51
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 06 May 2024
51 points (88.1% liked)
No Stupid Questions
2174 readers
2 users here now
There is no such thing as a Stupid Question!
Don't be embarrassed of your curiosity; everyone has questions that they may feel uncomfortable asking certain people, so this place gives you a nice area not to be judged about asking it. Everyone here is willing to help.
- ex. How do I change oil
- ex. How to tie shoes
- ex. Can you cry underwater?
Reminder that the rules for lemmy.ca still apply!
Thanks for reading all of this, even if you didn't read all of this, and your eye started somewhere else, have a watermelon slice ๐.
founded 2 years ago
MODERATORS
Dude, I'm not trying to speak like a acoustician. At closest I'm speaking as an engineer with some knowledge of sound and acoustics from ages ago or maybe a musician, I don't know. If you expect random people to use professional terminology to have a conversation it's really your own mistake. I mean it in a constructive way from my own experience of taking with people on whatever I happen to know more about than them.
The contrast of a pulse as a rapid shift of air pressure and multiple ones in rapid succession of high amplitude in the context of causing damage to the inner ear? I am honestly struggling how to explain it any clearer.
Ok, I'll give it one more go.
As you say, it is not important what or how the pulse or burst of pulses are created, but digital to analog conversion of a signal can create impulses that are literally as rapid as can be by the laws of physics that are extremely rare organically and in particular by amplitudes that you get in headphones. A burst of such impulses, I'm avoiding the previously used terminology, of random but high frequency and amplitude is like having a tiny plunger jerking like crazy in your ear like nothing the ear has ever evolved to be able to deal with.
Not because digital vs analogue, vinyl vs CD vs mp3, gold plated monster network cables or helium cooled SPDIF connectors. No magical thinking. Only changes in air pressure. Changes in air pressure of the very fast and strong variety.
But good sir, a rapid change in pressure is the same as a high frequency sound wave.
It makes little difference if it has a long duration (a tone, or noise) or short duration (a puff of air).
And the higher frequencies neither carry more energy, nor are more damaging than lower frequencies.
But you are right in that the ramp up in amplitude matters, and which could theoretically be over a very short time period either in frequency or duration with the same amount of damage. In ear plug practice this would however be limited by the electrical pulse in the driver (both wattage and Hz), and the viscosity of air flowing through the back of the speaker cavity.
A significant ramp up is what is typically meant by high maximum instantaneous sound levels, LpFMax, and those are typically long term damaging at >115 dBA, unless other risk factors are present.
(Just to be overly clear, I'm not faulting your use of language (once I understood what you meant), you're doing admirably, and I fully understand that language is malleable and context dependent - I'm not hung up on the words.
I'm trying to get to your understanding of the physics behind it, which I read as a little muddled. It could still be due to language barrier, but what I pick up is some confusion in the differences between frequency domain and physical domain.)
On the other topics, which you seem to understand, but I'll try to explain again to see if our models can better converge:
On the topic of the tiny plunger, this is actually how virtually all speaker elements generate sound. You have a little element, called the driver, pushing on a membrane in the frequency and amplitude you're trying to convey. The driver and membrane can't be infinitely flexible or have infinite plunging depth, lest they need infinite energy to push an infinite amount of air, and so are typically carefully designed to certain specs, called dynamic range (frequency/speed of driver), and sound power (amplitude of driver).
As to what the ear is designed for, it is actually very well protected against high frequencies, this is a large part of why we can't hear higher frequencies than ~20 kHz. But you are right that it's not made for sudden loud noises (a steep ramp up in amplitude). And although I don't actually know, my motivated guess would be that human reaction time for the protection against sudden loud noise is at best 1/8 th of a second.
Yes, we agree on most everything and my understanding of both physics, mechanics and biology seem to agree with yours.
I guess the one main disagreement is if a pulse, either single or repeated, might potentially be more harmful than a sine wave of a single frequency. According to the teachings I've had, or my recollection thereof, a pulse or impulse may carry the sum (or zero sum) difference if any ramping wave, but the nature of the impulse it literally hits differently. A transition of difference in state versus a forceful immediate change. A push or a slap. Or a push and pull versus a slap and yank, should we speak of a complete cycle.
