These are a unique but very very good sounding headphone. Think High-Fidelity Beats -- extremely huge bass, but extremely tight, well-extended, low distortion bass. Nice midrange and good treble extension too. Speedy, clean, and deceptively spacious sounding. Also, these have insane build quality and isolate better than any other over-ear I've ever used. I have safely used these as hearing protection while mowing the lawn!
A close friend of mine used a phrase to describe how these sound and I haven't been able to get it out of my head since: "Wild Beast". Definitely accurate.
My measurements (replaced earpads w/ new ones from Koss):
EDIT: Here are Tyll's measurements for comparison. Largely similar results though Tyll had a bit of issue getting them to seal with the old pads:
http://www.innerfidelity.com/images/KossPro4AAA.pdf
A couple notes: the large rise in 2nd order distortion below 300Hz is an artifact of the vacuum-seal exhibited by the vinyl earpads. A similar effect is witnessed with other headphones that use this type of earpad and is simply a limitation of my microphone. Actual distortion performance is reflected in 3rd, 4th, and 5th harmonics.
There are three different versions of the 4AAA. This is a Series 2 model, which has the best version of the old Koss drivers. The first two have customizable transducer damping via a screw-on clamp -- I have my pair tuned ever so slightly tighter than stock. You want a cheap bass cannon? These can be customized to basically any amount you want and the bass does not
EVER bottom out.
Square Waves unavailable for now; will add later. Also, I accidentally captured distortion quantized in SPL, not percentage. Will change later.
Do not underestimate how difficult these are to drive. They are high impedance and need some serious juice to get going. They absolutely
sing out of an Audio-GD SA-31. Not so much out of a FiiO. Your source needs to be pretty darn good too.
