Power dome or open dome?

I decided to revive this thread because it encapsulates the experiment I’m doing (discussed already as a thought experiment in a couple of threads on molds and domes elsewhere). But the two posts in this old thread summarize very well the pros and cons of my experiment. There is also an excellent thread started by MDB on the theoretical and experimental considerations of open vs. occlusive domes but I didn’t want to pollute that thread with my own personal observations:

Article on open fit vs closed fit

OK. So I have age-related (noise-related?) ski slope high frequency hearing loss but reasonably good low frequency hearing. I wear ReSound Quattro’s and have been fitted with medium open domes. My audi assigned me the global user profile of “First-Time User,” which backs off my prescribed fitting in the All-Around general purpose (use it all the time?) program to avoid overwhelming a new user with new loud sounds. I’d rather be closer to my prescribed fit (~by NAL2) so I changed my global profile to “Experienced (nonlinear)” which at the very least puts more gain into the midtones.

My problem is that through the open domes a lot of low to mid frequency noise goes directly to my ear drums and my HA’s don’t have a chance to use their DSP power to deal with it.

Mark Chambers in one of those “thought” discussions predicted that power domes would not have a big effect at occluding outside noise but I said I’d be willling to take even a few dB of reduction to the bank.

So here’s what I’ve found so far on Day 1 with supposedly official ReSound medium power domes bought on Amazon to replace my medium open domes.

The bottom line, so far, is everything I hear is “more muffled” - because I’m not hearing two things at once. I’m hearing more through my HA’s and less directly to my eardrums. Sounds that I want to be relatively soft like opening and closing the microwave door are softer. But my impression is that everything I hear is noticeably cleaner and crisper. Voices with noise in the background seem much crisper (I could just be enjoying a great placebo effect!). I have noticed since that I’m hearing less directly through my ears that I’ve lost a little bit of spatial directionality, depending more on the mics behind my ears to provide that, but it’s a relatively small price to pay for my perception of crisper easier-to-understand speech.

But perhaps the most important thing I’ve found is that the mechanics of implementation are very, very important. Although in the ReSound fitting software the size designation of open domes and power domes is the same, the actual size of the lower, bigger mushroom on a power dome is several mm larger in diameter, making the fit in the ear canal much tighter.

A tight occluding fit in the ear canal means several things (at least to me). The inside of your ear will be more moist, softening the wax more. The larger size of the medium power dome as compared to my open dome means when I’m shoving into my ear canal, I seem to plow through more wax and I seem to have less control on making sure the receiver opening is centered in my ear and not blocked by wax. The first time I inserted the power domes, I had a really occluded bottom of the ocean sound (but I still noticed the cleaner crisper sound of voices).

With Sports Locks (concha locks) on my receivers, I’ve had the problem in putting on domes with the Sports Locks riding up towards the receiver openings and preventing me from realizing I don’t have the domes pushed fully onto the receiver ends.

So whaddya know?! When I decided maybe I should try to remove the power domes, see if they were occluded by wax and then reposition them in my ears, the right receiver and dome came out easily, since my ear canal runs forward in my head for that ear (the usual direction). But the ear canal for my left ear is unusual, it goes in and turns to the rear. Perhaps due to ~L-shape, the amount of sticky softened wet wax from the occluding dome, and maybe not getting the dome fully on the receiver, when I gently tugged to pull the receiver out, there was a lot of resistance and a big pop! Ouch! The receiver came out and the power dome was still glued in my ear (moral of story: if you wear medium open domes, buy small ReSound power domes, I think). I gave my physician wife a big pep talk: a trip to the emergency room or my audi might cost $$ money and if @Mark_Chambers wife can do a skillful job at it, you can learn, too! I found a set of forceps with a fine but rounded blunt tip with a raised serrated pattern on the gripping surfaces and laid my head flat against a table so as not to move. “Sterilized” the forceps tips with an alcohol wipe.

