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Old 21st March 2008, 09:01 PM   #1
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Default School project wm-61a question

I am building a mic preamp out of transistors and modifying a wm-61a capsule for a school project. On Linkwitz-Riley's website it says the capsule has a 5V peak to peak output voltage swing at about 140 db. This seems really high. Is this correct or is it a lower value. If its wrong what is about the output voltage from the capsule. Thanks
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Old 23rd March 2008, 03:51 AM   #2
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Nevermind I read the Linkwitz page wrong but I still was wondering if anybody know how large the voltage output is for a modified wm-61a capsule. I'm running it off a 9 volt batter with an 10k resistor in series with the capsule. Thanks
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Old 23rd March 2008, 11:37 AM   #3
Mooly is online now Mooly  United Kingdom
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Use a 'scope and measure it. 140dB, what are you trying to measure, a rifle shot ? In all fairness it's a valid question but one that is not easy to answer. Do as you say 9volt, 10k resistor and measure across capsule, clap your hand next to it and try and get a peak voltage reading. Not sure if this would work but why not use a speaker of known sensitivity e.g. 90dB for 1 watt @ 1 meter and try and calculate and interpolate readings yourself. Each doubling of power will give 3dB increase. 1W 90dB 2W 93dB 4W 96dB and so on. Measure the output and project results out to 140 dB.Would be interesting school project I would have thought.
Regards Karl
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Old 23rd March 2008, 01:10 PM   #4
bigwill is offline bigwill  United Kingdom
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As a side note, don't try to get 140dB out of the speaker
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Old 23rd March 2008, 05:37 PM   #5
AndrewT is offline AndrewT  Scotland
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50mVpp will come from 100db.
50mVpk from 106db.
These will be closer to the capsule maximum output for a sensible SPL.
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regards Andrew T.
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Old 23rd March 2008, 11:14 PM   #6
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Thanks. School was closed for the week so I didn't have access to the labs. This will help a ton.
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