soundhaspriority wrote:
"Mike Rivers" wrote in message
oups.com...
soundhaspriority wrote:
You may want to consider getting some Avenson Audio STO-2s.
They look
like an inexpensive alternative to Earthworks. But these mics have about
10
dB more self noise than typical.
The orignal Earthworks measurement style mics are a little on the noisy
side. They made better (quieter) models later. It comes with the
territory when you have a small diaphragm - not a lot of output for a
given SPL, so for the same voltage out of the microphone you get more
noise.
Also, they're
electrets, not AT back electrets, but real electrets, with the greater
noise
that implies.
An electret is the electrostatic equivalent of a permanent magnet.
They're all real, and they're all "back." Back when manufacturers first
started to make inexpensive mics, they used electrets to save the cost
of providing a DC polarizing voltage, and at the time, all of the
electret mic capsules were cheap and crummy. There's no reason why an
electret mic capsule can't be good, it's just that the only market for
electrets at the time were in cheap mics. The Shure SM-81, which has
been around for over 25 years, has an electret capsule and it sounds
fine and is reasonably quiet for mics of that period. New ones are even
quieter.
Don't perpetuate rumors about the technology based on when product
demand was for cheap electrets.
I stand corrected on the issue of the backplate. However, your assertion
that equally good microphones are made by either method is not supported by
this Wikipedia article: http://en.wikipedia.org/wiki/Microphone I quote:
Though electret mics were once considered low-cost and low quality, the best
ones can now rival capacitor mics in every respect apart from low noise..."
The article says that electrets can be made that are the equal... but also,
ARE NOT made that are the equal in terms of noise. The article does not
explain why quiet electrets cannot be made, but it quite unequivocally
states that they are not.
You should edit that entry and correct it. External polarization can be a
noise source that electrets are free of and electrets have no extra
mechanism for creating noise.
Noise in a condenser microphone is due to three factors:
1. Brownian motion (size of diaphram)
2. Noise figure of the FET amplifier
Good to here.
3. Strength of the polarization field.
Doesn't affect SNR. Affects sensitivity. Sensitivity is a kind of gain
and that due to polarization is applied identically to both the signal and
to the self noise.
A third noise source that is seldom reported but that can be larger than
either of the others is the noise of the pressure equalization port in an
omni or the acoustic front to back resistance in a gradient mic. An
acoustic resistance is as much a source of noise as is the electrical
equivalent.
The obvious candidate for the difference in noise between the best available
electrets versus the best available condenser microphones would be with
respect to factor 3.
If it were correct.
Therefore, this is not a rumor; it is a fact that in choice of an electret,
one gives up some noise.
Wiki is very subject to inclusion of rumor. :-)
Bob
--
"Things should be described as simply as possible, but no simpler."
A. Einstein