That's true- I didn't think through what I was proposing enough. If the pair of speakers are multi-way with passive crossovers, there could be quite a bit of mayhem at least in terms of filtering too, given the L-R wiring connection.
At least the more recent house (electrical power) wiring is 3 conductor usually 12 gauge, I think ("Monster Cable"). So an oddball idea that occurred to me would be to disconnect a run of electrical house wiring from the AC voltage and use that disconnected run to connect to a pair of remote speakers.
12 gauge copper wire has 1.6 Ohms of resistance per 1000 ft. So a 100 ft. run would be only 2 times 0.16 Ohm = 0.32 Ohm- that isn't going to affect damping. Or rather, any resistance will affect the damping factor, but that amount of reduced damping wouldn't be audible.
But anyways, doubling up on one conductor (the common one to the negative speaker output terminal of the amp) wouldn't increase the resistance in-series with each speaker system due to the connecting cable, would it?
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Your question made me review my statement about damping factor.
As a rule of thumb, to avoid “flabby” response, you want a damping factor above 20 at the speakers, 50 or so if you want to be really "Hi-Fi".
First of all, whether the effect of 100 foot 12 gauge wire would reduce damping enough for an audible effect depends primarily on the speaker impedance, at 8 ohms 100' 12AWG is OK, at 2 ohms, decidedly not.
Say we use an amp with an output impedance of .004 Ohms:
DF=8 /.004= Damping factor of 2000
Now, add a .32 Ohm speaker cable and the damping factor at the speaker is:
New source impedance = 0.004 + 0.32 = 0.324 Ohms (at the speaker)
8 / .324 = 24.69 DF, not "Hi-Fi", but "good enough" for 8 ohm remote speakers.
4/.324=12.34 DF (at 4 ohms) Not so good.
Bennett Prescott wrote an article about the subject:
http://campuspa.com/downloads/dampingfactor.pdf
Now on to your question- the series resistance on the shared common includes two parallel speakers in series with the amp output resistance, so becomes 4 ohms rather than 8, so with 12/3 AWG is not so good.
In addition, voltage drop in the wire would vary with the music mix.
If the music signal carried on the L/R were completely of different phase, as in a mix with everything panned hard left or right, the current carried on the common wire is the difference in current carried between the L/R, possibly less than either.
When the signal is in phase, as anything mixed center would be, the current in the common is the sum of the L/R, so most typical music which has vocals and bass instruments center would create more voltage drop with a shared common than with separate "-" wires.
The power loss due to the voltage drop for 100' 12AWG is only about 3% for 8 ohms, or 12% at 2 ohms, so whether double that drop would be acceptable is just a budgetary consideration.
Art
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I connected speaker wires, from amp + outputs, to a DPST switch. Wires from the DPST switch to + speaker binding posts didn't work. I moved wires, from the DPST switch, to - speaker binding posts and it still did not work. I do not understand why.
As a last resort, I connected speaker wires, from amp – outputs, to a DPST switch. Wires from the DPST switch were connected to - speaker binding posts and it worked. I moved wires, to the + speaker binding posts, and it worked. Can anyone explain this problem?
Thanks,
henrylrjr
As a last resort, I connected speaker wires, from amp – outputs, to a DPST switch. Wires from the DPST switch were connected to - speaker binding posts and it worked. I moved wires, to the + speaker binding posts, and it worked. Can anyone explain this problem?
Thanks,
henrylrjr
What problem, it works, right
?Your written descriptions are a bit hard to follow, if you completely draw out each of the wiring diagrams the problem you had initially will probably be apparent to you.
The OP uses a switch rated for 20 amps at 125 volts AC, it can handle switching 2500 watts all day long, you must play your system rather loudly or use a low rated switch to be concerned with arcing the contacts with audio
.
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1. IMO damping factor is a bogus concept. How well a driver is damped is described by system resonance magnification Qtc of the driver in a closed-box system. To keep things simple for the moment, I'd like to restrict what I have to say to the sealed system. From that it follows that resistance of the cable is of concern insofar as it might make Qtc of the system other than what it was designed to be. Cable resistance equal to 0.32 Ohm would only slightly raise Qtc of the speaker system, assuming DCR of the speaker driver of the system equal to about 6 Ohm, so it isn't of any concern.