This was what I attempted to illustrate with the plunger example. If you are familiar with a plunger, you'll know that the method of operation is not to keep a harmonious cycle, but to yank it aggressively in order to transmit a whole lot of impulse-like energy and forcefully release buildup or blockage in the pipes. My argument is that should we have two identical sinks with identical blockage and we'd manage to conduct an experiment where both plungers operate at identical frequency and amplitude, but that one plunger pumps in a harmonious cycle while the other does a pulse-like push pull, the latter would yield more successful results. Hence my conclusion is that despite the state being identical before and after, theoretically the amount of energy may be the same, there is a difference in how the energy is transferred depending on the curvature of the actuation on the plunger. Or the speaker cone. Though through air instead of water and air compress while water doesn't. But still.
So the frequency of a repeated waveform and the shape of the waveform are not interchangeable. I'm sound the frequency carries the root tone, the shape carries the multiples. A perfect impulse (or other digitally generated waveforms) carry in theory an infinite amount of frequencies. Again, carry may be a misnomer depending on the discipline and of course the perfect is unobtainable so in practice the frequency spectrum is limited to one bandwidth and spectrum or another. Not that really had any bearing in our discussion.
Finally, I disagree with the argument of the engineering in headphones. Those limits are with respects of quality of sound reproduction. They are not a guarantee of hard limit of potential output and not intended to be. I don't engineer speakers but it's quite common paradigm in engineering in general that you benefit in quality and reliability should you accept a modest degree of unused overhead. Mistakes and bugs happen and it is especially vulnerable when it is reliant on hardware and software in the earpiece itself, as with my personal experience of faulty earbuds that emitted bursts of painful high frequency noise despite playback being of moderate volume. There are no intermediate steps of filtering, as with analogue gear, so should a faulty component cause a pop, it may well do so from the one extreme to the other.
I apologize for my frustration. I've been experiencing lately that I try to communicate one thing and the recepient keep projecting it into their own frame of reference and insist I'm talking of something that I'm not. I'm a bit touchy and I'm sorry about that.
Thank you for taking the time to explain, we do indeed seem to be closer to each other's understanding.
This is contrary to what I remember having been taught about biomechanics and hearing, but as memory and understanding is unreliable, I'll cede that I'd need to look up a reference for better precision.
The crux of my argument hinges on there not being a difference. And my understanding of the physiology is that the hairs will primarily bend with pressure, and exhaust with flexion (repeated bending cycles leads to breaking), within the limits of survivable amplitudes.
If there isn't a difference, my argument continues in that it's physically very difficult to create a pulse with a ramp up faster than the 20 kHz the ear is evolved to take, that's 0,05 ms, not many physical processes go that fast to create a pressure wave and those that do typically get dispersed very quickly, unless as part of a harmonic excitation.
But of course all that is irrelevant if that's not how the ear reacts.
You may be right, the details of what the measure represents haven't been presented.
From context where it's being argued as a legal argument, I have assumed it to be part of the safety design, and not of sound reproduction.
Ear phones/plugs have no business reproducing good quality sound at >100 dBA, and would be sued into oblivion as the hearing damage and tinnitus reports rolled in. Which to be fair, is what the OP is about.
Having a physical limit at 105 dB would then be congruent with the same unused overhead you refer to, as it corresponds to a doubling of potential sound pressure, and is about typical as overcapacity for high fidelity engineering applications.
105 dB would probably be painful, and as a surprise would be jarring, which contributes to the perceived risk of injury. It should also not be loud enough to cause lasting physical injury, and you'd typically have full functionality within two weeks.
An earbud/head phone can be designed failsafe, so that casing, driver, or most commonly membranes will break at too high amplitudes. If nothing else, it will be limited by the amount of energy available, which for wireless or portable headphones is typically very low. I can't vouch for the specific gear in the OP, but given the rarity of recalled gear due to injury, I'd guess it would be widespread industry practice to design it fail safe.
What I'm saying is that it can still be hardware/physically limited at 105 dB, even though it gave a painful squelch before breaking.
I totally get it, it's a built in flaw of the Lemmy/social media format. Too little supportive language cues, and too little time and/or investment to actually listen.
I appreciate you having the patience to talk this through with me.