Fisher ST-425
A $79.95 bookshelf two-way that a magazine reviewer drove to clipping and still couldn't break. He warned buyers to fuse it anyway.
Overview
The ST-425 is a sealed-enclosure two-way. It has a 10-inch extended-range woofer crossed to a 1-inch mylar-dome tweeter, in a cabinet finished on all sides in walnut vinyl. It measures 12¼ inches wide, 10 inches deep and 22½ inches tall, and weighs 25 pounds. Fisher built it to sit horizontally or vertically. The rear panel is recessed, and the terminals and a three-position treble switch (plus, zero, minus) live inside that cavity. That way the cabinet can hang flush against a wall without the leads shorting or the connector getting crushed.
Fisher's published numbers were 55-20,000 Hz, 6-8 ohms nominal, and a minimum amplifier requirement of 15-20 watts at 8 ohms. Price at introduction was $89.95. High Fidelity (March 1974, p.3) listed the ST-425 at $79.95 in its Studio-Standard specification table, and HiFi-Stereo (March 1974, p.9) carried the same $79.95 figure. So the $89.95 in Fisher's own literature appears to be a later or alternate listing. Either way, this was the cheapest box in Fisher's Studio-Standard 400 series, under the ST-445 at $99.95 and the ST-465 at $169.95. High Fidelity (March 1974, p.4) ran a Fisher ad calling the company "probably the world's largest manufacturer of high-fidelity speakers," and the 400-series was clearly aimed at the entry end of that volume business.
The spec sheet is not the interesting part. The Audio equipment profile is. Richard C. Heyser put the speaker through the full battery in the January 1975 issue (p.48) and came away with a mixed but useful verdict.
He found the speaker could absorb wide-range signal at very high levels without complaint. Adding a wide-band crescendo 20 dB above a 440 Hz musical line reduced that line by less than a tenth of a decibel up to clipping on most high-power amplifiers. Several hours of high-powered use produced no serious overheating of the cabinet. It doesn't fall apart when pushed.
The catch is efficiency. Heyser noted the ST-425 is relatively low-efficiency, so you're more likely to run out of amplifier than out of speaker. Running out of amplifier is what kills low-efficiency speakers, because a clipping low-power amp delivers far more average power at a given loudness than a big clean one passing the peaks. His recommendation was blunt: fuse the speaker leads with fast-acting fuses rated no larger than 2 amps, and feed it an amplifier with 50 watts or more of peak capability to get a brisk level in a moderately draped room. Audio's editor appended a note saying this wasn't a knock on the ST-425. It was protection advice for a common misuse case.
Heyser's measurements and listening notes describe a shallow-dipped upper midrange, a small mid-bass bump, and missing extreme low bass. Piano lacked body and depth. Full chords had accurate overtone structure but suppressed fundamentals. Mixed choral groups pushed back in the stereo image, though sibilants were well articulated and percussion transients were excellent, with the extreme highs down even after treble equalization. The three-position tweeter switch, he found, was subtle enough to be inaudible on anything but the widest-range material. Best results came with the tweeter at zero and the top end lifted at the preamp. Best low-frequency balance came with a small bass cut. Overall stereo imagery was good enough that the listener didn't need to sit on a calibrated chalk mark, which he considered notable at this price.
One detail for anyone buying used: Fisher shipped the ST-425 with an original-owner five-year warranty covering parts and labor. It also included instructions inviting buyers to write the Customer Relations Department with a room sketch, furniture layout, and listening position for placement advice. If the original documents survive with a pair, that paperwork is worth finding intact.
The ST-425 is an entry-level acoustic-suspension bookshelf from a high-volume American manufacturer. It is competent within its limits, with a documented tendency to want more amplifier than its price suggests. The walnut vinyl finish on all six sides and the recessed connector panel make a pair easy to place. The low efficiency and the reviewer's fuse warning are the two facts that should shape how anyone runs a pair today. Matching original pairs with the treble switch and terminals intact are the ones to hold out for.
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