I have a phase inverter (some say this should be called a polarity inverter) on an old Denon CD player and the effect on sound doesn't exactly stand out like dogs' balls (to use an old Australian expression) . So I wouldn't worry about it too much either.
I am still curious about phase shift of a reflected sound , which we discussed some time back. I worked for several years with sonar engineers who never even mentioned it, and you would think if anyone would care about this it would be people who were making their living off reflected sound.
Trying to research this on the Interenet I came across a number of references which lead me to think that the phenomena is not a simple one. It seems to be affected by the angle of incidence as well as the rigidity of the reflecting surface and ties in with Newton's Third Law, impedance matching and the like.
http://www.avsforum.com/avs-vb/archive/index.php/t-1073322.html indicates no phase shift with a rigid wall.
http://paws.kettering.edu/~drussell/Demos/reflect/reflect.html Deals with string demonstrations in which there is phase shift with a clamped string but not when the end is free.
To which I add one thing I did learn from my sonaring colleagues, that you don't even get a reflection unless the the size of the reflecting object is greater than the wavelength (or was it some fraction of the wavelength) of the sound, so there are frequency issues affecting reflections as well.
As regards the Sigma, it seems to me that one of the profound differences between it and other phones is that because the drivers are located, ahead of the ear, no direct sound is getting to the eardrum from the driver. I would guess that the first sound to get to the eardrum would be that which is reflected off the pinna, with reflection from the the mineral wool coming later. How much and what frequencies come off the mineral wool are unclear to me because some energy may be absorbed.
Now to the extend that the Sigma gives you pinna reflections that is fine since that means that it is giving you something comparable to what your ear would get from a sound source in front of you. Normal headphones fire straight down the ear canal and that would only correspond to sound sources right beside you. This I suspect is one of the reasons why most phones don't sound quite right and furthermore are somewhat harsh sounding . Regualr phones have a pronounced direct signal from the headphone driver which you would not generally experience at a concert where what you hear are sounds that have been bouncing off and and around the parts of the ear.
But when you just run Lambda drivers in the open air, located where the Sigma drivers are, you don't get any bass. The mineral wool of the enclosure is necessary because it probably blocks some of the back wave and also creates a resonating chamber. But which aspect is more important i.e blocking the back wave or cretaing a resonance chamber I don't know.
I think the resonating chamber aspect is not good because it creates some artifactual sound. In this regard the AKG K1000 has an advantage in that it doesn't use a chamber. How it gets its bass up at all I don't know but I suspect some equalizing process must be at work. Still one major complaint about them is weak bass.
I wonder if it woud be possible to create a Lambda-type K1000 by using a second set of drivers in front of the main drivers, running like one of those active noise reduction phones, to cancel the back wave?
