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ADEL Technology - Discussion Thread - Update: March 27, 2016: Please Read 2nd Post of the Thread

Discussion in 'Sound Science' started by eaglewings, Mar 7, 2016.
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  1. Brooko Contributor
    Yep - it did.  Thanks :)
    Oh and the edit you see above was just me correcting the repeated quotes.  Sorry - slowly getting used to this Mod thing.
    It raises an interesting point and one that we can ask Stephen to get clarification on.
  2. WCDchee

    I'm glad that we can engage in a civil discussion here on this thread. I brought this very issue up on how I didn't believe in the claims of hearing protection on the main thread of 1964, and pretty much got slammed for being a troll, despite my efforts to bring it up in the most diplomatic manner...

    No worries, I'm typing all this on my phone and it is a real pain doing the quotes and edits :)
  3. BiggerHead
    This was my first thought.  I'm surprised nobody has touched it.  Same volume to the inner ear is same volume to the inner ear and same apparent sound. 
    So some quick "research" (wikipedia):
     The acoustic reflex mostly protects against low frequency sounds.[6]

    [6]  G. Lidén; J. E. Hawkins; B. Nordlund (1964). "Significance of the Stapedius Reflex for the Understanding of Speech". Acta Oto-laryngologica 57: 275–279. doi:10.3109/00016486409134576.
    Maybe I'll try to get access to the reference later.
    This could be a solution to the paradox.  If it only reduces low frequency sound this could reduce apparent volume even more than actual total volume, and may reduce high frequency volume none.
    Then the resulting turning up of the knob causing extra damage would make sense.
    This talk about sound escaping though, doesn't sound right.  DC pressure ok, I get the point, but if sound escapes it escapes right?  I mean, that's just called quieter. I don't see how that idea helps anything, not so long as you have a volume knob handy.
    I learned something else on that wikipedia "article": when you're about to talk, you can't hear.  That should be a good lesson for many people.  I suspect the mental block is still worse though in that case.
    Another thought, drinking inhibits reflexes right?  Solution: drink more beer.  [​IMG]  If anyone wants a test subject...
  4. Canyon Runner

    I original posted the link to this article, but figured just copying and pasting would be easier for everybody. But here is the link to the article http://audioundone.com/in-ear-monitors-why-do-they-sound-like-that-jay-kadis-and-stephen-ambrose )

    In-Ear Monitors: Why Do They Sound Like That? 
    Jay Kadis and Stephen Ambrose

    MAR 25, 2013   By Guest Blogger   Categories: Audio Equipment • General [​IMG]Providing good sound monitoring to performers is a critical part of producing a great experience for the audience as well as for the musicians.  When people on stage hear what they need to play their best, everyone benefits.  Providing such cues is the job of monitor mixers and their monitor playback system.  Traditionally this has meant floor wedge speakers aimed at the performers.  Unfortunately, these systems produce the potential for acoustic feedback as well as an unpleasantly loud stage environment.  These problems have driven a move to personal monitoring using drivers placed in the ear canal to replace the stage monitor loudspeakers.
    This solution has definite advantages, but the performance of in-ear monitors (IEMs) has been limited by changes caused by the insertion of a physical device into the ear canal.  Closing the normally open end of the canal changes the acoustics of the outer ear and drastically alters the behavior of the middle ear as a result.  Various attempts have been made to ameliorate these effects but so far, they have been only partially successful.  In order to understand why, we need to look at the auditory system and how it behaves in the normal open-ear condition.  We can then see how this behavior changes when we place a driver in the canal and how that change might be minimized without compromising the sonic performance of the system.
    When the ear canal is un-occluded, as it is when we listen to loudspeakers in a room, sound waves reach the tympanic membrane, or eardrum, by propagating through the ear canal.  The sound waves are tiny alterations of the static, or barometric, pressure of the air around us.  This static pressure is about 101 kPa or 14.7 lb/in2 at sea level.  Pressure changes that produce a just audible sound are 20 mPa while painfully loud sounds are about 20 Pa.  Just audible sounds vary the pressure by less than one-billionth of the atmospheric pressure!  That is the sound pressure variation that normally reaches the eardrum.
    When we seal the ear canal with an IEM device, we fundamentally change the conditions that affect the pressure in the canal.  By closing the canal, we create a sealed space that contains air.  The air pressure is the same as the atmospheric pressure until we turn on the driver.  When operating, the driver membrane moves in and out, slightly changing the volume of the closed space.  This generates a pneumatic pressure that we do not encounter in the open-ear; the driver acts as a pump.  The pressure generated by this pumping action corresponds to a sound pressure level of 120 dB SPL, close to the threshold of pain.  This high level then triggers a physiological response that attempts to reduce the level, the acoustic reflex.
    The human auditory system has a built-in compressor-like reflex designed to protect the cochlea from excessive stimulation.  When a loud sound reaches the inner ear, it causes the stapedius muscles of both ears to contract, reducing the transfer of sound energy to the cochlea.  This changes the quality of the sound we perceive as well as its loudness.  Even listening at normal levels with IEM drivers triggers the acoustic reflex due to the pneumatic pressure it generates.  In order to deliver high-quality sound, this effect must be reduced.  Attempts to reduce the pneumatic pressure include venting the IEM to the outside with tubing or passages to the outside.  These approaches work to some extent, but they do not perfectly counter the pneumatic effect and they do affect the sound quality.  The IEM produces relatively little output at low frequencies, though that is countered by the increase in low frequency pressure cause by the pneumatic pressure contribution to the overall pressure in the ear canal.  Thus, too much venting destroys the low frequency efficiency of the device.  We need a better way of countering the pneumatic pressure without losing the low frequency efficiency.
    A novel idea has recently been developed by Asius Technologies and is in the final testing phase.  The idea is to use an inflatable airbag-like partition between the driver and the eardrum.  With the proper choice of materials, the tiny balloon can be inflated to just fit the ear canal, sealing it with the user-adjustable pressure used to inflate the device.  The inflated device provides a semi-elastic seal that allows the pneumatic pressure to reach the outside while maintaining a sealed ear canal that transfers low frequency energy efficiently.  By eliminating the pneumatic overpressure, sound is transferred to the inner ear without eliciting the acoustic reflex.  Lower sound levels then produce a louder perceived sound without the alterations caused by the middle ear muscular contractions.  By adjusting the inflation pressure, the listener can determine the amount of outside sound blockage as well as the fit of the device.
    The new technology is not only ideal for stage monitoring; it is applicable to recreational music listening and to hearing aids as well.  The device reduces the occlusion effect for all listeners, making the listening experience more like listening to sound from loudspeakers rather than hearing sound as if it originated within the head, a common effect of conventional IEM devices.  Finally, in-ear monitors can sound like loudspeakers without the threat of feedback and without creating an unnatural sensation of sound in the ear!

