I don't think I would call a Quad 909 an old type amp.
The Shure crossovers make a nice platform for making basically your own crossover. They are very open and easy to work on. It was my idea to use a different larger driver to do the BSC for the smaller units, this offloads them a lot and reduces cone excursion significantly. The LFE signal is also captured and sent to the four 10" drivers.
I do not like to crossover in the speech discrimination band if possible. 2.5 KHz is still in the band, but I can't help it because of the break modes of the metal cones. I think the absolute worst region for crossovers is 1200 to 2500 Hz. I try and avoid crossing over in that range like the plague. There is also a lot of power in that range which stresses tweeters and blows them up.
The dispersion of the speakers is excellent. The black line is right out at 90 degrees.
This is the waterfall plot.
You can see at 2.5 KHz the crossover is not quite perfect, they never are, but it is very good. The vertical dispersion is obviously controlled, which is what you want as that reduces room problems from ceiling and floor reflections. Great care was taken with the crossovers and I followed Joe D'Appolito's teachings on MTM to the letter in the design. I used George Augspurger's mathematical model in the design of the lines.
This is the FR in the rear center listening position both speakers operating
There are no special room treatments and no room Eq. There is nothing amiss above 35 Hz. There is a rise to 27 Hz from 40 Hz but this just gives a little reinforcement to the 32 ft stops! It does nothing unpleasant.
The room is evenly filled with sound
This is the FR of the center line TL speaker. This was a difficult one for me. It uses 2 of the SEAS Prestige coaxial drivers. The lower driver is the main driver with cross to the tweeter at 2.8 KHz. I was careful to maintain the same phase response as the LR mains. The upper driver is used for active BSC. Unfortunately these drivers have a major suck out at 9 KHz which is audible. I had to equalize this out using the tweeter in the upper driver. As with all centers this design was difficult to say the least. However the result is satisfactory.
On axis response and impulse.
The waterfall plot.
The speech discrimination band is very smooth. The line is properly damped rolling off second order from an F3 mid 40s like the mains upper lines. The integration with the left and right speakers is seamless. Speech and all dialog are clear and natural.
Since you seem so interested in transmission line speakers, here is the FR and impulse response of my rear backs. The bass line uses two venerable KEF B 139 drivers. This is the grand daddy of all TL drivers, and was the one used in the great TL research project at Radford Audio. The two mids are from Dynaudio who assisted with this project and the tweeters are now Eaton due to a recent failure of a Dynaudio D 21 AF. The crossover between the lines is active at 180 Hz and the other drivers cross first order at 900 Hz and 5 KHz.
This was an horrendous project that took 10 years starting in 1984.
The frequency response is very good considering this almost impossible design brief.
However if you do a project like that this is the waterfall plot.
However there is a presence and sparkle about those speakers that is very attractive.
TLs just spoil you and after living with them nothing else will quite do.
I do not intend to give up my Panny Plasmas any time soon. I much prefer the color shading to anything available currently.
Finally this studio is a blend of old and new which is a big part of its fascination for people. For most of the equipment I'm the original owner. The three Revox A 77 are machines I restored from wrecks, the Revox A 700 and the very rare Brennel Mk 6 I have had since new.
