Almost a dead-ringer for the early-model Sharpe HA-10, Koss’s PRO-4 ($45) is readily distinguishable by a large knurled protuberance sticking out of the lower part of the right-hand phone. This, in case you’ve wondered, is a mounting for a “boom-type” lip microphone, for use in speech labs and for communication purposes. (Sharpe and Permoflux also provide facilities for attaching a lip-mike.)
The Koss is handsome, well constructed, and apparently quite durable. Noise rejection is extremely high, but the PRO-4 is not quite as comfortable for long periods as the Sharpe HA-10 (because of a smaller ear cushion).
The PRO-4’s sound was judged to be about midway in character between the new Sharpe HA-10 and the Jensen phones. The PRO-4 has a shade more bass and somewhat less brilliance than the HA-10. Some roughness was detected at the high end, but the phones otherwise appear to have a very neutral perspective, moving the sound only very slightly farther from the mikes than it originally was. Details were very well reproduced, and the sound was sharply focused, but as with most other phones, bass was quite thin.—J. Gordon Holt
Fig.1 Koss PRO-4, subjective frequency response.
J. Gordon Holt reviewed the Koss PRO-4A headphones in July 1968 (Vol.2 No.6):
Our reaction, after a brief listen: one of the smoothest, best-balanced and most natural-sounding headsets we’ve ever heard, with added bonuses of excellent noise rejection characteristics and a high degree of wearing comfort.—J. Gordon Holt
J. Gordon Holt reviewed the Koss PRO-4X headphones in May 1982 (Vol.5 No.4):
The X model-designation for these must stand for Xecrable; they are positively awful.
They are hollow-sounding and turgidly bass-heavy, with a pronounced “ih” coloration (rhyming with “if”), a recessed, sucked-out middle range and a tizzy high end. In view of the severity of these aberrations, any positive qualities that these might have pale into insignificance. The list price is $85. We suggest you compare them with, for example, Sony’s $65 DRM-5 phones.
Koss, you oughta be ashamed of yourself!—J. Gordon Holt
Fig.2 Solid upper line: Measured frequency response of the Koss PR0-4X. This is shown in comparison with (dotted lower line) the curve obtained under identical test conditions from the best-sounding headphones we have tested: The Stax SRX-I. Note that these measurements become unreliable above 5kHz because of the effect of standing waves between the cups.
Bill Sommerwerck reviewed the Koss Pro/4 AAA Plus headphones in August 1991 (Vol.14 No.8):
In the late ’60s and early ’70s, one of the rites of passage for any young audiophile occurred the day he moved up from his first pair of cheap ‘n cheesy headphones to a pair of Koss PRO/4s. The PRO/4 (with its distinctive screw post for a boom mike) was the first in the line. The current designation suggests that this is the fifth variation on the theme—a theme which has hardly varied in 25 years.
The PRO/4 seems to have been the first American headphone with drivers specifically designed for headphone use. (Previous headphones used transistor radio speakers or even dynamic microphone capsules!) The earpads were large vinyl pillows filled with silicone fluid. They conformed to your ears, at the price of occasionally evoking sweat. In the PRO/4 AAA Plus ($70) the fluid has been replaced with foam, and the new pads no longer resemble bagels. They are cup-shaped, rather like a moon crater, with steeply sloping sides. They fit much better (on my ears, at least). The PRO/4 AAA Plus is a comfortable, sturdy headphone.
The sound, however, is disappointing. It can best be described as somewhat heavy on the bottom end, combined with top-end dullness and hardness. The Equale Brass (Bacchanales, Nimbus NI 5004) were bright and slightly nasal. Ella Fitzgerald’s voice on The Irving Berlin Songbook (Verve 829 534-2) was a bit boxy, her backup brass brash (footnote 1). On this recording, transients generally sounded hard. The woman’s voice on the first band of the Opus 3 Depth of Image disc lacked coherency and focus. The woodwinds in Histoire du Soldat were honky and somewhat boxy.
A Liszt piano recording, which can sound startlingly lifelike on the best ‘phones, was reduced to a dark, boxy murk. Pictures was similarly dark, with honky horns. The Rachmaninoff cello recording was leaden-sounding and lacked definition. The Reference Recordings Tempest and the Nimbus “Scottish” symphony revealed nasal horns and woodwinds (respectively), along with a suppression of ambience in the latter, Ambisonic recording. Star Trek was just as bad, with a dull glass harmonica. Palestrina lacked any sense of excitement or involvement.
The PRO/4 AAA Plus is a comfortable, sturdy headphone with good isolation and attractive cosmetics. Its discounted price of around $40 and its lifetime warranty (footnote 2) is appealing, but its sound isn’t. If nostalgia for the “good old days” of American hi-fi tempts you to buy a pair, I urge caution and careful listening. I can’t recommend them.
Eyeglass compatibility: Good. Eyeglasses can be removed and replaced with only moderate resistance.—Bill Sommerwerck
Footnote 1: Ella sure comes up for her share of alliterate Bs, doesn’t she?
Footnote 2: Koss must be complimented on their lifetime warranty. It doesn’t matter what happens to the headphone, or whose fault it was. They’ll fix or replace it, free, as long as you own the headphone. The Koss ad demonstrates their warranty with a picture of Fido making a quick repast of a pair of Koss headphones (and they don’t even have a leather headband!). Koss says the warranty applies “from now on,” which vaguely suggests currently-owned headphones are also covered. However, it appears they aren’t. Second compliment—Koss clearly states “limited lifetime warranty.” None of this “full lifetime limited warranty” crapola. “Good doggy, Koss!”
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COMPANY INFO
Koss Corporation
4129 N. Port Washington Ave.
Milwaukee, WI 53212
(414) 964-5000
koss.com
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