FFT Analyzer Calibration - Microphone-Pistonphone

[kaiserman]

I am looking for some help regarding calibration of a sound measurement system. A rather basic problem. This is probably a "day 1" problem in any beginner acoustics lab. However, I am able to calibrate the system 3 different ways. And not to my surprise, I end up with 3 rather different values. I want to get it right. Instruction manuals are missing from the lab. AAAAAAHHHHHH!

I have what may be considered a simple laboratory sound measurement servo:
(1) IAC semianechoic chamber
(2) B&K condensor microphone
(3) B&K Microphone power supply/ preamplifier
(4) Ono Sokki FFT dynamic signal analyzer
(5) B&K sound calibrator

I desire to measure noise of a small stepper motor.

My main question involves how to combine 3 different unit types:
(1) The microphone calibration units: 49.5 mV/Pa
(2) The sound calibrator units: 94dB @ 1kHz
(3) The FFT analyzer units: V/EU

I'm not sure how to get the units to jive so as to calibrate my system so it will be ready to take sound measurements. Is EU any engineering unit I pick like Pascals?

Thanks,
Kaiserman

 

[GregLocock]

I don't know how to drive an Ono Sokki, so we'll leave that alone. Let's calibrate the thing so that 1 Pa= 1 EU

94 dB is 1 Pa (near enough)

the mic will generate 49.5 mV at 1 Pa

So you need to set the Ono Sokki to .0495 V/EU and it will read out in Pa.

BUT you probably want dB. the reference level for dB is 2*10^-5 Pa. Somehow you have to get the Ono Sokki to do that, it's probably a setting like dB ref = X EU

Your next surprise and delight will be when you put your 94 dB calibrator onto the mic, and try and measure the peak at 1000 Hz. You'll probably get a peak at about 90 dB, or .6 Pa

This is correct.

grin.


Cheers

Greg Locock