Allison Seven Speaker System Review

Some years ago, Roy Allison conducted a study that indicated that the room in which a speaker is placed, and the physical relationship of the speaker and the room, can produce a significant change in the actual acoustic low-frequency power response of the system. This is in addition to the normal standing-wave and room-resonance phenomena that usually cause variations in the low-frequency sound-pressure level throughout a room. The undesired interaction between room and speaker can be minimized by designing the speaker to operate together with the room as a system. From the beginning, therefore, Allison loudspeaker systems have featured what Allison Acoustics calls “Room-Matched” design.

The low-frequency power output of a speaker can be optimized for mounting against one, two, or three room-boundary surfaces (walls, floor, or ceiling). All Allison speakers have been designed to take advantage of this fact, although the various models differ considerably in their physical configuration and in their recommended placement.

The new Allison:Seven is a relatively low-cost, floor-standing, two-way speaker designed to be placed against a wall but at least 2 feet from a corner. Because of their broad dispersion, a pair of Allison:Seven speakers need not be placed against the same wall and will operate effectively when facing at right angles to each other. The oak-veneer cabinet is 27-1/2 inches high and 9-5/8 inches square, and each speaker weighs 22 pounds.

The 8-inch woofer of the Allison:Seven faces upward, and in the recommended placement its edge is within an inch of the wall. (This is necessary to avoid the partial cancellation of mid-bass output that occurs whenever a woofer is located a foot or so from a wall.) The woofer operates in a sealed (acoustic-suspension) enclosure with a volume of 1,775 cubic inches, and it resonates at 52 Hz. It crosses over to the tweeter at 2,000 Hz, with 6-dB-per-octave slopes. The speaker has no level or balance controls.

The forward-facing tweeter is located near the top of the front surface of the cabinet. Its voice coil is cooled and damped by Ferrofluid, and the tweeter has the patented Allison convex diaphragm, which gives excellent dispersion by virtue of being designed to simulate a pulsating hemisphere. The diaphragm is not hemispherical in shape, however. It resembles a rounded cone reminiscent of a giant spherical phono stylus.

The low-frequency response of the Allison:Seven is specified as — 3 dB at 41 Hz and —6 dB at 34.5 Hz. The system impedance is rated at 4 ohms, and its sensitivity is specified as 87 dB at 1 meter for a 1-watt input. The Allison:Seven is sold in pairs, and the price is $450 per pair.

Laboratory Measurements

The close-miked woofer response of the Allison:Seven was unusually flat and extended, varying + 0.5, —1.5 dB from 60 to 1,100 Hz. The response fell off at 12 dB per octave below 60 Hz, and there was a 7-dB dip at 1,500 Hz. The high-frequency response, measured in the reverberant field of the room, showed the usual variations in the midrange, where speaker-room interaction was unavoidable, but it was exceptionally uniform from 5,000 to 20,000 Hz, where the output varied only +0.5, —2 dB.

There was a peak of about 5 dB in the room curve at 1,500 Hz, corresponding to the dip measured in the woofer output in the close-miked measurement, as well as a smaller 3.5-dB peak at 4,500 Hz. When we spliced the two curves to derive a composite frequency response, there seemed to be a marked difference between them at 1,500 Hz. However, we concluded that the 7-dB dip in the close-miked woofer response was not significant since it was caused by the tweeter output refracting around the edge of the cabinet (that path length was consistent with an interference effect at 1,500 Hz). Thus the composite, room-corrected curve was used to give the unit’s frequency response, which was an excellent ±2.5 dB from 54 to 20,000 Hz.

The impedance of the speaker was about 4 ohms at 20 Hz and between 100 and 200 Hz. It fell to 3.5 ohms in the 10,000- to 15,000-Hz range and reached a maximum of 19 ohms at 57 Hz and from 1,500 to 2,000 Hz. The sensitivity of the speaker was almost exactly as rated, with a measured sound-pressure level of 87.5 dB at 1 meter with 2.83 volts of random noise.

The bass distortion was measured with input levels of 2 and 6.32 volts, corresponding to 1- and 10-watt power levels. At 1 watt, the distortion was between 1 and 1.4 per cent from 100 Hz to 60 Hz, rising slowly to 4.3 per cent at 20 Hz. At 10 watts, the distortion readings were in the range of 3 to 4 per cent down to 50 Hz and climbed to 11.2 per cent at 20 Hz. We found with our IQS 401-L FFT analysis system that the phase response of the Allison tweeter was as impressive as its other attributes, resulting in a group-delay characteristic that remained between 0.3 and 0.4 milliseconds from 2,000 to 20,000 Hz.

Comment

Over the years, we have tested most of the Allison speakers as they have appeared, and we have found them, despite their wide differences in size and price, to be uniformly excellent and generally very similar in their sound properties. The Allison:Seven is in that tradition.

In our listening room we were unable to place the speakers directly against the wall behind them because of baseboard heating fins and other obstacles. Much of the time, the speakers were about one foot from the wall. If this had any adverse effect on their performance, we were unaware of it. The sound was smooth, balanced, and without any apparent emphasis or de-emphasis of any part of the audio spectrum. The dispersion of the speakers was excellent, and there was no sense of spatial separation between the sounds from the woofer and tweeter.

The Allison:Seven is a compact speaker, and its pale oak finish is attractive. When given the opportunity, the system delivers an impressive level of clean, deep bass that seems almost inconsistent with its dimensions and light appearance. Considering that we did not have the speakers placed optimally for flat bass output, their performance is all the more impressive.

Priced competitively with a number of good but conventional “bookshelf’ speakers, the Allison:Seven offers definite advantages over many of them in both audible and visible terms. It is an excellent value, and the only possible disadvantage we can see for it is the requirement of a closely backing wall for theoretically optimum results. Allison claims, however, that no matter where the speaker is placed, its bass response will always be at least as good as a conventional speaker in the same location, and this seems to have been confirmed in our tests. Smooth, well-balanced sound, compact, and relatively inexpensive—a nice combination.

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