If I have a power amplifier, and instead of plugging 2 speakers to it, I plug 4 or 6 or 8, is that bad? Why?

Question

I want to know why it's not possible (or a good idea) to plug mutiple speakers to a power amplifier? I understood the signals may be split, but someone told me this can blow or overload the amp, and I want to know why?

Answer 1

Brian... sheesh... relax... but I do totally agree, this service needs a FAQ. The same questions get asked, day in and day out. Over and over and over...

Alright...

The basics... quick and dirty...

Amplifiers have a nominal impedance load for a given power output rating. If say for instance, the amp is rated at 8 ohms to 250 RMS Watts... it might be 375 RMS Watts at 4 Ohms, and if it can do 2 Ohms stable, then likely around 565 RMS Watts.

So... first you need to figure out what your amplifier is cabable of sustaining for an Ohm load. And this is assuming it's solid-state, and not tube. That's a whole other story. Anyways...

You have 8 speakers they're all the same Ohm rating.

And you want to run them at 4 Ohms...

So you'll have to understand the basics of Series/Parallel math...

Wired in series... you add... wired in parallel, you need to use the 1/(1/a+1/b+1/c+1/...) formula, where a,b,c,... are the respective Ohm ratings of all the drives you want to use...

If you 8 drivers are 8 Ohms... and you want a 4 Ohm load impedance...

All wired series in the rows... and then rows are wired parallel

Row 1 - 2 drivers... 8+8=16ohms
Row 2 - 2 drivers... 8+8=16ohms
Row 3 - 2 drivers... 8+8=16ohms
Row 4 - 2 drivers... 8+8=16ohms

overall load impedance of the system would then be 1/(1/16+1/16+1/16+1/16)=4 Ohms... So with the amplifier example above you're driving 375 RMS Watts of power through those 8 speakers.

Let's say you you have 4 drivers and they're 16 Ohms each, and you need a 4 Ohm load impedance...

Wire all the drivers parallel to each other...

1/(1/16+1/16+1/16+1/16)= 4 Ohms...

Let's say with the above we needed 16 Ohms...

Row 1 - 2 drivers - 16+16=32ohms
Row 1 - 2 drivers - 16+16=32ohms

1/(1/32+1/32)=16 Ohms...

Let's complicate things a little bit...

You have 2 drivers that are 8 Ohms, 2 drivers that are 4 Ohms, and 2 drivers that are 6 Ohms... what are the possible combinations of load impedance?

Row 1 - 2 8 ohm drivers - 8+8=16ohms
Row 2 - 2 4 ohm drivers - 4+4=8ohms
Row 3 - 2 6 ohm drivers - 6+6=12ohms

1/(1/16+1/8+1/12) = 3.7 Ohms

Which is close to a 4 ohm load...

Mixing things up a little...

Row 1 - 1 4 Ohm, 1 8 ohm, 1 6 Ohm = 18 Ohms
Row 2 - 1 4 Ohm, 1 6 Ohm = 10 Ohms
Row 3 - 1 8 Ohm = 8 Ohms
Row 4 - 1 6 Ohm = 6 Ohms

1/(1/18+1/10+1/8+1/6)= 1.37 Ohms... we just cooked out amplifier...

Try again...

Row 1 - 1 8 ohm, 1 6 ohm = 16 Ohms
Row 2 - 1 4 ohm, 1 6 ohm = 10 Ohms
Row 3 - 1 4 ohm, 1 8 ohm = 12 Ohms
Row 4 - 1 6 ohm = 6 ohms

1/(1/16+1/10+1/12+1/6)= 2.42 Ohms... the amp if can accept a 2 ohm load, is now putting out around 500 RMS Watt...

This presents a whole slew of other issues...

Mismatching drivers is generally a bad thing. You need to make sure that the RE (DC Resistance of the voice coil) on all the drivers is the same, or you're going to have drivers doing more work than others. This is mess. Won't function well, and you'll end up trying to figure out why your system sounds like crap...

Unless the speakers are all the same... don't bother. Otherwise the above should help. When you want to figure out how to wire series and parallel, google it. There's a billion pages on the internet about it.

Answer 2

I don't completely understand it, though I did at one time. Bad memory. It has to do with impedance matching and efficiency. Another phrase associated with impedance matching is maximum power transfer. AC systems use real, reactive, and total power. The only part you can actually use is the real power. If you know enough about the system, you can make modifications to adjust the impedance and keep from destroying your equipment. By the tone of your question, I am guessing that in your case it is better to simply not do it. You can learn about electricity and electronics and do something later when you know what you are doing. Hopefully you won't forget as many details as I have. Another factor to consider is the way impedances add. Connected in parallel, the resulting impedance is smaller than any single impedance. Connected in series, they add directly making the total larger.
Remember, some details may be questionable due to my memory. Hooking up your speakers in parallel will reduce the total impedance. The power is the same. If the power is the same and the "resistance" to current is less, the current will increase to the point of overloading the system or wiring. If my memory is correct, good-bye speakers and possibly the amplifier.

Answer 3

Well, Vandel actually cleared up quite a bit- don't know why it was marked as a bad answer. If you are running 8 speakers on one channel that is set to take 16 ohms, and each of the speakers are 6 or 8 ohms a piece, bad idea- that will cook your amp out. Let's say the channel can handle 16 ohms, and you have two of them- but you have 8 speakers attached to each one. Depending on the wattage your speakers are, the gauge of wire you are using- this can overload the amplifier because it's trying to power 16 speakers, and it still thinks it is only powering 2. OK. Lets say you are hooking up four speakers to a channel only set for one. Not only have you quadrupled the wattage the amp has to put to that channel, you have lowered the impedance by (16 ohms^4)/16 (in this instance) so, if your channel is set for 16 ohms, and each speaker you have set up is 16 ohms, you have just lowered the impedance to 4 ohms. That's only if you have 4 speakers hooked up to a single channel... If you have more hooked up, it lowers the impedance even more, and can burn out the amp really quick.

Answer 4

look....go buy a basic electronics book and read about impedance (which is measured in ohms for you amateurs) and then you'll understand the concept and why you SHOULD NOT do it

Answer 5

Im not sure why but that's what happened to me...it just kind of died