I’ve got four speakers in my living room. Two (larger) speakers are by the TV. The other two speakers are smaller and better, but because of the layout of the room, need to go in the “back” of the room (facing the TV). They’ll only fit if they’re mounted on the wall.
How far from the ceiling should they go? The ceiling is about 9 1/2 feet high. The speakers would be about 12 feet apart, and around 16 feet from the “front” of the room.
What signal is going to the rear speakers? Is this a surround setup or will the be playing the same signal as the front speakers?
Not really a surround set-up… wouldn’t I need a fifth speaker for that? It’s an identical signal to the front speakers.
For surround, yes you would need a center speaker, and the decoder as well.
As well as putting 4 speakers up, I don’t mean to rain on your parade, but if they are all playing the same thing, you may end up worse off then with just 2 speakers. First off the stereo effect may get screwed up because the rear speakers are reversed, and second, you the speakers may phase each other, resulting in reduced listening pleasure 
(it may sound like crap).
Perhaps you can tell us what you wanted to do, and we can figure out the solution. Was the set up for Movies? TV? Music? etc.
I’m a bit of an audio geek, and I want to be helpful.
It’s an all-purpose type set-up. It’s set up for all of the above.
The speakers don’t get reversed, but if it’ll sound like crap anyway, that’s worth knowing… what does that mean for me and the speakers to “phase” each other?
If you want a “poor-man’s” surround without a Dolby decoder, the rear speakers can be set up in what was known as “Hafler” or “bridged” surround. This is a classic technique from the '70s before all that fancy 18-channel digital stuff was invented.
Pay attention, lest you have barbecued amplifier for dinner. :eek:
The main speakers in front are connected in the usual way. The rear speakers are wired in series - the “+” terminal of one of them goes to the “+” terminal for the front left speaker and the “+” terminal of the other rear speaker goes to the “+” terminal of the front right speaker. A single wire connectes the “-” terminals of the rear speakers to each other and nothing else.
You can make the usual sort of cable run to each speaker, and just connect the “-” wires to each other behind the amp, rather than running a wire directly between the speakers and across the wall.
A [url=http://sound.westhost.com/project18.htm]drawing[/url of this should make it a little clearer.
The rear speakers can go pretty much anywhere on the back wall. Height is unimportant, and they’ll be fine wherever they look good - left-right symmetry to the fronts is important, though.
You said the rears are better than what’s up front by the TV. Why don’t you put the good speakers up front?
argh… one misplaced bracket. Here’s that drawing.
Without boring you to death. you risk the rear set of speakers partially canceling out sound from the front ones, and vice versa.
If you’ve ever played electric guitar or listen to some Hendrix you’ve heard it in action. Say we record a guitar, and then make a copy of the recording. When we play back both at the same time, they are in phase, which means the sound waves rise and fall at the same time. If we delay one of the recordings by a split second, they start to interfere with each other because the sound waves aren’t rising and falling in unison anymore, causing a whooshing type of sound. This is what is means to be out of phase. This was a pretty heavily used effect back in the day, and by just playing around right, you could get a cool effect instead of making it sound like crap. Flanging got it’s name from a person pressing their finger on the flange of the tape reel to slow it down slightly and induce phasing BTW. Now if you really phase it (keep in mind if we phase it too much it goes back into phase like a clock passing 6:00) one wave will be going up, while the other one is going down, and they will completely cancel each other out!
Anyhoo, any problems you would create with 4 speakers would probably not be noticeable, so I wouldn’t lose any sleep. If you are up for it check out Gotpasswords setup, it’s a pretty neat homemade setup.
Here’s a diagram of the poor man’s surround.
First off - stereo mains placement:
You should experiment a bit with the placement of your main front speakers to find what sounds best, but a couple of guidelines:
Speaker height should be such that the tweeters (high frequency transducers) are at ear height in the listening position.
Increased distance between the two speakers will result in a wider soundstage (better stereo separation). If you increase separation too far, cancellation at the listening position will become dominant.
Wherever you place them, angle them towards the listening position.
As for the rears, it is entirely possible to have a surround setup without a center channel (phantom mode), but the ideal placement of surround speakers is up high (seven feet or so), and not actually behind the listening position, but rather just slightly behind of directly to the side.
If you are using the rears as reinforcement on the same stereo channels as the mains, the same issue applies with respect to tweeter height, but your soundstage will quite likely go right out the window - whether this matters to you or not depends on how you like to listen to music. In a poor listening room (from an acoustic standpoint) you may not have good definition anyway, in which case you may as well use the additional pair of speakers to average out the frequency response curves. (What this means is that, since every speaker has a slightly different frequency response, small bumps and dips will cancel out at the listening position due to interference when more speakers are used). If you tend to move around doing other things rather than sitting in one spot listening, good stereo definition is probably not what you’re really after. Read on…
What you will notice as you move around the room, is that the sound you hear will seem to be coming from the speaker closest to you. This is due to “time alignment”, or lack thereof. If the balance control, and/or the fader if present are set to the center position, the only place in the room where you will hear sound at equal volume from all speakers is in the center. To solve this, you have two options. The first is to use very expensive time alignment electronics to get the sound you want. The second is cheap and deceptively simple: simply take advantage of the phase shift that occurs when speakers are wired in series (approximately a 15 degree phase lag), and wire all four speakers so that no pair is in phase, but not in direct cancellation either. You will have speakers in 0, 15, 195 (by switching polarity) and 210 degree phase, respectively. The end result of this will be sound which permeates the room at all listening positions and makes it difficult for a listener to tell exactly where it is coming from, regardless of his or her position in the room. The tradeoff, of course, is the absence of stoundstage definition.
Hope this helps.
-FK