I want to build a freaking wall of speakers

December 12, 2011 10:10 PM

I am planning a project for a new years party involving over a hundred speakers of assorted size and Ohm values , Basically the idea is to stack all the speakers to cover an entire wall of a room and wire them all up to an amplifier(s?) what would be the best way to wire them?

I have at my disposal , an endless supply of speakers , several high powered home theater systems and amps of various wattage and enough wire to connect all the speakers together... is there anything I'm missing ?

posted by 70klicks to home & garden (8 answers total)

Wire them up in series and parallel combinations so that they match the expected output impedance of the amps they're connected to?
posted by hattifattener at 10:14 PM on December 12, 2011

Wire them up in series and parallel combinations...
Two 8Ω speakers in parallel look the same (to the amp) as one 4Ω speaker. Two 4Ω speakers in series look the same as one 8Ω speaker. Lather, rinse, repeat.
posted by spacewrench at 10:23 PM on December 12, 2011

@hattifattener do you mean like two 4 Ohms together to make an 8 ohm ? could you explain a bit deeper ?
posted by 70klicks at 10:24 PM on December 12, 2011

Resistors in series add. That part's easy.

For resistors in parallel, the forumula is:

1/R1 + 1/R2 = 1/Rtotal

If R1 and R2 are 8 ohms, then 1/8+1/8 = 1/4 and the resistance in parallel is 4 ohms.

So if you have 4 8-ohm speakers, then create two parallel circuits (4 ohms each) and then wire those in series, and you're back to 8 ohms.

Note, however, that each one is going to take a quarter of the power fed to the whole system. If you do this with a lot of speakers, you're going to need a whomping big amplifier -- or several of them -- to run it.
posted by Chocolate Pickle at 10:53 PM on December 12, 2011

70klicks: Yes, as spacewrench and Chocolate Pickle describe in more detail.

In theory, the power output of the bank of speakers will be the same as what the amp could have put out through one high-power speaker. But I think they won't share power very well if the speakers are of varying wattages… actually, I'm not sure how to analyze that. You'd want to arrange your series-ing and parallel-ing so that not only does the final impedance come out to 8 ohms (or whatever the amp wants), but also so that the amp's power gets divided among the speakers in roughly the proportion they can handle. I'm sure there's a methodical way to do that but it's a bit late here.

(Also I suspect the frequency response of the whole thing will be very non-flat :) )
posted by hattifattener at 12:33 AM on December 13, 2011

Mind that you get the polarity of the speakers right, too. See for example http://www.techguys.ca/howto/speaker.html
posted by labberdasher at 1:35 AM on December 13, 2011 [1 favorite]

Ohms is only part of the problem: watts are the actual unit of power needed to drive each speaker, and those are (more or less) divided by each speaker, so 100w across 100 speakers is theoretically 1w of power to each. So, you'll need an amplifier able to drive all of those speakers, on the order of hundreds and hundreds of watts most likely. Trying to remember my EE 101, it's more complicated than that when using various resistors in series and parallel, once you get the same volts and amps split and replit and then run across a 4ohm vs an 8ohm speaker, and there's a chance that the path of least resistance might cross fewer points than you think and blow some speakers or fry an amp.

So, I'd suggest that whatever you put in your Wall of Sound be something you're willing to burn up spectacularly.

The better option might be to split one input signal between several amplifiers, each driving a simplified combination of speaker ohms and wattage.
posted by AzraelBrown at 7:59 AM on December 13, 2011

If you use speakers with too low an impedance (ohms) for the amp they are connected to you will fry the amp. The more speakers you add to an amp the lower the impedance. There are some amps made to handle low impedances but most don't do well with anything below 4 ohms at moderate to high volume. Speakers vary but are commonly 16 to 4 ohm. So you have to know what you have but that means in the very best case (amp handles low impedance and 16 ohm speakers) you're really only going to be able to plug 4 sets in before you get below 4 ohms.

To make it work: I'd use multiple amps, as many as possible and also pick up some impedance matching speaker selectors. The ones with a built in protection circuit will help you not kill your amps. Not as fun but why not do what the big guys do at rock concerts: have a few big speaker/amp combos blasting out the sound interspersed with a whole lotta impressive looking speakers just for show.

Also, google phase problems with sound so that you understand why frankenstereo sounds so strange and makes you feel vaguely nauseous.
posted by tinamonster at 1:07 AM on December 14, 2011