Altec 908 Compression Driver
1980s - 1990s
The Altec 908 is a high-frequency compression driver from Altec's 900 series, built in the ceramic magnet era. It gets confused with the 902 models, and often converted to them. It was made for professional audio work and has a few distinctive technical traits.
Specifications
| Type | High-frequency compression driver |
|---|---|
| Model Variants | 908-8A (8Ω), 908-16A (16Ω) |
| Throat Diameter | 1.4" (35mm) |
| Diaphragm Material | Aluminum |
| Voice Coil Diameter | 2" (50mm) |
| Magnet Type | Ceramic (ferrite) |
| Magnet Weight | Approximately 4.5 lbs (2.0 kg) |
| Nominal Impedance | 8 Ω (908-8A), 16 Ω (908-16A) |
| Power Handling | 30W AES, 60W program |
| Sensitivity | 109-110 dB SPL (1W, 1m) |
| Frequency Response | 500 Hz - 18 kHz |
| Recommended Crossover | 800 Hz or higher |
| Weight | Approximately 8 lbs (3.6 kg) |
Design Characteristics
The 908 shares many design features with the 902 series, but there are some important differences:
- Centering Rings: 908 drivers typically include centering rings that block the diaphragm from the space in the magnet chamber
- Voice Coil Assembly: Similar to 902 but with different suspension characteristics
- Phase Plug: Precision-machined phase plug optimized for smooth response
- Magnet Structure: Large ceramic magnet providing strong magnetic field
- Cooling: Adequate thermal management for professional use
908 vs 902 Comparison
The relationship between 908 and 902 drivers is complicated, and people often get it wrong:
| Feature | 908 Series | 902 Series |
|---|---|---|
| Centering Rings | Typically present | 902-8A: Usually absent 902-8B: May have rings |
| Conversion | Can be converted to 902-8B | 902-8A preferred by many purists |
| Sound Character | Slightly different due to centering rings | 902-8A: More open, natural 902-8B: Similar to converted 908 |
| Applications | Professional installations, some monitors | Wide range including studio monitors |
Conversion to 902-8B
A common practice in the Altec community is converting 908 drivers to 902-8B specifications:
- Diaphragm Replacement: Installing a 902-style diaphragm
- Removing Centering Rings: Some conversions involve modifying or removing the centering rings
- Re-labeling: Converted drivers are often referred to as "902-8B"
True 902-8A drivers, the ones without centering rings, are generally preferred by purists for a more open, natural sound.
Technical Performance
The 908 offers professional-grade performance characteristics:
- High Efficiency: 109-110 dB sensitivity allows for high output with modest amplifier power
- Wide Frequency Response: Capable of reproducing frequencies from 500 Hz to 18 kHz
- Good Power Handling: 30W AES rating suitable for most professional applications
- Low Distortion: Well-designed phase plug minimizes distortion
- Durability: Built for continuous use in demanding environments
Common Applications
The 908 was used in various professional and installed sound applications:
- Sound Reinforcement: Concert systems, theater installations
- Installed Sound: Churches, auditoriums, conference facilities
- Monitor Systems: Some studio and stage monitor applications
- Custom Installations: High-end home theater and music systems
Sound Characteristics
Users describe the 908 as:
- Detailed and Clear: Good high-frequency reproduction
- Efficient: High sensitivity for dynamic performance
- Robust: Can handle demanding professional use
- Slightly Constrained: Some users note a slightly more "closed" sound compared to 902-8A, possibly due to centering rings
- Versatile: Works well across various applications
Maintenance and Service
Common maintenance considerations for 908 drivers:
- Diaphragm Replacement: Original diaphragms may need replacement after heavy use
- Cleaning: Phase plug slots can accumulate debris affecting performance
- Inspection: Regular inspection of voice coil alignment and suspension
- Gasket Replacement: Original gaskets may deteriorate and need replacement
Historical Context
The 908 came out of Altec's ongoing work on compression drivers in the ceramic magnet era. It was not as famous as the 802 series, and not as advanced as the later 909 series with Tangerine phase plugs. It still filled a role in Altec's product line:
- Cost-Effective Performance: Offered professional performance at a competitive price point
- Technical Refinement: Incorporated lessons from earlier designs
- Market Position: Positioned between entry-level and premium compression drivers
- Transitional Design: Bridges earlier Alnico designs and later advanced ceramic designs
Legacy and Collectibility
Today, 908 drivers are valued for:
- Conversion Projects: Popular for conversion to 902-8B specifications
- Budget-Friendly Performance: Often more affordable than 902 or 802 drivers
- Professional Reliability: Built for demanding applications
- Historical Interest: Part of Altec's compression driver evolution
The 908 is not as collectible as the Alnico models, and not as advanced as the Tangerine-equipped drivers. It is a solid choice for practical use and conversion projects. Prices typically range from $200-$400 per pair depending on condition.
Images
The following sources may have images of this equipment. Always verify license terms and provide proper attribution when required.
Source 1: HiFi Wiki
- Link: HiFi Wiki
- License: Varies - check individual image
- Attribution Required: Yes
- Commercial Use: Unknown - verify on site
- Notes: User-contributed content. Attribution recommended.
Source 2: HiFi Engine
- Link: HiFi Engine
- License: User-contributed manuals
- Attribution Required: Yes
- Commercial Use: Reference only
- Notes: Great for specs/manuals. Request permission for images.
Source 3: Audio Database
- Link: Audio Database
- License: User-contributed
- Attribution Required: Yes
- Commercial Use: Unknown
- Notes: Verify license before use.
Source 4: Radio Museum
- Link: Radio Museum
- License: User-contributed
- Attribution Required: Yes
- Commercial Use: Unknown
- Notes: Attribution required for user photos.
Attribution Notice: This page links to external image sources. When using images from these sources, make sure you comply with their license terms. CC0 images require no attribution. CC BY and CC BY-SA images require attribution.
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