Speaker Ohms......

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Godsguitarist

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Speaker ohms and PA

Hey guys!! I am about to possibly buy a PA (as some of you all ready know) this will be my first one, and I was wondering about amp loads (ohms). Is there anything like a basic "ohm formula"? For example, if I had 4 8 ohm floor monitors, is there anyway or any formula that I could use to determine the over all amp load if these were daisy-chained together? I REALLY, REALLY appreciate any input on this. That's my main question, but I have another one. Ok, our first plan was to buy a Mackie 808S Powered Mixer. The only thing about this, it would be kind of hard on the sound man because it just has "knobs" and it (the eq, level, etc) is set up vertically (plus, I like playing with sliders more than knobs :D). Or, from the sound man's and overall view, would it be better for us to get the mixer and a power amp seperately, such as a Behringer 2004 (for live use only :)) and a Carvin poweramp, probably 1500 watts. Does anyone have any suggestions? I really appreciate all replies and I thank all in advance.

Brandon
 
Bruce, good buddy, old pal, could you PLEASE explain to me how to work that equation? I'd love ya forever!!???!! Seriously, I'm not completely grasping on, specifically as to why they all are under 1, I'm presuming that represents a fraction, but even then, I don't get it. I really would appreciate it, who ever replies. Thanks in advance!!!
 
Ok Brandon...

if you run the speakers in parallel, the equation is
Rt = 1 / ( 1/R1 + 1/R2 + 1/R3 + 1/R4 )

where R1, 2, 3, 4 are the individual impedance values of the speakers and Rt is the total impedance.

if you run the speakers in series (daisy-chained, as you described), the equation is

Rt = R1 + R2 + R3 + R4

As an example - you have 4 speakers, 2 have an impedance of 8 ohms, 2 have an impedance of 16 ohms.
In series, the total impedance will be:
Rt = 8 + 8 + 16 + 16, which gives Rt = 48

In parallel, the total impedance will be:
Rt = 1 / ( 1/8 + 1/8 + 1/16 + 1/16 ), giving Rt = 2.67

This help any?

Bruce :)
 
Well, it kinda helped, but not completely. I think what you're saying is that if I have the speakers in configuration as you mentioned, in series with 2 8 ohm and 2 16 ohm, I'm going to have a total load of 48 ohms? Or would the actual impedence be 2.67 ohms? Is there a difference? OK, let's say I've got 4 8 ohm speakers, and I put them in series, of which I think is coming out of ONE of the amp outputs going into the "in" of the first speaker, from the "out" of that into the "in" of the next speaker, ect., how would I use this equation to get my total impedence (of which I'm guessing is lower than 2 ohms in this specific problem)? I really appreciate you giving your time to help me with this. I wouldn't be stressing it so much, but I will probably need to know how to use it so much in the rest of my music life that it's not even funny. Thanks again Bruce!!

Brandon
 
The diasy-chaining you're talking about means you're running in series.... in that example, that's a total of 48 ohms - very high - you'd lose a lot of power from your amp... if it's a 2 channel amp, then you could daisy chain 2 speakers in series giving you a total of of 24 ohms per channel, still high, but better than 48!
If you wire them in parallel as in connecting each pair of speakers via a y cable to the each amp channel, the load drops to around 5 ohms...

Sorry, Brandon I still feel like I'm not being clear... but I don't know how else to explain it! (a little help needed here you guys!!)

Bruce
 
Maybe the first command of electronics can help...

U = I R (Voltage equals current times impedance/resistance)

What the impedance story is all about; look at it this way: your amplifier puts a voltage over the load, which is in this case your speaker. Let's say, 4 Ohm. To make shure that this voltage is there, it has to deliver a certain current (this equation must always be true...), so it has to deliver a current of I = U/4.

Now, if you connect a 2 Ohm speaker to your amp, it will have to provide a current of I = U/2. This is double the current that it had to deliver in the case of a 4ohm speaker. If your amp was designed to drive a 4 Ohm speaker, this means that it has to deliver to much current, and you will blow your amp.

If you connect more speakers to one amp, for example, two 4Ohm speakers:
- series: if you connect them in series, the current will first run to one speaker, going to 4Ohm, then run trough the other speaker, again 4 Ohm. The resistance it met on its way is 4Ohm + 4Ohm or 8Ohm.
In the all-mighty equation this gives: I = U/8. Your amp delivers less power than in the case of just one speaker...

