Originally Posted by john65537
I read an article somewhere saying you need a big room to actually hear low frequencies.
It's based on physics: Speed = frequency * wavelength
So if your room is too small, low basses you hear are actually resonances.
The question is: Since headphones (especially closed types) have so little space for low frequencies, how can we hear 20hz with headphones? Are they all resonances?
The article referring to bass in a room has very little application to bass with headphones. In room, far field bass response is dependent on "room modes", or "standing waves" that exist with wave lengths at multiples of one or more of the room dimensions. The idea is that these long bass waves are reflected by the room's walls, ceiling and floor, and the resulting waves "stand" with amplitude peaks in one place and nulls in another for every frequency related in size to room dimensions.
But with headphones, relative to the wavelengths of bass frequencies, the "room" is so tiny it's non-existent, even with full size sealed headphones, because the chamber is insignificant relative to base wave lengths. Headphones, and in particular IEMS, operate by producing changes in pressure at the ear, in very "near field", similar to a piston in a cylinder. You get just the initial pressure wave, and there's really nothing out far enough to create a mode, or standing wave.
By the way, the same sort of thing can be done with near-field subwoofers. Dr. Hsu of HSU Research has for years recommended placing the subwoofer so the listening position is "near field", which comes closer to working like headphones and bass, though the room is still very much involved.