@TLS Guy This is really fascinating. If I understood correctly the two drivers are not playing the same signal?\n\nI'm going to come forward and just say what's on my mind; long time ago you mentioned a DIY competition that also has a category for less skilled builders who use some proprietary parts in building their projects. From that moment on I kept wondering how would a TL speaker sound using the UniQ from LS50:\n\n\nBut going for the full range sound in an enclosure like this one:\n\n\n\nFirst of all you are correct that the drivers are not playing the same signal. However they are playing the same signal at the range that the pipe is operating. If that were not the case, then it would not work. However the lower driver is 'shelved' to provide the correct amount of baffle step compensation. The upper tweeter is providing a fill in signal. Mainly it is providing for a fill in dip in response at 9 KHz.\n\nNow as to using the KEF driver you state, I have considered buying a couple of speakers to get the drivers. However, I'm worried I would buy them, measure them, and find that they were not suitable for TL designs. So I stuck with the SEAS drivers which are a well known entity and it worked out very well.\n\nThe full rangers you show are classic horns, Lowther fashion.\n\nHere are the specs from one of the ranges of Lowther speakers for horn loading. Note that the sensitivity is very high and the flux densities enormous. The Qts is very low. It is these features that make them the most suitable for horn loading then any other drivers on the planet.\n\n\n\nBack when I was kid and pre Thiel\/Small and long before computer assisted design, if you wanted really good sound in the home, your option was basically Lowther and then Lowther or Quad ESL after its introduction. The rest in the main were pretty awful. The Wharfedale Airedale getting just about a passing grade also.\n\nLowther PM 6 from the fifties era.\n\n\n\nOriginal Quad ESL and amps from the mono era\n\n\n\nWharfedale Airedale\n\n\n\nIt is so important to remember where we came from in all of this.