After a successful “operation,” the wife advised me on future insertion/removal attempts to tug the ear lobe backwards and a little bit up to open up and “straighten” the ear canal and remarked “you have very small ear canals!” (wife says everyone’s ears are a little bit different so the recipe for anyone else’s ear might not be the same)

So now that I’ve “cleaned” my ears by softening the wax in my ears with occluding domes and pulling a lot out of wax on the domes on first removal, things sound a lot less bottom of the oceany and perhaps with the pulling backwards on the ear lobe suggestion I’ve managed to reinsert the occluding domes with the receivers better positioned in my ear. I’m going to order small power domes.

The point of this is in open domes vs. small domes, a lot may depend on just getting the right size domes and inserting them properly into your ear and not plowing up a ton of wax into and onto the domes in the process. I have never ever removed so much wax from my ears in withdrawing open domes.

Now I am enjoying cleaner, crisper sound as noise direct to my ear drums does seem to be reduced. Since I’m not hearing as much of two sets of sounds, soft noises don’t seem to be as loud. If I amp up noise reduction, I can better suppress for instance the noise of a refrigerator humming in the background.

I think Mark Chambers is absolutely right. This is not a miracle completely preventing noise from bypassing my HA’s but it’s at least a few dB step in the right direction. I like it so much so far that I may wear the power domes all the time. With the oversized power domes, there is more of a sense of something in my ears, more annoying pressure when I chew, yawn, or whatever.

I haven’t found the volume too loud on my normal volume settings, perhaps because I’m missing some of the sound volume that used to go through my open domes directly to my eardrum. I’d advise anyone who emulates me to best consult your audi, probably start with domes that might be too small rather than ones that might be too large, and probably not a good idea to just let anyone with any old instrument mess with your ears if you lose a dome like I did. You’re taking a risk with your hearing but I accidentally had a good tool and a wife who regularly inspects people’s ears as part of her job.

The software should calculate different gain depending on what dome info you have entered. I’m fuzzy on what changes actually occur, but the basic premise is that less sound is leaking out. One consequence is that if more high frequency gain is needed, but was feedback limited, more can be supplied. (This likely doesn’t apply to you) I forget what happens with lower frequencies so I’ll leave my contradictory hypotheses out of it. At this point though, it seems like you’re kind of shooting in the dark using a proprietary fitting algorithm without REM. General experience is that most fitting software underfits gain.

@MDB said:

The software should calculate different gain depending on what dome info you have entered

In doing the “thought” experiment before actually switching out the domes, I read a bunch of posts in this forum including the following by um_bongo (Stephen Bright):

Can I change SIZE of domes on ONE aid only?

Strictly speaking you’ll need to go back for an adjustment if you’ve changed the venting. However, as most of the effect is below 1Khz you’re not really going to suffer that much unless you either start getting more feedback (more venting) OR too much LF gain (Less venting). Further increasing venting my give you a ‘thinner’ sound experience overall as you lose the LF ‘warmth’ from the signal and you may start to lose some of the speech clarity too: which might be more apparent to others arou…

I found two threads useful to save links to, the one that Stephen’s post is in and this other one:

https://forum.hearingtracker.com/t/power-dome-concerns/24007?u=jim_lewis (member archive)

plus the one in which you posted the paper on analysis of open vs. closed fittings (I gave up reading after those so there still may be other very worthy threads I’ve overlooked).

Just to be sure, I have gone back to Smart Fit 1.3, changed the dome specifications for both HA’s, found the “Recalculate” submenu item on the Tools menu in the Right (horizontal) Center (vertical) bar for Smart Fit and find that the programmed gain settings do not change one whit between medium open domes and medium power domes - but you’d think that they would as for very low frequencies NO GAIN is prescribed for 250 Hz up through 1 K in my HA’s. Maybe the lower frequencies make it through the power dome somewhat as well as being replicated with no gain by my HA’s (I don’t yet really understand what a gain of 0 means in terms of output from the HA - I would think that it means that the sound is passed on at the same volume it was received by the HA).

