Amp to run 3 pairs of speakers simultaneously.
September 13, 2008 2:13 PM   Subscribe

I want to wire my house for sound - have 3 pairs of speakers running off the same source. I have the speakers, I have the source, I have the cables, but I need the amp - what good amp can I buy (used or new) that'll allow me to run 3 sets of speakers simultaneously?

I want to run a pair of Castle Harlechs in my living room, a pair of Castle Durham 300s in my bedroom, and then I have a crappy pair that'll be 1 for the kitchen, 1 for the bathroom. The source is a Sony Pro CDP-2700 which has analogue and digital outputs.

I know Yamaha did a nice M-series range of amps, some of which had 2, others had 3 stereo outputs, but I read somewhere that these do not support simultaneous output - you can only select one pair of speakers at a time. I'm not 100% sure about this though.

I'm open to suggestions - I've been to Best Buy and the like and they just have multi-channel home theater amps. Obviously I like nice audio equipment, but I'm not going to get all audiophile bent out of shape about the amp - $300 new or used sounds a good limit. That said, I'd rather not drop 3 hundy on some crappy Sony amp that's going to make my nice Castles sound like a boom-box.
posted by forallmankind to Shopping (11 answers total) 1 user marked this as a favorite
You probably actually want to have different amps in each room so you can control the volume independently. Normally if you have multiple sets of speakers on a receiver, they all use the same volume knob. Pulling a line out off one amp and routing it to another doesn't involve anything even half-way exotic.
posted by aubilenon at 2:33 PM on September 13, 2008

Depending on the length of the run, you may notice latency in your sound. I know people that can pick it out in 20 foot runs in the same room. Remember you cable isn't as the crow flies so the next room might be a hundred foot of cable.
posted by wavering at 2:45 PM on September 13, 2008

Response by poster: Should've added - the amp will be in a reasonably central position, so all the speaker cables can be the same length.
posted by forallmankind at 3:32 PM on September 13, 2008

Best answer: Latency isn't an issue. Electrical signals move through cables at the speed of light. You'd need something like a 500 foot run to get even a millisecond of latency.

Some amps have switches for two sets of speakers, but I think your best bet is to run the amp signal out to a monitor switching box (check radio shack), then from that box to the various speakers.

Sorry I don't have time to do any product research for you. I usually like to provide a link or two but I'm out the door...
posted by Aquaman at 3:38 PM on September 13, 2008 [1 favorite]

Sorry, wavering, that's just not possible.

Electromagnetic energy moves at nearly the speed of light. (On preview, I see Aquaman has already mentioned it, but I have links and equipment suggestions!)

The speed of light is over 860,000 times the speed of sound.

That means that a 1cm difference in head position is 1500 times greater than that of 6 meters of wire. (As an aside, the speed of sound does cause audible latency problems at even small distances, which is why some studio monitors have speakers mounted at different planes, so the wavefronts are in alignment when they come off the drivers.)

Runs of hundreds or thousands of meters can introduce measurable, audible latency. In runs of tens of meters latency isn't usually measurable by means available outside the lab.

Moreover, even if latency was audible at these wire-lengths, it isn't going to make a bit of difference when you've got speakers in different rooms because it would be drowned out by the off-axis reflections and reverb you will get from, say, listening to what's able to get out of the bedroom door while you're listening to the living room mains.

Back on topic, if you put the amps in the rooms, I'd be worried about the degradation of line-level signal, and introduction of noise. If you plan on going this route, either convert to one of the Cat-5 solutions out there, or use XLR and truly balanced signals. I wouldn't run unbalanced audio more than about 25 feet without expecting interference.

If you put the amps near the main entertainment center, you'll want an RF remote setup.

Me, I'd probably go with the amps by the entertainment center. You could get several two-channel amps, or you could go with one of the multi-room amps installers use. I've no idea what the sound quality is like on those.
posted by tomierna at 3:57 PM on September 13, 2008 [1 favorite]

Electrical signals move through cables at the speed of light.

Not quite. Electrical signal moves though cable at some fraction of the speed of light, determined by the dielectric constant of the material the signal passes through. But I'm being pedantic, latency won't be an issue here.
posted by tracert at 4:01 PM on September 13, 2008

Latency isn't an issue. Electrical signals move through cables at the speed of light.

Misconception. An amp and speaker have a push-pull relationship like a piston, the sound is not just a message sent by telegraph to the speaker. If the wires to each speaker are not the same length, the difference in resistance will cause noticeable differences in the operation.

If your speakers are 8 ohms, and your amp is too, then hooking the three speakers up to one amp with three wires to each of positive and negative will result in about 3 ohms for the amp, and some amps will die from that. Instead, loop the wire from in positive, out negative, in positive, out negative, etc. That way the load will remain at 8 ohms.
posted by StickyCarpet at 6:28 PM on September 13, 2008

Er, StickyCarpet,

Even at the 40%-70% of the speed of light that tracert's linked wikipedia article states, at the slowest, you'd be looking at less than 1ms of delay for each 100 meters of cable. And, I stand by my statement that propagation through speaker wire is "nearly" the speed of light, because the speed of sound in air amounts to a rounding error when comparing it to the 40-70% of the speed of light we're talking about.

Differences in resistance between a 20' and 100' 12ga zip cable are low enough to be hard to measure by the lay person, and in any case resistance would only cause a lowering in volume. So, if it matters that much to the OP, make each room's pair of cables the same length to match the lowering in volume for slightly higher resistance in the cable.

Longer cables can have differences in capacitance as well, but unless your cables are longer than about 100', you won't see but maybe 3db loss in frequencies between 10-20kHz.

So: length of cable will NOT cause any noticeable latency, unless we are talking about very long cable lengths, i.e. thousands of feet - much longer than the wire paths in most houses. It might cause a slight lowering of volume or a measurable but usually unnoticeable high-cut above 10kHz, but only if your wires are longer than 50 feet, and less than 14ga.

As far as the series and parallel thing, you've got that a bit wrong as well. While a three speaker 8 ohm parallel set might be about 2.6 ohms, a three speaker series set would be about 24 ohms. Either would be bad for most amps. If the OP chooses to go with this one-amp, no-control of the satellites method, it would be best to series the two satellites and parallel that with the mains in the living room. That would get you to about 5.3 ohms, acceptably between the 4 and 8 ohms most consumer amps can deal with.
posted by tomierna at 7:27 PM on September 13, 2008 [1 favorite]

You probably actually want to have different amps in each room so you can control the volume independently. Normally if you have multiple sets of speakers on a receiver, they all use the same volume knob. Pulling a line out off one amp and routing it to another doesn't involve anything even half-way exotic.

The only really helpful answer so far. To elaborate, if you don't want to put an amp in each room, put all the amps in one room and run speaker wire. The overall point being, one speaker, one amplifier channel. That isn't 100% necessary in all circumstances, but it is the right solution.

This speaker impedance thing has come up many times before -- Speaker Ohmage -- but you really don't want to go down that road.
posted by Chuckles at 10:40 PM on September 13, 2008

All amps in one: something like this Onkyo, using the analogue "DVD" inputs for mains, side surrounds and back surrounds.

I would be pretty confident that even a cheap consumer amp wouldn't make my speakers sound "tubby", unless there was some sort of weird processing applied: low-power, low-distortion, linear-as-long-as-you-don't-clip-them amplifiers are a commodity nowadays.
posted by Monday, stony Monday at 7:30 AM on September 14, 2008

Response by poster: Yes - this is a horrible mess in the amp world that can be easily fixed with a monitor switching box. Thank you!
posted by forallmankind at 12:11 PM on September 14, 2008

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