Complaint thread about speaker measurements

[Frank Dernie]

Nowadays, one can use devices that measure acceleration on the sides and such of the cabinet.

It would be interesting to see the results of such measurements.

My friend uses a laser vibrometer to measure the radiation from cabinet walls of speakers he is designing for clients. He uses the measurement to verify the FE analysis of the cabinet and to calculate sound radiation from the cabinet.
It is significant, and as I wrote up post the speakers using the well engineered cabinet with modest but well engineered drivers sound superior to SOTA drivers in a simple box of the same volume - his conclusion not mine, I haven't got any experience of such a comparison but he has been refining the technique for decades.

 

[Frank Dernie]

Well, there we go, somebody tried it out. I'm sure if you find a resonance or something you didn't know about, it's worth it.

Stereophile have been doing it in the measurements section of every loudspeaker test for many years actually. That is the only bit I read.

 

[pma]

Well, there we go, somebody tried it out. I'm sure if you find a resonance or something you didn't know about, it's worth it.

Yeah, however I am not sure of interpretation .

 

[Frank Dernie]

Yeah, however I am not sure of interpretation .

View attachment 48840

Yes, a plot like that tells absolutely nothing!

 

[pozz]

Yeah, however I am not sure of interpretation .

View attachment 48840

Can you turn that into a CSD plot?

 

[Juhazi]

In the video the guy made a pendulum knocking test to various pieces of board attached to a workbench. The analysis shows obviously frequency distribution, amplitude and decay. Another aural test was knocking pieces of board hanging in air. Sound was definitely different.

I have performend similar knocking tests with a microphone and looking at recording with Audacity, mainly for fun. Each hit was different, but difference between MDF and birch plywood were significant. Another knock test was with JBL LSR305 cabinet, and I got much improvement with an added crossbrace.

Vibrometers aren't awfully expensive, 715,-€ https://micromega-dynamics.com/prod...TCHzsb-c3PLj9kJSzlZ1PgEyP8ewXYYxoCLq4QAvD_BwE

https://micromega-dynamics.com/wp-content/uploads/2017/11/Feel_Manual_User_V0.pdf

 

[pma]

Can you turn that into a CSD plot?

I can do almost anything, however still I am not sure of interpretation. It was a short hammer tick on the cabinet side wall.

 

[hardisj]

I used an accelerometer on this subwoofer I tested back in 2013
https://www.hometheatershack.com/th...r-research-f12g-direct-servo-subwoofer.66876/

Ideally, a laser scanner would be better because placement of the accelerometer can skew results. Who knows, you might get lucky and put the acc at a spot where no vibration occurs while another spot may vibrate enough to detriment the actual frequency response. It's something I will continue to do in my future tests.

 

[pma]

The box is stiff, I tried more places, the differences are not too big.

 

[Biblob]

I can do almost anything, however still I am not sure of interpretation. It was a short hammer tick on the cabinet side wall.
View attachment 48841

Indeed the interpretation of these things are hard to do. What exactly are you measuring?
Is a speaker acting the same way as a pendulum on the walls of the cabinet? At what frequency is this happening? And then, where to put what kind of absorption to tackle this effectively?

It seems quite complicated to tackle panel vibrations effectively and accurately, without extensive simulation and/or with laser vibrometer.

 

[hardisj]

The box is stiff, I tried more places, the differences are not too big.

I think it would depend on the construction. I would imagine putting the acc at a brace point vs an unsupported point would yield a different result. Especially if there's a large area that is constructed differently in this regard. But I hated mechanics of materials in college so what do I know.

 

[hardisj]

I expect you would simply use the acc testing to compare that against the FR and the HD of the test. Assuming the MLS length was long enough to exacerbate any such ringing.

 

[pma]

It was a short hammer tick on the cabinet side wall.

Indeed the interpretation of these things are hard to do. What exactly are you measuring?
Is a speaker acting the same way as a pendulum on the walls of the cabinet?

It was a tick of hammer to the side wall of the speaker box, as already explained. Response measured on the same wall, in a distance of about 50cm. Frequency of excited damped oscillations is evident from both time record and waterfall plots posted. Decay can be seen as well from both measurements.

 

[Frank Dernie]

In the video the guy made a pendulum knocking test to various pieces of board attached to a workbench. The analysis shows obviously frequency distribution, amplitude and decay. Another aural test was knocking pieces of board hanging in air. Sound was definitely different.

