Beyerdynamic IRS 690 Headphones Review

Since the time when radio was called “wireless,” the profusion of wires involved in any working audio installation has contrasted sharply with that name. More recently, as the sophistication of consumer electronic products has increased and they have become an integral part of the modern household, there has been a welcome trend toward reduction of the wires external to the basic components themselves.

Examples of this trend include cordless telephones, wireless remote controllers for stereo and video components, wireless auxiliary speakers, and cordless headphones. Early remote-control systems used ultrasonic sound waves as carriers for the control information, and some used radio-frequency electrical signals, either radiated (as with telephones) or carried by house power wiring, but most contemporary systems employ infrared light-beam carriers.

Infrared stereo headphones were introduced a number of years ago, and many theaters now offer infrared phones for the benefit of hearing-impaired patrons, but they have not made a significant impact on the home hi-fi market. For one thing, although some of these headphones have had reasonably good sound quality, they generally did not offer much competition to the better conventional audiophile phones. Also, a wireless headphone is always more costly than wired phones of equivalent performance, because it uses a separate transmitter unit plus a receiver in the headphone assembly.

A new wireless headphone from Beyerdynamic of West Germany may help increase the acceptance of wireless phones among serious music listeners. Beyer phones have a well-earned reputation for quality, and the new IRS 690 system has been designed to meet true high-fidelity standards. The transmitter is a flat package about the size of a hand-held remote control. It is connected by a slender cord to a remote power supply that plugs directly into the wall and delivers 24 volts DC to the transmitter. The transmitter is designed to be installed in the base of a polystyrene display unit that also holds the headphones when they are not in use.

The headphones themselves resemble a conventional circumaural headset, with an adjustable plastic headband whose inner cloth band rests on the wearer’s head. An opaque dark-blue dome, about half an inch in diameter, is mounted on the top of the headband. It contains a photodiode that receives the radiation from the linear array of led’s across the front of the transmitter.

The headset also contains the receiver that amplifies and demodulates the left- and right-channel frequency-modulated carrier signals from the transmitter. The specifications provided with the system indicate the use of 95- and 250-kHz subcarrier frequencies for the two channels (modulating the infrared light-beam carrier), with a nominal frequency deviation of ± 30 kHz and a peak deviation of ± 50 kHz.

The left earpiece contains the on/off switch for the phones, which are powered by an 8.6-volt rechargeable battery. When the phones are placed on their stand, a plug from the transmitter power supply can be inserted into a socket on the bottom of the left earpiece to charge the battery. According to the manual, the phones can be used for about 4 hours on a charge and can be completely recharged in 14 hours. The right earpiece has a three-position slide switch, which selects stereo operation or sends a mono signal (either the left or the right channel) to both ears, and a volume-adjustment wheel that affects both channels.

The transmitter has a small power button on its front and a red led that glows dimly when its power supply is plugged into a 120-volt source. The led brightens or flashes when the audio-signal input exceeds 2 volts (the system’s overload level). A signal greater than 35 millivolts automatically turns on the infrared carrier, and if the signal drops below that level for 45 seconds, the carrier automatically shuts off.

The key specifications for the IRS 690 system include a frequency response of 20 to 20,000 Hz, a maximum acoustic output level of 114 dB, and distortion of less than 1.5 percent. The channel “synchronism” (presumably balance) is given as better than 1.5 dB. A nominal 1-volt input signal is required for the rated fm deviation. Price: $399 complete.

Lab Tests

We teted the IRS 690 phones on a standard headphone coupler. The transmitter, driven from the output of our Audio Precision System One measurement system, was located about 6 inches from the receiving dome of the headphones.

The transmitter’s overload light came on at signal inputs that varied with frequency from a maximum of 4 volts at 20 Hz to a minimum of 0.4 volt at 15,000 Hz, averaging about 2.5 volts over most of the midrange. The transmission area is specified as 4 x 6 meters (about 12-1/2 by 18-1/2 feet), and we found that it easily covered our 15 x 20-foot room. (It is important, however, that the path between receiver and transmitter not be obstructed by any optically opaque material.) When the signal level fell sufficiently, we heard a background hiss similar to the weak-signal hiss of an fm tuner.

The acoustic output of the headphones clipped at about a 119-dB sound-pressure level, well above the rated 114 dB. The frequency response was good, with a somewhat emphasized output in the lower midrange and upper bass and in the range between 1,000 and 5,000 Hz. Relative to the 1,000-Hz level, the output reached a maximum of about +6 dB at 180 and 5,000 Hz, falling off to —10 dB at 20 and 14,000 Hz.

The channel separation (relative to the clipping output of the phones) was about 35 dB through the midrange, falling to 20 to 30 dB in the 4,000- to 10,000 Hz-range and to 10 dB at 20,000 Hz. With the headphone level control set for the onset of clipping at a maximum 1,000-Hz signal input of 1 volt, the total harmonic distortion (THD) plus noise was about 1 percent for inputs between 0.3 and 0.7 volt. At lower levels the readings were higher because of the relatively greater influence of wide-band noise, and the distortion reached the rated 1.5 percent at the point of clipping. A spectrum analysis showed that the distortion was predominantly second and third harmonics.

The unweighted noise spectrum was —60 to —70 dB (referred to the clipping level of the output) from 100 to 10,000 Hz, falling to —80 dB at 20,000 Hz. Power-line hum obscured the noise at lower frequencies, which measured —33 dB at 60 Hz. This effect may have been an artifact of the measurement setup, however, since we never heard any hum in our listening tests.

Comments

The Beyerdynamic IRS 690 phones not only worked flawlessly, but they sounded excellent, ranking among the better headphones we have tested over the years. They had an ideal balance across the full audible range, with crisp but never strident highs and a deep but not tubby bass. The available volume was more than sufficient—most of the time we used about half the rotation of the earpiece volume control.

The headset was light and comfortable, and its circumaural ear-cups, which enclosed the ears completely, attenuated external sounds only slightly because of their open-backed construction. The infrared beam from the transmitter apparently reflected strongly from the room walls and ceiling, since the listener could be a full 90 degrees off either the horizontal or vertical axis of the transmitter without a significant increase in background hiss anywhere in the room. Only by covering the receiving-diode dome on the headband were we able to impair reception significantly.

The absence of the umbilical cord that normally links a headphone listener to the program source is a definite plus, and the infrared system never compromised the uncommonly smooth and balanced sound of the phones. These qualities, combined with their physical comfort, may well make the Beyerdynamic IRS 690 system the headphones of choice for people who cannot tolerate the limitations of ordinary headphones.

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