Hypothesis: custom molds optimize speech intelligibility for RIC w/ my audiogram

Hearing Aids
#1

More generally, my hypothesis is that I want to maximize occlusion to minimize feedback in order not to have to suppress high-frequency gain. Speech intelligibility, both live and TV/movies, is the most important consideration, above naturalness and comfort – providing that I can adapt to any initially-felt discomfort.

With my current HAs I have a vented custom mold in the left ear, and a closed dome in the right. In the experimental (no REM) diagram the heavy magenta line is feedback suppression. The circled areas between 6-8k are the ones of primary concern where gain is substantially suppressed by feedback avoidance. On the left (mold) the low point is 19dB; on the right (dome) it’s 12dB.

Motivation: in two weeks I’m going to be dispensed KS9s at Costco. The HIS will be expecting to fit to open domes. Should I try to persuade her to transfer the left-ear custom mold I have now to the KS9 (if it’s plug-compatible) and discuss a new one for the right?

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Hat tip to @Sierra for inspiring this hypothesis – but any errors or craziness are all mine.

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#2

I played around with the fitting options under instruments, acoustic paramaters, and found that the Power Dome’s gave the best feedback suppression. I would have expected custom molds to be better, but the options I saw there, were not. This is DSL v5 with Power Domes. The very highs would have to be suppressed some, but not a lot.

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#3

The new receivers are not compatible with the old custom tips, so you would need new ones. Make sure you’re getting the new M receiver and not the S.

I like the new power domes. You may find them more occluding than a custom tip with an appropriate vent, but if you get a bunch you can just snip little slits in them and see how you do.

Keep in mind that for a good proportion of people, the high frequency targets in the manufacturer software are maybe 6 dB lower than they need to be to hit targets using REM.

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#4

My result is after Feedback & Real Ear test, while I infer that yours is without. I guess I can try without just to see. Meanwhile I have some Power Domes coming for my current aids, but only to replace the one closed dome; I can’t replace the custom mold without getting another receiver.

#5

Thanks, Neville. The compatibility I was concerned about was with regard to the plug that goes into the body of the aid, at the exterior, above-the-ear end of the wire. If that were compatible, I figured the receiver buried inside the in-the-ear custom mold would work. Have I got something wrong (not unlikely)?

6dB REM rule of thumb is interesting. However, I hope to have REM at Costco for the final result. The current “research project” is in preparation for a discussion with a Costco HIS. Although there’s a chance I could persuade an independent provider to help me with my eccentric requests on a fee-for-service basis.

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#6

The newer receivers have a three wire connection and the older Phonak receivers have a two wire connection.

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#7

Your KS9 price should include new receivers, and the off the shelf fittings, like the Power Domes.

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#8

“Now with 50% more wires!” Interesting; I wonder what the new 3rd wire is for.

#9

Right. For now, then, my plan is to request M receivers with Power Domes.

#10

It looks to me like open domes would be brutal for feedback.

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The Slim Tip with the 1 mm or so vents don’t seem to do any better than the Power Dome.

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NAL-NL1 rolls off the highs and at least in the computer does not get limited by feedback.

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#11

What might explain the R-L differences, especially around 250Hz, in your open dome and Slip Tip simulations?

@drlaura likes NAL-NL1 for speech intelligibility, but I wonder if the fact that it shows no gain below about 450Hz would be an issue when using high occlusion in-ear gear.

#12

I think the differences in the R-L is just that your loss is about 5 dB greater in the right at 250 dB.

The formulas are trying to achieve a balance of sound levels across the spectrum according to the specific philosophy they are using in the prescription. It appears the NL1 is taking advantage of the attenuation effect of a closed fitting to reduce the lows. Keep in mind that hearing aids do not restore your total loss, and only recover in the order of 1/3 or so. If the objective is a balance across the spectrum, then that means the lows could be attenuated to put them in balance with the corrected high frequencies.

See your loss shown in the Connexx software. These graphs are from NL1 with closed sleeves. In this display the sound levels in the ear canal are predicted. You can see that the natural sound is 50, 65, and 80 dB, but at the low frequencies the in ear canal levels are slightly reduced. Notice that these curves are kind of the reverse of the gain curves. A wide spacing means less compression while on the gain curves a wide spacing is more compression.

I would show these from Target, but I have not figured out how. Perhaps it is buried in the REM tab, and that only works with instruments connected.

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#13

Oops, sorry, I forgot that you were simulating me rather than an abstract user!

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#14

yes! @Sierra is doing awesome work in plotting people’s audiograms

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#15

Wow! That’s discouraging! I’m picking up my Slim Tips on the 30th and was looking forward to the end of the screeching every time I get a foot or two near a wall in our house!

#16

I am not sure I am believing the Target software on this aspect. Both in the computer with Connexx and from actual experience with KS8’s I got a big gain in feedback resistance going to molds from closed sleeves. I wonder if Phonak is being optimistic in how well the Power Domes fit. I concluded that was the big difference between the closed sleeves and molds. The molds have less leakage around them. The molds are custom so have no reason not to fit perfectly. My problem with the molds was that I couldn’t tolerate them in my ears.

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#18

I hear speech more clearly with an occlusive fit (custom molds) but with me I think it’s more to do with blocking out potentially out-of-phase sound that bypasses my hearing aids and goes directly to my eardrums where it can potentially physically interfere with the phase of the same sound broadcast from my receivers and/or being potentially out-of-phase with the receiver sound just present a slightly out-of-sync sound in one’s brain. A more occlusive fit will also give your HA’s a better crack at noise suppression, which will also improve speech intelligibility (although I find if I am in a noisy environment without speech, my ReSound Quattro’s crank the volume down a few dB so my ears enjoy less racket, then if my soft-voiced wife starts to speak, there is a delay of a few seconds before the HA’s kick the volume up into the range designed to hear speech in noise - this latter phenomenon has nothing much to do with occlusion- just the limited processor speed and power of small, battery-operated HA’s.)

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#19

I believe Phonak uses the M receiver as standard on the Marvels, which are very close to your KS9s. The power domes I have seen actually are a double dome, and they very well might give more isolation that a mold. I have some aids that came with power domes, and I couldn’t take the occlusion. Oh, the 3rd wire is supposed to be a shield. The Marvels have a very good feedback supression system. I still wouldn’t want my fitting to rely solely on that. Good luck with Costco and your KS9s.

#20

Thanks for clarifying that!

#21

I think I am now wearing Phonak double domes but am unsure because I can’t find a picture on any Phonak website of anything called “Double Dome.”
Anyone have a website url or photo?