> Sorry, David, but EIN has nothing to do with microphones. It's the
> noise of the mic preamp when terminated by the specified source
> impedance (150 ohms). The Rane article follows.
Dan,
What we are discussing is comparing mics for noise. EIN can be
expressed as the equivalent input whatever the energy type or source.
When it applies to mics, it is referred to an equivalant sound input
energy level. This shows the importance of being precise with
definitions, something mic manufacturers are not good at. :-)
"Excess noise", or "Equivalent noise level" is the EIN compared to the
fundamental noise of the air. As an example for my MKH-416 mics it is
13dB with A-weighting. What this means is that the mic noise from
capsule to output is 13dB higher than the thermal noise of the air
itself as it would be heard through a perfectly noiseless mic,
whatever the gain settings.
The reason for using EIN sound level values is that it is difficult to
define the sound energy entering the mic. The EIN sidesteps thia by
using a known sound energy reference level so that both noise and
signal levels effectively have the same signal path.
Regarding gain, this can be the signal energy positive gain across an
amplifier or negative gain across an attenuator. With a transducer
such as a microphone, the gain can be defined across different types
of energy such as sound energy to or from electrical energy, in other
words with mics or loudspeakers. A tungsten lightbulb has a gain
(efficieny) from electrical input to light output of around -30dBs.
Decibels are a measure of energy no more or less, across any energy
exchange. The difference between sunlight and moonlight (with
frequency weighting from the atmosphere and our eyes) is 56dB.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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