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REPRINTED FROM STEREO REVIEW DECEMBER 1994

"Their stereo presentation was flawless..." "I cannot imagine another speaker in its price range that can surpass its overall sound quality. I tried to find their Achilles’ heel, but it eluded me."

"it ... could go toe to toe with others many times its price and more than hold its own."

PINNACLE AC 650 loudspeaker System
JULIAN HIRSCH • HIRSCH-HOUCK LABORATORIES

PINNACLE Loudspeakers recently introduced its Audio Cinema line, designed to meet the needs of home theater installations as well as conventional high-fidelity applications. The Audio Cinema series currently comprises seven full- range speakers, four of them magnetically shielded for use in close proximity to a TV receiver or monitor, and a passive subwoofer. The AC 650, roughly in the middle of the line, is the smallest of the three unshielded speakers. It is a compact two-way system based on a 6-inch treated fibercone (plasticized) woofer with a rubber surround operating in a vented enclosure. There is a 12-dB- per-octave crossover at 2.5 kHz to a 3/4-inch soft-dome tweeter with magnetic-fluid cooling and damping. Like other PINNACLE systems, the AC 650 uses the company's patented Diaduct bass-loading system, with the internal duct tube at an acute angle to the cabinet walls, which is said to enable greater bass extension than a given size of cabinet and driver could otherwise have.

The cabinet is finished on all surfaces in a vinyl wrap that looks and feels remarkably like real wood. All the front edges of the cabinet are beveled. The removable black cloth grille fits snugly into the front panel recess, and the drivers are approximately centered in the panel area. The back panel contains recessed five-way binding-post connectors and the Diaduct port. For proper operation, the rear of the AC 650 must be at least a few inches from the wall, and PINNACLE says that for best performance the speakers should be about 30 inches off the floor and at least a foot from the wall. We installed them on 26-inch stands 2 feet out from the wall.

The averaged room response of the two speakers spliced readily to the near-field bass response curve to form a composite response curve that varied only 3.5 dB from 35 Hz to 20 kHz. The portion below 2 kHz was a few decibels stronger than the range from 3 to 10 kHz, but the overall response was impressively uniform. In the uppermost octave (10 to 20 kHz), the output climbed back to the overall average level. A quasi-anechoic MLS frequency-response plot confirmed the basic shape of the measured room response, with a variation (on-axis, at 1 or 2 meters distance) of about 2.5 dB over the 300-Hz to 20-kHz range of this measurement.

Horizontal dispersion, measured at 45 degrees off-axis with a swept one third-octave random-noise signal, was typical of small dome tweeters. Up to 10 kHz, the on-axis and off-axis response curves were within about 2 dB of each other, diverging at higher frequencies. At 15 kHz, the off-axis output was down about 8 dB, and at 20 kHz it was down 15 dB relative to the axial response.

The system's impedance curve had two peaks in the bass, 18 ohms at 27 Hz and 20 ohms at 80 Hz. The impedance was a very uniform 3.8 ohms (the minimum value) to 4 ohms from 120 Hz to 1.5 kHz, reached just over 9 ohms at 4.8 kHz, and was 5 ohms or less from 10 to 15 kHz. PINNACLE nonetheless rates the system at 8 ohms nominal impedance and says that it has found the speaker to perform well with a wide variety of receivers and amplifiers.

That claim is probably justifiable in light of the AC 650's relatively high sensitivity rating of 91 dB sound-pressure level (SPL) at 1 meter with a 2.83-volt input of pink noise, which suggests that only a moderate amount of power will ever be needed for a comfortable listening level. Our measurements confirmed the 91-dB sensitivity rating.

Woofer distortion was very low at our standard test level (corresponding to a 90-dB SPL output, in this case 2.5 volts). Over most of the woofer's range, from 80 Hz to 2 kHz, the distortion readings were between 0.6 and 1 percent. Even at lower frequencies the distortion remained low, reaching 2 percent at 60 Hz and 5 percent at 30 Hz-impressive performance for a 6 1/2-inch woofer.

In our pulse power-handling tests, the woofer reached its suspension limits with a loud rasp (but without damage) with a single-cycle 100-Hz input of 350 watts. It is safe to say that very few people would ever attempt such abuse deliberately, but it is also reassuring to find that this little giant could survive such treatment without permanent damage.

As always, the acid test of a speaker is in the listening. Considering the AC 650's low price, we were already quite impressed by its measured performance, but we nevertheless found the listening evaluation to be the most surprising part of the test. To put it as simply and directly as I can, the PINNACLE AC 650 does not sound like any speaker of its price that I have ever heard. To be sure, there are some excellent speakers in its general size range, but they typically sell for at least several times as much.

The pair of AC 650's created a soundstage comparable to some of the best I have previously heard in my home. Their stereo presentation was flawless (the imaging test signals of the Chesky JD37 CD appeared and moved exactly as they were supposed to, which some speakers at ten times the price have failed to achieve), and their tonal balance, from bass to treble, was superb. There was no artificial boom, honk, or sizzle, or any other unnatural effect that I could find.

Also, these speakers do not have to be treated with kid gloves. As I began to appreciate their special qualities, I tried to find their Achilles' heel, but it eluded me. They will play as loud as I would ever wish to listen to orchestral music at home (85 dB average SPL in a 15 x 20-foot room) without sounding strained.

It has been a long time since I last encountered an inexpensive speaker that could go toe to toe with others many times its price and more than hold its own. If I had heard the PINNACLE AC 650 in an audio showroom or at a hi-fi show, I would have assumed that everything had been carefully "tweaked" (when I finally get such a speaker on my own turf, it rarely produces the effect that caught my attention in the first place).

The PINNACLE AC 650 is well worth going out of your way to hear. I cannot imagine another speaker in its price range that can surpass its overall sound quality-but, as always, you'll have to listen and decide for yourself.

Julian Hirsch  Stereo Review

Copyright 1994 Hachette Filipacchi Magazines, Inc. All Rights Reserved.

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