Film-Tech Forum ARCHIVE: Wiring Subwoofers in parallel

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Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 05:47 PM:

I need to wire two subwoofers in parallel. Should each woofer have separate "home-runs" running all the way back into the booth or could a single pair of wires be split between the two woofers behind the screen.

Also, I have "home-runs" for each surround speaker in one of my auditoriums. There are 6 surround speakers being connected to each channel of the amplifier. So, 6 wires must be connected to each of the amps output terminals. Should all six wires be connected directly to the amplifier outputs or is there an easier way to get all of the wires to "fit" onto the amp outputs?

I hope my question is clear.

Posted by Paul G. Thompson (Member # 655) on 02-16-2003, 06:00 PM:

As far as the subwoofers are concerned, either way would work, as long as the wire is heavy enough.

What size wire are you using, and how long is the run? If it is AWG-12 or smaller, I definately would use both runs, one for each speaker. If it were AWG-10 or AWG-8, do as you please, but since the runs are in place, you might as well use them anyway. The higher the damping factor the amplifier looks at, the better it will be.

Be careful about the surrounds. Presuming each surround speaker has an impedance of 8-Ohms, connection all six in parallel will force the amplifier to look at around a 1-Ohm load. Most (if not all) amplifiers that I know of will not tolerate that type of a load. There are many amplifiers that will handle a 2-Ohm load, but I would suggest you check the data sheets on your amplifier to see what it will and what it will not handle for a load.

Bring all six "home runs" in the booth, use a barrier strip and wire it for a series/parallel configuration to keep the load at or slightly above what the minimum load specifications are of the amplifier, and don't go any lower than that.

If you are using a dual channel amplifier, consideration should be given to splitting the surrounds. Use one side of the amp to drive the left surrounds, and the other side to drive the right surrounds.

Remember - phasing of your speakers is extremely important.

Edit: I just re-read your post. I guess you don't have subwoofer runs after all. In this case, I would use 8-AWG as a single subwoofer run, and terminate the speakers accordingly. Some will say 10AWG is OK, but the heavier the better. Make sure you use twisted stranded wire. Romex will not do. Solid conductor wire should not be used, either. Consult a good electrical contractor to make sure what you do meets NEC codes for your application.

Posted by Manny Knowles (Member # 1171) on 02-16-2003, 06:17 PM:

I've seen wiring blocks to handle surround arrays. Maybe somebody has a better way of doing this, but here's the tidiest method I've seen:

The individual surround cables are fitted with spade connectors and then matched up and terminated on the block. A single pair of cables feeds out to (er, from) the amplifier.

Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 07:03 PM:

Paul,
Im pretty sure that the amplifiers I am useing can only handle a load down to 4 Ohms. So how would I wire six 8-ohm surround speakers to keep the load to 4 ohms.

Posted by Paul G. Thompson (Member # 655) on 02-16-2003, 07:36 PM:

If you are using a single amplifier or a dual amplifier operating in the bridged mode, the easiest way I know is to series connection of the rights, and then series connection of the lefts. Then parallel the lefts to the rights, and the amplifier will then see a 6-Ohm load. There are other things you can do also. But that'll cost some money, and I don't really see any benefit in it.

Steve Guttag, John Allen, Mark, Gordon, and a few others might have some better ideas, let's just see what they have to say. But, that's what I would do.

Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 08:48 PM:

Paul,
Wouldn't that give a 12 ohm load to the amps?

What if i paired up the speakers into three groups with series wiring. Then if i parallel wired the three groups together, the amp would receive an 8 ohm load. Is that correct?

Posted by Phil Hill (Member # 371) on 02-16-2003, 08:53 PM:

Tom,
I would wire the 3 speakers of each side in parallel, and then series both sides for a total impedance of about 5.3 ohms to the amplifier.

>>> Phil

Posted by Randy Stankey (Member # 64) on 02-16-2003, 09:00 PM:

Do you have six speakers per side? Or... Six speakers total?

