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Ohms FAQ
- Thread starter IvanMike
- Start date
OK Mike, thanks so much, man! It happens that in this other thread (http://www.talkbass.com/forum/showthread.php?t=156096&postcount=10) Petebass adviced me about another problem when wiring cabs in series (different impedance peaks on each cab). I don't want to go on with the same subject in two threads so, could we go on contributing in the other thread. Thanks so much!
ANDRUCA
ANDRUCA
That's what I thought (I forget the proper engineering term for this differential in distribution), so imagine my surprise when I see that SWR and others appear to recommend this mismatching practice in their documentation.IvanMike said:
I want to get an extension cab for my SWR "Black Beauty," which is a four-Ohm (!) combo version of the eight-Ohm "Son of Bertha" 1x15", because this amp reputedly blows this single driver with some regularity, but I don't feel right with SWR's various recommended eight-Ohm cabs. Seems that four-Ohm would be more appropriate and the amp is designed to run from four or two Ohms.
Would "daisy chaining" two parellel wired 8 ohm cabs to one amp output, and ditto to the second amp output (So 4 cabs, 2 daisy chained per output) result in a 2 ohm load?
I'm talking about running 4 8 ohm monitors in a 2 daisy chain configuration through a single power amp rated at 4 ohms with 2 outputs (if that makes sense - I'm not sure that I'm clearly wording it but...).
Does that make sense? Would the above configuration result in a 2 or 4 ohm load?
I'm talking about running 4 8 ohm monitors in a 2 daisy chain configuration through a single power amp rated at 4 ohms with 2 outputs (if that makes sense - I'm not sure that I'm clearly wording it but...).
Does that make sense? Would the above configuration result in a 2 or 4 ohm load?
Jeb said:
If you have one amplifier with two output sockets, and each speaker has two sockets, the chances are that each pair of sockets are wired in parallel. So, connecting two speakers to the amp, and a further speaker to each of the first pair of speakers, would put all four speakers in parallel, and they would give you a 2 ohm load in total.
If you modified the cables/plugs/sockets, so that your daisy chained speakers were each in series with a speaker connected to the amp, you would have (8+8) in parallel with (8+8), which would be 8 ohms total.
Jeb said:
It depends. They could be all 16 ohm drivers wired in parallel. Or they could be all 4 ohm drivers wired series-parallel. What they can't be is all 8 ohm drivers.
Just read this post today 'cause I am Power Amp shopping. HEY, I've got a great idea...why not "sticky" this thread/topic to help our continuous quest for amplification knowledge 
?
?
I first read this post when it was in its infancy but find myself coming back to it often to better my understanding. Please sticky it so I don't have to search for it all the time!!
Ivan Mike,
Thanks again, just another quick question, if you're still reading and responding to this post.
Some cabs like the GK 400rbh state that they can be either 4ohm or 8 ohm, do these cabs have the ability to switch from one to the other or do you buy them one way or the other?
Second, are there any amps out there that will work with 2ohm loads? I've been looking at the Schroeder cabs but I'm worried that if I buy a 4ohm cab and want to add to it later I'll need a second amp to power it.
Third, are there advantages to having a 4ohm vs 8 ohm cab other than more watts when running it alone?
Thanks as always for the expertise.
Thanks again, just another quick question, if you're still reading and responding to this post.
Some cabs like the GK 400rbh state that they can be either 4ohm or 8 ohm, do these cabs have the ability to switch from one to the other or do you buy them one way or the other?
Second, are there any amps out there that will work with 2ohm loads? I've been looking at the Schroeder cabs but I'm worried that if I buy a 4ohm cab and want to add to it later I'll need a second amp to power it.
Third, are there advantages to having a 4ohm vs 8 ohm cab other than more watts when running it alone?
