Re: MIC for LF SPL metering?

[Rich Andrews]

(Miles) wrote in
om:

> Hello,
>
> I would like to build an SPL meter for car audio applications. It
> will be used to measure sound levels for tunning stereo's for db Drag
> competitions. The rules stipulate a freq range of 20 - 80 Hz, so HF
> response is not an issue. It must however handle very high SPL
> levels, 150dB - 160dB ideally. Linearity across the dB scale is not
> an issue, as that can all be compensated for in software.
>
> Do you know of any resonably priced microphones that will work for
> this purpose?
>
> Thanks alot.
>

150-160 db at 20-80hz? What's wrong with a seismometer? (:>)

Better make sure you are wearing hearing protection or else that big bass
will be the last thing you ever hear.

r


--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

[Richard D Pierce]

In article >,
Miles > wrote:
>Hello,
>
>I would like to build an SPL meter for car audio applications. It
>will be used to measure sound levels for tunning stereo's for db Drag
>competitions. The rules stipulate a freq range of 20 - 80 Hz, so HF
>response is not an issue. It must however handle very high SPL
>levels, 150dB - 160dB ideally. Linearity across the dB scale is not
>an issue, as that can all be compensated for in software.
>
>Do you know of any resonably priced microphones that will work for
>this purpose?

No. low frequency microphones capable of those sorts of sound
levels are not something that lends to cheap implementation.

I would recommend instead you consider finding good used
professional unit. I regularily see good condition Bruel & Kjaer
2204, 2205, etc, for around $100, General Radio 1561, 1565 and
such for similar money. These will get you to 150 dB, and the
mikes that typically come with them are good to below 20 Hz.

But above 140 dB anyway, it's a REAL tough job. few if any
professional mics are built with guaranteed linearity at those
levels, and they ain't cheap.

As an aside, precisely what idiot wants to be subjected to these
sorts of utterly absurd sound levels and for what purpose?

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

[Tony Pearce]

"Arny Krueger" > wrote in message
...
> No. In fact I know that one reasonably-priced measurement mic that is
> generally quite good, the Behringer ECM-8000, rolls off below 40 Hz.

And is not rated for 160 dB SPL anyway. Any acoustical attenuation will
probably make the response worse.

TonyP.

[Richard D Pierce]

In article >,
flint > wrote:
>
>"Miles" > wrote in message
om...
>> Hello,
>>
>> I would like to build an SPL meter for car audio applications. It
>> will be used to measure sound levels for tunning stereo's for db Drag
>> competitions. The rules stipulate a freq range of 20 - 80 Hz, so HF
>> response is not an issue. It must however handle very high SPL
>> levels, 150dB - 160dB ideally. Linearity across the dB scale is not
>> an issue, as that can all be compensated for in software.
>>
>> Do you know of any resonably priced microphones that will work for
>> this purpose?
>>
>> Thanks alot.
>
>Have you considered using a 10" speaker in a small enclosure or on the end
>of a long tube that sticks out of the car? You could calibrate it by
>comparing the output from the speaker with a good, calibrated, mic at, say,
>110dB, 105dB and 100dB, then extrapolate the levels higher than that.

And such a "microphone" would be essentially useless about a
a few hundred Hz, given the huge size of the diaphragm. Further,
ANY attempt to extrapolate assumes, quite incorrectly, linearity
in both the mechanical suspension and the Bl product of the
driver.

Look at the physical dimensions of microphones useable at very
high levels: they are quite small, not large.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |