Acoustic Research AR-7 Speaker
had about 2-dB less energy in the area above 3,000 Hz. The output fell below 60 Hz, but the low-frequency harmonic distortion was quite low, reaching 5 per cent at about 50 Hz, using either a IO-watt drive level, or maintaining a constant 90-dB SPL (sound-pressure level) at a distance of three feet from the speaker. At lower frequencies (as could be inferred from the rapid decrease in output), the constant-output condition produced more distortion than the constant-ddve test. We would judge the effective lower limit of the A R-7 to be about 40 to 213 Hz- which is a very respectable figure for a speaker system of its size. The impedance ranged between 5 and 10 ohms at most frequencies, reaching its maximum of just over 10 ohms at the bass resonance of 70 Hz. The tone-burst response was on a par with that of the other AR speakers we nave t~sted-ab6ut as close to ideal as can be measured in a ':Iive" environment. I he effiCiency, though low, was 'slightly higher than that of the top-of-the-line AR speakers such as the AR-3a or AR-LST. A drive level of 3.5 volts at mid-frequencies (about 1.5 watts) was needed to produce a 90-dB SPL. Comment. The measured characteristics of the AR-7 were so outstanding that we were not surprIsed at Its excellent performance using our simulated "live-vs.-recorded" test technique. The only audible difference be'tween our original program and its reproduction through the AR-7 set to FLAT was a very slight dulling of the extreme highs above 10,000 Hz. Even though the AR-7 tweeter has very fine dispersion by contemporary standards, it was not Quite the equal of the dome radiators u~'ie.d in the more expensive AR speakers. Our overall rating of the AR-7 in this test would be a "B+". In this respect, it compares with many speakers selling for twice its price or even more-which clearly makes it one of the more outstanding under-$l 00 speaker systems, irrespective of size. AR has designed this speaker, we surmise. to satisfy (Colltillued on page 34)
MOST "bookshelf" speakers are comparable in size and weight to a set of encyclopedias, and they must therefore be supported by correspondingly rugged shelves. In contrast, the new Acoustic Research AR-7 would be quite at home on a shelf of paperbacks. It measures 153/4 inches wide x 93/4 inches high x 61f4 inches deep, and weighs a mere II pounds. The walnut enclosure can also be hung directly on a wall, using picture hooks and the hardware furnished with the speakers. The AR-7 is a two-way system, consisting of a widedispersion, ll/Z-inch tweeter (essentially the same as that used in the AR-6) and a newly designed 8-inch acousticsuspension woofer. The crossover frequency is 2,000 Hz, and a two-position switch in the rear of the unit provides a choice of two tweeter levels, identified as FLAT and NORM. The system impedance is 8 ohms, and the moderately low efficiency requires an amplifier capable of at least 15 watts continuous output. The AR-7 comes packed two to a box, and carrying the standard AR fiveyear guarantee; Price: $60 each.
Laboratory Measurements. The AR-Ts frequency response was measured in a "normal" reverberant environment that integrated the total energy output of the system. With the tweeter-level control set to FLAT, the measured curve was among. the flattest we have chartedwithin 2 dB from 65 to 15,000 Hz. In the NORM position, the response went out as far as the flat curve, but
The AR-7's tOile-burst respOllse, showll here j(Jr. (left to riNht) 70, 3,000, and 8,000 Hz, was excellent overall.
the special needs of the quadraphonic listener. It should be possible to install four AR-Ts inconspicuously (and inexpensively) in almost any room, and the resulting sound quality should leave little to be desired. The efficiency and other characteristics of the AR-7 are Quite compatible with the larger AR. systems, thus making it suitable for use in the rear channels when a pair of AR~ax.9r AR-3a speakers are used in the front. This compatibility was drqrnatically demonstrated when w.e switched

(in stereo) between a pair of $60 AR-T's and a pair of excellent $600 AR-LST's (see the LST test report iJ the October 1972 issue). The audible similarities between the two were much more apparent than were their differens~ - differences that occurred. naturally. at the verUigh. and very low ends of the audio spectrum. There are not~ many speakers of any size or price that can ac uit them'selves so well sloe-by-sloe With the AK-LS. -Por more information, cirCle105 on reader service card