The other thing I’ve noticed about using the Power domes is that it makes my HA’s less sensitive to feedback - that’s a by-the-book observation of what occlusion is supposed to do for you. Off to gym to exercise lazy butt and try power domes in very noisy environment. They worked great on a walk last night using my noise cancelling headphones to stream talk show podcast to my HA’s. Speech very crisp and clear compared to open vents even with same headphones on. Gym will be tougher test. Eventually the noisy restaurant test.

@MDB said:

The software should calculate different gain depending on what dome info you have entered.

Actually, I’ve reconsidered what I previously wrote. When I am prescribed, due to my hearing loss, essentially 0 gain at 250 Hz through 1 KHz with an open fitting, then I switch to a closed fitting, here’s what approximately happens (according to my ignorant brain).

The sound coming in at these frequency regions and by passing my HA’s has the same gain as that produced by my mics hearing the sound and reproducing it: namely, 0 gain. It’s passed through my open domes or produced by my HA’s at its same natural volume.

OK. Now I put on closed domes. The closed domes do two things. They attenuate somewhat the sound that would have bypassed my HA’s by going through the open vents (now closed) and they reflect back more sound in these frequencies produced inside my ears by the HA receivers.

To understand why the ReSound program does not recalculate the gain here at all, consider this crude assumption. The sound bypassing the HA mics was the same volume sound as the sound in these frequencies produced by my receivers. The barriers should roughly behave the same going in either direction. As much sound as gets deflected back by the closed domes that would previously entered my ears is ~exactly compensated by the same amount of sound of the same volume inside my ears that used to escape my ears and now gets reflected back inside to my eardrums.

It would be an entirely different story if I had a moderate to severe low frequency hearing loss and some gain (worse if considerable gain) were being applied to the sound produced by my HA’s in the frequency ranges we’re talking. Now I block the vents by going to close domes, the normal bypassing sound that has no gain can’t get in but the sound inside my ears from the HA’s, part of which used to get out, is trapped, and now I’m blasting my ears with a lot more gain than prescribed by my fit so the fitting curve does need to be recalculated in this instance.

So if the effect of open vs. closed is mainly in the region < 1 KHz, with a zero gain prescribed in these regions, no big deal to switch dome types without changing fitting and if I get a few extra dB of high frequency sound retained, I don’t mind! At some point, I will ask my audi to do REM’s on my different domes but since I’m going to try smaller power domes, tulip domes, and think about a custom mold, I’m not ready to rush back and make her do a whole lot of work on one type of dome just to decide to go to something else the next day.

To me, REM is fitting to NAL-NL2 prescription (or DSL-5) What I’m hearing you say is that the audi said you were close to what the (typically underfit) Smart Fit wanted to achieve.

What I’m trying to communicate is if you had REM to one of the established fitting formulas, you might find that you had the additional clarity you want with open domes and no occlusion. So the REM you had was with the initial “inexperienced” settings? I’m confident you’ll be able to achieve what you want with your approach–just seems backwards to me.

@jim_lewis said:

right ear at 4K was a little off and she didn’t think it was worth the effort of correcting that.

That is odd. It’s a 5 minute hook up and a few clicks

OTH, lots of DIY’s on this forum are apparently playing around and, AFAIK, not doing any REM’s. I think the main difference that we’re discussing here, open domes vs. closed domes, is not a gain issue but a likely interference issue. I actually seem to hear speech softer but much clearer with the closed domes. So I don’t think that increased gain is the basis of improved speech clarity. That’s the amazing thing - how clear the speech is for how relatively soft I perceive it.

