Sound meter microphone

[fred]

Is there any particular reason why sound level
meters have some sort of housing for the
electret. Is it a cosmetic thing so that people
will know where to point with the meter, or is
supposed to prevent sound from entering into
the microphone from the sides or from inside the
plastic box ?

 

[Ben Bradley]

In sci.electronics.basics, fred222@btinternet.com (fred) wrote:

Is there any particular reason why sound level
meters have some sort of housing for the
electret. Is it a cosmetic thing so that people
will know where to point with the meter,

I suspect the mic in suc a meter is omnidirectional, and it doesn't
matter which way you point it.

or is
supposed to prevent sound from entering into
the microphone from the sides or from inside the
plastic box ?

The electret mic element is not only "out separate" from the case,
that area of the case is rounded like a cone, rather than just being a
short cylinder connected to a rectangular case. Older sound level
meters used to be made that way.
The problem with the old design is that sound would bounce off the
meter housing and back into the mic as well as being picked up
directly. Depending on the length between the main housing and the mic
and the frequency, the original and reflected waves would add
constructively (causing a higher reading than it would otherwise
have), or destructively (causing a lower reading). The modern design
prevents sounds reflected from the housing from being picked up by the
mic.
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