- parallell: in this case, there is a different current running trough both speakers. The voltage over the speakers is constant. Both speakers need a current of I=U/4.
The total current is I = U/4 + U/4 or I =U/2.
This means: your amp has to deliver twice the power it would have to deliver to drive only one speaker. This is a very common way of blowing amps...

If you get this, you can see where the formulas come from. Hope I didn't confuse you even more.
 
Ok...I get it.....

for the most part, but I have a question now. Ok, we're a young band and we're getting a PA. We are considering "in ear monitors" for some of their convienences, but let's say we use speakers. If we need four monitors, how could we do that? My understanding was that when you put them in series together, of which I think is what I'm doing, that your impedance number was lowered, and I base this on magazine ads and the like (of which can be rather dumb, hence marketing strategies and the like, but still there are numerous ones, specifically Fender and Carvin). For example, here's a quote from fender's website about their 16 ohm Artist Series Floor Monitors, "Each model features 16 ohm design (ideal for stringing several speakers together)." So that's kind of got me confused, but that's ok, I'll make it. I guess I will just have to go somewhere and talk it over with someone in person, no offense to anyone here because I really appreciate your inputs. Does anyone happen to have info on what would generally be better as far as monitors go, floor or personal? I may have to start a new thread. Thanks in advance!!

Brandon
 
Nope. In series the impedance is simply summed.

Think of it as your signal standing in line at the DMV.

The impedance is the time you have to spend in each line.

If you get referred to another line that's like in series.

If you're in parallel that's like you had someone holding your place 3/4 of the way toward the front of the next line. :)
 
Well crap. Does anyone have any suggestions for hooking up 4 monitors to a PA? I know this question is kind of open ended, but I have no idea where to even start. In this case, we may just get ear monitors, we'll see. Thanks to everyone for their input!!

Brandon
 
It's really easy.
If you connect the speakers like this:
Code: 
+---+
|   |------+-------+
|   |      |       |
|   |   +----+  +----+
|amp|   |spkr|  |spkr|
|   |   +----+  +----+
|   |      |       |
|   |------+-------+
+---+
The impedance will half. So two 8 ohm speakers will become 4 ohm. Thats the Rt = 1 / ( 1/R1 + 1/R2 + 1/R3 + 1/R4 ) formula.
But put em like this:
Code: 
+---+
|   |------+
|   |      |
|   |   +----+ 
|   |   |spkr|
|   |   +----+
|amp|      |
|   |   +----+ 
|   |   |spkr|
|   |   +----+
|   |      |
|   |------+
+---+
And it will double, so two 8 ohm speakers will be 16 ohm. Thats the Rt = R1 + R2 + R3 + R4 formula.
Makes sense, right? Think of the speakers as traffic jams and the wires as freeways, and current like cars, and it becomes obvious.

So, connecting four speakers to one output? Well, try this:
Code: 
+---+
|   |------+-------+
|   |      |       |
|   |   +----+  +----+
|   |   |spkr|  |spkr|
|   |   +----+  +----+
|amp|      |       |
|   |   +----+  +----+
|   |   |spkr|  |spkr|
|   |   +----+  +----+
|   |      |       |
|   |------+-------+
+---+
This the BOTH doubles AND halves the impedance making it a total of 8 ohms again. Unless your amp wants two ohms, then put it all in parallell.
 
Oh, ok, I got ya now!!! So, in other words, if we are to have to power four monitors, we are pretty much just going to have to get a seperate amp to operate them. Ok, now then, I unfortunately have another question, how would I run them in parallel, as far as hooking the speakers up to the power amp in parallel? Ok, for a specific example, let's say I get 4 8 ohm speakers, how would I connect them in parallel to a 600 watt (300 x 2 at 2 ohms, or 600 @ 4 ohms bridged) poweramp to them from the two 1/4" out puts it has?? I'm really sorry about all of these questions, but I need to know for when I buy, what I buy, etc. so I will know what my options are and see what I will need financially because, as previously stressed, we are on a very tight budget and are considering in the ear monitors for cost and basic convienience, although we're not positive just how convienient they will be, but that's beside the point, but if you would happen to have any info, I would be extremely grateful for your input on that as well, that being in ear monitors vs. floor monitors. I really, really, really appreciate your input on this. Thanks and have an awesome night!!

Brandon
 
The 300 x 2 at 2 ohms and 600 at 4 ohms bridged usually means that you basically have a stereo amp that works it's best at 2 ohms output, and also has the possibility to work as a mono amp at 4 ohms.

