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Mismatching speaker wattage? Answered

Hey guys,

So I've recently gotten into making DIY speaker systems, but I'm having trouble understanding the whole ordeal about wattage and ohms.
I have four speakers I managed to salvage from some old speaker systems that I got from an old thrift shop. I have two 15W 4ohm speakers, a 20W 8ohm speaker and a 2W 8ohm speaker (but I don't think I'll find a use for that one, I'm not sure)
I plan on buying the Lepai LP-2020A+ amplifier, it's a two channel amp and delivers 20W/ch with impedance of 4-8ohms.

What I want to know is what set up would be best with what I have? Can I run the two 4 ohm speakers on 1 channel even though they would draw 30W of power? I'm a bit new at this, and my understanding is still a bit unclear so if anyone could please explain, I would very much appreciate it :)

Thank you



5 years ago

They do not draw 30 watts--that's max power capacity, not current. Together the two will constitute an 8 ohms in series--well within the specs of the amplifier. Can't ask for anything more.

So yeah--connect the two 4 ohm 15 watters in series. That's equivalent to an 8 ohm load, with 30 watts power handling capabilities. Use that for one channel.

Use the 8 ohm 20 watt speaker for the second channel.

You should be covered--both channels will see the same load (8 ohms), and should at least be close to handling the max power (depends on the amp). I'd like to see more than a 1:1 ratio of speaker rating:amp power, but don't turn it up all the way.

Note: The efficiency of the speakers (SPL) might be radically different, so there's no guarantee that that the channels will sound balanced...


5 years ago

Stick with the pair of matched speakers you have and drop the rest. Just be sure you don't crank the amp all the way up or your'll blow the speakers. The wattage ratings are the max that the speakers/amps can handle/deliver.

When you combine speakers on the amp you change the impedance that the amp 'sees'. The amp can handle 4-8 ohms. Any more or less and you could have problems. If you wire 2x 4 Ohm speakers in parallel they will look like a 2 Ohm speaker to the amp. If you wire them in series they will look like a single 8 Ohm. In parallel the power to the speakers will be split evenly, for the most part, between the speakers. In Series the power will not be split or used evenly. One speaker will be loader than the other. So there are trade offs. In the end it's best to keep one speaker per channel.


5 years ago

I may be wrong but I don't think the 30 watts is what they will draw. Rather it is how much they can handle before they are damaged.