richpeet wrote:
>
> I have now spendt way to much time trying to get up to speed in the
> data given by manufacturers of microphones to figure out what is good
> and what is not, for natural sound. I am either missing a few
> building blocks in my knowledge or we simply are not given the
> information.
>
> It seems to me:
>
> 1. Sensitivity of a condenser mic is only determined by the after
> element electronics that determine how "hot" the output is and only
> lets you know if you need another preamp that already exsists in all
> condensers.
Sensitivity is also a function of the element design and does vary quite
a bit.
Sensitivity is a tricky business since so many parameters can effect it.
The measures given are normally sound chamber measures. They can be used
to compare, though it's complicated in that different specifications are
given by different manufacturers. You have to research just what the
spec means, it's some specific test and often you can find at least a
general description of what it means either from the manufacturer, or
searching the internet.
For nature recording one thing to note is that sensitivity tests are
actually done at pretty high noise levels. When, in fact we are
recording much quieter stuff. It would be nice to see, say, sensitivity
tests done at 40 dBA or even lower. The numbers provided are designed
much more for studio or concert recording.
> 2. Self noise is not represented as a AC voltage within the audio
> range by any manufacturer and therefore we have no tool to evaluate
> the specs given.
This all depends on the specs given, you don't need a voltage. Signal to
noise, usually given in dB is against 94 dB most times. The other way,
generally used by Sennheiser is to give equivalent self noise. This is
usually the S/N subtracted from the reference level. For instance the
MKH-20 lists it's A weighted inherent noise as 10 dB. That means the S/N
is 84 dBA. Sennheiser, as many manufacturers do lists a code with this
rating, which is the particular test done to determine the rating. You
can hunt up those codes on the internet if you want to examine the protocol.
Note A weighted means exactly what it says, the sound measurements are
in the A weighted sound profile that more or less represents human
hearing. Different profiles will give quite different results, and
Sennheiser also reports the CCIR weighted version, which is less
influenced by human hearing profiles and typically results in a higher
self noise measurement.
And the measure of self noise in dB as Sennheiser gives it relates very
well to the actual recording environment. In the case of the MKH-20 this
means that the environment has to approach a 10 dBA level as measured by
a noise meter before mic self noise will be much of a problem. Note this
is not the averaging dBA measure, but the fast measure.
It would be nice if all manufacturers would use the same measures and
provide all the info necessary, converting measures can be tricky.
> 3. db is a bad measure and should be tossed when comparing condensers.
Depends on what you are used to and what you are doing. Since I own and
use a noise meter, I can easily relate to a noise floor given in dB. I
prefer it to the voltage related measures. What I'd like to see is a
standardization on dB for all manufacturers for the mic noise, giving
the equivalent mic noise. It would probably be nice to have sensitivity
in the form of dB or dB related too. So, for instance if I go out and
measure the calls with the noise meter and get, say 50 dBA, I have some
idea what sort of signal I'll get from the mic.
> It seems to me what we need is two AC sonographs of the audio
> spectrum, at silence and when the sensitivity is brought to a
> constant output voltage, such as a constant of say 20 mv/pa when
> exposed to a white noise. The sonograph then needs a
> voltage/frequency view both at the constant full white noise output
> and at the silence levels.
Sonographs are not necessarily all that precise, and would certainly
introduce more chance of error. I also doubt they would be that
informative vs numeric measures.
> Without something like this I don't have a clue how to evaluate any
> one mic to another. Am I missing something or are condenser
> microphones currently impossible to evaluate against each other?
They can be evaluated, but the use of different measures by different
manufacturers does complicate it. Keep digging, in particular study how
the tests are done for better understanding. Condenser mics are really
no harder to evaluate than any other type. I hardly claim to be a
expert, and I've been digging in it for quite a while. I'm slowly
getting better at this arcane art. It does take a lot more time than it should.
Of course the cheating way is to come in the group and ask. For most of
the common mics used in nature recording someone will be able to provide
a comparison.
Walt
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