115w amp -> 80w speakers? ohms\confused


Ex Member
Feb 14, 2004
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I'm getting a Yamaha RX-V540 rated at 115w at 4 ohms and rated at 70w at 8 ohms.

Speaker package on manufactures website says speakers are 80w at 4 - 8 ohms.

What on earth does that mean? How will the amp know to output at 70w (8 ohms) and how will the speakers know what its receiveing (4 or 8 ohms)

Is there a switch or something.
You dont mention which speakers you are talking about but I would assume that the manufacturers have said "80W at 4 - 8 Ohms" to give you some idea of the upper and lower limits of the load they present to your amplifier, Speakers unfortunately are not purely resistive, the load is complex and correctly known as an Impedance (which is also measured in Ohms which is why people often assume it to just be a resistance)

The speaker cone is moved in and out by a coil in a magnetic field and this coil acts as a small inductor, there are also inductors and capacitors in the crossovers and so depending on the frequency of the wave being applied to the speaker the load it presents to your amplifier varies.

I would simply suggest that you dont push the speakers too hard, yes it does sounds possible that your amplifier has the capacity to damage the speakers but it will not do so unless you tell it to (by turning it up too loud! ;) )

Basically, dont worry about it! For a start, none of the ratings are likely right.

The speaker rating suggests the use of an amp with 80W and that the speaker impedence varies largely between 4 and 8 ohms. As far as the power goes, 80W is what the speakers are rated for, the impedence really doesnt matter since any given power actually will account for the impedence.

You probably look at the amp and see it as being too high power. However, as i suggested, these powers are likely for 1 channel at a time and likely with large distortions. In use the power will likely be dramatically less seeing as all channels will be going and they will all derive power from the same source. Even were the power higher than the speaker rating, the rating is only a guideline so unless you are silly it should be ok. There are even those (im one) who wouldnt flinch at using power amps which on the surface seem way way too big.

in any case, sum and substance is you have nothing at all to worry about with this combination

Nothing to worry about as they seem a good match.

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