2. I don't understand how you came to the conclusion that using a common wire to the virtual ground of the amp (the black speaker output posts on the amp) results in each amplifier output stage "seeing" a load that is the pair of speakers connected in parallel. Using the principle of superposition, for example the left channel (LC) amplifier sees the load of the LC speaker in-series with the parallel connection of the resistance of the common wire (0.16 Ohm) and the right channel (RC) speaker. So essentially the load to the LC amplifier is the load of the LC speaker and the 0.32 Ohm of the cable connected to the LC speaker.
3. I agree that there would be some voltage drop across the common wire to virtual ground, but it would be very small. The LC amp would see say 8 Ohm of the LC speaker system in series with 0.16 Ohm of the "return" section of the cable. So by voltage division the voltage drop across the cable would be 0.16/ 8.16 times the net voltage.
0.16/ 8.16 = 0.02
I suppose that there might be some mixing of the voltages applied to the pair of speakers (distortion) as a result of using a common "return" cable.
-cT
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Hi all,
I have been trying, without success, to use a dpst, to turn remote speakers on or off. The first setup tried was connecting the positive wires from the amplifier right and left channels to the common lugs on the dpst, then connecting wires from the dpst output lugs to both positive speaker binding posts. The negative wires were connected, without interruption, from the amp to the negative speaker binding posts. I used a meter to check the dpst and found both right and left common and output lugs had continuity, in both the on and off position.
I disconnected all wires from the dpst and found the unconnected positive wires had continuity. To reduce work in resolving the problem, I focused on the right channel speaker and disconnected it's positive wire.
I reconnected the amp positive wire to the dpst common lug and the speaker wire to the dpst output lug. The switch worked properly. What caused the continuity problem in the first setup. How do I make this work?
Thanks,
henrylrjr
I have been trying, without success, to use a dpst, to turn remote speakers on or off. The first setup tried was connecting the positive wires from the amplifier right and left channels to the common lugs on the dpst, then connecting wires from the dpst output lugs to both positive speaker binding posts. The negative wires were connected, without interruption, from the amp to the negative speaker binding posts. I used a meter to check the dpst and found both right and left common and output lugs had continuity, in both the on and off position.
I disconnected all wires from the dpst and found the unconnected positive wires had continuity. To reduce work in resolving the problem, I focused on the right channel speaker and disconnected it's positive wire.
I reconnected the amp positive wire to the dpst common lug and the speaker wire to the dpst output lug. The switch worked properly. What caused the continuity problem in the first setup. How do I make this work?
Thanks,
henrylrjr
Assuming you connected the positive L/R channels to the proper lugs on the DPST, and connected the proper DPST lugs to the L/R positive speaker binding posts, with the negative wires connected to the negative amplifier speaker binding posts, and there are no short circuits in the speaker wiring (errant staples, cut insulation, strands of wire between binding posts), and the switch works properly, it should work for turning on and off your remote speakers.
If it does not work, something is wrong, and I have no clue what, other than the suggestions above.
I 'm assuming you mean the negative wires are run directly, from the amp negative outputs, to the speakers negative binding posts?
Wouldn't the same results be achieved by connecting the amp negative outputs to the dpst and negative speaker wires run from the dpst to the negative speaker binding posts? In this setup the positive wires would run directly from the amp to the speakers positive binding posts.
Thanks,
henrylrjr
Wouldn't the same results be achieved by connecting the amp negative outputs to the dpst and negative speaker wires run from the dpst to the negative speaker binding posts? In this setup the positive wires would run directly from the amp to the speakers positive binding posts.
Thanks,
henrylrjr
Thanks for all the replies. The switch is installed and works fine. I was checking it incorrectly by testing continuity with all wires connected from amp to dpst and from dpst to speakers. That created a circuit that showed continuity, at the dpst in both on and off positions, as it should have. I disconnected the speaker wires and checked continuity at the wires and all was fine. That was a lesson, I will not forget, in how circuits work. Sorry for my misleading posts.
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