🚀 go-pugleaf

cstevens@uswest.com (Clarke Stevens) wrote:

>In need some instrumentation microphones and accelerometers for some
>multi-channel (16) DSP tests I am running.  My current choices seem to be
>B&K and HP's DSA brand.  Both of these are quite expensive.  Does anyone
>know of some less expensive options that would meet the following
>criteria?

>* Flat frequency response from about 30 Hz to about 8 kHz or better
>* Consistent quality
>* Battery powered power supplies/amplifiers
>* BNC output
>* Reasonable environmental tolerance (i.e. mounted to a vehicle in the hot sun).

I use KE4-211-2  (Part #172280) omnidirectional electret condenser
capsules from

SENNHEISER ELECTRONIC KG 
Am Labor 1
D-30900 Wedemark
Germany

Phone: +49 5130 6000
Fax:       +49 5130 6312

They are specified by the manufacturer to have a frequency response
from 20Hz to 20kHz (40Hz to 10kHz within +/+ 2.5 dB). The response
above 10 KHz is not shown in the data sheet I got. 
_But_
I tested several of them in camparison to a Bruel & Kjaer Mic and
found them to be flat from 100 Hz to >20kHz with a max. deviation of
+/-0.5 dB !
From 100 Hz down to 20 Hz there was a decraese of about 3 dB, which
could be corrected by means of a simple filter.

The price is 50 DM, which is $34.

If   your intend is to do conventional sound pressure level
measurements I recommend them without any doubt. But if you are going
to do something like a Fourier analysis, the response to impulses will
be relevant, which is something I did not test.

Output voltage:                    10 mV/Pa +/- 2.5 dB
Output Impedance:            app. 1.5 kOhms at a supply voltage of 5 V
Power consumption:         app. 0.15 mA at a supply voltage of 5 V
Operating temp. range:    -10 to +50 degrees Celsius
Equivalent noise:               app. 29 dB

Diameter:                              4.75 Millimeters (0.187 inches)
Length without wires:         4.20 Millimeters (0.165 inches)

To preserve the good high frequeny response, you should mount them at
the top of a grounded metal tube which is 4 or more inches long (The
longer the better). The diameter of the tube should not exceed 5 to 6
Millimeters.

Such tubes fit well into the cable outlet of an XLR Connector.
Because  the capsule is a three pin type (One for the supply voltage,
one for the output and one for the GND pin) you can not use a BNC
connector at the microphone itself unless you mount the battery at the
end of the tube. 

I think that because of the low price and high quality of this
microphone it would be worth to send a fax to SENNHEISER in order to
get a list of their international distributors.

Please make sure that you get the KE4-211-2  (Part #172280) capsule,
because the different types look all the same.