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cheap SPL meter for subwoofers
cheap SPL meter for subwoofers
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Old 14th July 2009, 12:21 PM   #1
Lope is offline Lope  South Africa
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Question cheap SPL meter for subwoofers

I've done some reading on the WM-61A.

The problem is most preamp schematics suggested for it for it are only good til 110dB or 118dB.
How do you measure louder signals?

What is the simplest way to measure relative SPL dB?

For example, measuring the SPL of a speaker at 40hz, then measuring the SPL at 50hz. If one is x the other is y, I just want to know for example, y is 5dB more than x. or the 40hz signal is 80dB above my silence measurement.

So I'm thinking I just need a linear mic like the panasonic WM-61A and a computer with speakerworkshop running on it? or some RTA?
Then possibly a preamp?
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Old 16th July 2009, 02:51 AM   #2
Ron E is offline Ron E  United States
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Radio Shack (Tandy in some parts of the world) has an inexpensive meter if you want to measure actual SPL.

A measurement system like speaker workshop is not meant for measuring high SPL. In order to do that, you need a SPL meter.

You can make an SPL meter, but probably not for what the shack sells them for.
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Old 16th July 2009, 12:25 PM   #3
Lope is offline Lope  South Africa
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the radioshack one can't do below 60hz though.
the WM-61A can do 134dB apparently, which would be pleanty for a SPL meter. i just need a means of measuring it. I could even use an oscilloscope maybe.
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Old 16th July 2009, 04:39 PM   #4
adason is offline adason  United States
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here is usefull info how to midify radio shack to be more accurate fo low frequencies:
http://forum.audiogon.com/cgi-bin/fr...6&openfrom&3&4
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Old 16th July 2009, 07:09 PM   #5
GM is offline GM  United States
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I imagine this info is from Eric Wallin's extensive work on the various RS meters, so there may be some more info here: http://mysite.verizon.net/tammie_eric/audio/audio.html

Also: http://www.hometheatershack.com/foru...n-results.html

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Old 19th July 2009, 05:03 PM   #6
danielm is offline danielm  United States
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How about making the measurment at 10m and adding the 10db loss?
That's how I do it using the rat shack.
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Old 19th July 2009, 06:35 PM   #7
danielm is offline danielm  United States
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Oops... make that 20db for 10m vs 1m.
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Old 21st November 2015, 01:01 PM   #8
dotneck335 is offline dotneck335  United States
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This post from gaetan8888 shows the schematics for the Radio Shack digital (2055) and analog meter (2050):
FS: Classic (and superior) Radio Shack Analogue Sound Level Meter 33-2050
It appears that the main problem is the woefully low value coupling capacitors.
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Old 21st November 2015, 06:24 PM   #9
basreflex is offline basreflex  Spain
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the wm61A can handle a lot more mechanically. all the distortion is generated by the jfet and mostly it's non linear gate drain diode.
by bootstrapping the drain, and setting the fet in source follower mode by not loading it, (bootstrapping load impedancr as well) the fet keeps operating at constant voltages.
I built various mikes this way and they all calibrated the same sensitivity of 14mV/Pa. I used the behringer mike as a case. it turned out a classI mike as well
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Old 21st November 2015, 07:24 PM   #10
cbdb is offline cbdb  Canada
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Quote:
Originally Posted by danielm View Post
How about making the measurment at 10m and adding the 10db loss?
That's how I do it using the rat shack.
At that distance your measuring the difference in room modes at different freqs not the speaker. (Unless you do it outside. ).

There are free apps for most smart phones you can try out for.... free. I have one from rta audio that does 20hz
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