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Impedance etc

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OK, I've read this thread through and there's loads ( :) ) of great advice - assuming I understand it all correctly! Ohm I God!!

One thing though, that I am not sure about, is the issue of series vs parallel wiring!

Within the cab itself, presumably the speakers can be wired up either in series or in parallel? If so, what are the relative benefits of each? And one assumes that the info plate on the back of the box will inform the user of how the speakers have been wired if this is important?

On the other hand, can cabs themselves be connected to the amp in either series or parallel? If the amp has 2 jack outputs then if you want to connect two cabs there are two ways this can be done

1. Take one lead out of the amp into the first cab and then connect the first cab to the second cab - so only one output socket from the amp is being used. I used to do this with my old Trace Elliot stack, but using XLR connectors rather than 1/4" jacks...

2. Run two leads out of the amp, one into each cab, so that the cabs are NOT connected to each other.

Does it make any difference? Is one series and the other parallel? Does any of this make sense?!? :wacko:

Edited by Conan

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You don't need to worry about how the speakers are wired inside the cabinet and it won't tell you on the plate anyway.

What it does say on the plate is the total impedance of the cabinet and the power handling, which are the only details that matter to the user.

Inside, how the speakers are wired depends on how many there are and the impedance of each speaker.

Generally you cannot connect speaker cabs to an amp in series. With very few exceptions*, everything is geared towards parallel wiring. Unless stated otherwise, if there are two speaker outs on the amp then these will be wired in parallel.

If there are two speaker connections on a cab (to allow daisy-chaining) then these will be wired in parallel too.

So it makes no difference to use both speaker outs on the amp, or to daisy chain the cabs together - in almost every case* they will both be wired in parallel.

The only thing to note is that if you are daisy-chaining two cabs then ALL of the power for both cabs will go through the single cable connecting the amp to the first cab, so make sure this is a heavy duty speaker cable.

(*note - the reason I keep qualifying this is that there will be a serial wired amp or cab somewhere. I've never come across one but that's not to say there aren't some out there, which is why you should always read the manual or check what it says on the rear of the amp or jack plate).

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Cheers BOD2!

That's kinda what I thought but its nice to have it confirmed! Good advice about the cables BTW. I only found out recently that I had been using the wrong type of cables (i.e. instrument leads) to connect amps to cabs! Nobody tells you these things!! :wacko:

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How are 4 x 10 cabs normally wired? (eg: 400W Hartke 410 cab)
Is it 4 x 8ohm speakers wired in S+P to give 8 Ohm total resistance?
Is it possible to rewire them to give a total 4 Ohm impedance thus get more power from the amp?

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[quote name='Al Heeley' post='705381' date='Jan 8 2010, 12:46 PM']How are 4 x 10 cabs normally wired? (eg: 400W Hartke 410 cab)
Is it 4 x 8ohm speakers wired in S+P to give 8 Ohm total resistance?[/quote]
Yep, if the total impedance is 8 Ohm, then that would be the most likely scenario (alternative is 4x 32 Ohm drivers all wired in parallel)

[quote]Is it possible to rewire them to give a total 4 Ohm impedance thus get more power from the amp?[/quote]
No, not if you're running from a single amp output.

Of course, if you're running two power amps or a head with two separate power amp sections that can both drive into 4 Ohms then you can split the cab into two i.e two drivers (8 Ohms) wired in parallel will give you 4Ohms. Therefore the cab will go from a single input with 8 Ohm nominal impedance to 2x 4 Ohm.

Hope this makes sense?

Ta, Ian

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[quote name='Conan' post='688426' date='Dec 18 2009, 03:09 PM']Within the cab itself, presumably the speakers can be wired up either in series or in parallel? If so, what are the relative benefits of each? And one assumes that the info plate on the back of the box will inform the user of how the speakers have been wired if this is important?[/quote]

The benefits of parallel wiring:

If one of the driver goes open circuit for some reason, the other one will still work.

Um, that's about it.

There's probably cost benefits as well. 8 ohm drivers are the most common and therefore cheapest, 4 ohm and 16 ohm drivers are also available. This means it's easy to get a 4 ohm 2x10 or 2x12, or an 8 ohm 4x10 using the cheapest versions of the drivers.

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[quote name='Johnston' post='827897' date='May 4 2010, 09:16 PM']I have a Fender M-80 combo with a 1x15". Going by the interwebs it is putting out 80watts through the 15" but if you plug in another cab you get the full 160w it advertises on the front.

