The usual way is called a low pass filter.

If you listen to electronic music you probably know what I’m talking about even without knowing it by name. It’s the sound in breakdowns where nothing really changes about the patterns or the music being played, but the sparkle and definition goes away and all you can really hear is the baseline and kick drums. The high hats are still playing and “in the mix”, their high pitched sound is just being filtered out electronically when the person playing turns a knob.

In everyday life it’s the sound of music through a closed door or rolls up window, muffled and low pitched. When the person opens their door or rolls down the window suddenly you hear more than the subs.

Waves propagating through a medium follow the inverse square law so the more dense or thick the “door” that sound has to go through, the quieter the blocked frequencies on the other side will be.

Since ultrasonic waves will be higher in frequency than audible ones, they’ll be scattered and absorbed much more readily than low frequency ones. Something that will absorb them well would be a flexible damping layer between the microphone and air, like the material of a disposable glove stuck over the top of the microphone hole.

This solution is better than a software one, because instead of relying on your software to correctly intercept and filter input from the microphone, you’re preventing it from ever reaching the mic in the first place!

Now you still need to be worried about solid objects. They can transmit sounds just like the air and are even better at high frequencies! Someone could have an ultrasonic exciter mounted on the bottoms of a table and vibrate your phones mic directly through its own chassis! So maybe stick your whole phone in the glove instead of just cutting out a little diaphragm for the chassis mic hole.

It’s extremely hard to understand what you are trying to say with this post

A chrome extension? Ahahah!