I have performend similar knocking tests with a microphone and looking at recording with Audacity, mainly for fun. Each hit was different, but difference between MDF and birch plywood were significant. Another knock test was with JBL LSR305 cabinet, and I got much improvement with an added crossbrace.

Vibrometers aren't awfully expensive, 715,-€ https://micromega-dynamics.com/prod...TCHzsb-c3PLj9kJSzlZ1PgEyP8ewXYYxoCLq4QAvD_BwE

https://micromega-dynamics.com/wp-content/uploads/2017/11/Feel_Manual_User_V0.pdf

Measuring at one spot is not particularly informative and the mass of the transducer will change the measurement of a panel by being there.

 

[Rick Sykora]

Yeah, however I am not sure of interpretation .

View attachment 48840

Why does it matter when you have the ”world’s second best speaker” ...

Ignoring the click bait title, like how he explains why the design has merit.

Anybody, built or heard these Voight speakers?

 

[j_j]

... and as I wrote up post the speakers using the well engineered cabinet with modest but well engineered drivers sound superior to SOTA drivers in a simple box of the same volume - his conclusion not mine, I haven't got any experience of such a comparison but he has been refining the technique for decades.

For many reasons, I agree with that. Not only does one have to consider panel resonances (although using a hammer is misbegotten in my book, you have a driver in that box, USE IT for (*(* sake, and you'll know things like coupling, interaction between panels, etc, that tapping with a hammer or a controlled weight may not tell you, because the driving force inside the box is not applied at one point), but also reflections to the back of a driver, etc. There is a lot to be considered, and I have more than once annoyed a woodworker with "HOW BIG DID YOU SAY" *!*!*!*!* referring to the precision of interior measurements, not the overall size. Yes, there is a reason it was 7 13/32 x 13 3/8, specifically. Yup. And yes, there's a reason that you put an extra piece of wood inside the box on one side so the driver is centered externally, but not internally, etc, etc.

 

[Frank Dernie]

For many reasons, I agree with that. Not only does one have to consider panel resonances (although using a hammer is misbegotten in my book, you have a driver in that box, USE IT for (*(* sake, and you'll know things like coupling, interaction between panels, etc, that tapping with a hammer or a controlled weight may not tell you, because the driving force inside the box is not applied at one point), but also reflections to the back of a driver, etc. There is a lot to be considered, and I have more than once annoyed a woodworker with "HOW BIG DID YOU SAY" *!*!*!*!* referring to the precision of interior measurements, not the overall size. Yes, there is a reason it was 7 13/32 x 13 3/8, specifically. Yup. And yes, there's a reason that you put an extra piece of wood inside the box on one side so the driver is centered externally, but not internally, etc, etc.

Exactly. Use the actual excitation source!

 

[andreasmaaan]

Hi @amirm, wow - these speaker measurements are amazing! Thank you

One quibble: I find the directivity charts quiite difficult to read with so many measurements bunched in, all in the same grey. Could I make two suggestions please (assuming the software is capable)?

1. Colour code the measurements, with a different colour for each off-axis angle.

2. Where a speaker is symmetrical along a particular plain (typically the horizontal plain), post only positive (or negative) angles - but not both.

3. Where a speaker is asymmetrical along a particular plain (typically the vertical plain), post two separate measurements, one for positive angles and another for negative angles.

Here's an example something like what I mean:

 

[flipflop]

Hi @amirm, wow - these speaker measurements are amazing! Thank you

One quibble: I find the directivity charts quiite difficult to read with so many measurements bunched in, all in the same grey. Could I make two suggestions please (assuming the software is capable)?

1. Colour code the measurements, with a different colour for each off-axis angle.

2. Where a speaker is symmetrical along a particular plain (typically the horizontal plain), post only positive (or negative) angles - but not both.

3. Where a speaker is asymmetrical along a particular plain (typically the vertical plain), post two separate measurements, one for positive angles and another for negative angles.

Here's an example something like what I mean:

View attachment 50139

Welcome back.
Have you checked out the directivity charts posted by @MZKM along with the predicted preference ratings? They're often on the first page in the review threads.
Vertical directivity isn't split into positive and negative angles, but I still find them easy enough to read.

 

[andreasmaaan]

Welcome back.
Have you checked out the directivity charts posted by @MZKM along with the predicted preference ratings? They're often on the first page in the review threads.
Vertical directivity isn't split into positive and negative angles, but I still find them easy enough to read.

A-huh. Yes, much better, thanks