On the back of the Head it has two outputs the 15" is in one and underneath it says 160w rms at 4ohms minimum.

Now I got given two 12" PA speakers I was thinking of building into a cab to try and help with the muddiness of the 15" . Both speakers are rated at 40w 4 ohms.

Can I wire these up run them with the 15" and not blow my amp??[/quote]
Hmmm, not sure?

Sounds like the 15" in the combo is 8 Ohms, therefore putting another 8 Ohms in parallel will bring it down to the 4 Ohms required to get the full output power. To do this you'll need to wire the two additional speakers in [i]series[/i], then connect to the extension output on the combo.

HTH, Ian :)

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[quote name='algmusic' post='907771' date='Jul 28 2010, 01:01 AM']ok last question. I have two a 2x10 [email protected] and a 1x15 [email protected]

The amp is switchable 500w @ 4 or 8ohms

When I'm using the 2x10. I should keep it at 8ohms. but when I using a both the amp should be at 4ohms.. right?[/quote]

Provided however you are connecting the pair is parallel (mnost are, but anything with two jacks should be marked how they relate). Usually two jacks on the back of amps say 'Outputs (parallel)' or somesuch.

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[quote name='Mr. Foxen' post='907777' date='Jul 28 2010, 01:20 AM']Provided however you are connecting the pair is parallel (mnost are, but anything with two jacks should be marked how they relate). Usually two jacks on the back of amps say 'Outputs (parallel)' or somesuch.[/quote]

It actually doesn't say it's the terror bass. It must be parallel ?

Just being a geek. What would you do if wasn't then?

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Just had a quick 'skim' through this thread, interesting.

Just a thought, if your using 2 cabs with one head, theres alwys the chance of a dodgy lead, so one cab not working, you wont neccesarily notice with a band playing at full tilt, all the power goint to the one that is working could result in knackered cab. Had it happen to me years ago. so its always worth Checking your leads by pulling em one at a time, and having a good tug at the connections while you listen for anything untoward.

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I apologise now if I am repeating something already covered, but as I can't find the answer I thought I would post my question anyway....

I understand the combination of ohm rating in different wiring combinations and the effect on the amps power output.
I also believe the more air you shift in total the 'louder' the rig (if power/ohm matched efficiently).
But does anyone know if a 400w 8ohm amp into 500w 8ohm 4x10 cab produces more or less db than a theoretically identical 4ohm rig; i.e. 400w 4ohm amp into 500w 4ohm 4x10 cab?


My grey matter can't decided the outcome :) ! - thanks for any comments.


Juice

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Good question, but one I don't believe could actually be answered. I know many manufacturers will make 4 & 8 ohm versions of cabs, but don't know of any that make 2 identical amps that run at the different loads to test your theory. The wattage of the cab doesn't really get taken into account, just as long as it can handle what it's being asked to draw.

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[quote name='juice' post='977951' date='Oct 5 2010, 07:28 AM']I apologise now if I am repeating something already covered, but as I can't find the answer I thought I would post my question anyway....

I understand the combination of ohm rating in different wiring combinations and the effect on the amps power output.
I also believe the more air you shift in total the 'louder' the rig (if power/ohm matched efficiently).
But does anyone know if a 400w 8ohm amp into 500w 8ohm 4x10 cab produces more or less db than a theoretically identical 4ohm rig; i.e. 400w 4ohm amp into 500w 4ohm 4x10 cab?


My grey matter can't decided the outcome :) ! - thanks for any comments.


Juice[/quote]
So long as the enclosed speakers are identical in efficiency across the frequency range, I would think that the end result would be similar. The speaker coils are going to receive similar power, which is then used to drive the cones. At least that's what I think. As ever, I have no embarrassment whatsoever in being proved wrong, the only way to learn is to be brave enough to ask questions and have your reasoning tested. Good question as xgsjx says.

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[quote name='juice' post='977951' date='Oct 5 2010, 07:28 AM']But does anyone know if a 400w 8ohm amp into 500w 8ohm 4x10 cab produces more or less db than a theoretically identical 4ohm rig; i.e. 400w 4ohm amp into 500w 4ohm 4x10 cab?[/quote]

If the cabs are identical (bar the impedance) and the amps have identical frequency response, distortion and power output then the output will be identical. However I've yet to come across a loudspeaker where the 4 and 8 ohm versions have absolutely identical performance, let alone getting everything else to match!

