Dahlquist DQM-9 Speaker System Review

The Dahlquist DQM-9 is a three-way, vented-enclosure system constructed in a conventional box format (unlike the well-known Dahlquist DQM-10). Since the woofer-compartment ports open to the rear of the cabinet, the speaker should not be placed closer than about 6 inches from the back wall, and the installation instructions also suggest floor placement on low stands.

The DQM-9 uses three matched drivers made by the West German firm of Magnat, by whom Dahlquist is licensed. The drivers are vertically aligned, and all visible metal surfaces are finely finished. The 11-inch woofer has an edge-wound ribbon voice coil and operates up to 450 Hz. The midrange employs a 5-inch cone, also with an edge-wound ribbon voice coil. The tweeter, which takes over above 3,500 Hz, is a 1-inch dome radiator.

The enclosure of the DQM-9 is made of a special particle board (also apparently of German origin) whose several layers of wood particles increase in density toward the outer layers of the board. The side walls are formed of a combination of 3/4- and 5/8-inch boards coated with a damping material on their inner surfaces. The entire exterior of the enclosure is covered with 3M “Nextel,” a grey material resembling flocking that is said to damp surface resonances and lower the “Q” of the cabinet. The front baffle is covered with a black flocking material to control diffraction effects. The black, acoustically transparent grille cloth is held in place with magnetic fasteners at the corners of its wooden frame. According to Dahlquist, the special cabinet construction and surface treatment of the DQM-9 are responsible for reducing mid-band resonances which could otherwise impart a “boxy” quality to the sound.

The Dahlquist DQM-9 is nominally an 8-ohm system with a minimum-impedance rating of 6 ohms. It is recommended for use with amplifiers delivering from 25 to 200 watts. The drivers are protected by a 8/10-ampere fuse which is mounted in the rear near the input binding posts (they are spaced on 1/4-inch centers to accept standard dual banana plugs). The DQM-9 is 25 inches high, 14-1/2 inches wide, and 13 inches deep. It weighs approximately 65 pounds. Price: $600.

Laboratory Measurements

Our reverberant-field measurements showed the Dahlquist DQM-9 to have a smooth, well-dispersed output with a slightly rising high-frequency characteristic. The response curves from the left and right speakers were very similar over the full audio range, confirming the good dispersion qualities of the dome tweeter. The bass response was measured with the microphone close to the woofer cone and also at one of the two identical port openings in the rear of the cabinet. After correcting for the relative areas of the cone and port openings, the curves were combined and spliced to the mid- and high-frequency curve. There was a broad peak in the upper bass (around 100 Hz), but, even so, the overall response was a very good ± 4 dB from 55 to 20,000 Hz. The output in the low bass remained strong (typically about 5 dB below the average midrange output) down to 30 Hz or below.

Having installed our new computer test facility shortly before receiving the DQM-9, we also measured the speaker’s anechoic response under various conditions. Mounting the speaker on the floor produced a sharp “suck-out” in the response at about 8,000 Hz (this did not appear in our regular measurements, which average the acoustic output of the speaker over a wide angle and include any absorption by the room surfaces and furnishings). Moving the speaker to shelf height eliminated this effect and resulted in an impressively flat response, ± 3 dB from about 200 to 18,000 Hz.

The system impedance measured between 5 and 16 ohms from 20 to 20,000 Hz, with the minima occurring at 40, 120, and 10,000 Hz. The sensitivity was high, so an input of 1 watt of noise in the midrange produced a sound-pressure level of 90 dB measured 1 meter from the speaker grille. The only unexpected (and difficult to explain) test result was in the upper bass range, where the distortion was somewhat higher than we would have expected, but it increased only moderately at lower frequencies. With a 1-watt input, the distortion was under 2 per cent between 50 and 100 Hz, rising to about 4 per cent at 35 Hz. These numbers apply to measurements at the cone for frequencies of 60 Hz and above, and at the port for lower frequencies, where its radiation is predominant. At 10 watts input, the distortion ranged from 3 to 8 per cent between 100 and 35 Hz.

The distortion characteristic of the DQM-9 was quite different from that of most speakers we have tested. For one thing, the principal component was the second harmonic, and the third-harmonic distortion was very low (a small fraction of 1 per cent above 70 Hz or so). Also, the distortion did not increase suddenly at some low frequency as happens when a speaker’s available cone excursion has been reached. Instead, it rose gently and smoothly. Since the DQM-9 is rather more efficient than most speakers we have tested recently, it is delivering a higher acoustic output at the 1-and 10-watt drive levels than an average acoustic-suspension speaker (two to four times as much). These facts, among others, helped reconcile the slightly higher-than-normal measured distortion with the obvious excellence of the speaker’s sound quality.

Dahlquist engineers agreed with our findings, stating that the speaker was deliberately designed to have a very low percentage of higher harmonics (especially the third and fifth) since the auditory offensiveness of harmonic distortion rises rapidly with the order of the harmonic (the second harmonic is generally agreed to be the least offensive and the least unmusical in its effects). Since the DQM-9 was designed specifically for minimum odd-order distortion, the trade-off was an inevitable—but certainly acceptable—increase in the second-harmonic level.

Comment

As is our usual practice, we listened to the Dahlquist DQM-9 for some time before making any measurements (our instruments are less likely to be swayed by what we hear than vice versa). Our immediate reaction was that the DQM-9 was an uncommonly smooth and easy-sounding speaker. It was quite comparable to the best we have heard in its balance and overall musicality. If the DQM-9 could be said to have any special characteristic, it is that its sound is soft, almost velvety (by coincidence, an acoustic analog of its exterior finish). This might seem inconsistent with our response measurements, which indicate an unusually strong and extended high-end response, but in our opinion there is no single measurement that can describe the sound of a speaker. From the first, we were impressed by the effortless quality of its sound with any type of program. This is one of those speakers we could listen to indefinitely without the urge to switch to something else.

The appearance (and literature) of the Dahlquist DQM-9 indicates that it was meant for studio monitoring rather than for home use, although its sound certainly would do justice to the finest home system. The DQM-9 may have its aesthetic limitations as a piece of furniture, but as a high-quality reproducer we would say that the Dahlquist (and Magnat) design does very well.

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