Beyerdynamic DT 990 Headphones Review

Beyerdynamic DT 990
Beyerdynamic DT 990

The Beyerdynamic DT 990 is a lightweight, circumaural 600-ohm stereo headphone set that was designed to meet the criteria for a subjectively uniform frequency response established by Gunther Thiele of the German Radio Institute in Munich. By making a series of measurements using tiny probe microphones inserted into listeners' auditory canals, Thiele was able to determine the actual frequency spectrum of the sound that reached their inner ears after modification by the external ear structure.

Thiele used this technique to compare the ear's response to test signals from loudspeakers (in a reverberant chamber) with the response when the same signals were applied through headphones. These comparisons enabled him to establish the headphone equalization needed to make the two responses identical. His study showed that most popular high-fidelity stereo headphones are deficient to some degree in this respect, even though their frequency response might appear to be relatively flat when measured in the conventional manner on an "artificial ear" stereo headphone coupler.

Using Thiele's criteria for headphone equalization, Beyer's engineers designed the DT 990, which is internally equalized to give a relatively uniform "diffuse field" response characteristic. The frequency response is rated (without a stated tolerance) as 5 to 35,000 Hz. Although the DT 990 is a circumaural headphone (that is, the ear cushions surround the wearer's ears), its earpieces have open backs and do not exclude ambient sounds. According to Beyer, the newly designed diaphragm and moving-coil assembly is about 40 percent lighter than the moving system of its popular DT 880 headphone.

The light plastic headband of the DT 990, which supplies the force needed to hold the earpieces against the ears, contains a soft leatherette inner band that rests comfortably on the wearer's head. Its position on the outer band is adjustable for a comfortable fit and cannot shift accidentally. The earpieces are made of molded plastic, with soft foam cushions, and pivot for proper coverage of the ears. The short, separate cords emerging from the earpieces merge into a coiled cord fitted with a molded plug, providing a maximum extension of about 12 feet. The headphones (without cable) weigh 230 grams, or about 8 ounces. Price: $175.

Lab Tests

Since we measured the frequency response of the Beyerdynamic DT 990 on a standard headphone coupler (and were limited to a 20- to 20,000-Hz measurement range), we could not verify its response rating. In fact, given the strong effect of the coupler design on this measurement, especially at high frequencies, and the lack of meaningful published response curves for most headphones, such verification is almost never possible in headphone measurements.

We can say, however, that the response of the DT 990 was flat within 2.5 dB overall from 90 to 3,600 Hz, sloping off gently to about - 6 dB at 20 Hz. At higher frequencies the measured output increased considerably (and became irregular, as is typical of coupler measurements). Between 10,000 and 17,000 Hz, it averaged 10 to 12 dB higher than through the midrange. The sensitivity of the phones was almost exactly as rated, producing a sound-pressure level (SPL) of 96 dB though the flat region with a 1-volt input. Its impedance was 600 ohms over almost the entire audio range, reaching a maximum of 750 ohms between 60 and 120 Hz.

Beyer also rates the DT 990's distortion as less than 0.2 percent and its maximum power-handling capacity as 100 milliwatts (about 116 dB SPL), corresponding to a 7.75-volt input. These ratings are based on DIN standards with which we are not familiar, but we measured the phones in our own way and were highly impressed with the results. The total harmonic distortion, with inputs from 0.5 to 8 volts, was between 0.3 and 0.6 percent at 1,000 Hz and between 0.4 and 0.8 percent at 100 Hz. At both frequencies the acoustic output from the phones clipped at 8.5 volts input, corresponding to an SPL of about 115 dB. This is about the highest level consistent with safe listening, and the DT 990 delivered it with negligible distortion.

Comments

The Beyerdynamic DT 990 phones delivered a superb sound, ranking among the best dynamic headphones we have used. Compared with some other high-quality phones, whose response had not been equalized to meet the Thiele diffuse-field criteria, the DT 990 had a noticeably light, airy, and extended top end. The low and middle frequencies were also quite free from coloration, which was consistent with the phones' measured flatness and the absence of the peaks and valleys that are characteristic of many headphone response curves.

We confirmed that the DT 990 can play very loud without sounding strained or distorted (and, of course, without requiring much amplifier power-any 10-watt amplifier will drive them to their limits). Aside from their excellent sound, these phones were remarkably comfortable to wear, having no tendency to press on one's head or ears. No matter how you look at them, or listen to them, the Beyerdynamic DT 990 is an exceptional set of headphones.