Infrasonic Speaker - Need advice for undergrad thesis project

[myhrrhleine]

I can think of 2 unrelated possibilities.
One- Use vented enclosures tuned to the desired frequency
You may need more than one tuned to a different frequency.
Two- Use headphones with very small enclosures.
Meaning hearing protectors covering headphone speakers.

[myhrrhleine]

One more idea
Vibrating water in a swimming pool.

[cyclecamper]

Originally Posted by myhrrhleine

One more idea
Vibrating water in a swimming pool.

The lack of high-frequency requirements allows the use of heavy fluids and radical "hydraulic horn" geometries. Indeed, it you had a large-displacement "driver" of some sort, you could easily use something like water as media for the transform to coupling more surface to more air. Variations on "stick of dynamite in a crater lake".

[cyclecamper]

...although you were probably taking about more efficient coupling to the underwater ear...?

[Nanook]

earlier in the thread someone suggested the "Buttkicker" items available at PartsExpress. These are within the $800.00 budget you suggested. And here's an idea. Borrow a tympani from the music department. Use the "buttkicker" to excite the typmani (attach the bottom plate of the Buttkicker to the tympani's kettle (temporarily). You're starting with a drum with the capability to play naturally quite low.If you excite the kettle it should vibrate at the desired frequency.

Another might be to get a good AC induction motor. Make a wheel that could be attached to the end of the motor shaft. Make a connecting rod and attach it to the wheel off-centre (the distance mounted off-centre multiplied by 2 is the stroke of the infra-woofer). The other end of the connecting rod should be mounted to a rigid plate, perhaps plywood or rigid foam or similar. This becomes the transducer's radiating surface.

Attach the rigid plate to a suspension or surround. Perhaps an automotive innertube could be used.The suspension must now be mounted to some sort of baffle. I'd cut one from plywood and reinforce it. Now a "tube" or enclosure needs to be constructed. Something as simple as a vertical tube (maybe a concrete casting?). It must be vertical because I do not believe that you can hold the radiating surface centred if mounted pointing in the horizontal direction.

There are a bunch of alternatives that could be a combination of a tympani drum combined with a motor drive. Oh, you need a method of controlling the transducer. So a frequency generator and the ability to amplify that frequency to a working voltage for the AC motor.

If it seems like I've made this all sound trivial, it is not. I might suggest (as others have) that you get someone in the Engineering or Physics departments involved, perhaps an undergrad looking for a project in acoustics.

If it is successful, it should only be tested outside with excellent hearing protection or within a performing hall capable of allowing wavelengths in the 200 ft range to be reproduced, and under strict supervision. The hall should be completely closed to all except those required to supervise the implementation. If it doesn't shake itself apart it could be very interesting.

[DrDyna]

I'd still be a fan of constructing an enclosure that you can get inside. I did this once when I was younger, using a refrigerator sized box and an old 15" woofer, but I think you could probably build it big enough to get a few people in, so long as you take proper care to seal it up.

You're going for a pressure vessel instead of a room, think "hyperbaric chamber". Maybe find an old fluid or fuel tank that you could get people into and cut out a bunch of driver holes on each end of it.

Or, even something like a short bus with a wall up halfway through it. Seal it up real nice with great stuff and mount a dozen woofers in it at the mid point on a rigid wood wall. Enough room to seat 6 or 8 people and you could EQ it down to pretty much wherever you wanted so long as you pick the right drivers and don't get too wild with the volume.

Edit: Does your college have an old bomb shelter? lmao.

[Moondog55]

Also I do suggest watching the "Brown Note" episode of Mythbusters.
Take a monetary note here I believe that EACH of the drivers in the multiple driver boxes used in that episode cost more than your whole budget ( Meyersound aint cheap)

[cyclecamper]

Originally Posted by cyclecamper

Danley "Intersonics" brand of rotary-drive subwoofer...start with surplus capstan motors from large mainframe disk drives.

Should have read "tape drives" not "disk drives"...oops.

[cyclecamper]

Using the most conventional hardware, of course the idea of pressurizing and depressurizing a very small room is the most economical. Could also be difficult to demo to a large audience, possibly dangerous.

You could also look into renting commercialy-available defensive infrasonic weapons. I recently saw the Japanese using them on ships to discourage the Greenpeace folks trying to disrupt whaling and harvesting dolphins and other protected species in international waters.

Finding some Intersonics seems the best bet. Several in a row can get infra-sonic. Most subs don't.

[Moondog55]

Getting a well sealed room is not going to be difficult tho; just look at dis-used commercial cool-rooms/freezers, hire it for a week or so then setup; conduct experiment take down and go. Just use the door opening as the place to mount the driver array and fabricate a replacement to suit from chipboard and ply the seals on those doors is usually airtight to a large factor.
But I still think your budget is too tight to do a realistic test, it is about what I have budgeted for my new HT setup.
Hiring the gear may be cheaper, have you contacted any of the local sound people to see what is available commercially??