Hearing aids with hollow earmolds, domes, or a large vent are suitable for listeners with near-normal low-frequency hearing and mild to moderate hearing loss of up to 70 dB HL at mid and high frequencies. Otherwise, more closed fittings are recommended.
It seems that 70dB is the loss at which the closed domes are recommended
I don’t think it can be quite so rule based. Here’s a quote from Um Bongo from awhile back.
Somewhere back in the mists of time I put together a fairly authoritative answer on this particular question as it had come up for serious debate - I tried searching for it, but I think the terms were too common.
Put simply you have two routes - Occluded and Open, though frequency compression gives you some more room at the margins, the overall approach is the same.
Occluded: essentially stuff the biggest receiver on there, block the canal with a mould and drive enough sound to allow the 6-8Khz to be audible. Yes it can be done, but is it a good idea - possibly not for two reasons. Namely: the sensation of your ear being blocked and the subsequent overproduction of LF sounds AND the effect called the downward spread of masking, which prevails over your better hearing in the lower pitches.
Open, smaller receiver, much more open fit and accept you just can’t hit the (probably dead) regions of the cochlear, used with a very little bit of frequency compression to bring some of the higher sounds back into play. You end up with a much kinder fitting to wear every day and perhaps miss an octave of sound that you would be otherwise overloading your entire cochlear with.
Nearly all my fittings go down the #2 route - less is more etc.
I have an open fit because I did not like the occlusion while testing in the store.
I think what the authors of the article wanted to say is that with the higher loss the benefits of the closer design are greater than the negativity of occlusion. So more pluses than the minuses given by the greater loss users to the closed design
That quote was in response to a question dealing with steep losses - it does cover the occlusion trade-off though.
I guess I was just objecting to the 70 dB cutoff. It clearly depends at what frequency/ies. If somebody had normal hearing up to 6000, but had a profound loss at 8000, I don’t think anybody would even suggest hearing aids, and certainly not a closed fit. Still highly doubtful aids would be suggested if normal to 4000 and profound at 6k and 8k. It becomes a tradeoff of how much normal hearing is one willing to give up to try to solve another problem (Would be really cool to be able to push a button in a noisy situation to turn the aids into a closed fit and activate a good speech in noise program!
Cool - dynamic venting - If you’re quick we can patent this.
My personal choice would be a smart material in the domes that gets stiffer when you put voltage through it. Link it directly to the receiver output. So you put in a very flexible dome for all people, but when you drive the receiver harder the seal is improved/orifices are closed etc. You wouldn’t make it resonate with the actual speaker frequency, but over a smoothed average. End result, less fatigue, less feedback and more venting - obvious flaw might be the action when speaking yourself, but there’s no reason that the detection of occlusion can’t happen via a mic/processor in the receiver unit.
I lke the idea!
How about a material that sound transmission ability varies depending on frequency (lets lower frequencies through to prevent occlusion, but reflects back higher frequencies?