Rob Danielson wrote:
>
> Thanks for the clear explanation Walter!
Just remember it was pretty simplistic, I don't claim to be a expert on
mic spec measurements. Just some rough rules I've worked out in trying
to read specs. Once I have a mic in hand, I work out different rules for
using it without worrying about the numbers too much. Practical ones
from what I get when it's hooked up in my system.
> Number-wise, my simplistic understanding is that mics capable of
> excellent transparency (especially in low sound level environments
> where high-gain is common) will almost always possess sensitivity
> ratings higher than their self noise ratings. For example, the
> Sennhesier MKH-20 has 10 dB Equivalent Noise Level (A-weighted) with
> a Sensitivity of 25 mV/Pa+/- 1dB. The AKG 414 is 14/12-- only 4dB
> more inherent noise but ~13dB less output. The difference in
> transparency in field recordings made with the two mics is dramatic.
> Walter, know how sensitivity is measured? Something to do with the
> gain required to achieve a certain output,..?
> Rob D.
I had not thought about that relationship, but I suppose it might be so.
Or maybe the two specs just relate to other aspects of the mics.
I'm not near as clear on all the methods of sensitivity measurement.
Every time I think I understand it, some specs throw a wrench in that.
Most of the sensitivity measurement systems are giving you some idea of
the output of the mic when exposed to some calibrated sound level.
Generally for most of it higher numbers are better. Though that may be
too simplistic. You have to be real careful you are comparing the same
measurement between two mics.
Here's a few links I've got in my bookmarks connected to the subject,
none really cover all of it:
http://www.shure.com/support/technotes/app-sensitive.html
http://www.audio-technica.com/using/mphones/guide/charact.html
http://www.cs.columbia.edu/~hgs/rtp/microphone.html
http://members.aol.com/mihartkopf/index.htm
There's plenty more can be gleaned using web searchers. A lot of it
about as clear as mud. Or incomplete. Part of the problem is that
manufacturers consider those specs as selling points or ad copy. And
will choose measures to show their mics of in the best light. Another
problem is there are regional differences in testing mics. The Japanese,
for instance will test and report in different ways from the Europeans.
One thing to note is that the measurements are mostly related to the
sound levels of voice at close distances. I'd really like to see some
other measures, like say, how many feet out the mic could pick up a
standardized sound signal in a usable manner. Or even just do the same
tests but at a much lower sound level. Which would be more use for us.
It would be much harder to standardize such a test. And would take a
whole bunch of discussion to even agree what to test there.
Probably the best source (at least by the sound of it) is the newly
released Microphone Book which has tried to provide standardized specs
for a large number of mics. I've not gotten a copy as it's pretty
expensive, but it's tempting:
http://www.microphone-data.com/
Walt
________________________________________________________________________
________________________________________________________________________
|