Can my Ultrasonic/Directional/Parametric speaker cause hearing loss?
Hi it took some time but after a while, I got it right and made an Ultrasonic speaker!
With the help of these vids:
https://www.youtube.com/watch?v=TQOabMOMGoE&t=232s
https://www.youtube.com/watch?v=9hD5FPVSsV0&t=13s
https://www.youtube.com/watch?v=aBdVfUnS-pM&t=1s
The last problem I needed to solve was the low volume.
I cranked it up to 24V to get it louder, but now I am scared that it can maybe cause hearing loss. It's not that loud only "really hearable in a quiet room".
The internet says a lot of things about ultrasonic being able to cause hearing loss, even it doesn't sound loud due to the unhearable frequencies.
Is there a way I can maybe measure the decibels?
Or does someone have more information/a way to calculate the decibels?
It's 40 kHz, the input is aux from my iPhone, and the amplifier is an L293n. Not sure if that's enough info to calculate decibels if it's even possible.
Genuine question what do you want to use this for? How do you know how loud it is? You can't hear 40khz
Check out the vids, it gets audible when you sound waves hit something so you are able to steer the sound/make sound come from a place where there is no speaker
My understanding of hearing loss is that it is frequency dependency, i.e. only the parts you can actively hear are capable of significant damage to your hearing.
Dangerous post:
Dear henrebotha, this is dangerous. I'm not sure if the willingness to express some ideas, without foundation, actually fits the definition of "understanding". And, for such an important safety issue... well.. I don't even see a brief contemplation on the opposing possibilities. I'm sorry to call you out on this, but perhaps it will contribute to anyone's ability to consider a bit more in-depth. Again, I'm sorry, but this is just a dangerous and misleading post.
What frequency is a punch to the face? A slap to the ear? What about the frequency of going to a high or low elevation, and the pressure it causes on the ear? These are all very low frequency (ignoring the other sounds of the slap, and the groans from the punch.)
What about the ultrasonic frequencies used in surgeries to emulsify tissues (literally vibrating the tissues so they rip apart and mix into fluid mush)? Or ultrasonic cutters capable of ripping solids apart?
Ultrasonic (everything above audible?) has its own nature, and can be of very high intensity. Waves interact based on their frequencies and amplitudes and resonances -- interacting differently based on the qualities of each thing they encounter. Your body, and auditory system, are made of different types and shapes of tissues and materials, from the liquids to the hairs to the membranes and bones -- each interacts with vibrations differently.
Ultrasound can cause cavitation in fluids, where the fluid produces "bubbles" of vacuum that collapse and can rip apart adjacent materials.
This is all from me just considering -- just *thinking* to see if I have anything in my past memory that can serve as warnings before I say "nah, it's fine... I think." -- because it's not.
Source: Thinking about anything that comes to mind that might bring up safety concerns w/r/t this topic. (But my background, while not terribly relevant, is in physics, engineering, medicine, medical imagery, medical-device design, etc. None of this is crucial when life has provided us little bits here and there as warnings.)
First off, a post about some research, so we know it COULD present some danger, and is a worthwhile endeavor to really try to understand it. Even though ultrasound is above the threshold of human hearing (>20 kHz), it can still present real health risks at high intensities and "SPL" (sound pressure levels)... even outside human audible frequency ranges. You're right, imo, to consider the potential risks, and we have to look further to see if the final intensities of the frequencies, especially in an array, reach a level where they could cause damage (whether short or long term). The effects of it have been evaluated in industrial (and other occupational) environments.
Some research findings (I walked through a convo with chatgpt, having it actually look up the actual research, then i edited, checked the references (I did not read them all. Choose your own adventure.)):
Occupational Exposure to Ultrasonic Cleaners Workers exposed to ultrasonic devices emitting 95 dB SPL at 20 kHz and 115 dB SPL at 40 kHz reported symptoms such as fatigue, buzzing, nausea, and headaches. These symptoms persisted for hours but improved when the machines were enclosed. Source: NIH / NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7199630/
High-Intensity Ultrasound and Hearing Threshold Shifts Exposure to ultrasound at 150 dB SPL at 20 kHz for 15 minutes resulted in measurable hearing threshold shifts in the audible range, indicating potential for long-term hearing damage. Source: NIH / NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8954895/
Ultrasound and High-Frequency Hearing Loss Operators of ultrasonic devices showed worse hearing thresholds between 4–14 kHz compared to control groups, indicating that ultrasonic exposure may contribute to high-frequency hearing loss. Source: NIH / NCBI https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10464771/
Potential Mechanisms of Damage
Cochlear Stress: High-intensity ultrasound may cause mechanical stress to cochlear hair cells.
