Subject:
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Interesting audio puzzle
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Mon, 8 Jan 2001 14:06:36 GMT
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Viewed:
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80 times
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Over the weekend I experienced a puzzing thing with my home stereo
system.
My stereo system includes a powered subwoofer, which started humming
when I stepped or stood in various places in my apartment. The stereo
was on, but the CD playing was paused at the time. At first I thought
the noise was a neighbor, but I quickly realized that it was
synchronized with my steps, and then experimentation showed several
locations where I could step or stand to cause the effect. Some
locations only aroused a short tone in conjunction with placing my foot
down in a spot, but many locations resulted in the tone continuing while
I stood on a spot.
I strongly suspect the tone was 60hz, but didn't do anything to verify
that. The question is how was my stepping in certain places resulting in
an audible tone and others not? I assume a minute amount of 60hz power
was leaking through the system, so the subwoofer was probably humming
away the whole time, just usually not loud enough to hear.
One thought I had was ground currents flowing in the carpet or padding
underneath. I think most of the locations were spots where the carpet
had more compressibility. My father thought it could have been
mechanical vibrations and as I moved around, I changed the resonance
characteristics of the floor, with the vibration then causing some part
of the circuitry in the subwoofer or stereo to start resonating (and of
course as the subwoofer became louder it pumped more mechanical energy
into the room, which could result in a positive feedback path).
Any thoughts? Any ideas for experiments to try to understand it better
(unfortunately I don't have an osciliscope to monitor the subwoofer).
--
Frank Filz
-----------------------------
Work: mailto:ffilz@us.ibm.com (business only please)
Home: mailto:ffilz@mindspring.com
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Message has 2 Replies:
 | | Re: Interesting audio puzzle
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| (...) <snip> (...) A couple things that may or may not help, but might be fun... Place a heavy object in one of the places that appears to generate a constant tone, and stand in another such place. How does that affect the tone? "Jump" in place (...) (24 years ago, 8-Jan-01, to lugnet.off-topic.geek)
| | | Re: Interesting audio puzzle
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| (...) Umm, did you verify this with two people in the room? One moving about, one sitting still. It could be that the noise wasn't changing, but as you moved about the room, you were moving in and out of zones where the noise was audible. Sounds a (...) (24 years ago, 8-Jan-01, to lugnet.off-topic.geek)
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