Allison CD 8 Speaker System Review

Allison Acoustics’ CD 8, the newest speaker in the company’s line, is a compact, A floor-standing, three-way system that closely resembles the three-way Allison:Seven. Like all Allison speakers, the CD 8 is designed to couple bass energy to the listening room without the upper-bass or lower-midrange power-response variations that affect most speaker installations. After extensive investigation designer Roy Allison concluded that in conventional speaker installations, reflections from room boundaries (walls, floor, ceiling) produce a dip in a typical speaker’s actual acoustic power output (not to be confused with room-resonance effects) at frequencies usually on the order of a few hundred hertz. His solution, used in every Allison speaker, is to locate the woofer(s) as close as possible to any adjacent room boundary (floor or wall). When this is done, in combination with a proper choice of the woofer crossover frequency, interference from boundary reflections occurs at a frequency above the woofer’s operating range and thus has no effect on the system output.

In the Allison CD 8, the 8-inch acoustic-suspension woofer is on the top, facing upward. It is recommended that the speakers be placed within 1 inch of the wall behind them for best results, but Allison claims that in any location, the CD 8’s mid-bass acoustic output will be less influenced by room boundaries than will that of any conventional speaker placed in the same location. The unique Allison convex diaphragm tweeter and midrange drivers, near the top of the CD 8’s columnar cabinet, face forward. The woofer crosses over at 450 Hz to the 3-1/2-inch midrange driver, with the second crossover, to the 1-inch tweeter, at 3,750 Hz.

The Allison convex diaphragm is a modified dome driver design whose unusual shape is said to give it excellent dispersion qualities. The midrange and high-frequency drivers use magnetic fluid for damping and cooling. Both crossovers have 12-dB-per-octave slopes, and air-core inductors and computer-grade non-polarized capacitors are used. Nominal system impedance of the CD 8 is rated at 4 ohms, and sensitivity is given as a 90-dB sound-pressure level measured at 1 meter with a 2.83-volt input.

Recessed into the rear of the enclosure, together with the binding-post terminals, are two toggle switches that can be used to adjust the midrange and tweeter outputs slightly. With both switches up, the response is essentially flat; in their down position, they produce a gently downward-sloping frequency response. The CD 8’s oak-finished cabinet measures 28-5/8 x 10-1/2 x 10-1/2 inches, and the speaker weighs about 35 pounds. Price: $395 each.

Lab Tests

In our listening room, we had to place the Allison CD 8 speakers on a narrow ledge some 28 inches above the floor in order to get them the recommended 1 inch or less from the rear wall. Actually, since this placement put the higher-frequency drivers at approximately the ear height of a seated listener, it was for us a nearly ideal placement. We also listened to them briefly using a conventional floor placement that put the speakers about 15 inches from the wall. Although the sound was virtually the same, we chose the first position for our testing and listening. We used the flat setting of the two response-adjustment switches throughout, since this gave what we considered to be the best overall sound balance.

In spite of the frequency-response irregularities inherent in every live-room measurement, the CD 8’s curve was very smooth over the whole range, sloping downward gently but remaining within 5 dB of flat response from 200 to 20,000 Hz. The woofer response, measured with a close microphone spacing, was excellent, flat within 2 dB overall from 52 to 500 Hz and sloping downward steeply at higher frequencies. The output dropped at 12 dB per octave below 50 Hz. When we spliced the bass curve to the room curve, smoothing out the sharp irregularities that were obviously functions of the microphone position, the resulting composite frequency response was an impressively flat +2, —4.5 dB from 40 to 20,000 Hz. The dispersion of the Allison convex diaphragm drivers was excellent, with no more than 6 or 7 dB difference between the on-axis and 45-degree off-axis response curves at any frequency up to 20,000 Hz.

Quasi-anechoic response measurements made with our IQS FFT analyzer showed an unexpected ± 5-dB response variation from 3,000 to 5,000 Hz that was not present in the room measurements (which are more indicative of overall acoustic output power). But we found that this effect occurred only on the speaker’s front axis; even at 30 degrees off axis the overall response was fairly similar to the excellent composite room measurements. In any case, the effect was not audible as such. Close measurements of the midrange driver’s output produced one of the flattest speaker responses we have measured, within 1 dB overall (!) over virtually the full operating range of the driver.

The phase linearity of the Allison CD 8 was as good as its frequency response, with an overall group-delay variation of less than 0.4 millisecond between 1,000 and 20,000 Hz, except for an additional 0.2-millisecond “jog” at approximately the 3,750-Hz tweeter-crossover frequency. The impedance curve was at its maximum of 15 ohms at 49 Hz, and the minimum of 3.5 ohms was in the 90- to 150-Hz range, justifying the speaker’s 4-ohm rating. The settings of the response-adjustment switches had only a minor effect on the speaker’s high-frequency impedance.

Speaker sensitivity measured 89 dB sound-pressure level (SPL) at 1 meter with an input of 2.83 volts of random noise in an octave band centered at 1,000 Hz. Our reference SPL of 90 dB required a 3.18-volt drive level, which we used for measuring low-frequency distortion. Distortion was just over 1 percent at 100 Hz and increased smoothly and gradually to 5.3 per cent at 25 Hz.

The power-handling ability of the Allison CD 8 was determined by observing the onset of acoustic-waveform distortion when the speaker was driven by a short tone burst (one or two cycles on, then an interval of 64 or 128 cycles off) at frequencies of 100, 1,000, and 10.000 Hz, each of which falls in the operating range of one of the three drivers. The woofer emitted a rasping sound, showing that the linear limits of its suspension had been exceeded, at an input of 78 watts. At 1.000 Hz the waveform clipped at 200 watts, and at 10,000 Hz it clipped at 20 watts. These results are consistent with the speaker’s amplifier power rating of 30 to 200 watts per channel and with the spectral power distribution of typical music programs. We drove the speakers with amplifiers rated as high as 350 watts per channel, and at any level which we found comfortable the speakers sounded unstrained and were not damaged.

Comments

Like other Allison speakers, the CD 8 does not produce a “flashy” sound. There is no particular emphasis on any part of the frequency range (even in the 100- to 200-Hz range where so many speakers have response irregularities that unnaturally color male voices). These are “easy sounding” speakers that one tends to forget about after a short period of listening since the music comes through with uncolored clarity. In our view, this “forgettable” quality is one of the most desirable characteristics of any piece of audio equipment, and it is typical of all the Allison speakers we have tested and used.

The virtues of smooth, uncolored middle- and high-frequency response, wide polar dispersion, clean and undistorted bass, and independence from room boundary effects have been a hallmark of Allison speakers from the beginning. If you are looking for “fire and sizzle” in your sound, the Allison speakers are probably not for you—nor is most live music likely to be sonically satisfying! However, if you want to enjoy sound that suggests “the real thing” and your budget won’t stand for a pair of Allison:One speakers ($ 1,020 per pair), you would do well to listen to the Allison CD 8. It is about as close to its senior siblings as you are likely to get.

Read all

Allison reviews

Read all