I also think that if one believes the 2016 review paper that you cited on open vs. closed fit and the 2006 Widex technical paper that I added a link for in that thread, except for any annoyance with occlusion and some loss of sound directionality, a more closed fit will always be better for speech clarity than an open fit, no matter what the fitting algorithm and REM or not to go with the fitting algorithm. So what I’m mainly doing is deciding whether I like the occlusion, which type of occluding device is most comfortable, etc., before I worry about anything else.

The Smart Fit software does have NAL-NL2 and DSL-5 in it as programming options. So when I have time, I can fit my hearing loss with those algorithms and see if the resulting gain curves are significantly different from the Audiogram+ and also, when running under of either of those fitting algorithms, whether changing from open to closed domes makes any significant difference in the predicted, desirable gain output relative to the Experienced profile that I am currently running under. I’ll also see if I can find out what ReSound claims makes the Audiogram+ fitting algorithm different from NAL-NL2, etc. Surely they’d have something to say about this professionally to audi’s who might need convincing to deviate from NAL-NL2 in any significant way. So it would be instructive if that can be found out (but it might just be more whitepaper type fluff!).

BTW, a really interesting aspect of fitting, that I learned about from reading the Starkey Compression Manual (discusses fitting in general) is the time constant for “attack” and for “relaxation” of compression.

https://starkeypro.com/pdfs/The_Compression_Handbook.pdf17

(And, @Don, after reading the Starkey manual, I have concluded that fitting IS rocket science! There’s quite a bit of complex stuff to learn)

The most important lessons are that for speech intelligibility you want fast onset for compression and a fast recovery whereas for listening to music, you want a much slower onset and recovery.

What this basically means, I think, that if one wants to listen to music, everyone should use the music program provided for their HA. Using a general purpose program would not be as good an idea, since it probably has a fast attack/relax setting (can any HA automatically detect one is listening to music and switch to appropriate music settings?).

Sure enough, when I look in my ReSound Smart Fit settings, just as the Starkey manual explains, all my “speech” programs have a per syllable attack/relax time constant setting whereas for the Music program, the attack/relax constant is set to slow.

So the details might be too gory for everyone but DIY’ers but it sounds like besides having a Music program that is more linear with less compression, you want changed compression time constants, too, but I guess that automatically comes with everyone’s music program, as long as you’re actually using it!

@jim_lewis said:

(And, @Don, after reading the Starkey manual, I have concluded that fitting IS rocket science! There’s quite a bit of complex stuff to learn)

Ha, ha. Yep. If I had to master all that before making adjustments I’m sure I wouldn’t make it. Luckily the software does it for us. When I change the gain I notice it changes the compression ratio a little. I don’t see or know the details of that.

The way I think if it is, my pro and the software get it 90% there, and then I make very minor adjustments to fine tune the last 10%.

@Mark_Chambers said:

I decided that in most cases there wasn’t enough difference to bother with it

Hi, Mark

I think that one thing that’s pretty different between us is that I have much better low frequency hearing. So by my cockamamie interference theory and much less added gain added to my HA output in low frequencies, any sound that bypasses my vents is going to be closer in strength to the low frequency sound produced by my receivers. So maybe whether you are venting to any extent or not, the sound from your receivers will dominate. In my case, given the extreme openess of my open domes, I surmise that the amount of “outside” sound that gets to the vicinity of my HA’s is enough to cause problems mixing in with what’s coming from my receivers. I think it’s the 2006 Widex paper that’s cagey, allowing that outside sound could be in phase with your HA receiver sound or out-of-phase, causing some cancellation or distortion, depending on a particular individuals setup. So it’s probably one of those things where for an excuse for explaining things, I can throw in “everyone’s ears are different” (as probably are the acoustic properties of said ears when you start cramming various stuff into them!).

No doubt that everyone’s hearing is different and you do have much better hearing on the low end. I struggled with getting a good bass until I got the Evoke. And it was bass I was searching for when I was playing with the various domes.

Let me add that now that I have that bass I find that due to my lousy left ear I have to volume down a bit on that side when there is music with a heavy bass to mitigate distortion.