The vent(s) (either 1 or 2) in the bass dome is more about letting some sound in to minimize occlusion, than it is about letting low frequency sounds in. But of course some of the sounds (lows and mids and highs) still get in through the bass dome’s vent(s) nevertheless, albeit at a lower level because it’s not wide-open like the open dome.
So letting sounds in is not a priority of the bass dome like that of the open dome. The bass dome will rely on the hearing aid to give you the amplified sounds you need to hear instead. The priority of the bass dome with vent(s) in my opinion are
-
To keep more sounds out (although some amount still goes into the vent(s)) which helps with the natural noise attenuation and makes the hearing aid noise reduction more effective.
-
To help keep the amplified sound in more, not as well as completed closed domes or molds, but still… it prevents sound leakage -> this helps contain the low frequency sound leaks and streaming content, especially music, sounds less tinny.
The small vent(s) is a effective trade-off to help reduce occlusion, yet still be able to achieve 1 and 2 above, although not as well as closed domes. Usually with a vent or two, occlusion only remains significant when you have mouth movement like when chewing foods. Maybe also when you talk but then you’re too busy talking to notice any occlusion while you talk anyway. But if you don’t have mouth movement, the occlusion is minimized because the vent(s) connects the inside world with the outside world.