ismala: Semi-open is indeed a difficult term, because in fact most open headphones are semi-open designs. The damping (that causes the semi
) can vary from very little (Grado...) to noticable (K240M/MF/S...) - nevertheless, I'd assume the isolation of the K240 to be just around 3 to 6 dB. That won't be enough to block out a noisy environment - and not enough for not bothering the folks around you, either. Maybe you should look into the Beyerdynamic DT250/250 instead... Or an AudioTechnica, maybe... The Pioneer acidtripwow dug out looks promising, too...
Greetings from Munich!
Manfred / lini