# Using REW to measure speaker vibration?



## jramos (Aug 9, 2011)

Hello

I am a new user and still getting to grips with the this great program.
I am trying to do some vibration analysis on my new speakers and would appreciate some advice with this. I have the ACH-01 accelerometer which I have connected to the mic input of my computer. The ACH-01 is stuck on the speaker side wall.
I have done some measurements and generated a waterfall plot but cannot really get an idea of whether I am seeing anything which would allow me to assess vibration of the speaker wall.
If any of you can advise me on how to do this, I would be most grateful.

Regards

Jose


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## JohnM (Apr 11, 2006)

Resonances at the location of the accelerometer will show up as peaks in the frequency response and extended decays on the waterfall plot, just like modal resonances in acoustic measurements. You have the same issues as encountered in room measurements, in that the results are specific to the location of the sensor, so you should measure several locations on the panel.


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## jramos (Aug 9, 2011)

JohnM said:


> Resonances at the location of the accelerometer will show up as peaks in the frequency response and extended decays on the waterfall plot, just like modal resonances in acoustic measurements. You have the same issues as encountered in room measurements, in that the results are specific to the location of the sensor, so you should measure several locations on the panel.


Thanks John

My concern is that the measurements are very low in amplitude and REW tells me this when doing the measurement. I am just not sure whether what I am seeing is valid. Are there any specific parameters or types of measurement which would be more suited to vibrationa analysis?

Regards

Jose


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## GGA (Oct 31, 2006)

I did this a while ago also using the ACH-01 accelerometer. The problem is providing enough clean gain for the ACH-01. They do make a dedicated preamp for the ACH-01 but it was fairly expensive. 

I tried several sound cards before I could get one enough gain, but I still don't think I was happy with the results. I never tried the mic input on the computer.


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## jramos (Aug 9, 2011)

I calibrated the computers sound card as per REW instructions but do not know if the gain of the card is sufficient. When I do measurements with the ACH-01 the program tells me that the level is very low - about -36dB IIRC.
I am just not sure whether what I am seeing after a measurement represents cabinet vibration or not as the levels are very low.
I did a measurement with the accelerometer is free space and then another with the accelerometer attached to the speaker wall. I then did an overlay of the two measurements to look at the difference hoping that this would give me an indication but could not really see significant differences. 
Unfortunately I cannot yet post images but will try to do this once I have reached 5 posts.


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## Mr BA (Jul 1, 2011)

Hello, I'm interested in measuring panel vibrations as well.

I've bought the ACH-01, initially connected it to a Tascam US-122L and the gain was n't enough. The only amplifier which I had to hand was solid state phono stage with mc & mm inputs. I used the feedback calibration to negate the effects of the RIAA equalisation in the phono stage. (I ignored the REW error message saying that calibration error was greater than 28dB) and found that I needed ~ 58dB of gain from the phono stage to get a sensible input into REW.

I can then see frequency response & waterfall plots.

I'm interested in replicating the plots that are in Stereophile magazine. They state "cumulative spectral decay plot calculated from output of accelerometer fastened to centre of sidewall (MLS driving voltage to speaker, 7.55V, measured bandwidth, 2kHz). Is this possible using REW, if yes how do you do it?


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## JohnM (Apr 11, 2006)

For an REW equivalent make a full range sweep measurement and use the waterfall, it is not directly equivalent but should give comparable results. You could adjust the sweep level and/or amplifier volume to get 7.55V pk-pk at the speaker terminals during the peak for equivalent levels, might be on the loud side though so I'd be inclined to measure at a level that results in SPL at the listening level you are aiming at.


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## Mr BA (Jul 1, 2011)

Thanks for your help. I'll also move the accelerometer from the middle of the the side panel so that it is in line with the woofer cone & measure there.

Initial results are promising in that the frequency response plot with microphone shows a dip at 250Hz and the accelerometer is measuring a peak at 250Hz in the cabinet.


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## omholt (Jun 5, 2007)

Hi guys,

I also have the ACH-01 accelerometer and a Linearx LP201 preamp:
http://www.linearx.com/products/accessories/LP201/LP201_01.htm

I'm not able to get a high enought level. The result below is measured with very high level.
What can I do?


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