The reason why I use covers instead of buying IEMS is because I have bought IEMs - some that use TWFK - and these $15 earbuds with covers sound better than the $150 IEMs. I actually did address this earlier in this thread. I think it is better to pay $15 and use covers and get a better sound rather than spend $150 for IEMs that do not sound as good. I can understand that some people want to spend $150 for something that sounds worse than $15, but I'd rather buy the better sounding $15 part, put a cover on it, and use the rest of the money for something else.
I like your frugality
However, the covers do affect the sound tremendously, I guarantee it.
All of my wide-bored IEMs sound
MUCH better with wide-bored tips - Heaven IV/VI, Sennheiser IE80, RE-262, Piston 2 etc.
When I put the narrow-bored tips on them - they sound way worse, especially the
BASS and the mids.
And in this case, the narrow tips usually are smaller by maybe 50% - your covers decrease the area by 90-95%.
The size of the driver is important! If all things are equal - ie distance to ear canal, membrane material - the larger driver is able to have a larger magnetic field - and the increased surface area of the membrane is easier to drive at lower frequencies. It is the laws of physics. Something that is 10mm is going to more difficult to drive at lower frequencies than 50mm. The increased surface area of the larger membrane is going to move more air than something made out the same material but is 400% smaller. It is true that the closer it is to your ear canal, the less the size matters. But it still matters a lot, and to say it doesn't matter is just plain wrong!!!!!
First of all, let's get your math straight. If you take 50mm, and reduce it by 400%, you end up with -150mm.
Second, do you know any earbud with a much larger diaphragm than TG-38S? You can go may be 10% larger, before it stops fitting in the ear and becomes an on-ear.
Most earbuds have a 13-15mm diaphragm. If the bass would really depend so much on the size, then all these earbuds would have the same bass.
It's all in the tuning, size isn't that important.