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Why no frequency response plots for bass cabs?

#42
agedhorse said:
Anechoic?
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Not anechoic--just one room's worth of data. Most large manufacturers claim anechoic measurents (if they can be believed) and I think that there is a Canadian government sponsored lab that measures anechoically for manufacturers and reviewers. All rooms will sound differently (deliberate use of adverb), but this is a starting point to compare speakers.
 
#43
agedhorse said:
What you are missing is that the room is not results that can compared with other measurements.

Measuring the same cabinet in 2 different rooms (or different positions in the same room) and getting 2 different measurements means that the measurement is not an accurate representation of the cabinet itself. It’s misleading no matter how much you want to believe your measurements. It’s fine for a hobbiest, but not something other people will rely on to make a decision.

I’m pretty experienced with acoustic measurements, mic guy is 10 times as experienced as I am (I know his background and work). You don’t know you are arguing with.
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Although this was not addressed to me, I'd like to apologize if I came across as arguing. I have tremendous respect for you, I know that I don't know what I don't know, and pose questions (perhaps poorly) to learn.
 
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#44
My overall point, as is micguy’s, is that you can measure the same speaker in different rooms and get entirely different results.

Comparing 2 such measurements makes it impossible to know if the differences are the speaker or the room.
 
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#45
Speaking strictly as a DIY'er, I concur with @micguy about using the T/S parameters rather than trying to precisely measure cab response. The measured low frequency response curve of a ported speaker is a function of five parameters, and at low signal levels, behaves close enough to theory for all practical purposes. Also, you can find out enough about what you need to know, at least below a couple hundred Hz, from a nearfield measurement close to the cone. You can probably learn more about the higher frequency response from the driver datasheet than from attempts at home measurement. As a check, you can also measure an impedance curve.

Where I think it rises to the next level of difficulty is with large signal levels. This is true for both speakers and amps.
 
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#46
Having a EE background as well as falling down the rabbit hole of high end audio, including versions of home audio equipment that comes with calibrated microphones for the purpose of using frequency sweeps and software to use room compensating filters it’s not an easy subject to understand. I’ve owned several subwoofers that cost more than most high end bass cabinets where the manuals explain that due to the non directional nature of low frequencies, the best place to put a subwoofer is by experimenting with where it sounds best. Impossible to implement in a live music setting where the crowd size and location make that location a moving target. Anechoic measurements at least give a common basis for comparison. For me, the decision to buy something is based more on the user interface and features as well as availability. I like the Darkglass offerings, but it’s not intuitive to use out of box. I needed to pull up the manual on my phone just to know what each switch did. I ended up buying GK, despite the inability to demo it locally because it was more intuitive because it was designed by an engineer.
 
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#50
-Asdfgh- said:
Probably one to take to live sound, but can REW be used effectively to improve a PA live?
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You can find more info at avnirvana.com, including tech support - often from the platform creator himself. Extremely useful tool.

Regards,
Wayne A. Pflughaupt

Pedulla Club #45 Unique Arrangements of Hymns, P&W Standards, and Original Tunes
Administrator, Official Tobias Club #133
Administrator, Fretless Club #943
Big Cabs Club #23
My Basses
My Rig: Stage and FOH Friendly
Pedulla Club #45
 
#51
WayneP said:
You can find more info at avnirvana.com, including tech support - often from the platform creator himself. Extremely useful tool.

Regards,
Wayne A. Pflughaupt

Pedulla Club #45 Unique Arrangements of Hymns, P&W Standards, and Original Tunes
Administrator, Official Tobias Club #133
Administrator, Fretless Club #943
Big Cabs Club #23
My Basses
My Rig: Stage and FOH Friendly
Pedulla Club #45
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I quite successfully used it to get a flat response for my living room hi-fi. Apparently turning up the bass and treble was very close which saved me trying to run everything through masses of EQ!
 
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#54
micguy said:
A nearfield measurement of the cone of a ported speaker is a very misleading way to measure the system - that misses the contribution of the port, which is significant - at resonance, it's most of the output.
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Very good point.

I wrote a little blurb on that topic, which disappeared when I moved my web page, but I'll dredge it back up. Turns out that you can infer the port response curve from the nearfield cone response curve.

It does require a flat microphone.
 
#55
fdeck said:
Very good point.

I wrote a little blurb on that topic, which disappeared when I moved my web page, but I'll dredge it back up. Turns out that you can infer the port response curve from the nearfield cone response curve.

It does require a flat microphone.
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If you know all the parameters of the design (including the Thiele Small parameters of your specific woofer) you can infer the output of the port Then again, if you know all the parameters of the design, you don’t need to do the measurement. Doing the measurement doesn’t really add value at that point, as far as the low frequency performance is concerned

Oh, and as far as a flat mic goes, characterizing your mic is a lot harder than you think. Most folks take a B&K mic as “gospel” and correlate to that. We had issues once correlating frequency response measurements between manufacturers - both using B&K mics (same model) as references. Turns out some of the difference was in technique, but once we fixed that, we still had a difference. Their B&K mic and ours were different.
 
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#56
micguy said:
If you know all the parameters of the design (including the Thiele Small parameters of your specific woofer) you can infer the output of the port Then again, if you know all the parameters of the design, you don’t need to do the measurement. Doing the measurement doesn’t really add value at that point, as far as the low frequency performance is concerned

Oh, and as far as a flat mic goes, characterizing your mic is a lot harder than you think. Most folks take a B&K mic as “gospel” and correlate to that. We had issues once correlating frequency response measurements between manufacturers - both using B&K mics (same model) as references. Turns out some of the difference was in technique, but once we fixed that, we still had a difference. Their B&K mic and ours were different.
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Well stated.
 
#58
agedhorse said:
Well stated.
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I think, if people who whip out a software program and a flat-ish mic and do some measurements in a regular room, had any clue what was involved in making precise repeatable measurements of electroacoustical devices entails, they’d be a bit humbled by it. Everyone today thinks that anything can be fixed by software, but that ain’t always the case.

Our anechoic chambers (there are only a few folks that make good ones) were non-standard - the normal wedges used in other folks’ anechoic chambers weren’t good enough for precise measurements on microphones, the manufacturer of the chamber had to develop new wedges for us. Precise acoustical measurement is not something that you can do at home - it’s very specialized.
 
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#59
micguy said:
If you know all the parameters of the design (including the Thiele Small parameters of your specific woofer) you can infer the output of the port Then again, if you know all the parameters of the design, you don’t need to do the measurement. Doing the measurement doesn’t really add value at that point, as far as the low frequency performance is concerned

Oh, and as far as a flat mic goes, characterizing your mic is a lot harder than you think. Most folks take a B&K mic as “gospel” and correlate to that. We had issues once correlating frequency response measurements between manufacturers - both using B&K mics (same model) as references. Turns out some of the difference was in technique, but once we fixed that, we still had a difference. Their B&K mic and ours were different.
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Turns out the equation for relating one to the other only depends on the resonant frequency, and not the other parameters. I'm still digging. If I don't find it, I'll write it up again.

It's a surprising result, but fun. And still not what I'd recommend for commercial work, just DIY analysis.
 

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