Why do headphones sound so good...

Headphones move so little air that they usually outperform most consumer speakers in terms of distortion. They also help cut out or reduce ambient noise. For critical listening or adjustments, headphones are very useful....but the sound is awful!

Unfortunately we learn from birth to have an awareness of space (natural reverberation) from the way the brain processes the signals reaching the ear. (If you step into a anechoic chamber it can actually be nauseating as your eyes tell you something that your ears contradict!)

Unfortunately headphones sound far from natural - they seem claustrophobic or closed in or like the sound is coming from "within your head". The brain correctly detects the spatial information in the stereo sound as coming directly from one side or the other and following a line through your ears into your head. In essence, the brain figures out that the source is not from the front, above, behind or underneath but directly from the sides; so the sound image just seems to pass through your head from side to side (the band is playing in your head).

Basically the diffractive role of the pinea is negated in this configuration.

I would add excellent headphones have very little phase shift, as their single diaphragm moves nearly/almost as one solid piston through the range of 200Hz to >8kHz

In that same range, most all speakers have hundreds of degrees of phase shift (time delays), which change with the frequency being reproduced.

Roy,

Agreed. Minor and gradual (smooth) changes in phase seem to be extremely important in tranducer design between about 300 and 4 Khz (preserving timbre over the senstive mid range frequencies ).

I suspect this is one of the reasons speakers with similar frequency response sound so different. I suspect that another reason stems from differences in off-axis response or dispersion.

So two alike speakers in on axis frequency response can sound totally different. So why do the audio magazines and specs all look primarily at on axis freq response?....go figure!!!

Other factors are IM and harmonic distortion ( again something audio mags rarely delve into and are often horrific in many speakers at higher or realistic listening levels and especially at low frequencies but also, suprisingly, bang in the upper mids/treble where it is most audible (ringing, breakup)...again nobody seems to look at this....go figure!!!)

Further factors are baffle and edge diffraction.....again nobody examines or measures these effects as a test on commercial products....again ....go figure!

BTW: I still have my trusty AKG 240's (1979 vintage Stucio headphones), the first headphones that really blew me away. I think the Koss were stunning too - although I found them a bit heavy/uncomfortable to wear. (However, I do find headphone listening an unnatural sound even if distortion is more easily heard. It is not just the "in your head" sound but the lack of reverberation that I don't like... a certain reverberation of a live room is quite essential, IMHO, in hearing more detail in the music as the reverberations help seperate sounds and let the brain/ear gleen more - so I rarely use headphones as a good pair of loud speakers simply wins hands down!)