Thanks as always for the expertise.
most cabs available in either 8 ohm or 4 ohm are either or - not switcable.
the one exception i'm aware of are some cabs by accugroove which have a top secret method of changine impedance via the "accuswitch"
doing a search you shold fibd the thread of heads that will do a two ohm load - there are more than you think
the big advantage of the 4 ohm cab is that it gets more power. soem 4 ohm cabs are just so darned loud you really dont need a second one. i still prefer the 8 ohm cabs so i can use more, but the catch is you have to buy, and transport the extra speaker
the one exception i'm aware of are some cabs by accugroove which have a top secret method of changine impedance via the "accuswitch"
doing a search you shold fibd the thread of heads that will do a two ohm load - there are more than you think
the big advantage of the 4 ohm cab is that it gets more power. soem 4 ohm cabs are just so darned loud you really dont need a second one. i still prefer the 8 ohm cabs so i can use more, but the catch is you have to buy, and transport the extra speaker
lol - you are absolved my childtommytoughnuts said:i am eternely in your debt ivanmike you are my new god
honestly, i've made myself many new "gods" since joining this site. i've learned quite a bit of stuff from lots of players, even some that i've gotten into some tiffs with. like anything on the internet, you have to wade through some misinformation but i've found this site to very good in terms of people presenting accurate info. when they don't, usually about six other members chime in and do damage control before long.
Ivan Mike
This post, and many others like it, have made all the difference in making my bass playing experience worth while. So I did what I've been planning on for months and upgraded to supporting member.
Of course it was a lot easier to coax $25 from my wife for the membership than it will be to get the $2000 I want for my new amp/cab set up.
Thanks again, the info you provide is truly like manna from heaven for those of us who have formal training that falls elsewhere.
This post, and many others like it, have made all the difference in making my bass playing experience worth while. So I did what I've been planning on for months and upgraded to supporting member.
Of course it was a lot easier to coax $25 from my wife for the membership than it will be to get the $2000 I want for my new amp/cab set up.
Thanks again, the info you provide is truly like manna from heaven for those of us who have formal training that falls elsewhere.
If anyone is willing to entertain another question.
Bridging--I just read Joris' fine FAQ and finally have an idea what this means, but still have a few questions. If I buy an amp with two channels--and bridge it to my cab it gets the power from both channels right? But, the minimum ohm load of the amp doubles--is this correct? So an amp with 2ohm minimum, if bridged would now have a 4 ohm minimum?
How does one accomplish the bridging--is it a control on the amp, a special connector?
Sorry, but I'm doing my homework before buying a new amp and keep coming across things that I don't fully understand.
Thanks in advance.
Bridging--I just read Joris' fine FAQ and finally have an idea what this means, but still have a few questions. If I buy an amp with two channels--and bridge it to my cab it gets the power from both channels right? But, the minimum ohm load of the amp doubles--is this correct? So an amp with 2ohm minimum, if bridged would now have a 4 ohm minimum?
How does one accomplish the bridging--is it a control on the amp, a special connector?
Sorry, but I'm doing my homework before buying a new amp and keep coming across things that I don't fully understand.
Thanks in advance.
Surgeon said:If anyone is willing to entertain another question.
Bridging--I just read Joris' fine FAQ and finally have an idea what this means, but still have a few questions. If I buy an amp with two channels--and bridge it to my cab it gets the power from both channels right? But, the minimum ohm load of the amp doubles--is this correct? So an amp with 2ohm minimum, if bridged would now have a 4 ohm minimum?
How does one accomplish the bridging--is it a control on the amp, a special connector?
Sorry, but I'm doing my homework before buying a new amp and keep coming across things that I don't fully understand.
Thanks in advance.
i wish i had foud Joris' FAQ sooner. i only got hipped to it about 3 months ago. glad i finally linked it to the top of this forum. it's a great read.
anyhow, yes, when you bridge an amp each side "sees" 1/2 of the load so a 4 ohm load "appears" to be a 2 ohm load to each side of the amp, hence an amp with a 2 ohm minimum per side limit, would have a 4 ohm minimum in bridge mono mode.
