation, what am I missing?
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Thanks for the questions. The relationship between the compression measurement and THD measurements are based on the THD measurements being taken at the same time. Compression is not necessarily indicative of high distortion. Take the SVS SB-13 Ultra, which is an awesome sub by the way, if you look at the Max output before compression you can see that the signal falls on itself at around 80Hz but the THD at that point was only 2%. So compression does not necessarily indicate higher distortion is present.

AudiocRaver said:
2. As I see it, your measurements are half-space measurements, due to obvious physical limitations. How does that compare to typical manufacturer's measurement methods and specifications for subs? It is clearly a restatement of the obvious that whole space versus half space versus quarter space versus corner loading would have a big effect on frequency response measurements for a sub. Is there any industry-standard for how manufacturers approach this, and what is your feeling for how it affects your ability to correlate your measurements with manufacturers specs and measurements?
Click to expand...
Normally most manufacturers will only post their response but not the actual measurement graph. It has been my experience thus far that those that do not post graphs usually post their frequency response then a typical in-room response. I am starting to get in the habit of taking an in room measurement to add to the tests or review.
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theJman
AudiocRaver said:
1. It would seem that there should be a direct relationship between the compression measurements and harmonic distortion, i.e. as the measurement level reaches onset of compression, harmonic distortion would also be going through the roof. Does this appear to be the case? If so, is there any value in correlating the two as a measurements sanity check of some sort? If there is no such correlation, what am I missing?
Click to expand...
To add to Dales comments...

You can almost look at compression as "when does it stop getting louder". The deeper the bass goes the more it requires from the amp and driver, that's why you'll most often see the compression occur on the lower notes first. But that "collapse" in the linear response curve doesn't always mean distortion.

A lot of budget subs don't have effective limiters, so they'll just keep getting louder until you either can't handle the dreadful sound from all the distortion or they self destruct. But the better subs will use a DSP (Digital Sound Processor) to 'tailor' the frequency and compression response. Using Dales example of the SB-13 Ultra it appears the SVS engineers decided to start limiting the volume/output before the driver produces distortion. That essentially means it won't get any louder at certain frequencies, but it won't sound like garbage either. Makes the parts last longer too, which for me is always preferable.
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AudiocRaver
Thanks for the detail. I was wondering if there might be an actual compressor/limiter function built into the signal processing somewhere to protect the driver. Shows how much I still have to learn about subs.
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