Koss PortaPro Headphones Review

The small size, light weight, high sensitivity, and startlingly good bass response of the Koss PortaPro headphones make them ideal for use with a personal-portable radio or cassette player, and they are equally suitable for a home component system.

Despite its lightweight construction, the PortaPro is designed for rough use (within reason, of course). To protect the earpieces during transit, the flexible metal headband can be curled up around the folded earpieces, forming a compact and sturdy circular assembly about 3-1/2 inches in diameter, easily stored in a pocket or purse.

The earpieces are mounted on pivots that allow ample movement to fit anyone comfortably. The headband itself has what Koss calls “temporal pads,” pieces of padded foam that come between the headband and the wearer’s head, thus placing much of the inward pressure of the headphones on the side of the head rather than on the ears themselves. The temporal pads also help to hold the phones in place during jogging or running, and each has a three-step adjustment of the remaining force exerted on the ears by the earpieces.

Each earpiece is about 1-3/4 inches in diameter and has a replaceable foam plastic ear cushion. Exclusive of the cord and plug, the Koss PortaPro weighs a mere 2 ounces.

A light, rubber-covered cord connects to each earpiece. The two cords join in a “Y” to form a thin, straight cable about 6 feet long. At the “Y” junction is a small round mute button with a clip to hold it to a pocket or shirt front, so that even the slight weight of the connecting cord can be removed from the weight of the phones themselves (and from the wearer’s head). The cable is fitted with a miniature stereo plug (1/8-inch diameter) that fits any personal portable player, and a sturdy screw-on adapter is furnished with the standard 1/4-inch phone jacks of home hi-fi components. Price: $59.95.

Lab Tests

In general, supra-aural headphones (which rest on the wearer’s ears but do not seal around them to maintain acoustic pressure at very low frequencies) are comfortable and light to wear, and often they deliver a very satisfying sound quality. However, most of them sacrifice much of the low bass range because, unlike conventional circumaural phones, they do not provide an airtight seal between the phones and the wearer’s head. Though it is a supra-aural design, the Koss PortaPro has a strong, clean bass response that rivals or even surpasses that of many circumaural phones. As a matter of fact, our IQS FFT analyzer measurement indicated a healthy bass output down to 10 Hz or so, although this is below the audible frequency range.

There was a prominent rise in output to a maximum of about 20 dB at 11,000 Hz, above which the response fell off steeply (the response of the microphone we use in our ANSI headphone-coupler measurements also rolls off above 15,000 Hz). It appears likely that much, if not all, of the 11,000-Hz peak was an artifact of the coupler measurement, since the sound of the PortaPro did not exhibit any of the stridency or edginess that would normally be associated with such a peak in an amplifier, loudspeaker, or phono cartridge. Besides, we have seen this peak before on measurements of quite different-sounding headphones.

Overall, the frequency response of the PortaPro headphones, as determined by a warble-tone sweep, was an impressive ±3.5 dB from 20 to 3,500 Hz. Above the latter frequency, coupler resonance effects begin to show up in the response curve.

The impedance of the PortaPro was slightly higher than the rated 60 ohms, measuring about 85 ohms over most of the audio range and rising only to about 125 ohms at 90 Hz. Harmonic distortion with a 0.33-volt drive level at 1,000 Hz was about 0.3 per cent, and it actually decreased slightly at higher levels, to 0.15 per cent at 1.5 volts (which produced an ear-shattering 120 dB SPL). At 100 Hz the distortion was still under 1 per cent at levels of 100 dB or so, and it was only 3.6 per cent at a 1-volt input (120 dB SPL).

Comments

The listening quality of the Koss PortaPro phones was excellent— good enough, in fact, that we would have no qualms about recommending them for use with a good home hi-fi system. When we listened to low-frequency sine-wave signals through them, it was plain that they could deliver a very healthy amount of low bass energy (in the 30- to 60-Hz range, for example). At first, the strong bass output of the phones (whose output in the 60- to 150-Hz range was about 5 dB greater than between 500 and 1,500 Hz) tended to give an impression of insufficient highs, but further listening dispelled that impression.

Although we did not use these phones with a personal portable player, we have no doubt that they would do justice to any of them and, because of their high sensitivity, will probably deliver a higher sound level than the phones that come with most such units. Caution is advised when driving the PortaPro phones, even from a low-power source, to keep the sound level at a reasonable point. Only 100 milliwatts are required to generate a deafening 120-dB SPL! The mute button seems to lower the volume only slightly—we would guess by 6 to 10 dB—while held in (there is no locking provision).

No treatment of headphones is complete without a consideration of their wearing comfort. While this is a very personal and subjective matter, we felt that the PortaPro was one of the most comfortable phones we have had the pleasure of using. One is hardly aware of their presence on the head, since when they are adjusted properly there is almost no pressure on the ears (the “temporal pads” produce a rather different sensation on the side of the head than ordinary earpieces do on the ears). However, you will probably have to read the instructions to discover how to convert the settings from “light” to “firm,” a simple procedure that is nonetheless not at all obvious!

Finally, although the PortaPro phones are light and small, they are surprisingly sturdy. We would have no hesitation in rolling them up and stuffing them in a pocket, for the earpieces are well protected by the steel headband. The bottom line, as we see it, is that these are excellent phones, suitable for a number of very different and demanding applications.

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