http://www.audioheritage.org/images/...racts/L400.jpgAbove is an excerpt from JBL's 1975 catalog illustrating a "mystery speaker" referred to as the L400. The only description says, "Coming soon. The L400, with the promise that it will be the most exciting fusion of art and technology yet presented by JBL." It never came.
Originally, the speaker was planned to be a domestic conversion of the 4340 monitor, similar to the L300 conversion of the 4333 monitor. It would be a four-way speaker using a 15" low frequency driver, 10" midbass, 1" throat compression driver midrange and slot tweeter. The main development work in converting this speaker for domestic use centered on network design changes, a revised midrange horn and aesthetics suitable for a home environment
There were three separate attempts to bring this speaker to market. All failed before a final decision was made to cancel the project. The primary difficulty was developing a system that could be sold at a reasonable cost. However, there were also technical issues and no one was satisfied with the ultimate sound of the prototypes.