Altec Lansing MR931 Compression Driver
The Altec Lansing MR931 is a high-efficiency compression driver made during the 1960s and 1970s as part of Altec's professional audio lineup. It was built for cinema, theater, and public address systems. It was commonly paired with multicellular horns and used in systems such as the Altec A7 Voice of the Theatre.
The MR931 has an alnico magnet structure and a phenolic diaphragm. It sounds dynamic and articulate, and it is particularly strong in the midrange. It is a component rather than a standalone speaker, and vintage audio enthusiasts, DIY speaker builders, and restorers of classic theater systems still hunt for it.
Specifications
| Parameter | Specification |
| Manufacturer | Altec Lansing |
| Model | MR931 |
| Type | Compression Driver |
| Production Era | 1960s–1970s |
| Impedance | 16 ohms (typical) |
| Sensitivity | ~104–108 dB (1W/1m) |
| Diaphragm Material | Phenolic |
| Magnet Type | Alnico |
| Throat Size | 1-inch |
| Horn Compatibility | Multicellular horns, 16-ohm systems |
| Typical Applications | Cinema sound, professional PA, studio monitors |
| Weight | ~2.5 lbs (1.1 kg) |
Historical Context
The MR931 came out when Altec Lansing dominated the cinema and theater sound market. It was often used as a high-frequency driver in systems that needed high output and reliability, such as the A7 Voice of the Theatre enclosure. Those systems were installed in movie theaters across the United States, before modern cinema audio formats arrived.
Altec did not sell the MR931 as a finished product. It went into larger horn-loaded enclosures. The alnico magnet gave strong magnetic flux at relatively low weight, and the phenolic diaphragm offered excellent rigidity and transient response, which suits clear, dynamic high-frequency reproduction.
Altec used multicellular horn designs with drivers like the MR931. This gave controlled dispersion and reduced high-frequency distortion.
Sound Signature
The MR931 sounds bright, punchy, and highly efficient, with a pronounced midrange presence typical of vintage Altec drivers. With a compatible horn and crossover, it offers exceptional clarity and dynamic range. It is very sensitive and has the alnico character, so it can sound bright or even harsh in mismatched systems, or when driven with modern high-powered amplifiers without proper filtering.
People often describe its sound as "lively" and "immediate," with a vintage character prized by audiophiles and restorers seeking authentic mid-century audio reproduction.
Maintenance and Restoration Tips
Because of its age, the MR931 may need maintenance or restoration to perform its best:
- Magnet Recharging: Alnico magnets can lose strength over time. If output seems low, consider having the magnet recharged by a specialist.
- Diaphragm Inspection: Check the phenolic diaphragm for warping, tears, or degradation. Replacement diaphragms and repair kits are available from vintage audio suppliers.
- Voice Coil Clearance: Ensure the voice coil moves freely and is centered. Re-gapping may be necessary if the driver has been overdriven.
- Horn Interface: Clean the throat and mating surface. Use appropriate gaskets to ensure an airtight seal with the horn.
- Corrosion and Terminals: Inspect terminals and wiring for corrosion. Replace if necessary to maintain signal integrity.
- Mounting Hardware: Verify that mounting screws and flanges are intact. Original hardware may be brittle or stripped.
Restore it carefully, because originality affects collectibility and value.
Collectibility and Market Value
The Altec MR931 is a desirable component among vintage audio collectors and DIY speaker builders. Its association with professional theater systems and its high-quality construction add to the appeal.
- Collectibility Rating: 7/10
- Market Value: $100–$300 per driver, depending on condition, originality, and demand
- Factors Affecting Value: Complete original finish, working condition, presence of original labels, and provenance (e.g., theater use)
Unrestored drivers in original condition often bring premium prices from purists. Fully restored units are favored by buyers who want functional performance.
Conclusion
The MR931 is not a standalone speaker, but it played a central role in A7 theater systems. Its efficiency and clarity keep vintage audio enthusiasts interested, whether in a restored A7 or a custom horn project.
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