Design Acoustics DA900 Floor standing speakers
The DA900, one of Design Acoustics' Summit Series of loudspeakers, is a floor-standing three-way system. The cabinet is a slender column finished in black wood-grain vinyl on all visible surfaces. A single 8-inch woofer, facing downward at the bottom of the cabinet, operates in a vented enclosure. The bass vent is on the rear of the cabinet, about halfway up. The speaker's four supporting feet (spikes are also provided for optional use on carpeted floors) raise the system 2 inches above the floor for omnidirectional radiation of the bass frequencies.
The crossover from the woofer to a 5-inch midrange driver is at 130 Hz. The midrange speaker, 33 inches from the floor, faces forward at the top of the front panel and operates up to 3,500 Hz, covering most of the range of musical fundamental frequencies. Just below it is a 3/4-inch metallized dome tweeter with magnetic-fluid cooling. Design Acoustics says that placing the midrange driver above the tweeter tilts the speaker's polar response upward in the crossover range between the two drivers, directing the energy toward the listener rather than down toward the floor. The tweeter is also surrounded by a foam-plastic pad to minimize cabinet-edge diffraction. Like the other Summit Series loudspeakers, the DA900 is magnetically shielded to allow placement next to a television set without risk of picture distortion.
The DA900 is sold in matched (left and right) pairs. To enhance the system's imaging, the front outside edge of each cabinet (the one closest to a side wall) is angled at about 60 degrees to the front panel. The speaker's five-sided cross section and asymmetrically placed internal braces are said to diffuse standing waves within the cabinet and minimize panel vibration. Each speaker has two removable grilles, retained by plastic fasteners. The upper one covers the midrange and high-frequency drivers, while a larger grille just hides the lower portion of the cabinet. The input connectors, recessed into the back panel, are spring clips that accept only stripped wire ends.
Design Acoustics' specifications for the DA900 include a bandwidth of 40 Hz to 25 kHz, a recommended amplifier power rating of 15 to 200 watts, a sensitivity of 88 dB sound-pressure level (SPL) at 1 meter with a 2.83-volt input, and a nominal impedance of 8 ohms.
The averaged room response of the two speakers with a swept one-third-octave warbled sine-wave test signal fell off smoothly by about 7 dB from 300 Hz to 3 kHz. There was a 4-dB peak between 4 and 7.5 kHz and another of about 10 dB from 7.5 to 17 kHz, falling back by 7 dB from 17 to 20 kHz. A deep drop (about 10 dB) from 250 to 125 Hz was followed by an equal rise to a broad maximum from 60 to 100 Hz. A close-miked measurement of the woofer response yielded a curve that peaked at 70 Hz, rolling off steeply above and below. Unfortunately, it is difficult to splice such measurements to produce a meaningful composite response when the sources are a couple of feet apart (or on opposite sides of the cabinet). Horizontal dispersion on the axis of the midrange driver was notable for its uniformity with frequency. Although the level measured 45 degrees off-axis was lower than the on-axis reading's, the variation with frequency was very similar.
A variety of other measurements confirmed the essential features of the room-response curves. The quasi-anechoic maximum-length-sequence (MLS) frequency response showed a reasonably uniform output from 300 Hz (the lower limit of this test) to 2 kHz, an abrupt 4-dB drop at 2.5 kHz, and very flat response from there to 5 kHz. The output rose with equal abruptness to its original levels between 5.5 and 10 kHz. The high-frequency peak of the room curve was equally prominent in these measurements, which showed an 8-dB rise from 10 to 16 kHz followed by a return to the original level at 20 kHz.
A number of measurements made by the manufacturer on our test samples confirmed some of the key features of our curves, although the test conditions were very different and their curves did not agree with ours in all respects. The on-axis peaks at 5.5 and 16 kHz also appeared in the manufacturer's data, although they were much diminished in Design Acoustics' off-axis measurements.
The minimum system impedance was 4.5 ohms from 300 to 500 Hz, with three small peaks to 10 or 12 ohms between 18 and 100 Hz and a maximum of 24 ohms at 3.8 kHz. Our sensitivity measurement showed an output SPL of 87 dB at 1 meter with a 2.83-volt input, essentially confirming the manufacturer's specification. Distortion in the midrange driver's output at a 4-volt input level (equivalent to our 90-dB SPL reference) was between 0.6 and 1.5 percent from 130 Hz to 2 kHz. The woofer's distortion at the same level was between 0.5 and 1.5 percent from 130 to 80 Hz, rising rapidly to 4.5 percent at 50 Hz and 11 percent at 40 Hz.
Despite their modest size, the Design Acoustics DA900's drivers were able to withstand very high peak inputs without damage or unreasonable distortion. The tweeter and the midrange driver absorbed single-cycle peaks of 650 watts at 10 kHz and 960 watts at 1 kHz, respectively, which were the clipping levels of the driving amplifier into the speaker's impedance at those frequencies. More unusual was the DA900's ability to take everything our amplifier could deliver at 100 Hz into its 12-ohm impedance at that frequency (about 500 watts) without damage, although its output waveform was distorted at that level and started sounding rather hard at about 300 watts input.
The only way to judge the significance of these measured or observed effects is to listen to the speakers in their normal operating condition- playing music. As is our practice, we had used them for a week or two before making any measurements and found them to be highly listenable. The slightly bright, crisply defined character of their sound suggested a high-frequency peak, but well above the range of any musical fundamentals. So although we had not anticipated the magnitude of the measured 16-kHz peak, its presence was not too surprising. The 5.6-kHz peak was in the normal range of speaker-response irregularities.
At the lower frequencies, the absence of upper-bass boom was welcome and immediately apparent, and there was surprisingly healthy output down to 50 Hz or so. The rather large dip at 120 Hz was not much different from ordinary room standing-wave effects, and no more damaging to the overall sound of the system, although (like the 16-kHz peak) its measured magnitude was unexpected.
Despite these measured anomalies, the DA900 speakers sounded very good, especially in respect to their crisp, well-defined highs and boom-free lows. They are attractive-compact and unobtrusive-and an interesting alternative to small boxes on stands or shelves.
