Sony SS-7200 ULM2

At 590mm tall and nearly 16kg, these walnut-finished bookshelf speakers are dense for their size.

Overview

The Sony SS-7200 ULM2 is a high-end speaker from the early 1970s Japanese hi-fi boom. It belongs to Sony's ULM (Ultra Linear Motor) series and was positioned as a bookshelf system, though the word hardly fits a speaker 590mm tall and 16kg in mass. It's compact only next to a floorstander. Built in Japan, it came out while Japanese manufacturers were aggressively challenging Western audio dominance with tightly engineered, lab-optimized designs. The SS-7200 is a three-way, airtight-type system with a bass-reflex enclosure finished in walnut.

Sony made distortion reduction the central goal of the SS-7200, particularly in the magnetic circuit. The design team reportedly identified theoretical sources of magnetic distortion and went after them directly. The most visible fix is a notch in the center pole of the motor structure, capped with thick copper plating. The idea was to model the non-linearities and eliminate them at the source. The voice coils use a special synthetic resin adhesive, chosen for heat resistance and mechanical strength, so the speaker could take sustained high-power input without degrading. The woofer's metal bobbin backs that up, since it dissipates heat better than the paper or aluminum alternatives common at the time.

The drivers are a 25 cm cone woofer, a 12 cm midrange and a 2.5 cm dome tweeter. All three use corn paper for the cone material, which Sony claimed gave superior theoretical and audible performance. Whether that's measurable or marketing is open. The edge is a cloth base coated with a special thin rubber, for airtightness and consistent flex. The baffle has no decorative trim and no flared edges. The Saran frame is streamlined to minimize diffraction and reflections that could smear the soundstage.

The most unusual feature is the pair of switches on the rear panel. One is a multi-selector that adjusts the high-frequency level across a wide range, from +4 dB to -36 dB, for room acoustics or listener preference. The other disconnects the LC network entirely, so the crossover is bypassed and each driver can be driven directly. That one is for experimenters and technicians, and for anyone running bi-amped or tri-amped setups with external crossovers. It suggests Sony expected these speakers to end up in semi-professional or highly customized systems, not just living rooms.

Specifications

Manufacturer	Sony
Model	SS-7200 ULM2
Type	3-Way, 3-Speaker, Airtight Type, Bookshelf Type Speaker system
Production years	early 1970s
Made in	Japan
Playback frequency band	50 Hz to 20000 Hz
Output sound pressure level	89dB/W/m (New JIS) 95dB/W/0.5m (Old JIS)
Impedance	6 Ω
Maximum allowable input	70W (weighted pink noise 24-hour guarantee)
Crossover frequency	1000 Hz, 4500 Hz
External dimensions	Width 350x Height 590x Depth 300 mm
Weight	Approx. 16 kg
Woofer	25 cm cone type
Mid-range	12 cm cone type
Tweeter	2.5 cm dome type
Enclosure	walnut finished bass-reflex structure
High-frequency level control range	+ 4 dB to -36dB
Features	multi-selector switch and a switch to disconnect the LC network so that you can drive the woofer, mid-range and tweeter directly

Key Features

ULM Magnetic Circuit with Notched Pole and Copper Cap

The magnetic circuit is the core of the SS-7200's design, and Sony applied theoretical modeling there to reduce distortion at the source. Unlike conventional drivers of the era, the ULM drivers have a notch machined into the center pole of the motor structure. A thick copper plating or cap over the notch was intended to stabilize the magnetic field and reduce harmonic and intermodulation distortion. Sony wasn't just measuring distortion here. It was trying to predict the root cause and remove it through physical design. The exact audibility of this feature remains undocumented.

Corn Paper Cone Drivers with Airtight Rubber-Coated Edge

Woofer, midrange and tweeter all use corn paper for the cone material, which Sony claimed gave an optimal balance between rigidity and damping. The edge surround is cloth treated with a special thin rubber, for airtightness and consistent mechanical behavior over time. The 25 cm woofer also has a metal voice coil bobbin, which improves thermal handling during high-power operation. The synthetic resin adhesive used in winding assembly was selected for both mechanical strength and resistance to heat degradation.

Direct Drive Mode via LC Network Disconnect Switch

The switch that disconnects the internal LC crossover network is one of the most distinctive features of the SS-7200. It bypasses the passive crossover entirely, so the woofer, midrange and tweeter can each be driven directly from separate amplifier channels. That makes bi-amping or tri-amping with external active crossovers possible, and it's aimed squarely at advanced users. Add the multi-selector high-frequency level control, and the SS-7200 is unusually flexible for customized systems.

Diffraction-Free Baffle with Streamlined Saran Frame

The front baffle is deliberately minimal - no decorative trim, no raised edges, nothing that could cause edge diffraction or sound wave interference. The baffle's frame is made of Saran, a type of saran-coated fabric, shaped smoothly without brims or flares. This prioritizes time coherence and clean wavefront propagation, and it reduces early reflections that could blur imaging.

Collectibility & Value

Owners report ongoing problems with driver reliability, particularly the midrange and tweeter units. Forum posts from Sony speaker enthusiast groups mention difficulty sourcing replacement midrange drivers, and at least one user noted a pair where both tweeters and one midrange had failed. Repair appears to be common - another owner stated they had at least five SS-7300s (a sibling model) in need of service, suggesting similar fates for the SS-7200. Even so, the speakers keep circulating in the vintage market. A pair sold at auction on March 29, 2024, and another listing on HiFiShark showed the model offered for €30 as of August 23, 2024. Whether that reflects working condition or parts-only value remains unclear. The original price was ¥27,000 (1 unit, around 1971), though contemporary listings suggest it was positioned as a premium product.

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