Acoustic Research TSW-115P
A pair of powered minimonitors that get a genuine 50 Hz out of a 0.12-cubic-foot box. The catch is a captive speaker cable.
Overview
The number to look at is 0.12 cubic feet. That's the internal volume of each TSW-115P enclosure, 3.34 liters, roughly the displacement of a hardback novel. Acoustic Research still rated the system down to 50 Hz at the half-power point. The trick is that this is an active speaker. The built-in amplifier's response is shaped below about 150 Hz to make up for the natural roll-off of the tiny 4-inch woofer, with bass boost climbing to a maximum of around 7 or 8 dB at 80 Hz. Audio (December 1988, p.156) ran the system in an "Auricle" profile and confirmed the approach works. It reported that the clean bass these small enclosures delivered was among the two most impressive things about them.
The layout trips people up. Only one cabinet contains electronics. The dual-channel amplifier lives in the "active" unit, so the pair is really one powered speaker and one passive partner. A 9½-foot twin-conductor cable is permanently attached to the active enclosure and ends in a polarized two-pin plug that feeds the second box. The reviewer at Audio (December 1988, p.156) liked the system but wished AR had let owners supply their own interconnecting cable. Bring the speakers closer together and you coil the excess. Need them farther apart and the only remedy is to cut and splice the fixed run. The insulation is at least marked for polarity, so a careful owner won't invert one speaker against the other.
Each enclosure carries a 4-inch filled polypropylene-cone, acoustic-suspension woofer and a 3/4-inch titanium-dome, liquid-cooled, shielded tweeter. The shielding is the point of the "Audio/Video" designation. No harmful magnetic field escapes the cabinet, so the speakers can sit beside a video screen or computer without staining the picture. AR's own catalog copy billed the 115P as the smallest of the TSW series, aimed at VCRs, guitar preamps, electronic keyboards, computer music setups, and "surround sound" video rigs. It also promised "astonishing volume levels" from the self-contained amplifier. That's marketing talking. The independent numbers are more interesting.
Input comes in on an 11-foot dual shielded cable, mini stereo plug at one end and RCA phono plugs at the other, intended for a preamp, CD player, portable stereo, stereo TV, or the rear channels of a surround processor. Tiny concentric dual input-level controls trim the system's gain when the source has no volume control of its own. About 300 mV of input drives the system to full output, so a CD player delivering 2 V or more needs those level controls turned well down. The active unit has a rocker power switch and must be plugged into a 120-V, 60-Hz outlet. The dual-channel amp draws a maximum of 60 watts.
The amplifier's rated output is 16 watts per channel. Audio (December 1988, p.156) measured distortion as a function of frequency at that constant 16-watt level into a 4-ohm load, the impedance the amp was clearly designed to drive, even though no load impedance is specified. THD+N came in at 0.55% at 1 kHz, rising to 0.8% at 20 kHz and just over 1% at 50 Hz. At lower levels it cleaned up considerably: around 0.1% below 4 watts per channel, climbing gradually to that 0.55% figure at rated output. None of that is state-of-the-art amplification, but it's honest small-speaker electronics. The review noted the system hit peaks of 105 dB SPL with little or no distortion or overload, the figure AR itself claimed.
The listening impressions from that same profile are specific. On a Delos organ recording, the lowest pedal notes showed some doubling, but the sense of power and space came through surprisingly well for the size. On chamber material, clarinet and piano, the system reportedly excelled, with excellent clarity on the clarinet and good transient quality on the piano. Orientation mattered. A slight toe-in toward the listener produced a more stable stereo image than firing straight ahead, as the owner's manual recommended. The reviewer's verdict was blunt about the use case. This is no substitute for a large primary system, but for surround-sound rear channels, a bedroom, den, or vacation home, it beats the "totally unacceptable boom box" handily. The price was $400 per pair.
The package is compact and, by the description in Audio (December 1988, p.156), nicely finished: solid hardwood walnut or oak top and bottom panels, black vinyl veneer on the cabinet sides, black grille cloth. The enclosures measure 10½ inches high by 7-1/16 inches wide by 6-5/8 inches deep. AR recommended mounting them near a wall with the tweeters at ear level.
A buyer today should weigh the captive-cable arrangement and the one-active-one-passive layout. If the amplifier in the active cabinet fails, the whole system goes quiet, and there's no passive fallback. The permanently attached 9½-foot inter-speaker cable constrains placement in a way most modern powered monitors don't. The 300 mV input sensitivity means the level controls will live near the bottom of their travel with any digital source. None of that is disqualifying for the intended job of desktop, bedroom or surround rear. Collectors note that the TSW-115P turns up as the odd small powered member of a large TSW family. Its appeal is mostly to AR completists and to anyone who wants a period-correct small active speaker that genuinely reaches 50 Hz.
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