I would like to build something like this:
These directional speakers throw sound in focused beams like a spotlight | Yanko Design
But I want it to be quite a bit larger, capable of high SPL. I only need it to produce audio above 5 or 6 kHz, so I'm thinking of using a compression driver for the audio part. I want to use pipes to mix the sound waves.
I was thinking of simply summing the audio and ultrasound by putting a pipe inside a pipe, both possibly having an exit throat at the same point, perhaps a flattened pipe (see attached images). Would this be sufficient to modulate the pressure waves?
I was wondering if anyone here would have any tips for me, or if anyone knows of some online acoustic simulator that could aid the design?
This is a personal project as an exercise. I looked up uni-directional drivers, and found the link.
These directional speakers throw sound in focused beams like a spotlight | Yanko Design
But I want it to be quite a bit larger, capable of high SPL. I only need it to produce audio above 5 or 6 kHz, so I'm thinking of using a compression driver for the audio part. I want to use pipes to mix the sound waves.
I was thinking of simply summing the audio and ultrasound by putting a pipe inside a pipe, both possibly having an exit throat at the same point, perhaps a flattened pipe (see attached images). Would this be sufficient to modulate the pressure waves?
I was wondering if anyone here would have any tips for me, or if anyone knows of some online acoustic simulator that could aid the design?
This is a personal project as an exercise. I looked up uni-directional drivers, and found the link.
Attachments
It's hard for people to give useful feedback without some more details.
What specific transducer are you looking at?
What do you mean by "high SPL"? What SPL at what distance?
These ideas have been around awhile. There are more examples and some of the basics presented here:
Sound from ultrasound - Wikipedia
At that distance, absorption and spreading may significantly impact things.
This paper suggests a loss of 1-2 dB/meter at 50 kHz.
Absorption of ultrasonic waves in air - A. Vladišauskas, L. Jakevičius
https://pdfs.semanticscholar.org/c408/db1cbccdc558cdb76ad761bc149eae8504c7.pdf
another estimator
Choosing an Ultrasonic Sensor for Proximity or Distance Measurement -- Part 1: Acoustic Considerations | FierceElectronics
This paper suggests a loss of 1-2 dB/meter at 50 kHz.
Absorption of ultrasonic waves in air - A. Vladišauskas, L. Jakevičius
https://pdfs.semanticscholar.org/c408/db1cbccdc558cdb76ad761bc149eae8504c7.pdf
another estimator
Choosing an Ultrasonic Sensor for Proximity or Distance Measurement -- Part 1: Acoustic Considerations | FierceElectronics
Thank you for that article. If I average 1.5 dB per metre, then at a loss of 45 dB, I guess I'll just need to output 140 dB. 
I'm thinking of using those ultrasound transducers because the ones I can get output 117 dB. If I use 6, I should be able to get 132 dB. I could possibly shape them into a paraboloid with a 20-30 metre focus.
I'm thinking of using those ultrasound transducers because the ones I can get output 117 dB. If I use 6, I should be able to get 132 dB. I could possibly shape them into a paraboloid with a 20-30 metre focus.
There are some very high output ultrasonic transducers. The ones I've seen have typically been the stepped-plate variety, like these:
A highly-directional ultrasonic range sensor using a stepped-plate transducer
A HIGHLY-DIRECTIONAL ULTRASONIC RANGE SENSOR USING A STEPPED-PLATE TRANSDUCER - ScienceDirect
Airborne ultrasound for the precipitation of smokes and powders and the destruction of foams
Airborne ultrasound for the precipitation of smokes and powders and the destruction of foams - ScienceDirect
I don't know if they're suitable for what you are trying to do though, or if you want to take on that much work and/or cost.
Output is probably the most significant hurdle for your project, so some experiments seem in order there. If you can get the 117 dB capable transducers cheaply, an array of those seems like a reasonable starting point. Keep in mind that the wavelengths you're dealing with are quite small, so physical alignment will likely need to be precise to get the most output. A simple flat array with more transducers may be easier to implement than a shaped array or reflector.
A highly-directional ultrasonic range sensor using a stepped-plate transducer
A HIGHLY-DIRECTIONAL ULTRASONIC RANGE SENSOR USING A STEPPED-PLATE TRANSDUCER - ScienceDirect
Airborne ultrasound for the precipitation of smokes and powders and the destruction of foams
Airborne ultrasound for the precipitation of smokes and powders and the destruction of foams - ScienceDirect
I don't know if they're suitable for what you are trying to do though, or if you want to take on that much work and/or cost.
