“ These are amazing. If you can get them for a low price, do so. They are a bit uncomfortable, so you might not want to use them for long periods of time. Their clarity is fantastic though, the bass while not being big in quantity is extremely accurate and with a decent amp (I'm using the 300 Ohm version of the headphones) it is just fantastic in quality. Despite being a closed headphone...” --FirsToStrike
From an old MB Quart brochure (circa late 80s): The Quart Phone 50 Dynamic, semi-open headphone. Coupling: circumaural. Frequency response: 10 Hz - 22 kHz. Nominal Impedance: 120 ohms (x2). Sound Pressure Level: 96 dB. Rated Power Handling: 0.1 watt. Distortion <0.5%. Weight (without cord): 245 grams.
MB Quart QP400 is top of the line semi-open headphone from the last MB Quart lineup. QP400 have cardamatic suspension that together with soft plush earpads make them very comfortable.