Now that those bass drivers are in production again, it would be nice if someone posted design schematics. Would have to be a real enthusiast as most collectors would be leery about dismantling a rare vintage speaker. I assume the crossovers would have to be redesigned as the mids and tweeters would be long out of production.
That is an interesting speaker. I could hardly believed it when that picture popped right up on my feed. The carpentry of that speaker is very complex, so it was easily the most expensive speaker in the world when released. John Wright was the principal designer of the lines for the BBC monitor. Others involved where Peter Walker of Quad who provided the amps that were modified 405 II boards, and he designed the active crossovers. Jim Rogers was also involved as was Raymond Cooke of KEF. As told to me by John Wright, the key to dual lines is to have the F3 of the lines half an octave apart. John Wright died suddenly in 1999 of a heart attack. TDL was sold, as usually happens in the UK to pay death duties. So few of those speakers were made, I do not know how many.
Now those lines were designed before HT and did not allow for the incorporation of the subwoofer feed. In any event those TDL speakers were passive. The other issue is that they were designed before George Augspurger published his landmark paper on TL design in the AES journal in 2000. The landmark piece of that research is that the volume as well as the length of the pipe is crucial. I suspect that John Wright got is close by trial and error. I have never heard those speakers.
Raymond Cooke had a devastating stroke around 1990 and KEF was sold to the Gold Peak Group out of Hong Kong in 1992. Raymond Cooke died in 1995.
Anyhow when I was planning my AV room for the our lake home in the early 2000s I had the benefit of George's work.
I also made the decision that the speakers would be active except the tweeters, I did not thing it justified to employ Quad amps to drive speakers. I wanted a truly integrated full range design, and not have separated subs. I also wanted to include the SUB and LFE outputs. This has been achieved.
Care was taken to minimize phase shifts to preserve coherent sound. The crossover between the two lines is entirely acoustic to preserve phase coherency. The active nature of the speakers allowed me to make baffle step compensation fully adjustable to location.
Of course the elephant in the room with TL designs and especially a full range design is the size of the speaker.
Two of those TDL designs would really fill up a room.
My mains are huge and only fit in with the room specifically designed and built to take them. But they do take in John Wright's precepts for dual lines and take advantage of George Augspurger's enormous contribution.
So, the question becomes: - is it all worth the trouble? In my view it is a resounding yes. The bass quality is noticeably improved by several orders of magnitude, and truly like it really is.
So, I have feel really fortunate to have known and spoken to some of the real pioneers in all this.