there are a few different ways amps are bridged. almost always there will be a switch on the back that should be adjusted when the amp is off. that switch will allow you to switch between "stereo" or "parallel/dual mono" to "bridge mono". after that, most amps have you use channel 1/A's input and gain control exclusively when running in bridge mono. as far as hooking up to the speakers, there's a few ways to do it. one of the most common is to have an amp with two banana jacks side by side in the back for the seperate channels. red is positive and black negative (BTW, banana plugs generally have a little tab on the side that is supposed to be connected to negative). when running in bridge mono mode a lot of these amps have you use one banana plug from your speaker cable connected sideways to both RED outputs from the channel 1 and 2 output jacks, treating channel 1 as positive. Other amps have a special bannana or speakon jack only to be used in bridge mono mode. No matter what, any amp will have a manual that lets you know how to go about doing it.
Passinwind
I know nothing.
- Dec 3, 2003
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Surgeon said:Bridging--I just read Joris' fine FAQ and finally have an idea what this means, but still have a few questions. If I buy an amp with two channels--and bridge it to my cab it gets the power from both channels right? But, the minimum ohm load of the amp doubles--is this correct? So an amp with 2ohm minimum, if bridged would now have a 4 ohm minimum?
How does one accomplish the bridging--is it a control on the amp, a special connector?
Typically there is a switch on the amp, and you wire the speaker output a bit differently than for stereo or dual or parallel mono operation. In a few cases, you use a specialized input cable as well.
You have the concept of the impedance relationships right, but it still is wise to check the manufacturer's specs to avoid unpleasant surprises. Some stereo amps will not bridge, usually because each channel already is bridged to begin with.
a little late to the party, but awesome post, mikey...
and yea, why the heck is this NOT a sticky?
and yea, why the heck is this NOT a sticky?
One thing to remember about bridging too. Normally you plug the banana connector to the red and black posts for the speakers. Red=hot. Black= ground. When you bridge, you plug the banana jack into only the red posts.
So what? Old news? Wait, if you aren't using the black posts, which red connector functions as ground? NEITHER.
They're both hot, they're out of phase with each other. Thats how they take 2 110V AC lines to make a 220v line. (Its actually the other way around, you take 1 leg of a 220v line and a ground = 110v). Instead of the amp putting out 100v (red) to ground (0v black), it puts out 100v+ (red) to 100v- (other red). Its really ac voltages out of phase, but you get the idea.
Think about your speaker cable. Nice sturdy construction, possibly terminating in a big beefy 1/4" jack with a steel shield threaded onto the plug to cover/protect the internal connection. to plug into the speaker?
That metal cover is now electrically HOT. If you touch it while you're grounded, you can get a shock. Depending on how many watts your amp is and how loud you are at the time, it probably won't hurt you too bad.
But if you drop a grounded cable on it, feeding mike cables behind your amp for instance, and the metal ground of the cable touches the metal shield of your speaker cord, you have a dead short across one channel of your power amp. That can't be a good thing.
I suggest electrical tape or something to protect the bare metal shield of the speaker cable. Just in case.
Randy
So what? Old news? Wait, if you aren't using the black posts, which red connector functions as ground? NEITHER.
They're both hot, they're out of phase with each other. Thats how they take 2 110V AC lines to make a 220v line. (Its actually the other way around, you take 1 leg of a 220v line and a ground = 110v). Instead of the amp putting out 100v (red) to ground (0v black), it puts out 100v+ (red) to 100v- (other red). Its really ac voltages out of phase, but you get the idea.
Think about your speaker cable. Nice sturdy construction, possibly terminating in a big beefy 1/4" jack with a steel shield threaded onto the plug to cover/protect the internal connection. to plug into the speaker?
That metal cover is now electrically HOT. If you touch it while you're grounded, you can get a shock. Depending on how many watts your amp is and how loud you are at the time, it probably won't hurt you too bad.
But if you drop a grounded cable on it, feeding mike cables behind your amp for instance, and the metal ground of the cable touches the metal shield of your speaker cord, you have a dead short across one channel of your power amp. That can't be a good thing.
I suggest electrical tape or something to protect the bare metal shield of the speaker cable. Just in case.
Randy
