Design Acoustics PS-10 Speaker System Review

IT is widely accepted that stereo imaging can be improved by using the smallest possible sound sources. Therefore, the Design Acoustics “Point Source” PS-10 speaker was designed to radiate sound from the smallest area consistent with the necessary dimensions of its drivers and enclosure. It is a three-way bookshelf speaker with an unconventional appearance and driver configuration. The 10-inch woofer faces downward and radiates frequencies up to 190 Hz through a 1-inch-high slot between the speaker’s enclosure and its base. The other drivers face forward in the usual manner. Most of the frequency range containing fundamental tones from musical instruments—from 190 to 2,600 Hz—is radiated by a 5-inch acoustically treated cone driver mounted near the center of the 11 x 12-inch front panel. The 1-inch soft-dome tweeter, located near one corner of the front panel, operates above 2,600 Hz. The asymmetrical tweeter placement permits pairs of PS-10’s to be installed with both tweeters either at the inside or the outside, providing some control of imaging at different speaker spacings.

The front baffle of the PS-10 is covered with resilient rubber to reduce diffraction at the edges of the enclosure. On the front -panel is a small knob that provides a continuous ±3-dB high-frequency level adjustment. The brown cloth grille is retained by plastic snaps. The speaker’s connectors, recessed into the rear of the cabinet, are insulated and spring-loaded like those often used for speaker outputs on amplifiers and receivers. They are spaced on 3/4-inch centers, and their openings are large enough to accept dual banana-plug connectors.

The PS-10 has a nominal 8-ohm impedance and a sensitivity rating of 90 dB sound-pressure level at 1 meter when driven with 1 watt. The overall frequency response of the system is rated at 48 to 22,000 Hz, and the speaker is intended for use with amplifiers rated at between 15 and 250 watts per channel. The cabinet is covered with walnut-grain vinyl veneer and measures 14 inches high, 11 inches wide, and 13-3/4 inches deep. It weighs 23-3/4 pounds. The PS-10 is packaged and sold in pairs. Prices: $500 per pair.

Laboratory Measurements

The woofer of the Design Acoustics PS-10 is an acoustic-suspension design that operates in a sealed enclosure. We measured its output by inserting the microphone through the base slot to place it as close as possible to the cone. The output reached a maximum level at 100 Hz and fell off at 12 dB per octave above and below that frequency. A second response maximum was measured at 650 Hz, where the woofer’s output equaled its 100-Hz level, and there was also a much smaller response peak at 1,200 Hz. These higher frequencies, however, do not radiate through the slot with equal effectiveness and thus do not have a major effect on the total output of the system.

Although we do not usually measure the response of midrange drivers with a closespaced microphone, since this type of measurement is valid only when the cone diameter is small compared with the wavelength of sound at the highest measured frequency, the size of the PS-10’s midrange cone (the company calls it a “mid-bass” driver) appeared to be small enough for such a measurement. The resulting curve varied less than ±2 dB from 115 to 1,900 Hz.

The averaged room response from our sample pair of PS-10’s was very flat above 1,500 Hz. The 30-degree-off-axis tweeter dispersion was excellent up to 10,000 Hz, then the response dropped to —20 dB at 20,000 Hz. There were the usual response variations through the midrange, normal results of interference with reflections from room surfaces. The spliced curves showed a system response within ±2.5 dB from 140 to 20,000 Hz, with the woofer output rising at 100 Hz to a peak of about 7 dB above the average midrange level before falling off at 12 dB per octave at lower frequencies. We also plotted the composite response with the close-miked midrange curve substituted for the room measurement between 150 and 1,100 Hz. The junctions between the various curves matched very closely, but the overall frequency-response variation was not greatly reduced by this technique. The tweeter-level adjustment tilted the response curve above 1,000 Hz, with a maximum effect of ± 3 dB above 5,000 Hz.

We could also see the woofer’s secondary peaks (though greatly attenuated) in the room response. They appeared as a pair of peaks and dips with peak-to-peak amplitudes of 3 to 5 dB at 650 and 1,200 Hz. Such small aberrations (as well as considerably larger ones) frequently appear in our speaker-response measurements, and they are usually the result of room resonances or room-boundary interactions with the speaker. In this case, however, the variations in the room response corresponded closely with the measured anechoic woofer response, and we are inclined to link the two effects.

The woofer distortion was measured with a constant input voltage equivalent to one that would generate a 90-dB sound-pressure level at a 1-meter distance. This level was based on our own measurement of the speaker’s sensitivity, which in the case of the PS-10 was 91 dB for a 1-watt input, almost exactly the rated value (and unusually high for a small acoustic-suspension system). With the same microphone placement used to measure its frequency response, the woofer’s distortion was less than 1 per cent down to 66 Hz, rising to only 3.5 per cent at 45 Hz and 6 per cent at 30 Hz.

The PS-10’s system impedance was unusually uniform, between 6 and 10 ohms at most frequencies from 20 to 20,000 Hz, with one dip to 4.5 ohms at 130 Hz. The axial frequency response, measured with our IQS FFT analyzer, was ± 3 dB from the 180-Hz lower limit of the measurement up to about 20,000 Hz. This measurement, made at a 1-meter distance with the speaker placed well away from walls and floor, also showed the anomalies in the upper woofer range revealed by our other measurements, although the analyzer’s frequency resolution was somewhat limited in this test.

The FFT analysis clearly showed the directivity of the PS-10’s tweeter when we subtracted the 45-degree-off-axis response from the axial response. The two curves began to diverge above 10,000 Hz, with a maximum difference of 24 dB at 20,000 Hz. The group-delay (phase) characteristic varied about 0.3 millisecond overall between 2,000 and 20,000 Hz.

Comment

The Design Acoustics PS-10 is best operated close to ear height, although not necessarily against a wall. Its considerable depth may prevent its installation on normal bookshelves, since it will extend over the front of even a 12-inch shelf. We did our listening and room-response measurements with the speakers placed against the wall on a ledge about 27 inches above the floor. For the FFT measurements the speaker was placed on a stand several feet from a wall.

In our listening tests, the PS-10’s delivered a smooth, balanced sound that was generally consistent with our measurements. We were pleased to find that the audible bass response remained strong and clean far below the measured 100-Hz maximum-output frequency; in fact, the lower limit for truly effective bass response seemed to be about 50 Hz, confirming the manufacturer’s 48-Hz rating. The highs sounded best to us with the tweeter level set at “0” (which also gave the flattest measured response). The slight bass emphasis at 100 Hz produced a moderate heaviness on male voices, but the PS-10 was similar in this respect to many other speakers we have tested. Overall, we found the sound from the PS-10’s to be as satisfying as we would expect from a good $250 speaker. It is quite possible that different placements of these units could make substantial changes in their sound quality, but we found them impressive enough without attempting to optimize the installation. No doubt there are some homes for which the PS-10’s unorthodox configuration is especially well suited, but its compact size and unobtrusive looks should enable it to fit in almost anywhere both aesthetically and acoustically.

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