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Old 11th June 2013, 09:46 PM   #40441
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Originally Posted by gpapag View Post
These three files I found in my laptop may be of help.

George
I have to give up on searching for the original device I saw there has been so much cosolidation and variation on the theme, it's possible the current products are different. The power and performance of what I saw was very limited.
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Old 11th June 2013, 10:02 PM   #40442
gpapag is online now gpapag  Greece
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In my twenties I had the bright idea to build an enclosure-less sub using two crossing modulated ultrasonic beams.
I had built 555 oscillators and two four-quadrant multipliers for driving the UT transducers.
The result at the crossing point was mosty noise and a faint amount of inteligible sound but totally distorted.
I attributed the failure to badly implemented electronics.

George
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Old 12th June 2013, 04:45 AM   #40443
hhoyt is offline hhoyt  United States
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Default VHF Audio

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The question that I have had is that the audio band signal does not exist until the beam hits an object (including your ear). Since the audio propagates in all angles after the reflection, even on a hard smooth surface my thoughts were that the IM that generates the audio happens at the surface and not in the air before the beam hits the surface.

The DSP necessary to make the audio work must be pretty impressive.
At a boundary the velocity of sound is by definition low and the pressure is high. Perhaps the fact that air becomes non-linear in compression accounts for the IM at boundaries which gives the down-converted audio product.

Then again, I just helped set up a new system at a local brewery with the requisite QC duties, and that tends to simplify thinking somewhat...GN

Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
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Old 12th June 2013, 12:01 PM   #40444
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Default Spooky Sound At A Distance....

hss-450.jpg
hss-450 transducer.jpg
This is one of the models in my junkbox...HSS H450.
The second pic is the transducer frame....plastic with 2mm square channels moulded across, and a mylar like film with thin foil both sides (big capacitor like) is fixed to this frame.
Presumably the modulated driving voltage mechanically excites the unsupported film and produces the acoustic output.
The failure mode was arcing through the dielectric film.
The pcb is a bit industrial/agricultural, though it does incorporate a large earlier generation DSP chip.
With one of the two transducers disconnected, the performance was underwhelming, but it is a curious effect to hear sound emanating from a hard wall/surface......the output stage may not have been optimally loaded with only one of the two transducers connected.
One day I will get back to investigating the nature of the drive signal and understand it better...maybe even cough up for replacement drivers.

Elecktor magazine did a version of this idea...http://servv89pn0aj.sn.sourcedns.com...ve_Speaker.pdf

Dan.

Last edited by Max Headroom; 12th June 2013 at 12:04 PM.
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Old 12th June 2013, 12:30 PM   #40445
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Default There's someone in my head but it's not me....Pink Floyd.

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There was an inventor, one G. Patrick Flanagan, who developed what he called iirc the "Neurophone". It was also just an AM transmitter with pads for your ears. With a bit of help from my father I built a version in my first year of high school, and it did work, although the underlying mechanism was unclear.
https://www.google.com/patents/US339...ed=0CDQQ6AEwAA

A 1W AM transmitter attached to your skull !.

Dan.

Last edited by Max Headroom; 12th June 2013 at 12:49 PM.
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Old 12th June 2013, 01:06 PM   #40446
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He is a link to one of the hearing protection pages with min. standards.

http://www.europages.com/filestore/g...1_b6bf2771.pdf
I saw no reference to U/S levels, just a simple 20 uP peak pressure no BW.


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...... It was also just an AM transmitter with pads for your ears.......


I think Flanagan went off the deep end a bit at some point......,
Hmmm..one has to wonder about the correlation.

jn
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Old 12th June 2013, 01:12 PM   #40447
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Originally Posted by hhoyt View Post
At a boundary the velocity of sound is by definition low and the pressure is high. Perhaps the fact that air becomes non-linear in compression accounts for the IM at boundaries which gives the down-converted audio product.
I would also assume that the resultant lf content would retain the planarity of the U/S wavefronts. Flat enough, and I suspect even the LF would keep a tight beam longer, until edge effects compromise it sufficiently.
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Originally Posted by hhoyt View Post
Then again, I just helped set up a new system at a local brewery with the requisite QC duties, and that tends to simplify thinking somewhat...GN
I assume your contract included the standard every 24 hour tuning and checkup regimen for the first year, right?

jn
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Old 12th June 2013, 02:38 PM   #40448
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Originally Posted by jneutron View Post
I would also assume that the resultant lf content would retain the planarity of the U/S wavefronts. Flat enough, and I suspect even the LF would keep a tight beam longer, until edge effects compromise it sufficiently.


I assume your contract included the standard every 24 hour tuning and checkup regimen for the first year, right?

jn
Yes, hhoyt,jn are on a better track. The audio IS caused in thin air by the low frequency IM of a carefully computed ultrasound beam and that is why the forward planar wave is dominant. The IM is the non-linearity of the air itself, I might add part of the problem is cancelling the THD of the resultant audio. Early brute force systems had 50% THD worst case. You also can see how inefficient the process is.

hhoyt - been listening to the stream out of Chapel Hill on a regular basis (I also like the eclectic programming). Nothing like Japanese Acid Jazz at 8AM Saturday morning.
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Old 12th June 2013, 03:08 PM   #40449
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jneutron,
Perhaps this is better as far as standards go but it is just a list of places to look.

http://www.osha.gov/pls/oshaweb/owad...ards&p_id=9735
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Old 12th June 2013, 04:24 PM   #40450
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Originally Posted by Kindhornman View Post
jneutron,
Perhaps this is better as far as standards go but it is just a list of places to look.

http://www.osha.gov/pls/oshaweb/owad...ards&p_id=9735
Thanks.

I like the "cycles per second" axis. When did we switch to Hz, 40 years ago or so?

It also stopped at 8Khz (cycles per second).

You can see why the safety guys here didn't know how to proceed..nothing to go on.

I recall charts that ran to 200 milliseconds and 144 dB impulses, that linked page only dropped to 15 minutes duration per day and 115 dB..

I also recall back in the 60's, the US Navy already recognized the issue of noise and hearing protection such that they considered the release of high pressure steam to be one of the most dangerous sounds due to the amazing high frequency content and resultant energy delivery possibility within the ear canal, well above the 8Khz regime the OSHA chart ended at.

jn

ps..I found years ago that the ACGIH was actually a very good resource for this stuff. I note that now it appears to be a more commercial site, where you have to purchase documents. I suspect that googling acgih would get others access to the information, I think I'm subscribed..

Last edited by jneutron; 12th June 2013 at 04:38 PM.
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