Principles of Venting - open, closed and custom


#1

I’ve often read the phrase “properly vented custom molds” here on the forums. Can you please explain how this all works?
I imagine it has to do with the amount of loss at certain frequencies and the amount of amplification required. Not to mention the potential for feedback.


#2

A limited low-freq loss can use the open fit domes so a very wide access to outside sounds. Next is a tulip and then the two full dome models.

With a mold, the fitter specifies the opening. You’ll not get as much opening as open fit provides but it can match up well to the others. If you get a wider opening, it can be restricted later with a restrictor. There are a couple of types of those but they reduce the opening which helps with feedback issues.

With your audiogram, you were probably using the full/power domes and the mold will work well with your loss – providing added comfort (hopefully) and likely better understanding with better positioning.


#3

Thanks; If I got this right … the greater the loss on lower frequencies, the less opening or venting you want?
Decreasing venting => Open > tulip > closed > double?

The less opening or venting also decreases feedback? Does venting have anything to do with the higher frequencies?

I was wearing open domes just because they felt more comfortable. It is only recently that I’m starting to understand that the amount of venting does affect the sound. The Audi said they want to give me closed domes with no explanation.

I am repeatedly coming to the conclusion that informed consent it truly lacking in this profession.


#4

I found some answers since posting, I found a thread started by @MDB that references an article on open vs closed fit:

The article itself is a little technical and a long read. If you take it slow and easy the pieces seem to come together.


#5

Beside more access to natural sounds if you don’t have lower frequency loss, and feedback control, venting will also have an effect on the efficacy of the directional beam forming used to block out surrounding sounds for noise reduction in restaurants. Obviously the more venting you have, the less effective the sound blocking will be.

And finally, venting will also have an effect on direct streaming. More venting will leak out the lower frequency sounds when you use direct streaming because in this case you don’t care about the natural sounds around you, you only care about the streaming content. That’s why people with large vents usually complain that their receivers perform poorly because they sound tinny, while it’s actually the venting that causes to low frequency leak that makes it sound tinny.

So now you can see how there are so many factors that can come into play depending on your physical fitting that sometimes compromises must be made to achieve the effectiveness of the goals you truly care about because you may not be able to find a single fitting that’s perfect for all situations for you.


#6

I’m following this I just got HA’s from the VA last month and she ordered custom molds for me. She said something about not being able to turn mine up to what I need without them. I guess I’ll see what happens


#7

Regarding high frequencies. It will be easier to really push gain of high frequencies with no vents. This can be fine if you have a big loss in low frequencies too as no vents will allow more gain to all frequencies. Open vents will make it harder to push gain in high frequencies even though it’s appropriate if normal to mild loss in low frequencies. That’s one reason to consider some form of frequency lowering.