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I know there is some kind of mathematical equation for this, but im just wondering about this. I've got a reciever that outputs 100watts per channel with 6 ohms resistance. My speakers are 150 watts RMS and 8 ohm compatible. What will this match up yield as far as wattage?
 

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Quote:
Originally Posted by brosephus
I know there is some kind of mathematical equation for this, but im just wondering about this. I've got a reciever that outputs 100watts per channel with 6 ohms resistance. My speakers are 150 watts RMS and 8 ohm compatible. What will this match up yield as far as wattage?
You can figure this out from a first-order theoretical point of view if you make some assumptions. 1) Your 8 Ohm nominal speaker impeadance is a constant resistance, and 2) Your amplifier power output is voltage limited. In that case, the two equations you need are Ohm's law: Voltage = Current * Resistance, and Power = Voltage * Current. A little algebra re-arranges things: Power = Voltage squared / Resistance. By examination, and given our previous assumptions, we can see that for a fixed voltage, power is inveresly related to resistance. Therefore, the power you amplifier can put out at 8 Ohms is:


P = 100W *6 Ohms/8 Ohms = 75W.


Which is half the rated capability of you speakers. This is a rather academic exercise (but fun) as your speaker's impedance probably varies widely w.r.t frequency, and it's difficult to know what exactly limits the amplifier power (voltage or current) and receiver power ratings are often somewhat 'optimistic'. Keep in mind that speaker damage is usually the result of underpowering the speakers, not overpowering them. Overdriving the amplfier, resulting in clipping, destroys tweeters rather quickly, so be careful with the volume and turn it down if you hear any distortion.
 

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I should add that, in general, amplifiers can drive any speaker with a higher impedance than they're rated for, but with less power. Driving a lower impedance load draws more current, and can potentially blow the amp if it's not rated for it.
 

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wleehendrick,


hi, i am pretty new to the speakers game as well, and i am just trying to pick up as much knowledge as possible. you mentioned that speaker damage is usually the result of underpowering the speakers, not overpowering them. why is that? can you explain that a little more?
 

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Underpowering speakers means that at some point if you keep increasing the volume the amp runs out of headroom and begins to clip. The waveform, instead of being something a smooth sine wave (the actual signal is much more complex obviously), will reach a limit at the peaks will get clipped flat, essentially creating a great deal of high frequency sort of transient noise that can damage the tweeter especially. It is alwasy much better to have an amplifier that can provide clean signals, unclipped, and with plenty of headroom far BEYOND the capabilities of the speaker. You can still damage a speaker by overdriving it, but as mentioned, it's much much MUCH more common for people to have inadequate amplification and turn up the volume to loud and cause damage by driving the amp beyond its capabilities into clipping. If fed cleanly, speakers can handle a great deal of power usually.
 

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Sorry to bump this old topic, but I have almost the same problem, but from the other point of view.


I'm about to buy a Technics SU-V450 Class AA amp, 2x50W @ 8 ohms. My speakers are a pair of Infinity Reference 11 mk II, rated 75W @ 6 ohms.


Am I at risk of damaging my speakers with that amplifier?


Thanks.
 
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