Questions about Earmold Types and Venting to Reduce Feedback

The advantage of Select-A-Vent is that you don’t have to commit to a vent size but can play around and find the size that you like best. There is the following info that I posted out of Harvey Dillon’s 2012 Hearing Aid book - which you’ve seen before. Dillon says there are effectively only 2 or 3 actual venting sizes attainable with Select-A-Vent because, for example, it’s hard to achieve total occlusion due to leakage around the mold so, for example, he says that no vent will basically be about the same as a 0.5 to 1 mm vent, etc., (might be described in more detail in some other previous post of mine).

Yes, there is theory and then actual performance. One of the ways I have rationalized that I am having feedback when the size of the vent in my current closed click sleeves (1.6 mm) would predict I should be free of feedback, is that there is leakage around the click sleeves. When I went from open click sleeves to closed click sleeves the Connexx software reduces the streaming equalization for bass I presume on the basis that less bass would be lost through the much smaller vent. However in actual practice I am getting really poor bass with the closed click sleeves. I am no attributing that to leakage around the sleeves. My hope is that the custom mold will significantly reduce that leakage.

But, I guess where I am at now is that perhaps there is no “optimum” sized vent providing I am willing to deal with the occlusion. i.e. smaller is better… And perhaps when one is realistic about leakage and are willing to count on it, then perhaps no vent is an option.

I also see in your previous post with diagrams from the Dillon book, they seem to be the same ones as are used in the slide presentation I gave a link to in my recent post. They are quite helpful in understanding what is going on with vents.

My comments would be to look at the critical gain analysis to make gain adjustments and to be cautious of the custom ear molds as from my experience they do not necessarily fit as well as properly fitted domes or sleeves. Especially if you have small or twisted ear canals.

My mother has KS8 hearing aids with moderate to severe hearing loss. Her right ear is worse than the left. She has small ear canals that are also at an odd angle. She started with closed domes, but those would not stay in place. Went to closed click sleeves and still experienced problems with feedback and getting them in correctly. Next she tried custom ear molds which she and I were very disappointed with. They were large blocky and really only sat in the outer ear. They did not really fit in the ear canal. They were not what I thought would be custom. They were the worst of the worse as they kept falling out. She went back to the click sleeves while they sent them out to make new ones. She still experienced feedback, but learned to better insert them. When we went back to try the new custom which were really no different than the first ones. The tech ran a critical gain analysis and based upon that reduced the gain in the pinch point areas. With the gain adjustment and practice at putting them in and finally understanding that she has to check the click sleeve alignment she is very happy with them. We returned the custom ear pieces for full refund. She still has to watch the insertion and sometimes make an adjustment to get them to work.

Thank you for the comments. I will keep that in mind. My conclusions so far on custom molds is that a soft silicone seems to give the best acoustic isolation, and the more you have of the mold in the ear canal the better the isolation, and if you only have a short amount in the ear canal you really can’t make up for it with addition in the outer ear – other than to try and hold it in place.

The part about your mother’s experience that doesn’t seem to make sense is that a twisted ear canal is considered beneficial as it lets a canal type lock in place without a lot of assistance from the outer part. That said, I’m thinking that the smaller and more crooked the ear canal the harder it is likely to get it in place, especially if the mold material is soft.

I guess in the end I will have to rely heavily on the fitter’s experience in evaluating what can be done with my specific ear canals.

I’d say it’s one of these YMMV issues that depends on the shape and size of your ear canals, how good an impression your provider makes, and who makes your molds . Domes are made in a fixed set of sizes to a regular geometrical shape and the attachment point at the base on a tulip dome can be an odd, poor fitting solid object in your ear canal in spite of the ability of the tulip “petals” to accommodate various canal sizes. I had my molds made by ReSound and they follow a 16:4 rule, the mold from the entrance to your ear to the inside should be at least 16 mm long and go 4 mm past the first bend of your ear canal. If one has any waviness or undulations in the shape of your ear canal(I do), the mold captures that and the uneven mold shape forms a grip to hold the molds firmly in place (my molds do not slip in the least - but whatever dome I wore did not either, as I used concha (“sports”) locks when I wore domes). The undulations that I’m talking about can be seen in the shape of my right mold in the linked picture below, as well as a notch in the mold near the point of receiver insertion (red arrow) that appears to catch the crux helicis above my ear canal and also help hold the mold in place. In any event, one (bird) swallow of any sort does not a summer make, but looking over many posts on the forum, especially with severe hearing loss, most people who are willing to go to the extra expense of having good molds made get pretty satisfactory results and as far as trapping low frequency sounds within the ear to prevent loss of amplification when you most need it because of severe loss, molds offer a thickness of material compared to domes (don’t know about click sleeves) that better traps low frequency sounds within the ear canal. Works the other way, too. Because I’ve chosen an occlusive mold, when I want to block out extraneous sound, I turn my HA’s down or off, and much less outside noise comes into my ears with my molds in place than I’d hear if I were wearing tulip domes or power domes (again, have never tried click sleeves).

