Film-Tech Forum ARCHIVE: Surround speaker wiring

This is topic Surround speaker wiring in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Richard May (Member # 2627) on 01-29-2010, 10:10 PM:

What is the best way to wire 3 surrounds on a side wall to bring them to 8 ohms(or 4 ohms)? They are 8 ohms each.

Posted by Jeremy Weigel (Member # 4208) on 01-29-2010, 10:35 PM:

What amp are you using?

Posted by Tony Bandiera Jr (Member # 2365) on 01-29-2010, 10:39 PM:

Just wire all three in parallel, if I recall the math correctly it'll work out to around 3.5 ohms...or in any event if you have a modern amp it would handle the load even if it's under 4 ohms.

The other, less satisfactory solution is to wire two of them in series, and the third one in series with a 75 watt or higher wirewound 8 ohm resistor. Then wire the two series sets in parallel which will get you 8 ohms.

Posted by Paul Mayer (Member # 355) on 01-29-2010, 11:13 PM:

Agreed, definitely parallel if your amp can handle it - with modern amps this should be no problem.

Doing series or series/parallel plays havoc with damping and phase issues.

Also, if you have enough cable, home run 'em, that is run each speaker's feed back to the rack. Makes it much easier to work on things later on.

Posted by Tom Wienholt (Member # 1510) on 01-30-2010, 02:26 AM:

Actually, I believe that wiring the three 8 ohm speakers in parallel would put you at 2.66 ohms.

Posted by Tony Bandiera Jr (Member # 2365) on 01-30-2010, 12:08 PM:

Thanks Tom..I was pretty sure it was around 3 ohms, and had for some reason thought it was 6 ohms...I edited my first post.

In any event most modern amps, especially for the surrounds, can handle that load, I know the QSC DCA's will.

Posted by Phil Hill (Member # 371) on 01-30-2010, 12:32 PM:

Handy Speaker Impedance Calculator

Posted by Gordon McLeod (Member # 33) on 01-30-2010, 01:10 PM:

regretably many older ones can't as they have issues delivering that much current

Posted by Monte L Fullmer (Member # 2797) on 01-30-2010, 01:45 PM:

..pretty slick little calculator, Phil .. thx for this link.

Couple of years back, I did a single house that just had side surrounds and also with three speakers per side...and I wired them in parallel attached to Peavy 400 amps.

Since surrounds isn't going to be doing the large output demand like the front speakers, these amps could handle the usage.

-Monte

Posted by Cameron Glendinning (Member # 3516) on 01-30-2010, 06:10 PM:

quote: Tom Wienholt
Actually, I believe that wiring the three 8 ohm speakers in parallel would put you at 2.66 ohms

There are other real world factors, long cable runs and cable type can also increase the ohmage resistance.

Posted by Tony Bandiera Jr (Member # 2365) on 01-30-2010, 11:29 PM:

Phil, I also thank you for that link!! [beer]

Posted by Richard May (Member # 2627) on 02-01-2010, 12:42 PM:

The amp they have will not handle 2 ohms. I may just have to split the surrounds to a third channel on another amp.

Posted by Sean McKinnon (Member # 612) on 02-01-2010, 01:25 PM:

quote: Paul Mayer
Doing series or series/parallel plays havoc with damping and phase issues.

I was taught to series/paralell to reach a value close to the resistance of the speaker that the amp will tolerate. For example if the surround speakers are 4 ohm's try to come out as close to 4 ohm's as possible. Is this not right, and if so why?

( I know that it will cause some speakers to be slightly louder than others so I always tried to put those at the front of the house)

Posted by Sam D. Chavez (Member # 1841) on 02-01-2010, 05:50 PM:

You should try to go for the lowest impedance the amp will feed so 4 Ohms is doable for all good amps except when in bridge mode.

Now, the subject of where to place the loudest speaker in your situation is the matter of some debate.

Putting it in the front works if you believe it needs to be louder as you are closer to the main channels and of course they are louder as you get closer to the screen.

I would tend to put the loudest surround speakers in the last one back or on the back wall at it helps reinforce the idea that the surrounds are coming from the side and back.

The patron sitting in the good seats should not get the idea the surrounds are coming from in front of them.

This is just me talking here.

I hear Steve getting ready to correct me as I write

Posted by Steve Guttag (Member # 268) on 02-01-2010, 08:40 PM:

Not really, I'm in total agreement with you, Sam. I also have been known to put in power resistors (similar wattage to the surround speakers) to ensure an effective match. I also use amps like the QSC DCA-1222...it will safely run in to 1.6-Ohms...so five 8-Ohm speakers can run in parallel. That normally covers all of my situations as I will increase channels after that.

Steve

Posted by Sam D. Chavez (Member # 1841) on 02-01-2010, 08:49 PM:

I'm humbled by having Steve Guttag agree with me. My life is now complete.

Posted by Sean McKinnon (Member # 612) on 02-02-2010, 12:33 PM:

Thank you guys, What you say makes perfect sense!

