Acoustic Research TSW-710
Ninety pounds of Cambridge lab instrument dressed as a floorstanding speaker - if the documentation actually describes what collectors think it does.
Overview
The surviving documentation for the TSW-710 is a mess. The manual excerpt in the archive carries the TSW-710 filename and the TSW-710 attribution, but the text inside describes the AR-LST, the Laboratory Standard Transducer. It has a six-position balance switch, an autotransformer tapped in 1 dB steps, four mid-range hemispherical radiators, four hemispherical tweeters, and crossover points at 575 and 5,000 Hz. Maybe AR shipped the TSW-710 with an LST-derived manual. Maybe the archive's scan is a mislabeled LST document. Maybe the two models really share a design lineage. The available sources don't settle it. Collectors chasing a TSW-710 should treat the manual's numbers as applying to the LST until a TSW-710-specific document turns up. That is the most important thing to know before buying one.
If the document applies, this is a speaker built to a laboratory brief, not a living-room one. Stated sensitivity is 89.5 dB SPL average, ±1 dB, measured with the cabinet's back against a rigid wall. The placement matters, because the manual is explicit that low-frequency output rises in a corner and falls when the cabinet is pulled away from the wall. Efficiency is given as 0.8% average at the stated radiation angle. Impedance is not a single figure. It depends on switch position, and the manual points to a set of curves instead of a number. The switching network raises impedance at middle frequencies relative to an AR-3a, so on a low-powered tube amp the speaker will seem less efficient than an AR-3a on the same amplifier terminals, even though real efficiency is unchanged. The volume control just has to go higher.
Power handling is quoted against the FNM 2 fuse (with some documents specifying FNM 3): 180 watts for 10 seconds, 64 watts for 30 seconds, and 23 watts long-term average, all based on current into an assumed nominal impedance of 4 ohms. The manual spends real space warning owners not to bypass the fuse block and not to substitute any fuse other than FNM 2. Voice coils cooked by excessive input are explicitly excluded from the guarantee. The AR promise was a five-year guarantee covering parts, labor, and freight both ways, with new packaging thrown in. The manual begs owners to keep the original carton because the speaker is heavy for its size and will not survive generic shipping.
The documented cabinet measures 27⅜ inches wide by 20 inches high by 9¾ inches deep overall - 68.9 by 50.8 by 24.8 cm - and weighs 90 pounds, or 40.5 kg. Those are wide-and-shallow proportions, the kind that want a wall behind them. The driver complement as written is a 19-inch woofer with four 1¾-inch mid-range hemispherical radiators and four ¾-inch hemispherical tweeters. The metric restatement in the same document gives 30 cm, 38 mm, and 19 mm, which is a more plausible set of numbers for a real cabinet. OCR and unit transcription in these old manuals are not to be trusted blindly. Phasing is conventional: positive voltage on input terminal No. 2 moves the woofer diaphragm forward, out of the cabinet.
The design logic, as the manual tells it, is about power handling and repeatability. Multiple mid-range and tweeter units are wired in series/parallel, so the high-frequency load is spread across four drivers instead of one. That is also why the manual warns that at low balance-switch settings the tweeters see substantially more high-frequency power than an AR-3a tweeter would at the same loudness, and that care is needed to avoid cooking them. The switching offers six spectral profiles, from a gently rising response to progressively greater downward slopes. Mid-range output is held roughly constant across positions, so changing the switch does not change the perceived loudness. One position is specified as flat within the limits of the day from 30 Hz to 20 kHz. Laboratory and commercial users wanted a repeatable, accurately known spectral energy profile, and this is how it was delivered.
Period reception, where the archive's review chunks touch this corner of the AR line, is thin and mostly concerns siblings. HiFI-Stereo (February 1989, p.116) catalogued the TSW-910 four-way floorstander at $800 per pair. It is a columnar acoustic-suspension design with the Tetra-Helix tweeter mounting plate, a 10-100 W power range, 8-ohm impedance, and half-power points at 54 Hz and 40,000 Hz. The TSW badge covered a broad family with wildly different specifications, so nothing about the TSW-910's numbers should be read across to the TSW-710. The same publication's 1989 and 1991 speaker surveys list other AR models in passing without giving the TSW-710 a specification entry of its own. No independent measured review of the TSW-710 specifically appears in the available chunks.
For collectors, that absence is the story. A speaker with no confirmed production years, no confirmed original price, no independent measurement, and a manual that may belong to a different model is hard to value or to service. The five-year guarantee and the fuse discipline suggest AR expected these to be driven hard in professional settings. The 90-pound cabinet and wall-loading requirement suggest they were never meant to be moved often. Anyone who finds a pair should confirm the model designation on the cabinet itself, check that the fuse block is intact and unfettered, and treat any seller's specification claims as unverified until matched against a TSW-710-specific document.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.