I'm considering building a new center channel with the following components.
Scan Speak 7" 18S/8535 woofer (in ~50l sealed box)
Focal 5" "W" sandwich mid
Focal T-120 Tiox tweeter
Behringer electronic xover
I've used the focal's in my main stereo and have been very happy. I also use the behringer for the main stereo.

My questions...
1.Are shielded elements really needed? I used a compass and found that if the compass is about 30" from the speaker, no magnetic field shift is indicated. Since I used a RPTV, the top of the TV is a little more than 30" from the CRT's. My guess is if the compass can't tell a difference, neither can the CRT's.

2. Anybody found a better xover than the behringer at a reasonable price. The behringer uses XLR connections, which are a pain. I ended up building my own XLR-RCA cables.

3. Is the 7100 coming out anytime soon. I'd like to use the 7100 to drive this setup. I think 100w/ch should be plenty if tri-amped. I thought I even saw an ad for it, but I haven't seen it on the web site.

4. Anybody know of a good relay to use to switch speakers. I definitely want to stick
a relay between the tweeter/amp so stops on/off thumps when power is switched.

5. Is there a better forum outside outlaw for DIY questions.

What is the source of the turn-on thumps? Is it the power amp or an upstream component feeding the power amp?

Most turn-on thumps are fairly low in frequency and brief in duration. I would not put a relay in the tweeter circuit. The crossover will attenuate the turn-on thump also.

If the unshilded drivers are OK with your RPTV, fine. I don't know if a compass is sensitive enough to use as an indicator in CRT applications. For conventional CRT tv applications, shielded drivers ARE needed.
If shielded versions of the drives you are interested in are available, I would use them so that the center channel speaker can be used with other TVs

Paul

The crossover will be between the preamp and the amp. Any thumps in the amp will pass un-attenuated directly to the tweeter. I've always protected tweeters in tri-amp configurations.
No plan on using the speaker with regular CRT TV types. For the larger screens, I think RP, plasma, or maybe the new projectors as they mature offer the best large format image. Regular CRT's just can't get beyond about 40" screens.

In my RPTV setup my main F/L speakers (sub section) are closer to the crt's than my center channel. My mains are not shielded but my center is. I have no problems with my nonshielded mains being within 24" of the closest crt.

Stabie, I understand now about your setup. I would suggest the possibility of a single capactior in line with the tweeter but a capacitor whose capacitiance value is large enough so that it is not affecting the high passed frequencies that you want to go to the tweeter.


But then again, you may not like that idea. Some people will argue that even one capacitor in the signal path, no matter how good it is, will adversely affect the sound quality. I would not agree or disagree with that arguement but recognize it as a valid arguemnt.

If the power amp is the source of the transient, then any protection would have to be between it and the speaker. If it were my setup, I would be reluctant to have a set of relay contacts inline with the tweeter. Instead of having the relay placing an open circuit for a set amount of time inline with the tweeter, how about making it a short circuit for a set amount of time. After the transient has passed, the relay opens and the contacts are effectively out of the signal path. Of course, timing is everything. Make certain that the relay is open (short is removed) before music is applied.

Just a thought.

Paul

------------------
the 1derful1

Stabie:

I have had problems with external electronic crossovers going into oscillation for an instant as the power is turned off, causing noise to be passed to the tweeters. I have dealt with it in two ways: I use a capacitor in line with the tweeter that has a cutoff of 1/2 the crossover frequency. It is cheap insurance in case an interconnect gets pulled, and has saved my tweeter on more than one occasion. The other is a timed delay turnoff device that turns off the crossover (or in your case any offending device) about 30 seconds after the power amps have shut off. This was constructed by taking a 24vdc coil relay and constructing a power supply with large amounts of storage capacitance so that the relay will remain pulled in for the required time after power shut-off. The relay controls the main AC to the crossover. This works like a charm.