Hearing aid mold selection: so very important

I have read quite a lot of comments on this forum and have come to realize how little emphasis is placed on the importance of the correct mold selection. Everyone seems to be focusing on the hearing aid selection. I am realizing that many performance issues can be addressed in the mold selection and fitting. I started off with open ear mold; I changed to #2 skeletal with SAV and am down to a pressure vent. Now I am about to try a semi canal with a flex canal going to the 2nd bend. Going down to a pressure vent has made a huge improvement in understanding speech in noise as well as now, I am able to use the cell phone in noise, and also I find I can hear so much better on a regular phone. All achieved without changing the hearing aid. I am now changing to a deep canal style in order to reduce the occlusion without losing the improved performance due to going down to a pressure vent SAV. I was also going to try a liby horn but decided that the digital aids should be able to compensate for the reduced high frequency gain caused by going to a deep canal mold. I have a great fear of going to a deep mold due to the highly sensitive area that is in the deeper part of the canal because of the concentrated blood vessels and nerve endings. But, as my present molds already are 20mm long, going another 5mm is not a great distance…I hope.
I am not in the hearing aid business, Its just that in order to maximize my hearing ability, I have taken it upon myself to learn as much a possible about hearing aids and hearing loss so that I can better assist the audi in making the best possible fit and selection.
Any comments Admin?

Yesterday, I was fitted with new molds. They are flex canal; that means the canal portion of the mold is made of silicone. It is very soft and I can hardly feel them even though they measure 24mm (about 1 inch long) that means they are very close to the eardrum. The fit is supposed to be “tight” but they do not really feel tight at all. They are semi skeletal design. Before, I had full skeletal. The SAV I have selected a pressure vent because this one works best with the phone. They stay in very well. The REM was checked and the gain SPL has been adjusted to suite the new resonance in the canal. What do I hear different from before? Not too much really. Slightly less high frequency: that was expected. Very much more comfortable though. The occlusion effect change? Maybe slightly less but not significantly so. I believe that is because they made the canal tapered so I did not get the seal close to the second bend that I was hoping for. As for the “second bend” shape on the canal, I cannot really see one. I understand that the eardrum is about 24mm in from the canal entrance so surely the mold canal must have reached it. In conclusion, I got greater comfort, they don’t come out, the sound is not changed much. I worry about how strong is the bond between the outer hard plastic part to the canal silicone part. The silicone is very soft.

withears,

You are right, mold selection is a very important part of fitting a non intra-aural hearing aid. When I originally qualified in 1994 it was still part of the practical exam as a separate section. I had to spend 15 minutes with a PhD audiologist showing me audiograms and asking me questions about molds. That was one sixth of the entire practical.

But the trend moved towards in the ear hearing aids for a while. I wonder if some hearing professionals got rather out of practice with fitting BTEs. However the pendulum has been swinging back the other way in the past few years with BTEs becoming a lot more popular again.

As for your questions. I don’t think you are all that close to your ear drum. If you were geuinely 2mm off the drum the otoblock used in the impression would have been touching your ear drum, and you would have been screaming and touching the ceiling!

The concept of the deep fit is to get into the bony portion of the ear canal. The theory goes that by touching that it reduces occlusion. Also the sound tube can be better angled to point right at the center of the drum. Of course you noted it made little difference to the occlusion, which tends to be the reality in the real world. The theory is all well and good, but often it remains just that; a theory.

I wouldn’t worry too much about the soft portion of the mold coming off. It is really rare. What is more likely to happen is that over the next few years it will become less supple and may discolor. At that point you will need to replace the molds. But a new set should be far less than $180.

Hi ZCT
Thanks for the response. After trying out the new molds with the prog correction for 1.4mm vents, in the everyday world it seemed fine. But, as soon as I was in the noisy classroom environment where I teach, I could not understand speech…really badly. Later my audi adjusted the high frequency gain whilst connected to the computer. She kept upping it until I said stop. She said that my gain preference was not consistant to my hearing loss but would comply. The result is I can now understand speech more clearly than ever. I really wish it were possible for us users to be able to have access to the computer programs used for making these adjustments; it would save a lot of time. Next time I buy hearing aids I am going to be looking for this option; either built into the aid or computer software.

withears,

There are several reasons why they won’t want patients to have access to this kind of software.

First off there is the opinion within the hearing aid industry that a patient should just get used to a hearing aid and not ‘mess about’ with it. To some extent I can see how this might be right. I remember when remote control aids were popular I heard a lot of reports about retired engineers and scientist types fiddling around with them way too much, and actually making their rehabilitation path harder for themselves. But all that said with the right individual it may be feasible.

I forget what kind of hearing aids you said you had but the top of the line ones I offer feature 8 independent channels with 12 bands. Each band has output control over soft, medium and loud noise, with a compression ratio of 1.0 to 3.0, and a maximum output limiter. I then have four different background noise filters that can be set to off, on or max. I have control over the speed of all features and compression which is an extra 243 or so options. I have nine different directional modes and a feedback calibration routine with three different modes. Then I have four different memory options that can each be independently configured according to the aforementioned specifications. I also have about eight math formulas to translate a hearing loss to an amplification pattern.

While the software is pretty user friendly, it requires extensive experience and training to operate it properly. And I think that at least 33% of hearing professionals don’t know how to program aids well. So I would be quite concerned about handing over that much control to a patient. Unless perhaps certain basic controls could be made available in something a little more user friendly than typical audiologist programming software.

I don’t like your audiologist comments that your gain preference was not consistent with your hearing loss. Frankly it is rare to find someone that perfectly fits the ‘recommended’ settings on a hearing aid. I think that a good specialist should always custom program the hearing aids until the patient is completely happy with the sound.

Hi ZCT,
I really appreciate your comments. My there really is a lot more to setting up hearing aids than I first thought. Makes me wonder how do hearing aid dispensing companies expect hearing aid fitter students with just 6 months college training to be able to make the optimum settings for a patient. Me thinks it don’t happen. This training period was quoted me by my Audi who has been fitting aids for many years.
Thanks for the bit about adjustments not having to be in strict accordance with the patients audiogram. As for my settings (I have Tego Pro BTE’s with semi skeletal flex long canal with bell ends and 1mm SAV. The sound in the class room (my most demanding chalange) is not bad. It is a bit on the loud crisp side but the consonants are clear. I have mild to moderate SNHFHL. Since I started wearing HA’s last July, I have gone from open ear with Oticon domes; Widex tulip domes to occluded #2 skeletel acrylic molds to the present flex canal molds. The present configuration seems to work for me.:slight_smile:

You are quite right, most Hearing Instrument Specialists spend less than a year getting qualified, it depends on the state. In addition to learning the software there is a ton of other stuff to learn, as you might imagine. But that said, an HIS usually has a mentor training them too. This mentor if he is experienced and good, will teach a lot of tricks of the trade when it comes to programming hearing aids.

That said an audiologist isn’t much better off. While their degree takes two years, they are not really learning that much about programming software during that time. They often have far less hands on experience than an HIS.

There is no substitute for experience. Which is why I would always ask my hearing professional how long they have been in the profession. I would also watch to see how confident they appear to be using the technology. I’ve had patients tell me that some call the factory for advice about programming an aid. This is usually a bad sign!