Now this might seem low tech....

But air leaks are high frequency noise.

add to this the fact that they tend to be fairly localized, and the answer
turns out to be a long tube not too dissimilar to a straw...

Kind a reminds me of ballancing two venturi carbs....

You feed the microphone into the straw, blocking side noise, to create
a sort of directional pickup. Then you monitor loudness of high frequency
noise components.... (High pass filter?) as volume increases, led scale
advances...

The neat thing about this is you can set the zero point to near to a place
that doesn't leak, and then trace the seals etc, with the sensor tip, and
actually pick out the place where the seal is leaking. Not only that, but
it saves on thickening of eardrums because you are not exposing the
workers ears to focussed high frequency sound.

Getting the sensitivity/frequency cut-offs will require some work, but
then, I don't get any money for the idea....;)

                                Grey

GRAEME SMITH                         email: grysmith@freenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Tue, 29 Jun 1999, Roger, in Bangkok wrote:

> I have a customer having problems with vacuum leaks (-50 kpa or so
> range) in equipment that they manufacture.  I expect their
> problem is with connectors and seals, and they have asked for help to
> locate and correct the problem.  Seems simple enough to sniff around
> with a tiny microphone.
>
> Thought...why not develop a simple handheld field
> tester...PIC...active filtering...LED bargraph...etc
>
> Unknowns...are there audio signatures that would allow this...has it
> already been cheaply and efficiently done...
>
> Appreciate any input.
>
> Regards/Roger, in Bangkok
> Roger N. Shane
> Suncolor Co., Ltd.
> P.O. Box 11-303
> Prakanong, Bangkok 10110
> Thailand
> Email:  roger@wnet.net.th
> FAX:    +1 (707) 276-1170
>         +66 (2) 291-3826
> ICQ     2152164
>
> SAHA GROUP...Thailand's Best!
>