Resonance Effects: Middle ear structures may resonate at ultrasonic frequencies, especially around 25–40 kHz.
Tissue Heating: Prolonged exposure can result in localized tissue heating, which may damage inner ear structures.
Safety Guidelines
OSHA recommends a ceiling limit of 145 dB SPL for occupational exposure to ultrasound in the 20–100 kHz range. Source: OSHA Technical Manual https://www.osha.gov/otm/section-3-health-hazards/chapter-5
Health Protection Agency (HPA) suggests a public exposure limit of 100 dB SPL for frequencies at 25 kHz and above. Source: Royal Society Publishing https://royalsocietypublishing.org/doi/10.1098/rspa.2015.0624
In short...
Inaudible ultrasound (20–40+ kHz) can affect human hearing and general health at high amplitudes.
Effects may include: temporary or permanent hearing loss, tinnitus, headaches, nausea, and fatigue.
Even though it's not consciously heard, the body can still respond physically and apparently possibly even neurologically to these frequencies.
Warning: I'm not an expert in this, so I'm picking ideal conditions, and worst-case scenario.
So, for for an array. I looked up some transmitters.. let's say they're 40khz. This one manufacturer lists theirs as 108 dB SPL at 30cm. Let's calculate based on 110 dB SPL. We want to get an estimate of a worst case scenario where they're all combined (but dropped down a bit due to some known reasonable issues, like the sound waves spreading): Let's say we have N emitters (let's say N=23).. for sound pressure we'd do spl_increase = 20log10(N), ie. 20log10(23) which is about 27.2. So our 110 dB SPL becoes 137 db SPL (at 30cm).
Now, we use a similar equation for figuring out what happens at a distance. spl_decrease = -20log10(newdist/olddist) So, at 3 meters away, it'd DECREASE by 20log10(3m/.3m) (where the .3m is our original rating's 30cm). That ends up being: 20*log10(10) ~= 20 (and don't forget we're subtracting), so our 137 db SPL - 20 = 117 db SPL.
Then there are some other real world losses from imperfect phase of the emitters, imperfect alignment, etc. I'm not sure how much those would drop the dB unfortunately, but I'd stick with the worst case of 117 dB SPL at 3m (and you can swap that 3m out for different distances): final dB SPL = 137(db SPL) - 20*log(desired_distance_in_meters/.3m)
Lastly, there are possibly other factors, like reflections, the wall behind the thing, objects nearby. Some of these could INCREASE the estimate. And I'm completely leaving out losses. It'd be nice if someone else chimes in here with actual experience in this, not just my calculations based on my bad understanding of the theory.
Oh, finally: It seems like an array can still possibly produce signals which, according to that research, might be concerningly close to what could be damaging. Keep your distance. :) I'm now looking into how we can do some various tests of the amplitude.
Okay, about testing at home without specialized equipment. I'm thinking you set up different objects of different sizes and shapes, so they resonate differently. A piece of paper, small things like pins, clips, pieces of tissue, tissue dangling, a sheet of paper dangling... cuttings of food (there's a lot of sound "damping" going on in wet meat, but just try different things). In general, if the solids are vibrating, that's an indicator of the strength (and resonance). I wouldn't say any of this is reliable. From what I'm reading, the resonance frequencies of the inner ear bones are within auditory frequencies, and they might not match any of your objects. (Plus they vary in characteristics, and have their own damping going on, AND are only part of what can be affected. From the research, we apparently don't fully understand what the disturbances and damages can all be caused by).
Keep in mind, much of this won't be evaluating the ultrasonic frequencies. I've done frequency sweeps to bring non-suspended particles in suspension (and I busted my speaker, driving it past its rated power). :} But it resonated within auditory frequencies.
Oh, hey, you might use eulerian video magnification to try to see slight movements) :) Here's one where I was using it, not for audio vibrations, but for trying to detect veins: https://www.youtube.com/watch?v=60qeAAZdJYo
Links to the software in the video description.