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Author Topic: Weird Sealing Phenomenon UERM  (Read 1250 times)

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dove

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Weird Sealing Phenomenon UERM
« on: May 24, 2014, 09:26:35 PM »
I only own one pair of CIEMs, the UERMs. My impressions were taken by Julie Glick in NYC, who comes very highly recommended from UE, and for this among other reasons I trust that my molds are correct. My molds were taken with a bite block.

I have been using my UERMs for a long time now, and have been very happy with them. I never thought I had any seal issues. Today, I was troubleshooting seal issues with a friend of mine who is currently on his first remolding of a set of IEMs that came out bad the first time around. During this time, experimenting with my own IEMs, I noticed a strange sealing phenomenon. I say strange because I can't figure out if I'm finding a better or worse seal with it.

I can very easily get a "good" seal. I pop them in easily, I feel them seal, I notice a significant attenuation. If I play some music on external speakers, then do some experiments with one ear having an IEM and the other having a foam ear plug in it (and switch), I find the attenuation is not quite as good as foam ear plugs, but it's pretty good. It's close. It's kinda hard to judge because there are definitely some spectral differences in the attenuation of the two. The ear plugs are fresh and the packaging says 27 dB. The acrylic UERMs are rated at 26 dB attenuation.

I know they are sealed insofar as if I contort my face in weird ways I can feel them break seal, attenuation disappears, etc. This is how I've been using them day-to-day for a long time.

Now, with music still playing on external speakers, if I press them in with my fingers and hold, I get significantly better attenuation, especially at the low frequencies. Then, and here's the ringer, if, while holding them firmly pressed into my ears, I open my mouth as if I was using a bite block (as wide as possible *vertically*), I feel air escape or something similar, they set in deeper, seal better. I close my mouth and take my fingers away. They now stay excellently sealed. They have more of a tight/suction feel. The attenuation is now as good as when I was pressing on them. If I press on them firmly again, the attenuation doesn't change...if anything it might get a very tiny bit worse. Now, if I do the earplug experiment, it seems to me that they are attenuating better than my foam earplugs. They are definitely at least as good now. My memory is failing me a little, but I believe I found the spectral attenuation differences between the ear plugs and the IEMs to be less now too.

So, I figured I had discovered that I was just using poor seal up until now, but then I checked the two levels of seal with music playing through the IEMs. If I transition from the first seal to the second "better" seal while listening to music, I definitely notice a significant decrease in bass presence. The music sounds significantly less full and it's significantly harder to hear detailed low-frequency rhythms. My two test tracks were "Downfall" by 12th Planet and "Won't You" by Nero, both of which are electronic with a good deal of low end.

So, which seal is "right"? Where by "right" I mean representative of the flat frequency response I should be expecting from UERMs.
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CEE TEE

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Re: Weird Sealing Phenomenon UERM
« Reply #1 on: May 24, 2014, 11:40:46 PM »
^Hi!  My guess is that you are creating a stronger vacuum with seal "#2" and that is causing greater external attenuation as well as making it harder for the drivers to work in a closed system.  Therefore, seal #1 where you have more sound from the drivers is the one closest to target.  One sign of a lack of seal is the loss of bass presence.  So if greater seal is causing bass loss then it seems to have crossed the threshold of seal and gone into a negative pressure situation or vacuum.

Have you ever experienced driver flex and/or "lock-up" with a pair of dynamic iems?  I have a particular brand of iem that flexes and locks up until I use seal/pressure to "de-flex" or un-lock the drivers.  It has been my experience that balanced armatures don't "lock-up" nor do they click as loudly when flexing due to canal pressure, but they do seem to click and function sub-optimally with too great a vacuum.

I could ask UE about this to confirm, but the design/tuning is for a proper seal yet not a vacuum.  Hard for me to imagine that the ear would perform better in a vacuum either.  And if the ear does not perform as well in a vacuum state, that could also help to explain the attenuation difference.

+/- margin of error on the accuracy of dB measurements might also have a part, methodology used, variability in efficacy of individual ear anatomy, etc.  Seems like it's fairly easy to pick the better signature and the better attenuator...trust your ears.  :)
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hiyu64

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Re: Weird Sealing Phenomenon UERM
« Reply #2 on: May 25, 2014, 05:13:43 AM »
IMO you should stick with your original seal.  Put it in like normal, give it a good push at the end, let it stabilize, and you're good to go.

There are two types of seals I've felt with the UERM.  The regular seal which works best for me: I place the earpiece into my ear, rotate it like a screw to get it comfy and snug, voila it's done.  If I try to push it in more, it'll rebound back until it stabilizes.  Everything sounds like it's suppose to sound. (If I forcefully contort my face, I can feel the attenuation break)

The second seal I've experienced is when there is sweat or some moisture in my ear canal.  With this when I push the UERM further in, it creates a suction cup effect.  This gives more attenuation, but music starts to lose some bass and sound off. 

