Beyerdynamic IRS 790 Headphones Review
Cordless headphones have been available for at least twenty years and are widely used in legitimate theaters as an aid to hearing dialogue that might otherwise be lost or masked by ambient noise. Most such headphones are monophonic types designed primarily for voice reproduction, although a few stereo hi-fi models have come to market.
Beyerdynamic now offers an unusually high-performance wireless stereo headphone intended for use in the home. Its IRS 790 system, like most other wireless phones, employs infrared light beams that are frequency-modulated by the audio program. To improve the sound quality, however, they use carrier frequencies for the two stereo channels that are much higher than those of earlier systems- 2.3 and 2.8 MHz instead of 95 and 250 kHz. Their infrared light beams also have a somewhat shorter wavelength (higher frequency).
The Beyer IRS 790 system consists of an IS 790 transmitter and one or more IRH 790 headsets (any number of headsets can be operated from a single transmitter). The slim, black, vertical transmitter resembles a remote control standing on end. About 8-1/4 inches high including its base, it contains a linear array of twelve infrared light-emitting diodes (LED's).
The transmitter, powered from a small plug-in module, can be left energized at all times, coming on automatically whenever a signal is applied and shutting off again after a period of silence. The program source plugs into a 1/4-inch stereo minijack on the back of the transmitter via a 7-foot cord with a stereo miniplug at each end (an adaptor plug for matching standard Vi-inch phone jacks is also supplied).
The headset appears conventional, with two full-size adjustable earpieces fitted with soft cloth ear cushions. The top of the sturdy metal headband is padded for comfort. Naturally, there is no cord or other external wiring. The right earpiece has a three-position slide switch that enables you to listen to either channel alone or to both in stereo. The left earpiece has a two-position yellow slide switch that controls power to the headset (each earpiece is powered by one AAA cell). A red LED above the power switch indicates that the phones are activated. A recessed thumbwheel on each earpiece adjusts its volume. There is no master level control, and channel balancing requires varying one or both earpiece controls.
We tested the Beyer IRS 790 system on a standard headphone coupler. The test signal, from our Audio Precision System One, drove the IS 790 transmitter, and the output of the B&K 4133 microphone in the coupler returned a signal to the System One for analysis. An input of 10 to 20 millivolts was sufficient to turn the transmitter on, and it remained on for several minutes after the signal was removed.
We measured the system's frequency response using several different test signals: swept sine waves, swept one-third-octave noise, full-range noise and a sweeping filter, and the MLS digital system with a burst of pseudo-random noise. Allowing for unavoidable differences in detail, the results from all these tests were very nearly the same. Maximum output was at 100 Hz, falling at about 18 dB per octave below that frequency. The output decreased at 3 dB per octave from 100 to 600 Hz, and there were variations of ± 5 dB between 1 and 8 kHz. The response rolled off steeply above 10 kHz, to about -14 or -15 dB at 20 kHz. Distortion was comparable to that of most conventional headphones or compact loudspeakers, with readings of one to several percent over much of the audio range and not much variation with level.
Listening tests, using FM radio as a source, confirmed the major features of these measurements. The phones had a warm, pleasant sound, and, although the level of the extreme highs was noticeably below that of the upper bass, the overall effect was very listen-able. The headset was comfortable to wear, and the coverage from the infrared transmitter was solid.
In fact, the solidity of the transmission from base station to headset was one of the IRS 790's most outstanding features. No matter where the transmitter was placed or aimed, or where the headphone wearer was located or facing (so long as both were in the same room), there was never a hint of noise or any other suggestion that the phones were not wired to the source. The transmitter could even be placed out of sight, on a shelf or facing in any direction, without degrading the sound detectably. Only by leaving the room could we induce a signal loss (which was instantaneous as we went through the door).