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[quote name='alexclaber' post='979516' date='Oct 6 2010, 03:47 PM']If the cabs are identical (bar the impedance) and the amps have identical frequency response, distortion and power output then the output will be identical. However I've yet to come across a loudspeaker where the 4 and 8 ohm versions have absolutely identical performance, let alone getting everything else to match![/quote]

Thanks alex, i guessed that it is impossible to test the theory really and i'm not really sure why the question kept spinning roud my head. these things do niggle without an answer though dont they!

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[quote name='Slipperydick' post='971515' date='Sep 29 2010, 11:15 AM']Just had a quick 'skim' through this thread, interesting.

Just a thought, if your using 2 cabs with one head, theres alwys the chance of a dodgy lead, so one cab not working, you wont neccesarily notice with a band playing at full tilt, all the power goint to the one that is working could result in knackered cab. Had it happen to me years ago. so its always worth Checking your leads by pulling em one at a time, and having a good tug at the connections while you listen for anything untoward.[/quote]

If you're running two cabs of the same impedance in parallel and one fails, the remaining speaker will continue operating at about the same power level as before. There may be a slight increase in power delivered to it due to the fact that many power amps are not quite able to deliver twice the power when load impedance is halved. The important thing though is that if one cab fails, the load impedance increases and so the amp delivers less power. The remaining cab does not "soak up" the power previously delivered to the failed cab.

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[quote name='xgsjx' post='979730' date='Oct 6 2010, 06:38 PM']So the answer to your question is "yes maybe, but I doubt it". :lol:[/quote]
Lol :)

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[quote name='dincz' post='979755' date='Oct 6 2010, 06:56 PM']If you're running two cabs of the same impedance in parallel and one fails, the remaining speaker will continue operating at about the same power level as before. There may be a slight increase in power delivered to it due to the fact that many power amps are not quite able to deliver twice the power when load impedance is halved. The important thing though is that if one cab fails, the load impedance increases and so the amp delivers less power. The remaining cab does not "soak up" the power previously delivered to the failed cab.[/quote]

99% correct! The power it receives will not increase but you will be able to turn the amp up a little louder (i.e. delivering more volts though fewer watts due to the increased impedance) before clipping because the increased impedance will reduce the demands on the power supply.

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[quote name='alexclaber' post='980187' date='Oct 7 2010, 07:28 AM']99% correct! The power it receives will not increase but you will be able to turn the amp up a little louder (i.e. delivering more volts though fewer watts due to the increased impedance) before clipping because the increased impedance will reduce the demands on the power supply.[/quote]

100% correct! :) I once installed an extra power transformer in an amp to help the sagging power rails. A very dodgy solution though as there is likely to be some small phase difference between the two secondaries.

And it was HEAVY! Unlike my Compact which must be almost ready for shipping.

Edited by dincz

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Right...Ive read every post and am still completly lost!

Ive got a Warwick profet 5.1 Head (500w/4 ohms) and have been offered some new cabs - both Peavey - 1 is a 2X15 @ 4 ohms and the other is a 4X10 at 8 ohms.

Basically will this work and will i get alot from my amp this way?

Thanks in advance

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[quote name='jnrwarrior' post='987275' date='Oct 13 2010, 07:53 PM']Right...Ive read every post and am still completly lost!

Ive got a Warwick profet 5.1 Head (500w/4 ohms) and have been offered some new cabs - both Peavey - 1 is a 2X15 @ 4 ohms and the other is a 4X10 at 8 ohms.

Basically will this work and will i get alot from my amp this way?

Thanks in advance[/quote]

If you plan to run both cabs together, you might get a lot of smoke from your amp this way :)

The two cabs in parallel will give you 2.7 ohms - well below the 4 ohm minimum - and I read somewhere that these amps have thermal problems anyway.

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[quote name='dincz' post='987286' date='Oct 13 2010, 07:02 PM']If you plan to run both cabs together, you might get a lot of smoke from your amp this way :)

The two cabs in parallel will give you 2.7 ohms - well below the 4 ohm minimum - and I read somewhere that these amps have thermal problems anyway.[/quote]


so for this amp should i run 2 cabs that are 8 ohms each?

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You wont be able to use both cabs at once as your amp runs a min lead of 4 ohm & the 2x15 is a 4 ohm cab (tho you could rewire it to 8 ohm). 2 8 ohm cabs run at 4 ohm.

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