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Multi-Way Conventional loudspeakers with crossovers

Anyone interested in Spica TC-50 mods?
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Old 18th September 2004, 03:03 AM   #1
PB2 is offline PB2  United States
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Default Anyone interested in Spica TC-50 mods?

I'm new here ( http://www.diyaudio.com/forums/showt...threadid=41118 ), started doing 1st order systems 30 years ago (I started young) but have moved on to higher order systems. I don't believe that phase linearity is important for an ultimate system but I'll take it if the cost is low, and am always looking for new ideas. The "phase linear" Spicas have been a curiousity of mine for many years and the crossover schematic for the TC-50 was recently posted on the web. I took a shot at simulating it in CALSOD and was able to come up with fairly good agreement with published data. There were some surprises from my perspective, I don't think this delay derived solution is anything special, I always used a touch of delay to bring my first order systems into phase alignment at the crossover point where it is most critical. I usually used quasi second order or mixed alignments, and believe the Spica would do better with a quasi second order filter on the tweeter. I also found that one of the low pass XO caps seems to do more harm than good in that it causes some serious peaking in the electrical response. I've never seen an analytical discussion of the Spica XO and would be interested if anyone knows of one. I've never heard the Spicas and was at first anxious to get a pair to hear and measure but now, having found that I probably would have done things differently, have much less interest. I got what I wanted, an understanding of the crossover, with the work I've already done.

I've prototyped something similar and a real woofer, but used much better drivers and my own higher order crossover, which has taken me off on a tangent. There was virtually no interest in the Spica page anyway, perhaps if there's more I'll continue with something closer to them. Progess is slow since I do this in my spare time.

Anyway, I'm real curious, if anyone has TC-50s that they're experimenting with I'd be curious to know if they sound better with the LP XO shunt cap removed as I discuss on this page:
The change will probably not be dramatic, and will require source material that excites the resonance and will probably be more audible standing on axis with the bass driver. It might simply be audible with sibilance, not sure.

Here for more background:
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Old 12th February 2005, 11:53 AM   #2
Co& is offline Co&  Netherlands
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I just read your mail about the TC-50 when I did a search for it on Google.
I bought my TC-50's in 1988, only to replace them with homemade ALTEC VOTs some 4 years ago. In the early nineties my hifidealer proposed a mod where the internal cabling should be replaced by a heavy gauge (1/10 inch) solid core copper wire. I went for the mod and found them even better in the midrange and more dynamic at both ends of the FS.

When I jumped into DIY, I dared to replace the filter with PP foilcaps and copperfoil inductors. At the same time I split the filter to bi-wire (filter outside the box!!!). I did take no notice of the bypasscaps and substituted for printed values on the components. All my diy experiences in the past years indicate that bypassing ruins the listenablity compared to a single capacitor.
There was a very slight imbalance between the speakers, reading on the internet makes clear that the matching was very tight and I should have used slightly different values for each filter. I didn't have the equipment to do this.
By the way the SPICAs sounded absolutely terrific and to some aspects I might prefer them to the Altecs, yet they have to low an efficiency for my present taste of tube amps.

Now they are collecting dust, with their filters in peices (dismantled for moving). One day I want to reinstall them and found your site very helpfull!

regards, Coen
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Old 14th February 2005, 02:21 AM   #3
PB2 is offline PB2  United States
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Hi Coen,

Thanks for your interest and taking the time to comment. Sure would like to know if removing that cap across the woofer improves the sound in any way. I'll probably get my hands on a pair of TC-50s sooner or later and would also probably outboard the crossover just to make it easier to experiment. Air core inductors should help a lot, they often make a difference in high current applications. I hear over and over raves about the TC-50s perhaps someone should revive them.

Pete B.
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