DCM QED Speaker System Review

The DCM QED is a floor-standing, two-way speaker system whose design emphasizes linear amplitude and phase response. It employs an 8-inch woofer operating in a transmission-line-loaded enclosure whose port is at the end opposite to the woofer (which is located at the top of the column-shaped enclosure, close to a seated listener’s ear level). The tweeter, which appears to be a dome driver (it is not readily visible through the opaque, non-removable foam-plastic grille), is located near the woofer and just below it. The crossover frequency is not stated. The manufacturer specifies only the system dimensions (36 inches high, 11-3/4 inches wide, and 9-1/4 inches deep), its net weight (41 pounds), and a few electrical ratings. These include a system sensitivity of 87 dB sound-pressure level with a 1-watt input at 1 meter in a normal listening room, a nominal 12-ohm impedance (8 ohms minimum), and the amplifier power recommendations (20 watts minimum, 100 watts with integrated program material, 50 watts with pink noise).

According to the manufacturer, the QED is the result of research into the audible effects of variations in crossover design. In the QED the acoustic outputs of the woofer and tweeter are in phase through the crossover region. The outputs of the two drivers are meant to combine to form a uniform acoustic power output over the crossover range. A part of the crossover design is the addition of a short time delay to the tweeter circuit. This places the “plane” of correct time compensation or alignment at the height of the drivers and thus at the expected height of a listener’s ear. According to DCM, the enclosure is designed to stand about 3 feet from the wall behind it for best (flattest) bass performance.

Oil-finished walnut plates are used for the top and bottom of the QED, the rest of it being covered by a snugly fitting sleeve of black foam plastic. The connectors in the rear are jacks that accept standard dual banana-plug connectors (furnished). Price: $504 per pair.

Laboratory Measurements

The close-miked woofer response of the DCM QED was flat within 2.5 dB overall from 60 to 650 Hz; it dropped another 2.5 dB from 650 to 1,000 Hz and fell more rapidly at higher frequencies. The contribution of the port to the total output was slight, affecting only frequencies below 35 Hz.

The smoothed and averaged room-response curve had the usual midrange peaks and dips, but it was notably smooth above 2 to 3 kHz. After correction for room absorption at high frequencies, the response was ± 3 dB from 300 to 20,000 Hz. When it was spliced to the woofer curve, the resulting composite response was flat within ± 3.5 dB from 45 to 20,000 Hz. Its general trend was downward with increasing frequency, with a peak of several decibels at 16,000 Hz and a ±2.5-dB irregularity in the 1,000- to 1,700-Hz range.

The quasi-anechoic axial frequency response was measured with our IQS FFT signal analyzer at a 1-meter distance from the microphone to the grille. It was fiat within ±2 dB from 300 to 17,000 Hz. A shallow depression in the response could be seen at about 1,500 Hz, and there were sharper peaks and dips between 3 and 4.5 kHz and between 7 and 8 kHz. These variations were minor in the context of the overall flatness of the system response, but they showed up at different microphone distances and even in a measurement made 45 degrees off the speaker axis.

The tweeter of the DCM QED had very good dispersion up to about 11,500 Hz, although the outputs of the left and right speakers (representing an angular difference of about 30 degrees as viewed from the microphone position) differed by 10 to 12 dB in the range of 12,000 to 20,000 Hz.

The phase response of the QED was very good over most of the audio range, the principal deviation from linearity being around 4.000 to 4,500 Hz, where the group delay fluctuated between 0.2 and 1.6 milliseconds. Otherwise, except for a smaller fluctuation at 7,000 to 8,000 Hz, the group delay was uniform within 0.2 millisecond from 1.000 to 20,000 Hz. The impedance hit a minimum of about 8 ohms at 35 and 140 Hz and about 7 ohms at 10,000 Hz, and its maximum was about 25 ohms at 67 and 1,200 Hz. We would consider its true “nominal impedance” to be 8 ohms rather than the published 12 ohms. The sensitivity was almost exactly as rated, measuring an 88-dB sound-pressure level at 1 meter when the speaker was driven by 2.83 volts of band-limited pink noise.

The woofer distortion at a 1-watt drive level was between 0.5 and 1 per cent from 100 to 65 Hz, rising to about 8.5 per cent at 30 Hz (the distortion was measured at the port for the lowest frequencies). Raising the drive level to 10 watts increased the distortion to 1.5 to 2.5 per cent from 100 to 65 Hz and to about 19 per cent at 30 Hz.

Comment

The DCM QED sounded about as smooth as it measured, with a slight but distinct warmth contributed (we surmise) by the woofer output’s being, on the average, a couple of decibels higher than the average tweeter level. Whatever the cause, the sound was as enjoyable to hear for extended periods as that of almost any other speaker we have used.

The QED is an excellent example of a well-designed speaker system created to produce a specific result (accurate impulse response, as described in DCM’s literature), making the inclusion of a tweeter-level balance control neither necessary nor desirable. Frequency-balance modifications for speakers, in our opinion, are best made with tone controls or an equalizer.

The virtues of the DCM QED become even more apparent when one considers that it is not only a very fine and musical-sounding speaker, it is also simply and attractively styled so as to be compatible with a wide range of home furnishings, its impedance properties will present no problems to any amplifier, and it is priced only slightly above the class of medium-sized bookshelf speakers.

Read all

DCM reviews

Read all