JM-3

Why it mattered

1. 01

   In 1971 Harry McCune, Jr. was losing money re-coning blown drivers and stacking ever more Altec boxes to reach the levels large pop audiences demanded. When the big U.S. manufacturers declined to build him a tougher loudspeaker, he turned to John Meyer, whose Glyph system at Pepperland in San Rafael he had heard about.

2. 02

   Holding a blown Altec 604, McCune asked Meyer for a three-way loudspeaker in one enclosure, small enough for a jet cargo hold, as clean as the 604 but ten times louder. Chief engineer Bob Cavin supervised the project and carpenter John Burke solved the enclosure problems; the box was named for Meyer’s initials and its three bandpasses.

3. 03

   Roxy Music mixer Chris Michie, a former AIR Studios tape op, later called the horn-loaded JM-3 the “gold standard of ‘70s integrated sound systems.” After its success Meyer went to research acoustics in Montreux, where he patented a low-distortion compression driver.

4. 04

   McCune refused to sell the JM-3, keeping it as a rental item for top clients; the costly project nearly broke the company, and the policy limited the design’s reach. Clair Brothers heard a JM-3 at a stadium event before developing its S4, and Showco followed with the Pyramid, precursor to the Prism.

5. 05

   Integrated, processor-tuned loudspeakers only went on sale when Meyer Sound reworked the idea into the UM-1 UltraMonitor for Jefferson Starship in 1979. Meyer’s MSL-3 and MSL-10 descend directly from the JM-3 and JM-10, and the UPA, created in 1980 at Abe Jacob’s request for Broadway, is a less obvious descendant.

6. 06

   Kennedy's FOH survey describes the JM-3 as an active, pre-packaged three-way system with dedicated external processing and electronics.

Engineering record

Drivers

Two horn-loaded 15-inch Altec 421A woofers; one heavily modified Altec 290 mid driver on a Meyer-designed exponential horn, flanked by the woofers in the same vertical plane for time alignment; two Electro-Voice T350 tweeters.[3]

Enclosure

45 × 26 × 32 inches (H × W × D), Baltic birch ply with extra bracing; first box weighed 245 lb. Production wood cut by Hard Truckers, mid horns moulded in fibreglass, final assembly at McCune’s shop.[3]

Amplification

Passive box driven externally by three Crown amplifiers (DC-300 lows, DC-150 mids, DC-60 highs), modified by Cavin to drive two boxes per channel, via a four-conductor cable with Hubbell twist-lock connectors.[3]

Processing

One limiter per band, adapted from Meyer’s Glyph circuit, and Cavin’s zero-phase crossover upstream of the amps, avoiding the polarity flipping Meyer felt smeared timing.[3]

Performance

Crossovers around 400 Hz and 4 kHz; initially 70 Hz–14 kHz (±3 dB); 60° × 40° coverage.[3]

1976 revision

After his Swiss research Meyer extended the range to 40 Hz–16 kHz, and his patented low-distortion compression diaphragm treatment (U.S. patent 4152552) went into all JM Series boxes.[4]

Companion boxes

JM-5 subwoofer with four Gauss 18-inch woofers; later JM-7 subwoofer in the JM-3’s cabinet size; JM-10 array (1977), sold as replacing ten JM-3s but in practice six, with bucket-brigade delay for high-frequency alignment.[4]

Known flaws

Forward-mounted high-frequency horns gave two apparent apexes, so side-by-side splays lobed and combed while vertical stacks arrayed well. Batches varied slightly; there were no true handles; worn wooden skids exposed screw heads. Heavy alnico mid drivers could snap fibreglass horn throats until 128 remaining boxes were retrofitted with metal-and-foam cradles.[4]