From: Tiago A. 
To: psnlist 
Sent: Mon, 22 Jul 2013 2:13
Subject: Subwoofer to reproduce sine waves at low frequencies?

Hi.
After searching a bit about subwoofers at low frequencies, i put the
cheapest subwoofer i have (90mm) near (2/3mm) from a L15B 4.5Hz
horizontal geophone. Using a sine wave tone, it recorded very well at
10Hz, <10Hz was a bit tricky but managed to get good results.
Then i tried at 10s, at first i was only getting a very weak noise at
5s from the subwoofer

Hi Tiago,

    The sensitivity of a geophone falls off as f^2 below the resonant
frequency, so the output at 0.2 Hz will be (4.5/0.2)^2 down on that
above 4.5 Hz =3D 506 ! At 10 seconds, it will be over 2,000 down.....

    Regards,

    Chris Chapman

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