    aussietanker likes this.
  5. Ruben123
    Im not too sure what that must mean. Sure not all IEMs at every volume put out some 120 dB SPL. While I dont disagree as I dont know too much about how IEMs work (I do know about the ears though), 120 dB seems ridiculous  to me. Relatively short listening to club music gives me enormous headache and ringing ears. I can listen hours to IEMs a day without any discomfort, as long as the IEMs are not treble focused.

    I am though very interested about this topic. Now Im young I have got enough time to save my hearing might this story be true. Im a bit skeptical, but as I said, Id like to know more.
  6. Canyon Runner

    Here is the Vanderbilt Study of Specific Coupling Can Affect Perceived Loudness in Insert Earphones. It's a PDF, so I'm not able to upload directly to Head-Fi. Had to upload it elsewhere.

  7. Ruben123

    Is it me, or is the conclusion, that the higher perceived loudness is due to the higher SPL in bass region, some bit silly? Of course a lifted bass gives the idea of a higher perceived loudness. But does this mean that bass focused earphones are better than treble focused because the perceived loudness is in the bass earphone higher at the same SPL ?
  8. WCDchee

    Thank you for both of the links!

    I think from these studies that Stephen am rose has, we can conclude that the sealing of the external ear can affect both the frequency response as well as the absolute volume for a perceived level of loudness, this is something that I will not dispute.

    What I will dispute, however, is what comes after this. Like I previously mentioned, this same perceived level of loudness means that the inner ear receives the same stimuli because of the damping mechanism, and as such, the would be no actual hearing protection since hearing loss occurs at the inner ear, and not at the ear drum :)
  9. BiggerHead
    Ok, but did you see my post about exactly that?  That's only true if the frequency spectrum is unchanged. We percieve low frequency sounds as relatively high volume.
  10. cjl

    But we don't. That's the whole point of the Fletcher-Munson curves. At a given true SPL, we perceive sounds in the 3kHz range to be the loudest. Bass needs much more energy to have a similar perception of loudness.
  11. WCDchee

    I think you're right there :)

