[Noisebridge-discuss] Speakers and amplified sound at NB

Gopiballava Flaherty gopiballava at gmail.com
Wed May 29 20:01:52 UTC 2013


On May 29, 2013, at 12:49 PM, LinkReincarnate <linkreincarnate at gmail.com> wrote:

> The optimal solution would be to build a set of ultrasonic emitter arrays to beam sound only to people who  want to hear it without headphones.

I thought that an array like that would be really cool, but when we got one it turned out to not work nearly as well as you'd hope:

a) It only works optimally in an anechoic chamber. When the in-phase superposed waves hit your ears, they mix to form audible sound. Unfortunately, when they hit the slightly echoic surfaces around you, the result is audible sound. The room we were in was a lot smaller than NB, so maybe the echoed audible sound would be quiet enough to not be an issue in a large enough room

b) There was extremely high pitched sound that was sometimes audible. I don't know if the unit we had wasn't high enough frequency, or if the wave superposition sometimes created annoying high pitch noise.

c) I think this was a construction artifact: you could hear some audible sound right by the unit. I believe that the grill or other structures would produce some diffuse vibrations right next to the unit that would superpose right there.

I don't actually know much of the technical specs of the unit we had. It was built by DaimlerChrystler in ~2004 as part of a research project. We had it mounted on a pan-tilt unit and pointed it at people to directly deliver text messages without interrupting people around them. The overhead projector system worked much better for that.

Thanks,

gopi.


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