Is there any rule-of-thumb for choosing amplifier wattage for the given speakers wattage?
For example, I have speakers, 100 W (max. input power) / 6 Ohm each. Is it ok to match them with 44 W (min. continuous power) / 8 Ohm / channel?
In general, is it ok to hook up large speakers to weak amplifier? Is it ok to hook up small speakers to powerful amplifier?
I've read that speakers should be able to handle twice the wattage of amplifier output. True?
Is there any rule-of-thumb for choosing amplifier wattage for the given speakers wattage?
Speaker wattage can be defined in many ways and the vendor will choose one to suit his intended market.
You can see from this that the power handling specification is not the full story.
For example, I have speakers, 100 W (max. input power) / 6 Ohm each. Is it ok to match them with 44 W (min. continuous power) / 8 Ohm / channel?
The power is OK but the speaker impedance is a bit low. At low volumes you'll be OK but at higher volumes you're asking the amplifier output transistors to deliver more current than they were designed for. Best not. Load the amplifier with greater than equal to the specified speaker impedance.
In general, is it ok to hook up large speakers to weak amplifier?
No problem.
Is it ok to hook up small speakers to powerful amplifier?
Yes, provided: - The amplifier switch-on thump doesn't destroy them. - You control the power (volume).
Use your ears to tell you when you're over-driving the speaker.
I've read that speakers should be able to handle twice the wattage of amplifier output. True?
It's generally a good idea. An amplifier will "clip" when it runs out of voltage at high signal levels. This happens at a very well defined point. The speakers, on the other hand, will gradually increase in distortion as the cone reaches the limits of travel or the suspension starts to behave non-linearly.
A high-fidelity speaker system will be specified in sound level output and will give distortion figures for the full spectrum.
From comments:
"The power is OK but the speaker impedance is a bit low". The amp data-sheet says: "Speaker impedance 4 - 16 Ohm" so I thought that those 44W/8Ohm rating could be "converted" to match the 6Ohm of speakers, adjusting the wattage a bit (say 55W/6Ohm). Isn't so that I can freely convert between various impedances, provided the amp (data-sheet!) supports it?
If the amplifier has an output transformer there may be a switch to convert or optimise for 4, 8 or 16 Ω speaker load. Since load should be >= amplifier output impedance you would set the amp to 4 Ω for a 6 Ω speaker. Transformer outputs were common on valve amplifiers but less common on transistor amps. If you wanted you could purchase one but I don't think it would be worth the trouble.
Bear in mind with all this that your ear has a logarithmic response to volume. To double the perceived volume you need ten times the power. A (right side) mismatch between amplifier and speaker impedance will not be very noticeable in most cases as you won't be running the system at full power.
There's a lot of misconception going around about this subject !
You do not have to match amplifier and speaker power.
So 10 W amp with a 100 W speaker is OK
So 100 W amp with a 10 W speaker is also OK
Which of these do you think is the safest combination ???
(answered below)
What ?? But... ?
The ratings of amplifiers is usually easy to measure and also the true power they can deliver.
For speakers it is much different ! The power they can handle strongly depends on the frequency of the signal.
So a 100 W speaker could for example easily handle 50 W at 500 Hz.
But that same speaker can only handle 10 W at 10 kHz !!!
And what happens if you use a 10 W amplifier to drive that 100 W speaker and you set this combination at a loud volume ?
At loud volumes the 10 W amplifier might need to deliver a bit more than 10 W but it can't so it clips see: clipping.
And that clipping generates lots and lots of harmonic frequencies which are high frequencies. And what do we know about that speaker and high frequencies ? Right, it cannot handle that: so POP goes your tweeter !
When using a 10 W speaker with a 100 W amplifier it will not be the amplifier which will give up first (clip) but it will be the speaker, it will distort. You will hear that and turn down the volume a bit. But no clipping so a 10 W speaker and a 100 W amplifier is actually a safer combination !
Oh, and regarding the 6 or 8 ohms:
An amplifier which can drive 4 ohms is OK with 4, 6, 8 ohms and higher
An amplifier which can drive 8 ohms is OK with 8 ohms and higher, but not anything below 8 ohms.
Amplifier clipping generates sharp signals and high harmonics. This creates extra power in the treble frequency band, which has to be processed by the tweeter. This is how clipping an underpowered amp can destroy the tweeters.
If the amp is too powerful and the volume set too high, the woofer will usually exceed its maximum mechanical excursion, bottom out and rip the membrane itself or its elastic surround.
In the end, what matters is whether the one in charge of the volume knob is:
Really, if the amp clips enough to burn the tweeters, it will sound so terrible that a sane person would turn down the volume. Same if the woofer bottoms out, bass is horribly distorted. You'll hear it.
Unless you make a house party (in which case... do yourself a favor and get some used junk speakers from a garage sale instead of letting the idiots play with your expensive gear) the only risk of blowing speakers is:
Now, if you listen to music that isn't too compressed, you can listen at 1W average but have much higher peaks. Loudspeakers have no trouble handling peak power much above their continuous rating (unless the woofer bottoms out, but that would only happen on very low frequencies). So an amp which has more power than the speakers is really useful for peak power and peak current.
The easiest is to listen to some dynamic music at your usual levels and check the output of the amp with a scope to see if it clips.
If you don't over drive the amp and speaker, a mismatch doesn't matter.
It becomes interesting if you start to push the envelope, especially with solid state amps with hard clipping. They produce lots of hf content.
A typical speaker have a lower rated tweeter which can be damaged quickly if overwhelmed.
As such if there is to have a mismatch, use a large amp on a small speaker, not the other way around. Obviously you run the risk of overloading the speaker.
