Design Acoustics PS-103 Speaker System Review

The newest and largest model in the Design Acoustics Point Source series of loudspeakers is the floor-standing PS-103. Most of the speaker’s sound is radiated by two drivers in an isolated pyramidal subenclosure at the top. The drivers are hidden from view at the front and sides by an opaque, nonremovable cloth grille but their enclosure is partially visible through a large cutout in the rear of the speaker cabinet.

A 6-inch cone radiates the frequencies from 100 to 3,000 Hz, where there is a 12-dB-per-octave crossover to a 3/4-inch dome tweeter. The lower bass frequencies are generated by a 10-inch acoustic-suspension subwoofer located at the bottom of the cabinet and facing downward. Its output radiates through the slot formed between the floor and the bottom of the speaker cabinet, which is held about 2 inches off the floor by four casters.

The PS-103 has a rated sensitivity of 88 dB sound-pressure level (SPL) with a 1-watt input to its nominal 8-ohm impedance. It is recommended for use with amplifiers rated between 30 and 250 watts per channel. A panel recessed into the rear of the cabinet contains three pairs of five-way binding-post terminals (each pair is normally connected by wire jumpers) and a three-position toggle switch that selects a flat, — 3-dB, or — 6-dB tweeter-level setting to suit personal preference or local listening conditions. The speakers can be operated with bi-amplification, using separate power amplifiers and an electronic crossover, by removing the jumpers and connecting the amplifier outputs to the indicated terminals. The low-frequency amplifier drives only the subwoofer; the other powers the two higher-frequency drivers from 100 Hz on up.

The PS-103 stands 38-1/4 inches high and measures 13-3/4 inches wide and 13-3/8 inches deep. The top and bottom of the cabinet and its side trim panels are made of solid oak. The casters that support it also simplify positioning the speakers for best results, although placement is not particularly critical and each unit weighs a moderate 55 pounds. The 2-inch spacing from the floor is important, however, for correct bass performance. Price: $950 a pair.

Lab Tests

In addition to our usual room-response measurements of the two speakers, smoothed and averaged to minimize the effects of room resonances and standing waves, we made close-miked measurements of the 6-inch bass/midrange driver and of the subwoofer (the latter being measured in the gap between the cabinet bottom and the floor). Combining both of these curves with the room response produced our composite frequency-response curve.

From 50 to 1,000 Hz, the response variation was only ± 3 dB, falling off at 12 dB per octave below 50 Hz. The effective crossover between the subwoofer and the bass/midrange appeared to be about 85 Hz—the subwoofer’s response peaked at 65 Hz and dropped off at 12 dB per octave above and below that frequency. The room response above 1.000 Hz was quite flat, but the average level was about 5 dB below the midrange plateau. There was a small tweeter-resonance peak at about 15,000 Hz, but the variation between 1,000 and 20,000 Hz was only ± 3 dB. The tweeter-level switch affected the output above 3.000 Hz by approximately the indicated amounts. We always preferred the sound with the switch set to FLAT.

Quasi-anechoic FFT response measurements with our IQS signal analyzer confirmed the response shape we had derived from swept sine-wave measurements. At certain distances and angles relative to the speaker, the FFT response showed irregularities or holes not present at other positions. These were probably caused by signal reflections from the edges of the cabinet (the pyramidal subenclosure is located slightly behind the plane of the front of the cabinet). In general, these irregularities were not present in the room measurements, which combine sounds arriving from many directions.

The speaker’s horizontal dispersion was excellent. Except for the effects mentioned, there was no significant difference between the response curves measured on-axis and 45 degrees off-axis until the frequency exceeded about 12,000 Hz. The group-delay variation, which was less than ±0.2 millisecond from 1,500 to 23,000 Hz, confirmed that the system had excellent phase linearity.

The impedance, which averaged about 6 to 8 ohms over most of the audio range, reached its minimum of 4.5 ohms at 65 and 350 Hz and its maximum of 19 ohms at 2,200 Hz. The speaker’s sensitivity, measured at 1 meter, was 86 dB SPL with an input of 2.83 volts of pink noise. Its bass distortion was measured from the subwoofer using a 4.5-volt input (corresponding to a 90-dB spl at 1 meter). It was under 1 percent from 100 to about 70 Hz, rising slowly to 4.7 percent at 40 Hz and 6.3 percent at 35 Hz, which appeared to be the speaker’s effective lower limit.

The PS-103 handled our high-level pulse-power tests well, emitting a faint rattle when the 100-Hz input reached 135 watts into its 7.5-ohm impedance. At 1,000 Hz, in the range of the 6-inch driver, the amplifier clipped, at an input of 850 watts into 8.5 ohms, before the speaker distorted. The tweeter, driven at 10,000 Hz, had no problems with the amplifier’s 1,100-watt output into its 6-ohm impedance.

Comments

From our first hearing, we realized that the PS-103 had a wide, smooth, and well-balanced response. Frankly, there was no indication of a level disparity between the high frequencies and the midrange or bass. This perceived smoothness may have been a result of the speaker’s overall excellent dispersion and the ultimate effect of that dispersion on the sound reaching our ears. Measurements cannot, of course, duplicate the full effect of a human brain’s interpretation of a complex sound field.

Even after the tests, when listening to the speakers we were more aware of their well-balanced sound than of any departures from an ideal, straight-line response (which has never been achieved by any speaker, and probably never will be). The PS-103’s delivered an excellent stereo image over a wide range of spacings. The sound never seemed to come from the pair of handsome enclosures at the front of the room—it was just there. That would seem to be a reasonable description of a really good speaker, and it is a fair description of the Design Acoustics PS-103.

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