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Measurement Microphone

This measurement microphone is very much inspired / copied from Linkwitz Lab's DIY construction (se here).

The microphone used is the Panasonic MCE-2000 which can be obtained from Monacor

Technical datasheet
Frequency range 20-20,000Hz, 2dB
Sensitivity 6mV/Pa/1kHz, 4dB
Output impedance 2kΩ, RL: 2.2kΩ
S/N ratio > 58dB
Coupling capacitor 0.1-4.7F
Admiss. ambient temp. 0-40 C
Power supply 1.5-10V DC current /0.5mA

An electret microphone needs a bias voltage to work. This is actually normally provided by the PC sound card, and you can therefore normally just connect the microphone directly to the PC. But in order to use long cords, e.g. if your measurement PC is not located near where you perform the measurement (I use a stationary PC located in a room adjacent).

The circuit is very simple. The microphone is connected to JP2 where R1 provides a +4,5 V bias. The bias is kept away from the amp by C2, which together with R3 provides a high pass filter. U1A is the amp, here with a gain of 2, which is easily changed by changing R4 to a higher value (gain = 1+R4/R5). As I'm using a single 9 V battery U1B provides a virtual ground. As it is a single supply construction C3 is needed to remove the bias on the output. JP1 is the battery connection, and JP1 is the amp output. I'have tried using TL072, which works just fine, but I will try out other op-amps as well to se whether there is any improvements in performance (which I really doubt for these kind of measurements.)

Update September 17: In order to use this microphone with different programs (like ETFand ARTA) that requires the mic to be connected to the line input through a pre-amp, I have changed the gain to 23x or 27 db by using R4=330k and R5=15k. Now it goes directly into the line input. 27 db is a bit to the low side, but seems good enough for this purpose. There is no audiable noise problems at all.

 

 

The PCB is double sided to provide a ground plane, but this is really not necessary, in such a small construction. I have had the PCBs produced by Olimex, who provides a really great and fast service, and the cheapest solution for making professional prototype PCBs. Highly recommendable.

I have a few PCBs in spare, that you can have for 4 US$ a pcs. + shipping (normal cheap postal service). Contact me on e-mail if you are interested.

Here is a picture of a populated PCB

Just to try it all out, I have mounted the mic on a pen using Gaffa tape and mounted it on an old lamp stand. I'm working on a more permanent solution :-)

The finished casing

... and the aluminium pipe where the microphone is mounted at the tip

The smal capsual mounted at the tip of the pipe