speaker for use with a small parabolic reflector

I want to mount a small speaker facing a small parabolic reflector (a few cm in diameter) for directing sound.

What kind of speaker component do I need? (What's it called, so I can find it in a catalog?)

Reply to
Bob Fnord
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Something much smaller than your reflector so it won't block the reflected sound. An earpiece? Art

Reply to
Artemus

Hello Bob,

If you mean with "audo" the frequency spectrum that we can hear, your parabolic reflector with few cm diameter will not give you any remarkable directivity.

To get useful directivity from a dish, the diameter should be very large with respect to the wavelength of the audio. 1 kHz in air is about 0.33m.

Does your few cm refers to the dish or the speaker you want?

With kind regards,

Wim PA3DJS

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Reply to
Wimpie

Look for piezoelectric transducers.

Assuming 100 kHz frequency (wavelength 3 mm) and reflector size 3 cm, you could expect to get a 6 degree beam :-) or lamda/D radians.

Reply to
upsidedown

"Bob Fnord"

** It might help if you told us the frequency involved.

Dickhead.

Reply to
Phil Allison

If a few cm in diameter, it can only direct ultrasound, not audible sound. Might as well just use a flat plate reflector.

Instead use a 30-50cm reflector taken from an inexpensive parabolic microphone.

For high acoustic power, probably best would be a high-watt full range

5" loudspeaker driving into a heavy plastic cone leading to a short pipe, with the mouth of the pipe placed at the paraboloid's focus. (Back of the speaker mounted in a thick wood speaker cabinet stuffed with acoustic damping material.)

(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb at amascicom

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amateur science, hobby projects, sci fair Seattle, WA 206-762-3818 unusual phenomena, tesla coils, weird sci

Reply to
Bill Beaty

I'm interested in 15 to 20 kHz in mind (so 16 to 22 mm wavelength) and thought 30 mm for the reflector. Thanks for the beam formula! (I may need to reconsider.)

Reply to
Bob Fnord

How about using a re-entrant trumpet speaker, just replace the driver with a sensitive mic element. Tom

Reply to
hifi-tek

ahh, never mind, didn't read the thread closely enough. Tom

Reply to
hifi-tek

15 to 20 kHz, so the wavelength is around 2 cm.

Huh, what's your problem?

Reply to
Bob Fnord

"Bob Fnord"

** You are the problem DICKHEAD

- for not including that essential info.

..... Phil

Reply to
Phil Allison

The dish. I'm thinking 15 to 20 kHz. TBH, I want to build Steve Gibson's sound raygun.

How good would an old-fashioned camera flash reflector work for sound?

Reply to
Bob Fnord

15 KHz is only very weakly audible to most "middle-age" American males. 20 KHz is audible at all among Americans mostly to 20-somethings and younger and to women as old as pushing 50.

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There gets to the matter of the transducer and any horn associated with it, likely needing to be at least about 1.2 wavelengths wide to focus its output largely into a cone 60-75 degrees wide. A mere wavelength or a little less is sufficient for 135-180 degrees.

At 10 KHz, which I think is more likely a practical lower limit, a wavelength is about 1.36 inches or 3.45 cm - for a 135-150 degree or so projection from a horn mouth that wide.

Oh, do you wanna push that output through a pababolic dish of width around or within 5rangeb of diameter 23 cm to 1 m?

--
 - Don Klipstein (don@misty.com)
Reply to
Don Klipstein

Did you see that piece a couple years back where a guy could whisper through his device up in the nose bleed seats, and a guy 200 yards away down on the field could hear it plain as day?

He used ultrasonic frequency as a 'carrier' and modulated that with the human audible range 'info' into a high frequency horn with a modified actual 'horn' part.

Reply to
Spurious Response

(...)

I thought that required a second ultrasonic CW carrier to 'beat' with the modulated carrier using eardrums as a nonlinear mixer. Not true?

--Winston

Reply to
Winston

Or a DSP to create a composite waveform of the CW carrier mixed with the (Frequency Modulated?) carrier. It's just ultrasound until it impinges on an eardrum, yes?

--Winston

Reply to
Winston

The person on the ground had no device, and the guy in the gallery had a singular device as I recall. I am not sure if a single mechanical transducer can fire two "main carriers" as it were Sounds like two horns would be needed

But what you say sounds like what would be required to 'create' movement at the eardrum in the range the auditory nerve responds to.Maybe it can all come from one horn, maybe another is needed for the second carrier, but it does sound like we need two like you are saying.

Reply to
Spurious Response

(...)

I'd be very leery of ear damage. (If I'd known that I would live this long, I would have guarded my hearing much more closely.)

Are you blessed with neighbors that want to listen to what you are playing, exactly when you play it? Me neither.

I suppose there are less pleasant ways to go..

So, my desk *wouldn't* have saved me?

--Winston

Reply to
Winston

Quite directional too. :-) Seems one could make a cool 'whole room' sub-woofer with this idea that would use a ceiling full of HF transducers to propagate an LF wave at the listener.

Naaahhh! I wanna feel (and know) that the walls are shaking/shakeable. Give me real moving air masses any day. Amplitude is important too.

One cannot be too close to certain explosive blasts as the shockwave alone bursts internal organs and such other nasties. That is amplitude.

I always thought the "Duck and cover" stuff from the fifties and sixties was pretty funny (the kind you are NOT supposed to laugh at).

If one "sees" the flash, it is already too late to go duck and cover. Might as well wander outside and await the shockwave to finish the job.

Reply to
Spurious Response

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