Koss PRO-4, PRO-4A and Pro/4 AAA Plus headphones

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!"

Koss Corporation
4129 N. Port Washington Ave.
Milwaukee, WI 53212
(414) 964-5000

dc_bruce's picture

were Koss Pro 4A's which I bought in 1968 or '69. They were a bit bass heavy and not particularly transparent. I replaced them a few years later with Sennheisers, which were lighter and far more comfortable. They also sounded better, albeit with less powerful bass. In 1971, I acquired a pair of used Stanton electrostatics, which were a revelation in transparency although lacking a bit in bass "thump." After a year or two they failed, and I never went back to headphones again.

I believe Koss gets credit for being the first to actually develop purpose-designed headphone drivers. It is sad that the company, after such a strong start, "lost the plot" so badly. They are still in business, I believe. One of their other problems was an accounting scandal a few years ago (the company's stock is/was publicly traded) which resulted in a wholesale clean-out of the executive suite. Sad to see this happen, especially when headphones have become a fashion accessory (Beats) as well as an audiophile "thing."

Bogolu Haranath's picture

Try Audeze LCD-1, $399, reviewed by Inner/Fidelity and Hi-Fi News ...... Easy to drive 13 Ohm impedance :-) ......

PAR's picture

You can't compare the Audeze LCD-1 with these Koss cans. The Audeze is current, these Koss reviews date from between 1963 and 1991 and the featured headphones haven't been manufactured for decades.

Bogolu Haranath's picture

Yes, I know ...... I was responding to dc_bruce's comments above ....... LCD-1s are in the same price range as some of the top model Beats headphones ...... LCD-1s are better quality for about the same price :-) ......

Metalhead's picture

Definitely a rite of passage as I was one of the folks moving from cheese-o to fancy Koss Pro 4AA headphones in 72. I think they were double A's but never saw that listed so maybe I may be the unreliable narrator. I did not have a mic connector and pretty sure I remember that correctly.

Enjoyed them but not too worried about quality as they were just playing Tull, Beatles, Zep and Floyd. I did move up to the first Koss electostatic phones and they were fantastic. Koss ESP-1 (think that was the model).

In any event LOVE the J. Gordon review where he calls out a set of Koss as being a dog and it is just refreshing to read a one or two sentence pan without the current three paragraphs or more of wrangling a redeeming feature out a component or piece in for a review.

Don't use headphones any more but appreciate you posting a blast from the past.

tonykaz's picture

They still sell on eBay for between $25 and $150. ( $11 Shipping )

I've owned two of these and remember them to be heavy, uncomfortably hot, awkward and replaced as soon as ANYTHING better came along. I've seen these things in a good many Audiophile's homes ( mostly unused ).

There wasn't much in headphones until Sennheiser came along. So people would have the Pro-4 or seek out the STAX ( that I carrried but were far too expensive ).

Seeing the KOSS photo reminds me of how incredibly far we've come.

Tony in Venice

ps. they were made in Wisconsin, my origin home, ( not chinesium ) so they seem to survive rather well and are not being thrown abandoned into another Waste Management Land Fill filler.

mrounds's picture

I bought a set of Pro/4AA (yes, double-A; sound is much like the original Pro/4A as reviewed) in college. Cans were necessary in the dorm, especially cans with the gel surrounds.

They were (and still are) heavy and uncomfortable for long sessions. Sounded much better than the 6" San Franciscan (Goodmans) speakers on my dorm stereo. A tad boomy, and somewhat rolled off in the treble, but that's what tone controls and a switch to turn off loudness compensation are for. The EPI 100 speakers I got after college (and still have) are far more neutral sounding.

The original set finally died - wiring problems - in the early '90s. Koss had never been very good about advertising their lifetime warranty, so I bought another Pro/4AA from Radio Shack - exactly like the original after about 20 years. Still have them. They work well when listening to stuff from the computer in the wee hours. They again developed a wiring problem about 10 years ago; sent them back, and Koss fixed them for free (except for the cost of shipping them there).

Yes, there are far better phones now, especially if the budget is unlimited, but these are here, and they work. Pretty well, actually.

otaku's picture

Yes, I ran out and bought a set after listening to them in the listening room at our college student lounge (anyone remember listening rooms?). After I drove two hours in the rain to go buy a set, my poor Dad had to make the same trip to get a set for my brother. I had them for probably 15 years, finally gave up fixing them.

Ortofan's picture

... the choice of Pete Campbell on the TV series Mad Men.



deckeda's picture

The air from the headband "squares" emptied, the air from the ear pads did the same (replaced them once) and I don't ever recall the sound as anything special. But they were my first. I was always interested in hearing the HV/1A and thought that style was the future. And in a way, it has been (for pretty much everyone else.)

I liked the tension adjustment innovation for the PortaPro, but never appreciated the "good sound" they were supposedly known for.

In subsequent years it was Grado for me, and modernity.