scs@foxvax1.UUCP (S.C. Schwarm ) (08/02/84)
>> 3) put a separate amp (or receiver) in each room (mentioned by another >> contributor). This is probably the best solution, although it does require >> distributing high impedance signals that are susceptable to RFI and EMI. >> If you go this route, it is ESSENTIAL that you use high grade coaxial cable >>to distribute the signals, and that the shields are well grounded (at one end >> only, to prevent ground loop problems). A better method is to use 600 ohm balanced lines. This is what the broadcasters use. There are transformers required, but hi quality one are available at reasonable prices. 22 gauge twisted pair can the be used for the wiring. (Make sure you ground the center tap) You still need an amp in each room. Steve Schwarm
sjc@mordor.UUCP (Steve Correll) (08/03/84)
W. Mitchell cited one disadvantage of wiring multiple speakers in series.
Another, and more drastic, problem with wiring speakers in series occurs
when the speakers are different models and therefore do not have identical
impedance-vs-frequency characteristics. For example, suppose speakers A
and B both present a 4 ohm impedance at 400Hz, but A rises to 6 ohms at
2kHz while B rises to 12 ohms at 2kHz. Then A and B will share the voltage
equally at 400Hz, but B will get twice as much as A at 2kHz, and therefore
B will sound too bright while A sounds too dull.
Nonetheless, AR used to recommend series connection provided the speakers were
identical models. I never tried it myself.
Running the signal from the preamp through the walls to a separate amplifier
at each set of speakers seems sensible compared with searching for exotic
kinds of speaker cable. Some preamps can actually drive fairly low
impedance loads (the old Dynaco PAT-4, for example) and, if you're nimble
with a soldering iron, Signetics NE5534 opamps can supposedly be made to
drive 600 ohm loads.
--Steve Correll
sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc
--
--Steve Correll
sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjcmwm@ea.UUCP (08/05/84)
#R:clyde:-52200:ea:1000004:000:554 ea!mwm Aug 5 03:24:00 1984 /***** ea:net.audio / clyde!saf / 6:31 pm Aug 1, 1984 */ I agree with Bill's prefered solution: distribute the low level signal and run a power amp in each room. However, I think the way to distribute the signal is via balenced, shielded line such as is used for recording studios (and all high quality microphones). Steve Falco AT&T Bell Labs Whippany NJ /* ---------- */ I agree, but you should make the signals digital. That way, you can avoid having to worry about the signal quality on your cables. What's a bit between friends? :-) <mike
newton2@ucbtopaz.CC.Berkeley.ARPA (08/10/84)
I agree (since I was one of those who proposed it) that the most sensible solution is to run low-level audio everywhere and have locally sited power amps drive nearby speakers. HOWEVER, well-intentioned mythology isn't limited to insisting on stranded bus-bars (bifilar niobium-tin braid, helium-cooled?). While so-called low-impedance lines (low source impedance, that is) are a necessity, this is largely to avoid high-frequency roll-off due to the shunt capacitance of long lines. For interference rejection, low impedance is most resisant to capacitively-coupled crosstalk. Balanced lines, however, are usually overkill, although an indispensible marketing ploy, particularly in semi-pro gear- likewise the use of "Cannon" or XLR-type connectors. Believe me, no one needs or will long tolerate XLRs at home- they seem neat when you're a hobbyist pretending to be Captain Video, but if you really are a professional audio drudge and have a living room cluttered with that fabled "professional" gear, it gets old fast. By and large, consumer stuff is as good or better *in performance* as just about any commercial or recording studio stuff- the difference is in ruggedness, serviceability, conformance to interface standards and other costly features you can't hear. And consider how one would distribute "balanced" audio: unless you resort to transformers, which are *VERY* expensive at the quality levels which bear mentioning on net.audio, you will have to set up some variety of kludged differential input at each amp, and will also consider how to derive an allegedly "balanced" *output* to drive the line. I say allegedly because the concept of "balanced" is ill-defined (or underdetermined) in audio parlance- sometimes one means "floating", i.e. both signal conductors exhibit a high impedance to ground; sometimes "balanced to ground", meaning equal but not large impedances to ground. Sometimes the source is single-ended but the load is differential, and so endlessly on. Each configuration has its applications in interference-rejection or particular measurement applications (consider the power-amp as measuring the signal-plus-noise presnted to it and trying to derive the best estimate of the signal alone). In most domestic installations, low source- impedance single-ended circuits will prove adequately immune (if shielded!) to *induced* noise; the more likely source of problems is from ground-loop hum, and possibly RFI. As much thought will be necessary to eliminate this with all but the floating transformer-to-floating transformer setup regardless of whether single-ended or differential circuits are used. I'm not disparaging differential approaches, just trying to keep effort/benefit ratios in perspective. The first thing to try is lifting the AC power grounds of one or more units of widely dispersed systems. By the way, I don't know what to make of the prescription "common mode rejection should be 100 dB or more". Is this like saying everyone should be healthy, wealthy and wise? Just the twisted-pair *cable* is likely to have worse than 100 dB CMRR over DC-20 kHz, and that's only a tiny slice of the spectrum of interest to *real* audiophiles, eh?