Once you know which type of headphone to get, there are two important statistical factors to consider, which are largely related. The first is sensitivity, which is rated in x amount of decibels per milli-watt (mW). This refers to how loud in db a headphone is when given a static amount of power (a mW is 1\1000 of a watt). This spec is important if you plan to use your headphones with a device that has a limited amount of output power (portable music players). Every 3db increase in output requires double the amplification. If one headphone is rated at 90db\mW, and a second is rated at 96db\mW, it will take 4mW for the first headphone to get to 96db. When hooked up to home stereo equipment or headphone amplifiers, this is largely irrelevant. However, most portables are limited to around 10mW or so, and sensitivity specs for high-end headphones can differ by as much as 30db, so for portable use, this is very important to look at.
The second spec to look at is impedance, measured in Ohms. Headphones differ greatly from loudspeakers in that most loudspeaker amplifiers are designed to operate between 4-8ohms, therefore, most loudspeakers operate at 4-8ohms. Headphones, on the other hand, have no impedance “standard” to adhere to. Headphones below $50 are generally designed with portable players in mind, and thus have a high enough sensitivity and low enough impedance for the portable player to drive them. Once you get into the high-end though, manufacturers stop assuming you’re going to use them with a portable player, and impedances can fluctuate wildly between headphones. You can generally assume that headphones with an impedance above 32 ohms are not portable player friendly. Unfortunately, if you plan to use high-end headphones with a portable player, this will drastically limit your options, as most of them have an impedance much higher than 32 ohms. (250 is fairly common, though I’ve seen as high as 170,000 ohms).
Now that you know what to look for when headphone shopping, I’ll take a closer look at the Sony MDR-V700DJs. Here are the specs from Sony’s website:
• Sony UniMatch plug systemwith fixed stereo miniplug for use with portable equipment; detachable phone plug for use with studio and home audio equipment
• TypeClosed supra-aural, Dynamic
• Drive Unit 50 mm
• Diaphragm PET
• Magnet Neodymium
• Impedance 24 ohms
• Sensitivity 107 dB/mW
• Power Handling Capacity 3000 mW
• Frequency Response 5 -- 30,000 H
• Headband wide, adjustable single headband with folding earcups
• Earcups swivel and reversible for single-sided monitoring; auto-return mechanism
• Cord Oxygen-free copper; Single-sided, 10 feet (3 m)
• Plug Straight, Gold-plated, stereo UniMatch plug with fixed miniplug and detachable phone plug
If you’ve been reading up till now, you’ll notice something about the V700s specifications, yes these are indeed one of those rare high-end animals that can handle portable players. In fact, the very low 24 ohm impedance and sky-high 107db\mW sensitivity is better for that specific role than any other headphone I have seen.