I'm not an expert on amps, but if I understand things correctly, it will probably work well at higher ohms too, so one solution would in this case to put two monitor cabinets in parallel to each of the channels. You put them in parallel by just connecting both sets of speakers to the amp output.
That would give you two sets of 4 ohm load. The amp would typically not give you 300 watts in a 4 ohm load, but rather 150 watts, but it would work. Also, the two sets would be controllable separately, so you could have different mixes in the different sets, having one set in front of the singer with his voice high, and maybe another set near the bassist and keyboardist with their instruments high,or something. Im just blabbing on at the moment, as you might notice, but anyway, that gives you an idea of what might be going on... :)
 
A L--->()spk1()---->()spk2()
M
P R--->()spk3()---->()spk4()

We run this way all the time. Floor monitor wedges are designed to run in parallel, so you really don't have to DO anything. Thats why you'll find two jacks on the speakers.

As far as in-ear systems, they're great, excellent. If you use them you'll never go back. I started out using this cheap Nady kind but got the good sure set. If you're using a comsole with 4-8 sends you can mix each one to the liking of each person. And it elliminates most feedback problems that used to happen on stage. The dynamics of the music will change, though. On stage becomes much quieter in general. I really love them
 
AAAHHHHHH!!!! That's what I was thinking!! I'm still not sure on what the difference is between wiring in parallel and series, but that's ok, I think it's a hopeless isue, for now at least. :) We're all debating the Personal Ear Monitor thing in our band. I personally think it would be really convienient, but we'll see. We've got some at church I'm going to use tomorrow to see if I like them. Yeah, the mixer I plan to get has 6 Aux's, but we'll probably only be able to get two transmitters if we get them. Thanks to everyone for their replies!!!!!

Brandon
 
Godsguitarist,

Maybe these slight modifications to regebro's very nice diagrams will help clear up your fuzziness on parallel versus series wiring:
Code: 
Parallel
+---+
|  (+)-----+-------+
|   |      |       |
|   |     (+)     (+)
|   |   +-----+  +-----+
|amp|   |spkrA|  |spkrB|
|   |   +-----+  +-----+
|   |     (-)     (-)
|   |      |       |
|  (-)-----+-------+
+---+

Series
+---+
|  (+)-----+
|   |      |
|   |     (+)
|   |   +-----+ 
|   |   |spkrA|
|   |   +-----+
|   |     (-)
|amp|      |
|   |     (+)
|   |   +-----+ 
|   |   |spkrB|
|   |   +-----+
|   |     (-)
|   |      |
|  (-)-----+
+---+

Notice that in parallel you hook the positive amp terminal to the positive terminal of both speakers, and the negative amp terminal to the negative terminal of both speakers. Assuming the speakers are identical, parallel wiring doubles the total sound output (+6dB) for a given input signal. In other words, the SPL of each individual speaker is the same as if it were hooked up alone. The price you pay is more current draw on the amp.

In series you hook the positive amp terminal to the positive terminal of spkrA, the negative terminal of spkrA to the positive terminal of spkrB, and the negative terminal of spkrB to the negative amp terminal. Again assuming the speakers are identical, in series the total sound output remains the same as a single speaker for a given input signal. In other words, each speaker is only half its original volume. The up side is it's an easier load on the amp, and you have twice the power handling of a single speaker.

hope this helps :)
barefoot
 
okokok... I hATe to nitpick... but this:

"say I've got 4 8 ohm speakers, and I put them in series, of which I think is coming out of ONE of the amp outputs going into the "in" of the first speaker, from the "out" of that into the "in" of the next speaker, ect., how would I use this equation to get my total impedence (of which I'm guessing is lower than 2 ohms in this specific problem)? "

is an example of wiring PARALLEL, if when you say "in" and "out" you mean the Jacks on the speaker box. (which, 99% of the time are wired parallel, right?) That WOULD give you 2ish ohms.... It is NOT series, even tho Bruce said it was. I think he just misunderstood. Usually those double jacks on cabs are paralell, and the Cabs THEMSELVES are wired series internally. so your 2x12 cab will have two 4ohm speaks wired series giving you an 8 ohm cab. If you chain two of them together using "ins" and "outs", thats 2 8ohm cabs in parallel, giving you 4 ohms again! killer.

xoox
 
Yeah, that's cool, man. That's kind of what I've gathered out of this, it would make the most sense and would explain alot of things I've seen and heard about. Hard2Hear mentioned this as well. Thanks again to everyone for their input!!!

Brandon
 
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