On a side note, when I got my impressions taken, my audiologist actually recommended against the bite block.  Every one of the impressions she had done with a bite block and sent to UE had to be redone or the final product had to be shaved here or there.  Instead she had me talk to her as the impressions were settling.  I don't remember why she said this was better, but I haven't had any troubles with my UERM since I received them several months ago.  Personally, I think it's because the bite block is unnatural.  I mean who listens to music with their mouth open the whole time(unless you're singing along)? Also, there is problems with the fit when the impression is taken with the mouth closed the whole time.  I guess talking establishes a middle ground between these these two?  my 2 cents.     
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mkubota1

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Re: Weird Sealing Phenomenon UERM
« Reply #3 on: May 25, 2014, 06:20:17 AM »
The bite block seems like a precaution against worst case scenario:  Pain or discomfort while chewing, talking, or general gritting of the teeth.  Maybe not so much for better acoustic coupling?

Back to the original post- could the pushing on the IEMs also be adding additional bone conduction and changing the sound that way?
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MuZo2

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Re: Weird Sealing Phenomenon UERM
« Reply #4 on: May 25, 2014, 10:44:57 AM »
How old are CIEM
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Kunlun

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Re: Weird Sealing Phenomenon UERM
« Reply #5 on: May 25, 2014, 02:44:01 PM »
Hello, I have a few audiologist friends and I occasionally ask them about ciems/iems. One thing that came up was the idea that a vacuum like seal can actually effect not only the drivers, but the ear drum itself.

Pressure or negative pressure can prevent the ear drum from moving so things won't sound right. Breaking that seal and allowing pressure to equalize, like CeeTee mentioned, and having a seal that doesn't cause a vaccum feeling is going to lead to better sound.
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Anaxilus

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Re: Weird Sealing Phenomenon UERM
« Reply #6 on: May 25, 2014, 07:18:15 PM »
Quote from: Kunlun on May 25, 2014, 02:44:01 PM
Hello, I have a few audiologist friends and I occasionally ask them about ciems/iems. One thing that came up was the idea that a vacuum like seal can actually effect not only the drivers, but the ear drum itself.

Pressure or negative pressure can prevent the ear drum from moving so things won't sound right. Breaking that seal and allowing pressure to equalize, like CeeTee mentioned, and having a seal that doesn't cause a vaccum feeling is going to lead to better sound.

This is true.  I've had IEMs in the past that sealed so well and put so much pressure on the driver (e.g. - Miles Davis), that they could flex the driver or resist it.  I'd have to break the seal and re-equalize the air pressure after a few minutes to give it room to breathe.
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OJneg

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Re: Weird Sealing Phenomenon UERM
« Reply #7 on: May 25, 2014, 07:42:20 PM »
Etys can do the same thing.
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dove

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Re: Weird Sealing Phenomenon UERM
« Reply #8 on: May 27, 2014, 11:18:51 AM »
Thanks for the responses everyone! Overall, the notion that this is causing a vacuum which is causing poor performance by any number of means makes sense and is mostly consistent with what I'm experiencing.


Quote from: CEE TEE on May 24, 2014, 11:40:46 PM
Have you ever experienced driver flex and/or "lock-up" with a pair of dynamic iems?

Hmm...no, I don't think so. At least not that I recall. I take it that's the sort of thing that's hard not to notice?

Quote from: CEE TEE on May 24, 2014, 11:40:46 PM
Seems like it's fairly easy to pick the better signature and the better attenuator...trust your ears.  :)

::nod:: Yeah. That's what I was thinking.



So, the only thing inconsistent with the vacuum theory is that I experience the same thing when I simply press them tight with my fingers, before I open my mouth and feel the air escape (out of my ears :P). At first I thought it was my fingers damping the acrylic, but that seems less likely after experiencing the vacuum seal. Maybe it's the opposite issue, higher pressure. I can definitely feel some pressure in my canals when I do that, vs suction during the second seal, vs normal during the normal seal. I'm sure neither my ear (as Kunlun points out) nor the drivers work well in higher pressures either. Although, it's interesting that it sounds identical to the negative pressure. Also, it's interesting that the positive pressure "seal" attenuates just as well. Maybe it's an illusion, as suggested, due to my ears actually hearing worse. Although, I don't think I notice much full-spectrum attenuation if any in music played through the IEMs. Only low-end attenuation. On the flip side, I guess it's low-end attenuation improvement I'm mainly noticing for external sound too.

In any event, the explanation isn't super important, as interested as I am in it. I'm just glad to see consensus on whats "right" that matches up with what I've been assuming.

CEE TEE, if you do get a chance to talk to UE about this, I'd definitely be curious to hear what they have to say, from a science/engineering perspective. So far, all things considered, it seems like a change in pressure primarily causing issues with the operation of the eardrum itself is most likely the largest contributor to this phenomenon.
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