Output is probably the most significant hurdle for your project, so some experiments seem in order there. If you can get the 117 dB capable transducers cheaply, an array of those seems like a reasonable starting point. Keep in mind that the wavelengths you're dealing with are quite small, so physical alignment will likely need to be precise to get the most output. A simple flat array with more transducers may be easier to implement than a shaped array or reflector.
Hello, a couple of thoughts:
1 - am I right in thinking that you want to generate side bands from the modulated ultrasonic carrier, that fall into the audio-band? Or are you wanting to demodulate through some acoustic nonlinearity?
2 - I would be careful about high spl ultrasonics and hearing damage. I guess there is research out there? I’m guessing the eardrum can’t move fast enough to transmit the energy, but I’d want to be 100% sure.
1 - am I right in thinking that you want to generate side bands from the modulated ultrasonic carrier, that fall into the audio-band? Or are you wanting to demodulate through some acoustic nonlinearity?
2 - I would be careful about high spl ultrasonics and hearing damage. I guess there is research out there? I’m guessing the eardrum can’t move fast enough to transmit the energy, but I’d want to be 100% sure.
There is research, but not as much or as much consensus as you might think. The apparent lack of significant hearing loss in industries that use high intensity ultrasound would seem to indicate it's not a huge risk. When testing any speaker at high intensity, it's a good idea to wear hearing protection though. Better safe than sorry.
One of our labs used to have a large ultrasonic cleaning bath in it, and I can attest to the annoyance factor even from that. You didn't really appreciate it until the end of the day when it was turned off, and it was like a wave of relaxation came over you.
Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing
'In 1955, Crawford published a novel case series linking ultrasound exposure to disequilibrium, fatigue, nausea, and headaches in laboratory workers from the UK that persisted after the exposure ended, as well as “loss of hearing in the upper audible frequencies” (74). Several years later, Skillern correlated similar symptoms with a frequency band of ultrasound centered at 25 kHz, and gave one of the first descriptions of ultrasound-associated ear pain from ultrasound devices for cleaning, welding, and drilling, stating “this pain was similar to a burning sensation in the auditory canal… pain was experienced more rapidly than while measuring other devices with sound pressure levels of greater intensity” (75). Parrack published an additional study focused specifically on hearing changes after ultrasound exposure, and found temporary threshold shifts at subharmonics as a result of 5-min exposure to discrete ultrasound frequencies between 17 and 37 KHz at 48–143 dB SPL, which resolved almost immediately after exposure. This evidence bolstered his assertion that ultrasound did not cause any permanent auditory damage (7, 76). However, it is important to note that this notion has been discredited, as recent data suggests that repeated temporary thresholds shifts results in permanent synaptopathic injury that may not be registered by conventional audiometric evaluation, termed “hidden hearing loss”'
. . .
"Since Acton and Carson's study, several other studies of ultrasound-related audiovestibular symptoms from industrial machines were published (6, 23, 26, 72, 79, 80). Mixed conclusions regarding permanent audiovestibular damage as a result of ultrasound exposure were reached, and many argued the evidence base across all occupation-related studies were not generalizable to the general public (7). Another confounding variable was the difficulty in separating the effects of ultrasound from the high intensity audible noise that often accompanied industrial ultrasonic machines. One early study conducted by Ades et al. attributed symptoms of ultrasound sickness to high levels of sound in the audible frequencies rather than ultrasound (64). An additional study several decades later found that all ultrasound emissions from a welding factory were accompanied by subharmonics in the audible high-frequency range as “a byproduct of industrial ultrasonic processes,” making it difficult to parse out whether the audiovestibular symptoms that industrial workers reported were related to ultrasound or high intensity audible noise (81)."
https://documents.dukane.com/TechNote/US_HealthEffects.pdf
"Ultrasonic equipment has been in use for more than 40 years. Medical and scientific literature reports no documented health hazard from airborne industrial ultrasonic energy reaching an operator."
. . .
"The human ear cannot respond mechanically to airborne ultrasonic energy; it therefore is inaudible. The associated audible noise and lower frequency subharmonics can in extreme cases, be disturbing, causing hearing discomfort, occasionally nausea, and sometimes a temporary shift in the threshold of hearing (sound pressure level, or loudness, that can be heard)."
This PDF is locked, so text couldn't be copied/pasted, hence the attached image.
https://pub.dega-akustik.de/ICA2019/data/articles/001374.pdf
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