JBL L300 Active Biamplification Project

The Speaker

This project started for two reasons, my absolute love for horn speakers and tube amplifiers. I've been in love with small single-ended tube amplifiers since I first heard one, but it's really hard to find speakers to make sound well. On the other hand there is this classic JBL L300 from 1973 that I got in excellent condition, it's carries all the JBL legacy from the first horn speaker systems in the theatres in Hollywood in the 40s but it's not sensible enough with 93db/1W/1m of sensitivity. I've tried before to build no-compromise horn speakers (there is another post about it here), another beautiful enterprise but they tend to be huge

So this project is an effort to combine both worlds, the beauty of low-powered single-ended tube sound with the performance of a more modern horn speaker.

JBL L300 at home during one of the many testing sessions

The JBL L300 Summit was introduced in 1973 (see specs here), and it was one of the finest speakers you could buy at that time, only surpassed by the Everest series 55000 which is the next level, a huge horn speaker with 100db of sensitivity and a wide dispersion horn that is ideal for any low powered single end tube amplifier. Only 500 hundred units of the Everest 55000 speaker were built for the Japanese market. The current model JBL Everest 66000 is still in production and it's the top-of-the-line speaker of the brand.

The L300 has a 15 in woofer JBL 136a crossed over at 800 Hz with a JBL compression driver LE85 with a long horn and diffused providing a dispersion pattern of 120 deg horizontal and 40 deg vertical. The JBL 077 tweeter is the same of the JBL Everest speaker crossed at 8500 Hz. A three-way passive crossover is stored inside the speaker cabinet and it exposes 2 tone controls at the front.

This is the published characteristic of the JBL L300 as published by the manufacturer