impedence question

[dfgh11]

my maths is terrible so although understanding ohms law is probably quite simple, no one has yet simplified it enough for my primative brain to handle. So my question is this: I have a pair of 4ohm(150w) monitors and a pair of 8 ohms(50w) monitors. I would like to hook them up through some sort of 4way/2way control box, but have no real idea of what the resulting impedence would be by doing so. My amp can take 250w rms 4ohms 150w rms 8ohms.

all help appreciated.

 

[mshilarious]

my maths is terrible so although understanding ohms law is probably quite simple, no one has yet simplified it enough for my primative brain to handle. So my question is this: I have a pair of 4ohm(150w) monitors and a pair of 8 ohms(50w) monitors. I would like to hook them up through some sort of 4way/2way control box, but have no real idea of what the resulting impedence would be by doing so. My amp can take 250w rms 4ohms 150w rms 8ohms.

all help appreciated.

If you run 4 ohms and 8 ohms in parallel, you'll have 2.7 ohms. In series you would have 12 ohms. Thus in order to use all four monitors together, you would need a series-parallel circuit in your control box, which would give you 6 ohms for the four monitors on a single channel of the amp. If the amp is two channel, you could run both 8 ohm monitors off of one channel, and one 4 ohm monitor off of the other.

 

[dfgh11]

Yes it does have two channels but if I hook my 150w speakers through one channel wouldn't that under power them, considering that the amp is 250w rms or would it use what's available from the other channel?

 

[Farview]

If you want to be equal on both sides, you will need to run one 8 ohm and one 4 ohm on each side, in series, giving you 12 ohms. There really is no good way to put this together. Are these floor wedges for your band or control room studio type monitors?

 

[mshilarious]

Yes it does have two channels but if I hook my 150w speakers through one channel wouldn't that under power them, considering that the amp is 250w rms or would it use what's available from the other channel?

Speaker ratings aren't like light bulb ratings, because a power amp doesn't provide a standard voltage. Thus a speaker rating doesn't mean that it will consume 150W, it means that is the max you should drive it.

If you hook one 4 ohm speaker into one side of your amp, then the max power output of the amp is 250W. That of course could be a bad thing for your speaker, since that exceeds its rating of 150W.

With two 8 ohms speakers in parallel into one side, they each could be powered to 125W, again a bad thing for 50W speakers

So with that setup, you'd have to be sure not to crank the power amp too much.

With two sides of 12 ohms total, your speakers are safe; although your amp isn't working at capacity, you don't want it to with the cabs you have. However you will need to wire your cabinets to work in series.

Farview is correct in that there's no way to really balance this. If you balance the impedance on both sides of the amp, then the amp is as happy as possible, but with cabs of different impedance, the volume at each speaker will vary (not only with power but also the sensitivity of the driver itself). This is why one usually tries to get identical cabinets with the same impedance, often 8 or 16 ohms, which enables you to use a lot of cabinets without dropping below a single amp's impedance rating.

 

[dfgh11]

. Are these floor wedges for your band or control room studio type monitors?

They are studio monitors.

Speaker ratings aren't like light bulb ratings, because a power amp doesn't provide a standard voltage. Thus a speaker rating doesn't mean that it will consume 150W, it means that is the max you should drive it.

If you hook one 4 ohm speaker into one side of your amp, then the max power output of the amp is 250W. That of course could be a bad thing for your speaker, since that exceeds its rating of 150W.

With two 8 ohms speakers in parallel into one side, they each could be powered to 125W, again a bad thing for 50W speakers

So with that setup, you'd have to be sure not to crank the power amp too much.

With two sides of 12 ohms total, your speakers are safe; although your amp isn't working at capacity, you don't want it to with the cabs you have. However you will need to wire your cabinets to work in series.

Farview is correct in that there's no way to really balance this. If you balance the impedance on both sides of the amp, then the amp is as happy as possible, but with cabs of different impedance, the volume at each speaker will vary (not only with power but also the sensitivity of the driver itself). This is why one usually tries to get identical cabinets with the same impedance, often 8 or 16 ohms, which enables you to use a lot of cabinets without dropping below a single amp's impedance rating.

But I thought that under powering speakers you were more likely to inflict damage onto them. As for over powering them I never turn the volume controls past the 12 o'clock position in the current 150w for each channel set up I currently have. Thanks for helping me through this by the way, I sort of figured that it may be a bit of a problem using two different impedences.

 

[Farview]

There is no reason to run both sets at the same time. You will have terrible phasing issues and it doesn't do any good. If you get a speaker level switch box, you can safely use either set, just not both.

 

[dfgh11]

There is no reason to run both sets at the same time. You will have terrible phasing issues and it doesn't do any good. If you get a speaker level switch box, you can safely use either set, just not both.

is there anyway to use speakers with two different impendences at the same time without phase problems. I see there wouldn't be much point, but just wondering?

 

[Farview]

The phase issues have nothing to do with the impedance. The phase problem comes from one set of speakers not having the same response and not being in the same place as the other.

 

[TMFK]

quike note

ALso a quick note that might help you out:
2x8 ohms in series = 16 ohms
2x8 ohms in paralell= 4 ohms

2x4ohms in series=2 ohms
2x4 ohms in paralell=8 ohms

2x16 ohms in series= well you wouldnt want to do that, but 32 ohms.
2x16 ohms in parralell=8 ohms

 

[Farview]

ALso a quick note that might help you out:
2x8 ohms in series = 16 ohms
2x8 ohms in paralell= 4 ohms

2x4ohms in series=2 ohms
2x4 ohms in paralell=8 ohms

2x16 ohms in series= well you wouldnt want to do that, but 32 ohms.
2x16 ohms in parralell=8 ohms

You have the 4 ohm ones backwards
2X4 ohms series=8 ohms
2X4 ohms paralell=2 ohms

 

[TMFK]

uh oh

GOSH! Im so sorry, I knew that .. typo on my part.. sorry for the misinfo guys!