I don't recommend you try this at home, but have you ever touched a speaker when it's playing music? I mean the speaker cone, not the box that it's in.
Speaker cones vibrate to make music, and our eardrums vibrate to receive it. Speakers are paper or plastic cones suspended with springs to rest right in the middle of their movement range. The cones can move out or move in, making sound the whole way.
Microphones and eardrums work the same way on a smaller scale: They can go back and forth, and normal air pressure has them resting in the middle when no sound waves are present.
So when you (gently) place your finger on a vibrating woofer cone — don't ever touch a tweeter by the way — you're restricting it's possible range of movement, and the sound gets reduced to its loudest notes. And even those are muted a bit. A speaker doesn't work so well when you're pressing on it.
This leads me to the question of the day: Why does anyone use in-ear monitors anymore? Also known by their acronym IEM, these are the most common and available kind of "headphones" today.
If you stick them in your ears, it's like you're listening to music with a finger on your eardrums.
In-ear monitors using rubber tips, or even many of the dense foam tips, go right into your ear canal and seal up the exit. So when the music starts, the pressure in the canal builds and your body activates a physiological effect called the "stapedius reflex" to respond to the relatively huge pressure inequity.
The stapedius reflex is our body's way of naturally turning down the volume. Unfortunately it is not something we can consciously control, and because it activates regularly and consistently with IEMs, long listening sessions make you feel fatigued in the ears and brain.
And even worse, the reduction in volume that happens when the reflex is activated causes music listeners to turn up the volume even more to compensate.
In case you're not paying attention, none of this is healthy for you or good for music. Music can't make you feel the way it should when your body is fighting back against it. And just like that woofer cone with the finger placed on it, the eardrum itself is picking up less of the music than it could in another setup.
There is a lot of information on the internet about listening fatigue, the stapedius reflex and the villainy of cheap IEMs being foisted on the unsuspecting public.
In fact, there is a company in Boulder called Asius Technologies that developed a patented approach to solve the whole issue. And they are not alone — several different designs that try to remove the pneumatic pressure from your eardrum are in development or on the market.
If you're curious to learn more about this topic, pay a visit to asiustechnologies.com and read up on their methodology and rationale. The human hearing system is a delicate thing and cannot regenerate its parts after damage. Protect those ears!