Slater
Headphoneus Supremus
It would be interesting to measure the iems with different kinds of tape and different arrays of holes added with a needle. What does tape do, generally? When I tried micropore tape on the Tennmak Dulcimer once, the sound was totally muffled.
We know that wide bore tips increase treble and possibly remove a bit of midrange, we know that taping vents increases bass, we know that adding metal screens adds treble and textile screen remove some. But what does tape do? I would like to see the respective frequency response curves.
The tape causes a restriction/resiatance (as well as providing a filtering effect).
So as it pertains to driver vents on IEMs and headphones, it in effect makes the vent hole 'smaller' because there is less surface area (like putting a coffee filter over a bath drain will cause the water to drain much slower because the water has to get through the small holes of the filter. When used on the magnet vent of full size headphones, it does the same thing (causes resistance/makes the area of the 'hole smaller'), which on most drivers tunes out some bass and/or makes the midrange more forward (it varies by driver and other factors).
You can also use it over BA drivers to filter out some of the output (ie reducing the sound and/or filter some frequencies).