Dahlquist M-905 Speaker System Review

Dahlquist’S first speaker, the DQ-10, was—and still is—an unconventional product: a free-standing system whose drivers are not mounted in the usual box enclosure. Reduction of coloration from box resonances and maintenance of an accurate phase relationship between its drivers are the key features of the DQ-10, which has been on the market for fourteen years and has been acclaimed for its sound quality.

The Dahlquist line has since been expanded to include a number of box-type speakers. Despite their familiar appearance, they have also been designed to be as free as possible of the usual box colorations. Moreover, they have the high sensitivity and linearity needed to reproduce the dynamic range of digital recordings. Typical of Dahlquist’s current line is the new M-905 High Performance Monitor, a moderately priced two-way system.

The walnut-veneered cabinet of the M-905 measures 24 inches high, 13-1/2 inches wide, and 12-1/4 inches deep. The black cloth grille has solid-walnut trim strips and is retained by plastic snaps. Each speaker weighs 35 pounds, and for optimum results they should be mounted on Dahlquist ST-9 stands ($80 a pair), which match the finish of the speakers and support them about 11 inches above the floor, with a backward tilt of 3.5 degrees for optimum coverage of the listening area. Like most free-standing speakers, the M-905 gives its best performance when it is placed at least a foot from the wall and angled slightly inward toward the listener.

The 8-inch woofer of the M-905 is a polyvinyl-acetate-laminated cone operating in a vented enclosure. The outlet of its tuned port is on the front panel of the speaker cabinet. At 2,500 Hz there is a crossover to a 1-inch soft-dome tweeter.

The nominal system impedance is 8 ohms (6 ohms minimum), and the M-905 is recommended for use with amplifiers rated to deliver from 20 to 125 watts per channel. The fiveway binding-post terminals recessed into the rear of the cabinet will accept dual banana plugs. The drivers are protected by individual fuses (0.8 ampere for the tweeter and 3 ampere for the woofer). The system’s sensitivity is rated as 91 dB sound-pressure level (SPL) at 1 meter when the speaker is driven by 1 watt at 1,000 Hz. The rated frequency response is 40 to 24,000 Hz.

Dahlquist refers to the cabinet of the M-905 as an “Un-box” enclosure, likening its construction to that of a violin. The wall panels are of varying thickness, and there is special internal damping and bracing designed to suit the individual characteristics of the drivers in the

system, all to minimize coloration of the sound by the box. The front panel is coated with a black flocking material whose thousands of fibers are electrostatically aligned perpendicular to its surface during application. The flocking and the flush-mounting of the tweeter are said to minimize diffraction from front-panel discontinuities, preserving image focus. Price: $590 a pair. Dahlquist, Dept. SR, 601 Old Wil-lets Path, Hauppauge, NY 11788.

Lab Tests

Preliminary listening tests of the Dahlquist M-905 speakers—in-

stalled on the ST-9 stands, as recommended—revealed a very wide-range and balanced sound whose smoothness and lack of coloration were far beyond what we would have expected from speakers in their price range. In fact, the sound from the M-905’s would be more than acceptable at several times the price. In view of this, we were not too surprised to find that with respect to flatness and freedom from peaks and holes the measured room response was among the best we have encountered.

The close-miked woofer (and port) response was also considera-

bly flatter than we have measured from most speakers, with a very small bass-resonance peak. At the system resonance of 60 Hz, the output was only about 2 dB above its average level in the upper part of the woofer’s range, and even that minor output variation was spread over almost two octaves. When the bass curve was spliced to the room-response measurement, the resulting composite frequency response was flat within about ±2 dB from 26 to 20,000 Hz. The horizontal directivity of the tweeter was only discernible in the room measurement above 10,000 Hz.

We measured the sensitivity of the M-905 as 87 dB SPL, which was lower than the rated 91 dB but still about average for speakers of its size. The difference may have been a result of different test conditions since we used a full-range pink-noise signal while Dahlquist’s rating was made at 1,000 Hz. The system’s minimum impedance was about 4.8 ohms in the 8,000- to 10,000-Hz region, and it measured 7 ohms at 150 to 200 Hz. Its maximum impedance was 28 ohms at 60 Hz, and there was a broad peak of 18 ohms in the vicinity of 1,500 Hz.

We measured the woofer’s distortion with a 4-volt drive level, corresponding to a 90-dB SPL at 1 meter. The distortion was less than 1 percent from 100 Hz down to almost 60 Hz, the effective crossover to the port. Below that crossover the distortion rose to 5 percent at 45 Hz and 9 percent at 35 Hz. In high-power tests with single-cycle tone bursts, the woofer began to sound “hard” at about 350 watts into its 8.5-ohm impedance at 100 Hz. At higher frequencies the amplifier clipped—at outputs of 490 watts at 1.000 Hz and 1,380 watts at 10,000 Hz—before distortion became visible on the acoustic waveform.

Quasi-anechoic FFT measurements showed an overall group-delay variation of about 0.1 millisecond between 4,000 and 20,000 Hz and 0.5 ms between 1,000 and 20.000 Hz, convincing evidence of the attention paid to the phase characteristics of the M-905.

Comments

Although we have often commented on the difficulty of correlating the measured response of a speaker with its sound, the Dahlquist M-905 seems to be an exception: whether you look at its response curves or listen to its sound, it has an extraordinarily smooth, uncolored response. We tried to find some recording that would reveal a weakness, but we soon realized that was a fruitless quest.

As so often happens, there is little in the speaker’s external appearance, or in the manufacturer’s description of its internal design, that would give a clue to its remarkable performance. Many speaker manufacturers claim unique qualities for their creations, which only too often turn out to be “just another speaker.” The M-905, however, really does what Dahlquist says it does, and we were very impressed by the way a two-way speaker with an 8-inch woofer could perform.

The best way to sum up our reaction to the M-905 is to say that it sounded like a far more expensive speaker than it is, especially in the middle and high frequencies. Regardless of its physical size and its price, its sound says, unmistakably, that it is a top-quality speaker.

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