JBL UT-405
The JBL UT-405 is a super tweeter system built from the UHF driver in JBL's studio monitors - specifically the ring radiator from the 4344 mkII and 4344M. It's a 1-way, 1-speaker design around a 2.5 cm tempered titanium diaphragm. The diaphragm gets a nitrogen-gas quenching treatment to increase hardness, and high-frequency extension runs beyond 70 kHz. The unit was priced at ¥150,000 per pair around 2001.
How it's meant to be used is the interesting part. It has a built-in high-pass filter, so you connect it directly to your amplifier in parallel with your main speakers, and it takes over the top octave. A crossover frequency selector offers 16, 20, or 24 kHz, with a steep -18 dB/octave slope. A three-position output level switch (0 dB / -2 dB / -4 dB) matches it to the sensitivity of your mains. The filter circuit uses JBL's charge-coupled linear definition network. It applies DC bias to the capacitors to eliminate crossover distortion, which JBL claimed gave cleaner ultra-high-frequency reproduction.
It's a substantial little box: 190 mm wide, 122 mm high, 172 mm deep, and 2.1 kg. The front baffle is 33 mm of MDF to anchor the driver firmly, finished in high-gloss black. The cabinet itself is natural wood black ash. Input is through large gold-plated binding posts that accept banana plugs or Y-lugs. It ships with cone-type pinpoint spikes and spike receivers to isolate it from vibration and protect the top plate of your main speakers.
The record on the UT-405 is thin beyond these specs. No production years, no period reviews, and no current market pricing have surfaced. A 2020 want-to-buy posting from someone in Seoul seeking both the UT-405 and its sibling UT-505 suggests it has a following among collectors. Forum chatter confirms at least one owner used it as an add-on tweeter for Bose 901s with good results. A Japanese auction listing for a tested pair with original box and manual indicates units in good condition do circulate. One passing mention says the UT-405 might share lineage with the slot tweeter from the Everest DD55000, but that conflicts with the studio-monitor origin and remains unconfirmed.
- Type: 1-way super tweeter system
- Driver: 2.5 cm ring radiator, tempered titanium diaphragm
- Frequency response: up to ~70 kHz
- Impedance: 8 Ω
- Power handling: 50W (RMS)
- Output: 95 dB / 2.83V / m (at 0 dB position)
- Crossover: 16 / 20 / 24 kHz selectable, -18 dB/oct
- Dimensions: 190 × 122 × 172 mm (W×H×D)
- Weight: 2.1 kg
- Original price: ¥150,000 per pair (c. 2001)
For a fuller picture of the driver's heritage, the 4344M studio monitor is documented elsewhere on the Archive.
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