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The DIY Ribbon Velocity Microphone, a home project

Testing and Specs

As it turns out, Spike is dangerously close in spec with the Test microphone we were using.  In fact (of course), Mr. Dellinger couldn't believe how much better the S/N ratio was compared to the test mic!  He had to run the test three times!    
 
I was shocked, but he was REALLY shocked.

natssinesweep.jpg

Here's what we've come up with so far...

The big boost below 200 Hz is from the proximity effect mentioned earlier, and the really big boost down at 30 Hz is from the resonate frequency of the ribbon itself. 
I believe that the second big boost is pronounced even more because of the windscreen and body size, so I'm going to try to compensate for it in the next mic I build.

It may look crazy until you realize that it's on a small scale.  In reality, the mic doesn't usually stray more than +/-3 or 4 dB from 0dB from 200 Hz to 20 kHz.  That's pretty damn flat for something I made in a Dorm Room!
 
 

Here's what were doing...
 
We're using Studio A control room at MTSU to set up a test.  We're using the Audio Precision to generate and interpret sine wave sweeps between my microphone and the B&K reference microphone the shop uses for certain reference tasks.
The B&K is an phantom-powered omnidirectional reference microphone with a frequency range of 20 Hz to 40 kHz.  It's very high quality, of course. 
 
Since we don't have an anechoic room to perform tests in, Alton suggested that we use this microphone to make a base for comparison, so that we might use the results from my microphone in an averaging of the two to create the true frequency response graph of Spike.  It worked well, especially the first time we did the tests. 
 
The mics were set up (at different times) in the identical spot, and a sine wave sweep was done.  The Audio Precision computer reads the sweeps, and displays them in the handy form shown above.  Theoretically, having the B&K as the reference would allow us to account for all variations in the room (since it is omni).  The frequency response of the B&K was wacky, as well as mine in the beginning.  But when I averaged the two using some elbow grease, it was shocking!
 
The results were so good, that I could hardly contain myself.

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For a preamp, we were using a Millenia pre, with a fair amount of gain.  We couldn't tell how much exactly, because it is not marked!
 
On the noise floor test, we closed both microphones up and isolated them from the room as much as possible.  The B&K came out with a -33 dB reading, and Spike came out on top with a -62 dB.  Of course, Spike is passive and very low noise by nature.
 
Since then, I have used Neodymium magnets for the mic, and the tests are off-the-wall.  Average of 10-12 dB over what they were.  And the response is even better!  The low frequency response is a little flatter, because of the translation with the new magnets, I believe.

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