Posted by Tony Bandiera Jr (Member # 2365) on 02-02-2010, 04:57 PM:

quote: Paul Mayer
Doing series or series/parallel plays havoc with damping and phase issues.

While the damping could be a (minor) issue for surrounds I don't think the phasing issues matter at all, especially since you are NOT supposed to be able to locate surround information to any given individual speaker (or point source if you prefer), in fact it is remotely possible the phasing effect could enhance the surround field.

quote: Paul Mayer
....Also, if you have enough cable, home run 'em, that is run each speaker's feed back to the rack. Makes it much easier to work on things later on.

And even if you don't have enough cable, go buy more and home run those speakers!! If a speaker is ever blown out, it makes it easy to bypass/disconnect without having to take speakers down.

Any installer who doesn't home run those lines is a hack and not worthy of being called professional.

quote: Sam D. Chavez
I'm humbled by having Steve Guttag agree with me. My life is now complete.

LOL That's one sign of the apocalypse!! (Steve agreeing with Sam that is..) [Big Grin]

Posted by Steve Guttag (Member # 268) on 02-02-2010, 05:57 PM:

That is not true...I agree with well over 95.83% of what Sam says.

Posted by Phil Hill (Member # 371) on 02-02-2010, 06:01 PM:

I always agree with 98.6% of what Sam and/or Steve sez...unless I have a fever. [beer]

Posted by Gordon McLeod (Member # 33) on 02-03-2010, 01:21 AM:

Tony said "I don't think the phasing issues matter at all, "
hmm
phasing is probably the single most important issue in designing a good surround coverage pattern

Posted by Tony Bandiera Jr (Member # 2365) on 02-03-2010, 10:48 PM:

Gordon, I am referring to the very subtle shifts that MIGHT be introduced by the series connection of the speakers.

Obviously a deliberate out-of-phase connection of any part of the surround array will introduce problems.

Methinks you sometimes read more into posts than what is meant. [Big Grin]

I stand by my theory that any phase shifts from the series connection of the speakers is NOT detrimental and can, given the right conditions, actually enhance the idea of a diffuse sound field that is the intention of a surround array.

Posted by Scott Norwood (Member # 30) on 02-04-2010, 08:49 AM:

It still seems to me that a 70v system would solve all of the above-mentioned issues. It also makes the math easier, reduces wiring costs, and can make it easier to meet some electrical codes.

Yes, I know that this has been discussed before and, yes, I know that it isn't very popular in modern cinema systems due to the cost of the transformers.

Posted by Gordon McLeod (Member # 33) on 02-04-2010, 10:38 AM:

No I was not reading more in
Serries/Parrallel is in my book fine and I also home run everything but that said my biggest issue is usually with phase issues due to delays from bad placement
The big issue with 70v is it is expensive to do right

Posted by Gordon Bachlund (Member # 124) on 02-04-2010, 11:50 AM:

Gord is quite correct.

The speed of sound (1,125 feet/second at sea level) must be considered in speaker placement.

As the speed of current flow in copper conductors is about 186,000 miles per second, the method of circuitry is immaterial.

Posted by Sean McKinnon (Member # 612) on 02-04-2010, 02:23 PM:

The North Conway Twin in North Conway N.H. uses a 70 volt system for the surrounds. As I recall that was the ONLY theatre in my service territory that did [Eek!]

Posted by Gordon McLeod (Member # 33) on 02-04-2010, 02:37 PM:

70v is expensive if one wants to buy quality transformers that will have a decent frequency response and powerhandling
One can buy new amps for less

Posted by Steve Guttag (Member # 268) on 02-05-2010, 09:45 AM:

70V also can actually ADD to one's electrical code issues as 70V is not considered low-voltage.

With amps capable of driving 2-Ohm or less, well, the desire for 70V or similar constant voltage system diminishes. With QSC's DCA 1222 able to drive 5 speakers on each channel...again, the desire for 70V diminishes to about zero as the sound quality will likely be higher on the 5-paralleled speakers.

Steve

Posted by Jonathan Bodge (Member # 4072) on 02-05-2010, 09:36 PM:

Agree, I usually put the softer speaker up front in this situation.

Posted by Louis Bornwasser (Member # 3063) on 02-06-2010, 06:47 AM:

A "quick" measure of a power amp and its overall quality is whether or not it has a seriously good power rating at 2 ohms. Good amps do and bad amps do not.

I have personally driven 8 JBL 8330 on a string across one amp output times 6 for a one-night rental (48 speakers).

As regards series parallel; National Amusements for years used 7 speakers for sides. 4 in parallel, 3 in parallel, then series for the 4 and 3. We put the loud 3 in front where they could better compete with the louder screen speakers.

I only use Ashly FTX 2000 amps. Louis

Posted by Sam D. Chavez (Member # 1841) on 02-06-2010, 10:19 AM:

Tom Holman and THX recommended a slight loudness bias to the front, but I never agreed.

I like to use QSC 4 channel amps for the surrounds as then you can group and power the speakers any way you damn please.