JBL 2307 / 2308 Horn & Lens
The JBL 2307 exponential horn and the 2308 slant-plate acoustic lens together make a bi-radial constant-directivity horn system. JBL used it in its flagship studio monitors. It gave controlled 80° x 45° coverage and a smooth frequency response for the midrange compression driver in systems like the legendary 4355.
Specifications
| Type | Bi-Radial Constant-Directivity Horn with Slant-Plate Lens |
|---|---|
| Components | 2307 Conical Horn + 2308 Slant-Plate Lens |
| Coverage Pattern | 80° horizontal x 45° vertical |
| Throat Diameter | 2 inches (50.8mm) - for 2441, 2420 series drivers |
| Construction | Polyurethane or fiberglass (varies by era) |
| Recommended Drivers | JBL 2441, 2420, 2421 compression drivers |
| Crossover Frequency | 1.2 kHz - 10 kHz (midrange to UHF) |
Design Overview
The 2307/2308 is JBL's approach to constant-directivity horn design. It is not a simple exponential horn. The system uses:
- 2307 Conical Horn: Provides the initial expansion with 30° nominal coverage
- 2308 Slant-Plate Lens: An acoustic lens with angled plates that shapes the wavefront to achieve wider, consistent coverage
The slant-plate lens introduces controlled phase shifts across the wavefront. That broadens the coverage pattern while keeping the frequency response uniform across the listening area.
The Bi-Radial Concept
JBL's "Bi-Radial" design gives constant directivity in both horizontal and vertical planes:
- Horizontal (80°): Wide coverage for stereo imaging and off-axis listening
- Vertical (45°): Controlled vertical pattern minimizes floor and ceiling reflections
- Constant Directivity: Coverage pattern remains consistent across the frequency range
A controlled pattern mattered in studios, where reflected sound could interfere with accurate monitoring.
Applications
JBL used the 2307/2308 combination in its most prestigious professional systems:
- JBL 4355 - Midrange horn in flagship studio monitor
- JBL 4344 - Four-way studio monitor
- JBL 4343 - Professional monitoring system
- JBL 4350 - Large format studio monitor
- JBL 2391 - Complete horn/lens assembly (2307 + 2308)
In the Wild
Featured in Resistor Magazine's restoration profile of Iwan Arjanto's vintage JBL collection. The 2307/2308 horn system is a key component in the JBL 4355 studio monitors that Arjanto has built from scratch for clients.
When building 4355 speakers, Arjanto had to source accurate measurements for horn mounting and positioning. The relationship between the horn, mid-bass driver, and cabinet boundaries is critical for proper time alignment and frequency response. JBL's original documentation for some aspects of the 4355 enclosure is limited, so the Lansing Heritage forum and Facebook groups supplied the information.
Construction Variations
The 2307/2308 was made in different materials over its production life:
- Early versions: Metal construction
- Later versions: Polyurethane or fiberglass for reduced weight and cost
- Color: Typically black or dark gray
Whatever the material, the acoustic performance stayed consistent when the part was properly manufactured.
Related Horn Assemblies
- JBL 2391 - Complete assembly combining 2307 horn and 2308 lens
- JBL 2311 - Alternative horn with different characteristics
- JBL 2390 - Flat-front Bi-Radial horn (2" throat, 100° x 45°)
- JBL 2392 - Horn/lens assembly with 2311 + 2308 (100° x 45°)
- JBL 2301 - Perforated plate acoustic lens (90° conical)
- JBL 2395 - Large slant-plate lens (140° x 45°)
Comparison to 2307/2311
JBL offered different horn/lens combinations for different applications:
- 2307 + 2308: 80° x 45° coverage (used in 4355)
- 2311 + 2308: 100° x 45° coverage (wider horizontal pattern)
The 2307 has narrower horizontal coverage than the 2311. That makes it suitable for nearfield monitoring where controlled dispersion is critical.
Maintenance & Restoration
The 2307/2308 horn assemblies are remarkably durable:
- Clean periodically to remove dust buildup
- Check mounting hardware for tightness
- Inspect for physical damage (cracks, chips)
- Ensure proper sealing to driver for optimal performance
Never modify or "port" the slant-plate lens. Doing so destroys the engineered phase relationships.
Legacy
The 2307/2308 represents an era when horn design was as much art as science. The slant-plate lens, in particular, exemplifies the innovative acoustic engineering that JBL brought to professional audio. While modern constant-directivity horns use different approaches, the 2307/2308 remains a benchmark for smooth, controlled dispersion in professional monitor systems.
Similar items on eBay
No exact JBL 2307 / 2308 Horn & Lens listings are live right now — these searches show current JBL and similar vintage audio gear on eBay:
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.
Documentation
- Lansing Heritage - Comprehensive JBL specifications, photos, and historical documents
- HiFi Engine - JBL manuals, service documents, and brochures
- Audio Karma JBL Forum - Community discussions and restoration guides