Watt distribution question


I have a stereo receiver that puts out 60w x 2. It has outputs for 2 sets of speakers. now, if I have 4 speakers hooked up to it, Set A and Set B, as the receiver designates them, how many watts is each speaker getting? this is something I am quite unclear on. I am pretty sure that means each speaker is receiving 30 watts, but again, i really dont know. I would really appreciate some clarification on this. also, if you can by the same token explain exactly what a 75 watt max handling capacity would mean on a speaker, that would be great too (ie if i had an 80w x 2 receiver, could I hook up 4 75 watt max speakers).

The answer is: it depends. It depends on the impedance of each speaker, and it depends on how the stereo is rated.

The power rating of a stereo doesn't mean anything unless it specifies what kind of load it is rated at. Most often, manufacturers state a rating for 8ohm speakers. Likely the rating on your stereo is 2x60W @ 8 ohms. However, that is not always true. Sometimes, manufacturers try to make their equipment sound more powerful than it is by giving a rating for 4 ohms. (as well, some manufacturers of low-buck equipment give you the peak power rating instead of the continuous rating. They can play with the numbers to make people think their equipment is more powerful than it would if they gave the ratings people expect to hear.)

As well, you need to know what the impedance rating of your speakers is. This should be stated on a label on the back of your speakers. The most common impedance is 8 ohms. However, there are many 6 ohm and 4 ohm speakers as well.

There are 2 ways of hooking up multiple speakers to a stereo terminal: parallel or series. Parallel is the most common way. Hook up the "+" of each speaker to the "+" on the terminal, and the "-" of each speaker to the "-" on the terminal. (Series is more complicated, and not needed except in special circumstances.)

When you have multiple speakers in parallel, then the impedance decreases. Total impedance = (Z1 * Z2)/(Z1 + Z2) where Z1 and Z2 are the impedance of speakers 1 and 2. So, if you have two 8ohm speakers in parallel, then the total impedance is (8*8)/(8+8) = 4ohms.

So how much power is your stereo putting out? Well, power is inversely proportional to the impedance (unless your amplifier is overloaded, in which case you will hear distortion and could damage your amp) So, if you decrease the impedance by half, you double the power.

So, if you've got a stereo that puts out 60W per channel into an 8ohm load, it can probably put 120W per channel into a 4 ohm load. If you have two 8ohm speakers in parallel on each channel, then each of the 4 speakers will carry 60W.

The thing to watch out for is that some amplifiers might not provide enough current to drive 4 ohm loads. If you've got a nice 1970s model stereo receiver with a knob that lets you select "A" "B" "A+B" speakers, then you can hook up a set of 8 ohm speakers to both "A" and "B" and run all 4 speakers at once without worrying. If you've got a new-model receiver and the manual says "WARNING: do not use speakers less than 8 ohms", I would be careful with the volume knob if I was hooking speakers up in parallel.

How many watts neccesary to support 2 8ohm speakers.
How many watts neccesary to support 2 4ohm speakers.
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