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Speaker wiring/ohms/?

PostPosted: Tue Jul 28, 2009 5:04 pm
by birddog
Looking for someone to point me to some links out there that explain speaker wiring, kinda the "speaker wiring for dummies" edition. Maybe something that explains how to wire an ohm switch so it could be used with different amps.
Doing some research for a speaker cab project I'm thinking on doing.
I think bignick may have got me into a situation here. :wink:

Wally

Re: Speaker wiring/ohms/?

PostPosted: Tue Jul 28, 2009 8:21 pm
by zhyla
If you ignore anything not related to resistance then this article is what you want:

http://en.wikipedia.org/wiki/Series_and ... l_circuits

Your switch is going to modify the circuit to achieve different impedances. Example, using the formulas on the above page you can calculate that 2 8-ohm speakers in series = 16 ohms, and 2 8-ohm speakers in parallel is 4 ohms. So you could have a switch that changes the speakers from being connected end-to-end to being connected in parallel (e.g. with both leads connected).

Draw out the two circuits you want on paper and then work out how you can change one to the other with a switch.

Re: Speaker wiring/ohms/?

PostPosted: Tue Jul 28, 2009 9:23 pm
by birddog
Thanks zhyla, thats a good start right there, don't know why I didn't find that while doing google searches.

Can anybody tell me what it does to speaker wattage when wiring say 2 8ohm speakers for 4 ohms ?
For say a 50w R.M.S. amp.

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 1:14 am
by thunda1216
Is your amp tube or transistor? In general, if it's a transistor (solid state) amp with an 8 ohm output, when you hook a 4 ohm load (lower resistance) more power is going to try to flow from the amp and can be potentially harmful to the amp. If you have a 4 ohm output and connect an 8 ohm load, less power is going to be drawn from the amp (so now your 50 watt amp is only putting out 25 watts).

If it's a tube amp, a lot of them have different ohm taps on the output transformer (mine has 4, 8, and 16 ohm outputs) and will put out the same power at any setting when properly set for the speaker's ohm rating. Again, if I use the 8 ohm setting and connect a 16 ohm speaker load, then my output power is going to reduced by 1/2.

Clear as mud, right? Hope this helps.

ty

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 1:33 am
by ricochet
I think he was asking about power rating for speakers. If they're all of equal impedance, their power ratings add up. Say you have two speakers rated at 50W, the total power they can handle is 100W.

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 4:01 am
by thunda1216
That would make sense, but he also asked about a 50 watt RMS amp in relation to ohms loads. I think he wants to know if he can get more power out of his amp (a 4 ohm load vs. an 8 ohm load with a 50 watt amp). Of course, I could be (and often am) wrong...

ty

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 2:12 pm
by birddog
Well actually your both on the right track.
Here's what I'm thinking, maybe this will get me to where I thinking I'm going.
A speaker cab that can be loaded with 2 10" speakers that are 8ohms.
I guess I could forgo the switch, the cab will come with 2 jacks. One for 4ohms and one for 8ohms. So I could use with either a 4ohm out amp or 8ohm out amp.
Will 8ohms speakers work to wire for 4 & 8 like I'm thinking ? Will the wiring either way affect the wattage ?
This seems like a simpler way for me to be able to use with a couple different heads.
I have a project head (vintage) coming, tube, 50w, 2 Ch, speaker jack says 4ohm out.
May be having evaluated for a mod that allows for one ch a boutique watts and one for full out as the is some world renowed amp tech in the area that does these I was going to check out.

Wally

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 2:47 pm
by zhyla
Two 8 ohm speakers can produce 4 ohms or 16 ohms, those are your options. If you disconnect one of the speakers (with a switch) then you would have 8 ohms.

Regarding power rating, theoretically two 50W-rated speakers combine as one 100W-rated speaker.

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 3:21 pm
by birddog
Tell me it aint's so :cry:
So to use 2 speakers with this 4ohm amp & wanting a 4ohm plus an 8ohm set up I need 4ohm speakers ? Oh, no that limits my speaker choices.
Is it to early to start drinking :|

Wally

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 6:12 pm
by ricochet
Two 4 ohm speakers give you 8 ohms in series, or 2 ohms in parallel.

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 7:04 pm
by birddog
So I can put in 2, 8 ohm speakers
Wire one circut in parallel & it will = 4 ohms :mrgreen:
Then I can wire the other circut series/parallel and it will = 8 ohms and I get what I want ?

If I read this right, help out an electronic ignoramus please !

http://www.usspeaker.com/speaker%20wiring-1.htm

Wally

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 7:58 pm
by zhyla
birddog wrote:So I can put in 2, 8 ohm speakers
Wire one circut in parallel & it will = 4 ohms :mrgreen:


Correct.

birddog wrote:Then I can wire the other circut series/parallel and it will = 8 ohms and I get what I want ?


No, the example on that page of a series/parallel circuit involves 4 speakers. You could take 4 8 ohm speakers, put pairs of them in series (16 ohm each pair) and put the pairs in parallel (16 ohm parallel with 16 ohm = 8 ohm).

Honestly I would do the 8 || 8 = 4 to match your head, and then have a switch to cut out one speaker to match your 8 ohm needs. Or do 8 + 8 = 16 ohms and plug your 8-ohm (tube) amps into that. It will be suboptimal but shouldn't be a big deal.

Re: Speaker wiring/ohms/?

PostPosted: Wed Jul 29, 2009 8:33 pm
by birddog
I understand now, Didn't really like the idea of only using one speaker if I'm going to build a 2 speaker cab, and with 8 ohm speakers I have so many choices.

What about using one of these, anybody ever use one ? Looks like a reasonable option.
Wouldn't need any footswitch.

https://taweber.powweb.com/store/2head.htm

Wally

Re: Speaker wiring/ohms/?

PostPosted: Thu Jul 30, 2009 9:35 pm
by thunda1216
You don't really need that to spend the bucks if you're amp is four ohms output - just use two 8 ohm speakers in parallel wiring and be done with it.

ty

Re: Speaker wiring/ohms/?

PostPosted: Fri Jul 31, 2009 2:17 pm
by zhyla
I'm not sure what's inside that Weber impedance matcher but it's unlikely to be transparent - more likely to have the downsides of an attenuator (isolating the speaker from your output transformer).

I'm not sure why you're building a 2-speaker cab, but there's nothing wrong with just using one speaker out of it, especially if it's an open-back cab. There's also nothing wrong with running an 8-ohm amp into a 16-ohm speaker load as long as it's a tube amp.