The less (unacceptable):
-If the volume is widely adjustable music listening, this is not (at all) if in conversation; although set to minimum, the sound is too high (beware ears).
This is why I advise against buying this product, deprived of one of its main purposes: the comfort of conversations (I personally had to add a volume controller VC 20- -type Koss, by accumulating the prices, was soon to regret the initial acquisition).
I paired this with different phones (Iphone 4, Sony Xperia, Samsung Galaxy S2), and have coupled with different headphones / headset; the problem persists.