Originally Posted by
Qwin
Mark - Coil Spacing - Yes You were about the fifth to mention it to me and I was allways open to the possibility after reading the test results on Troels Gravesen's site a good while back. Trouble was no one seemed to have tried it and this mod meant throwing originality out the window, so I was a bit hesitant.
It has cleaned up the sound, but only marginally, other things make as much or a bigger difference, internal wiring for instance. The early air core coils I have were wound quite loose, so that may also be effecting results, but renewing them would mean more expense with no guarantee of improvement. Having said that, one of the guys on diyaudio has replaced his early coils with the later ones wound on plastc bobbins and he recons there was a small improvement by doing this. All these things seem to be chipping away at the problem, but not really getting to the root of it.
The speakers are sounding very good, but I'm still not completely happy, I genuinely belive the drivers are capable of better and it is the x-over design that is the weak link. Changing to the Seas Tweeter makes a slight improvement to the top end, but it's not really necessary as the original unit is very good, this was more about long term sustainability as build quality on the originals was not fantastic and finding good second hand replacements will get harder.
Now I have a 6 channel Amp I may try going Active, or see if someone with a programable DSP will patch it in to my system for a try, just to see what kind of a difference that would make.
I don't belive an active solution is a cure all but with this speaker set up it may work, the drivers are pretty well matched and the x-over circuit is very simple with no notch filters or zoble networks, not even an L-Pad used, so the active circuit would just be providing the high and low pass filters. An easily adjustable DSP would also allow some exsperimenting with x-over points.
The bass crosses at 500Hz but this driver is also used in the ditton 25 and crosses at 2kHz in that application (if memory serves). Raising this a small amount would relieve the mid driver of some of it's low end duty where it is at it's limit. The Seas tweeter is flat way below the 5khz crossover point so again this could be reduced. I feel the 66 has a little too much emphasis on the mids and maybe tweeking the crossover points could give a more natural presentation. It would be trial and error and may not reep any benefits, but is up there to try. Once crossover points are established/confirmed a simple analogue opamp based active crossover could be constructed.
It's a major step to take but this hobby is all about stepping up to the challenge, so why not.
That's on the cards for after NEBO5.
Hi Ken, Never heard the Celestion 66's so looking forward to hearing yours at NEBO5.
Main system : VPI Scout 1.1 / JMW 9T / 2M Black / Croft 25R+ / Croft 7 / Heco Celan GT 702
Second System : Goldring Lenco GL75 / AT95EX / Pioneer SX590 / Spendor SP2