JBL 2405 Slot Tweeter (UHF Driver)
The JBL 2405 is an ultra-high frequency "slot" tweeter that extended the response of JBL's studio monitors well beyond the range of typical compression drivers. The bullet-shaped slot design is easy to spot, and the driver has a reputation for lasting.
Specifications
| Type | Slot Radiator / UHF Driver |
|---|---|
| Diaphragm | 3-inch aluminum with diamond surround |
| Magnet | Alnico V |
| Voice Coil Diameter | 2 inches (50.8 mm) |
| Nominal Impedance | 8 Ω or 16 Ω |
| Power Handling | 20W continuous program |
| Frequency Response | 7 kHz - 20 kHz (usable response to 40+ kHz) |
| Sensitivity | 110 dB/W/m |
| Dimensions | Approximately 115 x 115 x 140 mm |
Design Overview
The 2405 is slot-loaded. The diaphragm's motion is coupled to a narrow horizontal slot. That gives a line-source radiation pattern with good dispersion and minimal diffraction. The "bullet" shaped housing that gives the driver its nickname is actually a waveguide that shapes the output pattern.
JBL designed it to complement the 2420 compression driver in four-way studio monitors. The 2405 extended the system response well beyond 20 kHz, which covered the extreme highs of analog tape and early digital recordings.
Applications
The 2405 was used in JBL's flagship studio monitors and professional systems:
- 4343, 4344, 4345 studio monitors
- 4355 flagship studio monitor
- 4350, 4352 large-format monitors
- Consumer models like the L220 and L300 Summit
In the Wild
Resistor Magazine covered it in a restoration profile of Iwan Arjanto's vintage JBL collection. Arjanto specifically praises the durability of the 2405 alongside the 2420 compression driver.
"Vintage studio monitor speakers are more solid than JBL L100, but the horn and tweeter assemblies are unbreakable (JBL 2420 and 2405)."
— Iwan Arjanto
Restorers like the 2405 for that reason. Even after decades of use, these slot tweeters often need only minimal service to return to full operation. Arjanto notes that new JBL cones and networks need significant break-in time (50-100 hours) to sound their best. The compression drivers and slot tweeters deliver their characteristic sound immediately.
Variants
- 2405: Original Alnico version with diamond surround
- 2405A: Updated version with potentially improved surround materials
- 2405H: Later ferrite magnet version with similar performance
- 077: Similar slot radiator used in consumer speakers like the L65 Jubal and L300
Maintenance & Restoration
The 2405 is tough, but it may occasionally need service:
- Diaphragm replacement (original JBL or aftermarket diamond surrounds available)
- Cleaning of the slot aperture (carefully, to avoid damage)
- Re-magnetizing (rarely needed with Alnico versions)
- Terminal cleaning and connection integrity
The diamond-pattern surround on the diaphragm is a key identifying feature and should be preserved during any restoration work.
Related Drivers
- JBL 2420 - Compression driver often paired with the 2405
- JBL 077 - Similar slot radiator for consumer applications
- JBL 2404 - Smaller format slot tweeter
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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