Sennheiser HD650 Audiophile Open Dynamic Stereo Headphone

With no need to reinvent the wheel year in and year out, 2004's titanium/silver-colored HD 650 is only the third top-of-the-line incarnation since the HD 580, following the classy HD 600 (and not counting Sennheiser's made-to-order $15,000 Orpheus electrostatic headphone). Is each issue better than the last? Fundamentally, yes, though they're also simply "different." Taking as a starting point that each is truly excellent, the 580 might be said to focus on glorious midrange; the 600 makes a point of delivering extended, exceptionally airy high frequencies; and the 650, fittingly enough, tackles the most difficult area of sound for small drivers to handle: deep bass.

The 650 offers appreciable bass well below 40 Hz, the region responsible for the deepest frequencies generated by kick drums, timpani, double bass, electric bass guitar, and all manner of electronic sounds. Further, the 650 reproduces its low frequencies with only minimal emphasis in the upper-bass region, between the areas we commonly call "bass" and "midrange", in which undue emphasis can destroy clarity both above and below.

If you listen mostly to classical, jazz, and acoustic music, you'll probably embrace the headphone's low-end authority without reservation. If you listen to contemporary pop/rock and electronica, however--genres subject to a fair amount of equalization and bass boosting over the course of recording, mixing, and mastering--then you might find yourself facing, at times, a bit too much bass. Of course, most rock demands excellent bass response, and the HD 650 delivers. It just isn't forgiving of a musical production's gross errors of judgment, which would makes it a great asset for sound engineers.

The 650's driver material is a specially fabricated "acoustic silk" that minimizes harmonic and intermodulation distortion while maintaining a natural timbre. These drivers start and stop on a dime, ensuring dynamic transient "snap" while minimizing subtle, unwanted resonances that a given sound can induce.

Its broad frequency response is rated at 16 to 30,000 Hz, -3 dB (that is: the point at which the frequency extremes are reproduced 3 dB quieter than the frequencies in between), and 10 to 39,500 Hz, -10 dB. This makes the headphone a brilliant way to fully appreciating high-resolution audio formats like SACD, DVD-Audio, and LP records. Comparatively lower-res compact discs also sound fabulous. For best results, listen through a high-quality headphone amplifier, such as a dedicated headphone amp or the headphone jack in a high-quality preamplifier, integrated amplifier, or surround receiver.

The 650 performs remarkably well with portable audio devices (your iPod will likely never have sounded better), but keep in mind that a) you'll need to crank the volume (sucking battery power), b) the 650 will probably make you uncomfortably aware of how amazingly far MP3s are from CD quality, especially below 160 kbps, and c) the open-air nature of the drivers means they block no outside noise whatsoever and broadcast their high frequencies to anyone within earshot.

The headphone's detachable, Kevlar-reinforced OFC copper cable is over 9 feet long. While unquestionably durable and free from motion noise over most of its length--that is, noises audible in the ear cups when the cable is moved or touched--we noticed that the top foot or so (where it meets the earcups) is far more susceptible to motion noise than, say, any part of the cord for the HD 600. It's not an issue when one is either motionless or rocking out.

A nice touch for nighttime use and for blind listeners is a trio of small bumps above the left earcup to assist in orienting the headset. Other features include hand-selected, matched transducers with tight (+/1 dB) tolerances, computer-optimized and highly efficient Neodymium ferrous magnet systems, extremely lightweight aluminum voice coils, and a gold-plated .25-inch jack plug with a separate adapter lead for connecting to minijack .125-inch plugs.

As to comfort, the 650's elliptical ear cups use thick felt pads which circle the ears completely. It's perfect for extended listening, putting no pressure on the ears themselves and fitting snugly across the head. The 650 is the tightest of the three models, an asset for those who want to listen while upright and moving about. --Michael Mikesell

Pros:

• Great sound overall
• Uncommonly comfy fit
• Deep bass response
• Extended overall frequency response
• Dynamic performance
• Extremely low distortion
• Long headphone cord
• Mercilessly revealing of a recording's deficiencies

Cons:

• Top 1 foot of cord is susceptible to motion noise
• Mercilessly revealing of a recording's deficiencies
• You may hate your speakers after hearing this headphone

What's in the Box
Headphone, a detachable headphone cable, a .125-inch minijack adapter, a hard-shell storage box (silver with embossed blue lettering), a user's manual, and warranty information.