Should emphasize that good custom-made molds fit your ear canals perfectly, as mine do.

Thanks Jim for another good and detailed response. I’m learning!

As an update I went in for my mold impressions today at Costco. Took about 30 minutes to do both ears. Not unpleasant at all. Some learnings:

Costco in Alberta does not use the OTO Hearing company that I suspect they did. They only use them for custom ear plugs, and sometimes for receiver behind the ear tube type HA’s. For RIC HA’s they use the manufacturer – essentially Sivantos for Kirkland, and Rexton. Interestingly they ship the impressions out east to Ontario for scanning, with the digital details going to Holland in Europe for manufacture. So it takes up to 2 weeks to get them. I guess the reason is that RIC molds have to be made specific to each manufacturer’s receiver. I should have known that, but did not really think about it…

In any case I will be getting straight canal type silicone molds with no external retention features. The fitter did not think it was necessary. Assuming there is room for them, they will both have Select-a-Vents, so they can adjust the venting on site here. She says they will make the molds as many times as it takes to get them right and they can be returned if I am not satisfied with them. Seems hard to beat that for service. The Canadian cost is $80 each with some paid by our government health care to bring the cost down to about $135 for the pair – about $100 US.

I sure hope this is the solution to getting a good fit!


The 16-4 rule sounds good. Mold depth would seem to be very important. Not only for a proper seal but to hold the mold steady.
I should be getting my earmolds any day now. Lloyd’s did mention having them made extra long for greater depth.
Good luck with your new molds.

Let me know how you make out with the molds…

Will do.
Lloyd’s called yesterday to verify the power slim tube length, said the molds look good. The molds will be mailed today so should be here later this week.

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The new molds came in today.
They look great.
Initial fit is tight. I hope not too tight.
The sound from the Naida V90 aids is very impressive. Very full and natural. Absolutely zero feedback but really never had feedback issues with Phonak aids before.
Now it’s time to start taking notes and getting some word recognition back.

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Did they do the REM testing and adjustment again? It may be possible to push the correction a little harder with the improved acoustic isolation. That is what I am hoping for…

There is no they at this time. I will give this a few days before getting anxious about REM.
Lots of sound to get used to.

The molds are night and day different than any domes I have used.
I don’t use audiologist.

OK, I understand now…

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Have worn the new molds for 6 hours now, no pain.
There are new ear sounds while chewing and walking.
Also hearing new low frequency sounds. Like engines rumbling. That I like a lot!

Well, I am still waiting for the custom molds from Costco, but I did upgrade my Connexx 8 software to Connexx 9, and it seems to provide some enhanced functionality with respect to predicting feedback problems. To date I have tried vented click sleeves, closed click sleeves, and now have select a vent custom molds on order. Here is what the new software indicates for feedback potential (red and blue shaded areas).

Open Click Sleeves - The gain curves run smack into the feedback zone for my left ear and not on my right. This is pretty much exactly what I experienced.

Closed Click Sleeves - Improved, but left ear soft sounds still run into the feedback zone for the left ear, and the normal sounds are on the borderline. Again what I experienced.

Custom Molds - The prediction looks pretty good, but the proof will be in the pudding. However it would appear that feedback should be taken out of the picture. I sure wish this software had been available when I was making my decisions earlier. If I had seen these graphs I would have went for the custom molds right from day one. To be fair the fitter at Costco warned me that I would likely need a custom mold for my left ear, but I didn’t believe her. Hopefully she was right all along and this will be the silver bullet cure for my feedback issues. The computer seems to like it, but will I?

I am getting used to my new molds. They are pretty tight and caused some pain at first. Maybe my ear canals are stretching but the molds are getting much more comfortable.
I noticed some occlusion early on. The software has occlusion control that I adjusted up some and now occlusion isn’t an issue.
The range of sound in all my hearable frequencies has vastly improved. Music is actually pretty good again. I have the Compilot2 which is absolutely fantastic for TV and phone calls. I can now understand YouTube videos.
Feedback has never really been an issue with the Phonak aids I have used. I hope your new molds fix you up.

Well, I got my new molds today, and I would love to say they are perfect, but unfortunately they are not. There was some kind of mix up on the right mold and instead of a 2.5 mm SAV it came completely sealed. That is the bad news. The good news is that it fits really good. It does not move around even when eating. I have not had feedback with the right ear, and with a sealed mold, of course I still do not. It is kind of occluding though. They are going to remake it with the proper vent. Hopefully the fit on the replacement is as good as this one.

The left ear is pretty much all bad news. The vent came as ordered, and when she did the critical gain test, it predicted feedback, and sure enough I had some. She reduced the vent size and I went home with it. However, I am still getting some feedback, and the worst part is that the mold moves around in my ear all the time and especially when I am eating. It sounds like it is sticking and unsticking to my ear canal and makes noises each time it sticks and unsticks. The right one is totally silent. I am assuming this is not normal? And it is not being created simply from the higher gain in the left ear?

My thoughts are to request a new one that fits tighter and deeper or both? Comments?