beyerdynamic DT-911 headphones--review, teardown and analysis

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Beyerdynamic has been making headphones and microphones for a long, long time, and the company’s dedication to headphone research and engineering has made it a world leader in the field. Their line of non- wireless headphones is topped off by the DT 911 and DT 911 Special; the latter is a DT 911 packed in a light weight road-case with a two-disc demo CD, Dynamic Sound Power Test. The CDs’ short tracks include the sounds of various percussion instruments, from large bass drums all the way to tinkling bells. Other tracks include organ, brass band, and voice recordings as well as a section devoted to the sounds of high- performance cars and motorcycles. I think that the extra $50 for the Special version is a super value.

Upon opening the roadcase, I found the DT 911 Special headphones nestled in die-cut foam. The ply wood case, which measures 14 X 11 X 5½ inches, is sheathed in aluminum and has corner protectors, two large clasps that can be locked with a key, and four rubber feet on the rear side. The foam has a cutout for the demo CD, and I discovered that this cutout is also perfect for storing a portable CD player. The DT 911’s felt headband is a separate strip that floats within the yoke, each end terminated in a clamp that slides along the yoke. Detents hold the headband in place after it has been adjusted by the user. The detents are molded into the plastic yoke at intervals of about 1/32 of an inch, or 4 mm, like some other headphones I have tested recently. The bails holding the earcups are of the same plastic as the yoke, and they swivel slightly to allow the ear- cups to fit perfectly to any head. The headband tension that holds the ear phones on the head is very light. Thanks to the modest headband tension and relatively light weight, you can easily forget you’re wearing the DT 911s, even after prolonged listening. The earcushions, which are large enough to completely surround most ears, are made of soft foam-filled, velvet-like material and are very comfortable. The inner face of the transducers is covered by a very thin, reticulated, open-cell foam.

The cords from each earcup branch for about 14 inches before joining the main, coiled cord. Each earcup has a colored insert near the strain-relieved cord exit, with the right channel marked “right” in black lettering on a red background and the left channel marked “left” on a yellow background. I like this very much, since it makes the ear phones easy to put on correctly, even in dim lighting. I wasn’t able to open the DT 911s to look inside without damaging them, but the brochure shows that there are 10 parts, including the transducer element.

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SPECS:

Transducer Design: Dynamic.

Coupling to the Ear: Circumaural.

Diffuse-Field Equalization: Not specified.

Sensitivity: 98 dB for 10 mW.

Maximum Output: 115 dB for 50 mW.

Impedance: 250 ohms.

Price: $349.95; with hard case and two-CD demo album, $399.95. [1993 price]

Company Address: 56 Central Ave., Farmingdale, N.Y. 11735.

MEASURED DATA:

DC Resistance: 239 ohms (left and right).

Absolute Polarity: Positive.

Cord: 10 feet long, from both ear cups, with gold Y4-inch stereo phone plug.

Adjustments: Headband slides in yoke, with detents.

Weight: 9.7 ounces.

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EVALUATION:

The Beyerdynamic headphones are the open type, and their transducers are de signed to produce good bass output even without a perfect seal between the transducer and the ear. Normally, open ear phones have reduced output in the bass range compared to sealed types, but my measurements and comments from members of the listening panel indicate that Beyerdynamic engineers have overcome this problem quite well. Because of the open design, the attenuation of outside sounds is minimal, and it is quite easy to carry on a normal conversation while wearing the DT 911s.

I use a listening panel to assess the subjective sound qualities of products that I review. I asked its members to audition and rate the DT 911 while they were listening to various types of program material and to make written comments. I then tried to correlate their comments to my technical measurements of the headphones.

In the bass range, my measurements showed a gentle roll-off of about 10 dB from below 200 Hz all the way down to 20 Hz; this test was made without the seal between the DT 911s and the head that occurs naturally when you put on the ear phones. A perfect seal would result in a flat response to 20 Hz. Comments from the listening panel—such as “excellent timbre,” “bass very realistic,” and “lowest notes full and solid”—correlate well with my technical measurements. They also indicate that the DT 911s provide a sufficient seal to produce a flat bass response.

The articulation of voices was judged to be “very good,” while the sense of presence seemed “slightly forward” and “brighter” compared to my reference Stax SR-Lambda Pro Ear- speakers. When measured using a diffuse-field response equalization, the SR Lambdas have a broad dip in response in the presence range around 3 kHz compared to the DT 911s, so panel comments again correlate well with my measurements. It appears that Beyerdynamic engineers have done a reasonably good job in designing the DT 911 to have a diffuse- field response. (There is still no good consensus about the best way to measure headphones or about the exact equalization necessary to account for the way we hear sound when using them.)

Comments from the listening panel about reproduction of sounds in the high- frequency range—” smooth and extended” and “very realistic”—also correlated well with the measured response of the DT 911.

Fig. 1—Cosine-pulse test.

Figure 1 shows the Beyerdynamic’s output for a 20-kHz cosine-pulse input. The output waveform is very close to that of the input pulse, and listener comments (such as “excellent transients” as well as “superb details”) confirm the DT 911s’ excellent high-frequency extension and control; the output shows almost no ringing. The wave form also indicates that the DT 911s produce a positive acoustical output for a positive electrical input. All of the panel members commented that they could hear a change in the sound when the absolute polarity was switched back and forth. They also agreed upon the preferred polarity for particular selections.

The measured impedance of these headphones is 239 ohms for both channels; the impedance of the source, whether it is a receiver or CD player, will have a negligible effect on the output level or on the response shape. The DT911s have enough sensitivity to be used with portable CD players but won’t provide loud levels. My measurements also showed that the output level and frequency response of the left and right channels are more closely matched than with most other headphones that I have evaluated.

The Beyerdynamic DT 911 headphones are very comfortable even when worn for long periods. The listening panel rated them as “excellent” for overall sound quality and “very good” for physical attributes. The DT 911s are very close in sound to the Stax reference headphones. The high-frequency performance of the Stax is slightly better, but the upper midrange of the Beyerdynamic is a little more realistic sounding. Considering the price difference, I have to recommend the DT 911s to anyone looking for high-quality headphones at a reasonable price.