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Accelerometer Testing of Loudspeaker Drivers
Accelerometer Testing of Loudspeaker Drivers
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Old 25th September 2018, 04:13 AM   #41
bwaslo is offline bwaslo  United States
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Accelerometer Testing of Loudspeaker Drivers
The Murata PKGS-00GXP1-R is only a few bucks, weighs about nothing, and has bandwidth out to 20kHz. https://www.mouser.com/datasheet/2/2...1-R-792947.pdf

But that's only the good news.

The bad news is that it requires a buffer or a charge amplifier nearby, the output is low so amplification can be tricky (particularly at low frequency), and it needs to be in a fully shielded envelope. I made some based on the following schematic and got pretty good results.
Accelerometer Testing of Loudspeaker Drivers-accel-schemo-png
The sensor is represented by 'V1' and the 390pF cap -- don't put the cap in the circuit, just the sensor.

Vs is between 2.7V and 5V. The sensor is sensitive in the axis of the long edge, so either set the board on-end or mound the chip on edge. Again, the need for shielding is no joke. The two partially-connected transistors act as very-low-leakage diodes for bias and the impedances at the opamp inputs are very high so they pick up hum like crazy given a chance. You also need to keep the board clean (alcohol rub after soldering seems to do ok). The circuit can be made with very low mass, but the shielding can get heavy. The ACH-01 uses silver conductive paint (that can flake off if you use it for servo feedback in a subwoofer as I found out!). Perhaps this circuit can be made on a board, sealed in a small plastic jacket, and painted with silver print like that?

The ACH-01 has a heavy mass of metal (brass?) inside, which helps its sensitivity but adds mass to whatever is being tested. This guy is very light, but needs nearby, shielded amplification to get similar sensitivities.
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Old 25th September 2018, 04:09 PM   #42
gdan is online now gdan  Greece
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Accelerometer Testing of Loudspeaker Drivers
I have also done a lot of experiments using Murata PKGS-00LDP1-R (now obsolete) which is similar to PKGS-00GXP1-R. It is also very sensitive to hum and it needs shielding to be usable. In the photo, a small amplification circuit for the Murata sensor is shown with the shielding removed.

My system (based on ACH-01) that is described in the article is more suitable for vibration measurements of loudspeaker cabinets, turntables and similar things.

For these cases I think the ACH-01 is much more convenient and easy to use.

I also use the ACH for measurements on woofer's cone like the ones in previous posts but in this case it is not permanently attached to the cone.
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