Why are standard hearing aid fitting domes round?


Discussion in another thread has got me to wondering why virtually all the off the shelf click domes are manufactured round. I have never used these, as my KS8’s accept Rexton/Signia sleeves which are not round, but in fact quite oval shaped. I started with open sleeves, then closed sleeves, and now I have custom molds. When I measure these off the shelf sleeves they are approximately a 2:1 ratio shape instead of the 1:1 of a round fitting. I measured my molds which I presume reflect the actual shape of my ear canals and they are approximately 2:1 in ratio too. This would suggest the sleeves are a good fit for me. In fact so far the closed sleeves have worked as well as my custom molds, although I am hoping for better.

So back to my question. Why on earth do most manufacturers make round fittings? Is this a patent issue, and Rexton/Signia does not allow them to make them oval? Or are many ear canals actually round, and my 2:1 shape is odd? Just curious. It just seems to make sense to start with a fitting that approximates the shape of the ear canal in most people rather than trying to fit a round peg in a square hole.



The round ones are normally soft enough to conform to the ear canal, or at least that is the theory.



My custom moulds are oval also. Had problems getting domes to fit.

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One cynical thought I had was that dealers/manufacturers make no money on domes, and many like Costco even give them away. So, if they give you fittings that don’t work for free, that gets you in the door, and then they can sell you the molds! In other words, it is better for them that they don’t really fit!

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In all my years of nursing, 15 spent in an E & E Hospital. I’ve never seen any aural canal that looks anything but mostly round in shape. So I guess this is why the are round at one end going down to oval at the other.

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So it must be my ears then. The custom molds are not even close to round at either end of the mold.

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Yeah, molds I made earlier in life weren’t anywhere near round in cross section, but neither were they 1:1 H:V ratio. More like the 2:1 Sierra cites. But I don’t think it matters. The dome material folds and deforms and pretty much conforms to the irregular opening, and the tissue of the canal deforms somewhat to adapt. (If it has to deform a lot, you might get sore.)

Open domes don’t matter if they hit the edges all the way around. Any gaps would just be like the dome holes.

I guess it’s more of an issue with closed domes, but if they do the job at trapping-in low frequencies, you can bet they’re successful at closing off the canal pretty well, even with the irregularities of the canal.