    Besides if you think about it, when you listen to music, would you turn the volume up when the vocals are soft, or when the bass is lacking? :)
  12. BiggerHead
    Well I <STRIKE>was in fact kind of confusing the curves upside down the second time I said it and phrased</STRIKE> (edit, no I wasn't, see next post) it but it doesn't matter, that was secondary to the thought.
    Lets say you have 1 mW (the unit really doesn't matter) of lets call it apparent volume (1mW apparent  volume has the same percieved volume as 1mW transmitted into your inner ear at, say, 5khz, this is my definition for the sake of this argument)  
    If half your apparent sound power is below 1 khz and half is above 1 khz, that's 0.5mW of apparent power on either side of 1khz.
    Now if your ear reflex kicks in and blocks some of the < 1Khz sound, lets say it blocks half of that apparent volume, so that's 0.25mW blocked.  But it blocks none of the > 1khz sound.
    Ok, now you're at a total volume of 0.75mW apparent.  
    BUT you still have just as much actual power at 5khz as you did before, not a microwatt less (apparent or otherwise).
    So you turn the volume up a bit, about 1/3 up to get back 1.00mW apparent total. 
    Now the total volume sounds the same.  Ok. But it is NOT true that the sound power at 5khz in your inner ear is also the same.  It's now higher, by about 33%.
    This shoots down the argument that so long as overall volume in the inner ear is the same, damage is the same.  It doesn't work.
    5khz is more damaging than 100 hz isn't it?
    So ok, it might be somewhat true that we don't judge total volume as just the sum of the perceived volume at each frequency. Maybe 5khz gets a big bias beyond just the FM effect, just because we don't like to hear 5khz all that much and enough of it is enough of it.  Still there should be at least SOME tendency to feel that the overall volume went down and correct for it, thus increasing the 5khz power at least some.  It's probably not exactly clear how much.
  13. BiggerHead
    Oh and actually I didn't get the FM thing backwards either.  I  let you guys momentarily confuse me about my confusion, or lack thereof.
    The fact is at higher volumes the relative suppression of low frequency perception compared to 5khz decreases.  There is still relative suppression but it's less than at low volumes. The high volume FM curves are flatter.  That means compared to low volumes, high volumes seem to have more bass emphasis, and we associate bass with volume. This folds back into the idea that the impression of the overall volume of a sound spectrum is not the sum of the impression of the individual tones.
    This is why the "loudness" button on some recievers adds bass, because more bass means more impression of volume.
    So I would say that beyond the FM independent math above, there is an added impact from this.
  14. Canyon Runner
    Going over some of the things ADEL helps improve.

  15. Canyon Runner
    Wanted to post this in this thread, from the CanJam SoCal impressions thread.
    1. [​IMG]
    1. jude
    2. I've got a fever...and the only prescription is more CanJam!
    3. [​IMG]
    5. offline
    1. 10,604 Posts. Joined 6/2001
    2. Location: Metro Detroit Area

    I'll post more impressions later, but I wanted to post what was my favorite moment at any CanJam so far.
    My wife is deaf in one ear. Many years ago, she was diagnosed with an acoustic neuroma, which is a relatively rare, benign tumor on the acoustic nerve. It had been radiated, but grew after a few years, and eventually had to be surgically removed. Unfortunately, the surgery required the sacrifice of her left acoustic nerve (vestibulocochlear nerve), leaving her 100% deaf on the left side.
    (We're quite the pair: She used to be an interior designer, and I have significant colorblindness. I'm a headphone audio enthusiast, and she's deaf in one ear.)
    I'd seen a couple of videos about Stephen Ambrose's Active ADEL, and spoke with Steve (@Canyon Runner) from 64 Audio at CES about Active ADEL (aka "bubbles"). Here's one of the videos I saw:

    Some key differences: The young lady in the above video has moderate to severe hearing loss in both ears. My wife's right ear is outstanding, but her left side is, again, 100% deaf.
    A key similarity: My wife's response was a lot like the lady's response above.
    My wife loves music, every bit as much as I do. Her personality is one of serenity, calm, acceptance, so she has literally never complained of her situation, and has simply learned to enjoy music (and life) through her one good ear. Stephen and Steve placed the earpieces in my wife's ears. They asked me to pick some music on my phone, so I played Pharrel's "Happy." She immediately started crying happy tears, mixed with emotions from having forgot what it was like (for over ten years now) to hear music the way she used to. She said it was like the music was filling her head again--like she was hearing from both ears. (This is not what's happening, and I encourage you to watch the videos about it and/or read more about how it works.) We switched to stereo microphones, and tested directionality. While she'd have to be trained to localize perfectly, she was sensing changing direction as I walked around the table talking.
    Stephen then asked her (as we were running late for a dinner reservation) if she wanted to hear it again, and she jumped at the chance, and asked me to play "Keep Your Lamp Trimmed And Burning," performed by Susan Tedeschi and Derek Trucks on God Don't Never Change: The Songs Of Blind Willie Johnson, which is one of her favorite songs right now.
    The music started, and the tears started flowing again. She couldn't believe what she was hearing.
    Stephen asked her if she wanted to be involved in their ongoing work at Vanderbilt, as they continue to develop, perfect, and productize the technology. Of course, the answer was YES. I'll get her down there as often as they want to see her. It doesn't hurt that Nashville is such a groovy place, especially for two music lovers like my wife and me. Before we left, my wife practically jumped out her chair to hug Stephen. I had to hug him, too.
    Thank you to Stephen, Steve, and 64 Audio for your work on this, and for letting my wife hear music rather like she used to more than ten years ago. We'll see you in Nashville.

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