Sennheiser HD 490 Headphones Review

The new Sennheiser HD 490 stereo headphone was developed for use both with home hi-fi components and with Walkman-type portable CD or tape players and radios, which have traditionally been paired with distinctly different kinds of phones.

Headphones intended for use with home high-fidelity systems normally have a moderately high impedance, from 200 to 600 ohms. Such impedance presents no problems with the driving voltage available from any home audio source, such as a tape deck, CD player, or receiver. The signal levels available at these components’ headphone jacks are usually at least several volts, sufficient to develop a high sound-pressure level (SPL) in the listener’s ears.

Typically, home hi-fi headphones attempt to provide wide frequency response and low distortion, consistent with the quality of their signal sources. Obviously, they should also be comfortable to wear for extended periods. In general, a low price appears to be less important than good sound, as befits a component of a home audio system that may represent a sizable investment. In fact, some very high-quality headphones can cost as much as a good pair of loudspeakers.

Another broad category of headphones is intended primarily for use with small personal-portable tape or CD players or radios. Many of their performance characteristics and design criteria are very different from those of home headphones. And, consistent with the cost of their program source, these phones are usually relatively inexpensive.

Perhaps most important for such headphones is the need for high sensitivity—the ability to generate a fairly high sound level with a very small input power. Since the signal voltage available from their usual sources is small, these phones must have a low impedance, typically from 8 to 100 ohms. Wide frequency response and low distortion, which are important in home headphones, are often sacrificed in the design of portable phones. Most are also designed to be as inconspicuous as possible, which is achieved by using small ear cushions that rest lightly on the wearer's ears (sometimes even fitting into the ears) and a slender metal headband.

Sennheiser designed the HD 490 so that it could be used easily with personal-portable equipment and yet meet the listening requirements of a reasonably good home system. The German-made phones have normal-size earpieces with replaceable foam cushions. The single-piece plastic headband is cushioned at the top, and the phones are light (135 grams, or about 4 ounces). The 3-meter (about 10-foot) straight cord, which joins the earpieces in a Y-junction, ends in a stereo mini plug. The phones are supplied with a well-made metal adapter that converts the plug to the quarter-inch size used in home components.

Like all Sennheiser headphones, the HD 490 is designed for full user replacement of its basic parts, including signal cables, ear cushions, drive elements, and headbands. The company maintains a complete parts inventory for all headphones that it has ever sold in this country.

The HD 490 uses a diaphragm formed with a radial-ridge molding process that is said to minimize diaphragm breakup. It is driven by a three-layer aluminum voice coil in the field of a powerful neodymium-ferrous magnet. The signal cable features conductors of stranded steel, which is claimed to have ten times the strength of copper wire. A signal cable that includes a combination volume/balance control can be substituted for the cable normally shipped with the headphones.

The specifications for the HD 490, like those of most headphones, are sparse. Its rated frequency response of 18 to 25,000 Hz has no stated tolerance, and the sensitivity of 94 dB SPL with less than 1 percent total harmonic distortion plus noise (THD + N) is at an unspecified frequency. The rated impedance is 70 ohms per channel. Price: $129; optional cord with volume/balance control, $43.

Lab Tests

We measured the performance of the Sennheiser HD 490 headphones on a standard ANSI headphone coupler designed to simulate the acoustic load that the phones would “see” when worn by a human being. The microphone replaces the eardrum in this measurement, which is capable of giving a repeatable and reasonably meaningful quantification of the bass and midrange response of a headphone. Above several kilohertz, however, the response is affected to a major degree by individual ear shape and size or by the characteristics of the coupler. Therefore, the measured “frequency response” of a headphone is not even as meaningful as the measured response of a loudspeaker, though it does serve as a guide to some of the headphone’s characteristics.

The HD 490’s response was very smooth below 4,000 Hz, varying only ±1.5 dB from there down to 100 Hz. The output fell off at lower frequencies to -5 dB at 60 Hz and -10 dB at 41 Hz. Above 4,000 Hz, there was a “hole” in the response, probably caused by the interaction of the headphone itself with the coupler cavity. The output dropped to -10 dB at 5,800 Hz and returned to the midrange level at 7,500 Hz. There was a ± 3-dB variation from 7,500 to 14,000 Hz, above which our microphone’s response fell off steeply.

The headphone’s impedance varied between 61.5 and 70.5 ohms over the range of 20 to 20,000 Hz. The maximum impedance was at 130 Hz, the diaphragm resonance frequency.

Comments

Except for the 5,000-Hz hole, the Sennheiser HD 490’s frequency response was excellent, and even that aberration was not at all unusual in a headphone-coupler measurement. The sound quality of the phones was good, whether used with a home music system or a personal-portable unit. The sound was well balanced and free of any obvious colorations. The available listening volume was much more than adequate, even with our portable cassette player, which could generate a deafening level. It was not surprising, therefore, that a home CD player had no difficulty in driving the phones to high levels.

We compared the sound of the HD 490 with that of a considerably more expensive conventional headphone set. Played at any reasonable level, the HD 490 sounded as clean as the other phones, with slightly less output at high frequencies and possibly in the low bass. Although the high-frequency difference could be heard in an A/B comparison, it was not particularly noticeable when listening to the HD 490 alone.

The most obvious differences occurred at very high playback levels. The HD 490 overloaded more easily than the other phones, which appeared to have larger diaphragms, but at any reasonable listening level there was no evidence of dynamic compression at high levels.

The HD 490 was a comfortable set of phones to wear, with very little pressure on the ears and negligible weight. We would agree with Sennheiser that it is equally suited for use with personal-portable players and with any home system, and that it delivers a sound quality fully consistent with its price.

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