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Matching an amplifier to a speaker

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If I have a 15W 8Ω speaker, what power amplifier would be best to use? I guessed 15W (seemed logical to me), specified to drive 8Ω. Or should I choose an amp with a higher power rating?

A similar question: what are the consequences of mismatched power levels? If I have a 15W speaker, what happens if I use a 5W amp? a 25W amp? I assume there are no serious issues...
 

crutschow

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The amp power just affects the maximum loudness you can achieve from the speaker. A larger amp is often desired since it tends to have lower distortion at normal listening levels. The only problem with a high power amp is that it could blow the speaker if you crank up the volume too high (or from a sudden burst of noise such as plugging in an RCA audio cable with the volume cranked up).
 

forumlicker007

New Member
Can be peak rating too. Good option is say 10w rms amp. It won't blow up the speakers but higher amp certainly.
 
Can be peak rating too. Good option is say 10w rms amp. It won't blow up the speakers but higher amp certainly.
Is that a safe approach, generally? Choose an amp with an RMS power rating about 2/3 of the speaker rating? Or look for one that has a max power rating equal to or slightly less than the speaker? Thanks!
 
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audioguru

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A speaker with a power rating of only 15 Whats might not even list its puny rating in RMS watts.
15 Whats peak or maximum power might be as high as 7.5 Watts RMS continuous power. Or 5 Watts.

What is the size of the speaker? A cheap 8" PA speaker (used in stores) is rated at 10 Watts RMS.
 

audioguru

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The amplifier will be a good match to the speaker.
Did you motice that the speaker produces no bass?
Other 4" speakers produce most audio frequencies including pretty good bass.
 
I haven't hooked this speaker up yet - wanted to get the heatsink first. This speaker won't have any bass?

Got any good 4" speaker recommendations? I got this one because it's 93dB, which was louder than the others. And it's cheap.
 

Sceadwian

Banned
If you want quality, cheap is not what you should be looking for. Decibel ratings are always frequency defendant so me careful of what you buy.
 

flat5

Member
The problem with using a low power amp is the tendency to try to play it too loud. Many people (not me) will try to get thumping bass out of the 4 inch speaker or sizzling highs. The amp may very well clip the signal and send high or low frequency square waves to the speaker. Hi Fi speakers are not designed for this. Over time it will destroy the speaker.

Don't ask the impossible from the amp or speaker and any well designed power amp will be safe. For this speaker use an amp less than 35 watts and don't play it too loud. Amplifier head room is good.
 
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audioguru

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This speaker won't have any bass?
No.
Its free-air resonance is 170Hz. It will be about 250Hz in an enclosure.
No bass.

Got any good 4" speaker recommendations? I got this one because it's 93dB, which was louder than the others.
Fostex (available at Madisound) has two 4" full range speakers. They resonate at 77Hz and 80Hz. Their sensitivity is 87dB and 88dB.

And it's cheap.
It will sound very cheap almost like a cheap clock radio.
 

Sceadwian

Banned
Hey audioguru you might know this, what makes speakers of approximately the same size like that have such different frequency responces? Is it just the magnets or is there more going on with the coil/physical construction?
 

audioguru

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A cheap speaker usually has no bass and no high audio frequencies. The amplitude of the frequencies it plays are all over the place (peaks and notches). Its upper bass might sound boomy and it usually has a peak at around 3kHz to 6kHz so it shrieks. It probably will not last long. It sounds awful. It is cheap.

A good speaker produces deep bass and produces high audio frequencies. Its frequency response is flat without resonances or notches. It will probably last a long time. It sounds good. It costs more.

It is very difficult to make a good full-range speaker so usually a woofer and tweeter are used.
 

audioguru

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Having speakers at the back of a car results in deep bass due to the shape of the cabin.
 

Sceadwian

Banned
I know the acoustical difference between a good and bad speaker. But if they're approximately the same size, what is it physically about the speakers that make the one better than the other? Stronger magnets, higher/lower inductance in the voice coil? I'm guessing stronger magnets and some sort of sweet spot for the inductance?
 
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audioguru

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The strength of the magnet, the weight of the coil and cone, the stiffness of the cone, the width of the magnetic gap, the length of the magnet and coil, the stiffness and linearity of the suspension, etc.
 
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