If you have six speakers per side, may I suggest:

Hooking up two groups of three in series and then hooking those two groups in parallel. (12 Ohms load)

OR

Hook up three groups of two in series and then hook those three groups in parallel. (5-1/3 Ohms load)

Do whichever is closest to the specs that your amp wants to see. Probably the second option if your amp wants to see 8 ohms impedance.

For the subs I would home-run the wires and do the hook-up in the booth. This way, if you ever have trouble during a show you can do all of your troubleshooting/repairs from the booth without having to go into the auditorium. The only thing that would make you have to go out of the booth would be a cut wire or a blown speaker. If that was the case, you'd still have to go out to the house no matter which way you hooked them up. However, if you home-run the wires, you can use an ohm meter to test each speaker independantly and you can temporarily unhook one of the two speakers to do "process-of-elimination" testing if you want to. When both speakers are paralleled behind the screen you can't do that.

The only thing is you definately need big wires, just like Paul says.

Posted by Paul G. Thompson (Member # 655) on 02-16-2003, 09:00 PM:

Tom, the impedance of each side would be 12 Ohms. If the left bank of speakers was paralleled with the right bank of speakers, the total impedance would be 6 Ohms.

As you can see by Phil's and Randy's posts, there is definately more than one way to skin a cat. [Big Grin]

The thing that is important is making sure the load the amplifier sees is within specs.

Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 09:06 PM:

Paul
The speakers are 8 ohms. That would give me 24 ohms per side in series. Then if the left and right were paralleled that would give me a 12 ohm load. Am I wrong?

Posted by Steve Guttag (Member # 268) on 02-16-2003, 09:07 PM:

In series/parallel wiring...series is our enemy and should be avoided....

So if we have 6 8-Ohm speakers...parallel 3 speakers together for a load of 8/3 Ohms (2.67 Ohms)...do likewise with the next group of 3. Then series the two groups for a total amplifier load of 5.3-Ohms. This way, each speaker only sees a series resistance of 2.67 ohms.

Another advantage of the method described above is that if one speaker fails...the entire array is not brought down.

As to connections...barrier strips are nice and can make the installation look neat but...you are adding a bunch of connection points...each with the potential for failure. If you use crimps...you have just added yet more potential connection failure points. However, for troubleshooting, the barrier block method certainly has its strong points.

I normally wire-nut (using good grade wire nuts and properly sized for the bundle). If you are really paranoid about the wire nut connection...solder first.

As to two sub runs or one...separate runs are always preferred.

Steve

Posted by Paul G. Thompson (Member # 655) on 02-16-2003, 09:08 PM:

Tom, you are right! I really blew that one! Thanks for hammering me on that. I don't know my poor adding slipped by me. [Eek!]

Steve is correct in his method. One speaker failure won't bring down the entire array.

Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 09:33 PM:

Steve,
So basically all 3 of the + wires from one set of surrounds should be connected to the 3 - wires of the other set of surrounds. Then, the remaining 3 + and - wires would be connected to the corresponding outputs of the amplifier. Is this correct?

Posted by Phil Hill (Member # 371) on 02-16-2003, 09:47 PM:

Tom,

BINGO

>>> Phil

Posted by Paul G. Thompson (Member # 655) on 02-16-2003, 10:30 PM:

There is a special autotransformer that is made to match the impedance of the amplifier if the load goes below 2 Ohms. It eliminates the need for any series/parallel configuration. I presume autotransformers could be obtained for a 4 Ohm benchmark since many older amplifiers used today might not like a 2 Ohm load.

John Allen wrote an interesting article about this.

http://www.hps4000.com/pages/spksamps/surround_systems_don't_work.pdf

The autotransformer John Allen has will provide multiples of 2, 4, 8, and 16 times. It has a power capacity of 400 watts, and it was tested at 600 watts without distortion being present. They can be had for $100.00, and it might be "the way to go"....

[ 02-17-2003, 03:42 PM: Message edited by: Paul G. Thompson ]

Posted by Adam Martin (Member # 641) on 02-17-2003, 03:39 PM:

Ignore me. Stupid ubb. [Razz]

Posted by Paul G. Thompson (Member # 655) on 02-17-2003, 09:46 PM:

Adam, Brad got it solved. It did not like the ' in the don't.