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Old 4th February 2015, 06:03 PM   #1
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Smile LM3886 speakers

Hello guys, very awesome forum, love it and I am kinda new to audio systems, though have knowledge in electronics. Had this question, I am planning to build an amp for a 3 way passive crossover with two LM3886 IC's. Checked out its datasheet and it says, that it gives 50W output on 8Ohm load, but the Instantaneous Peak Output Power can jump to 135W, also the chart shows a bigger than 50W output on 8Ohm load (35V+/- supply) (seen in image). So with all that, what speakers should I choose so they could handle the given power? Because until now I though just to put 50-60W speakers
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Old 4th February 2015, 07:22 PM   #2
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Join Date: Feb 2011
it does not work that way
power handling of a speaker is one thing.
power available from an amplifier is a nother thing.

it is a mis-concept to think the amplifier power must in some way match the speaker driver. this is false.

you can connect safely a 2 KW amp to a 0.25 watt speaker. no issues there. (given the amplifier can drive the impedance presented by the speaker)
you could blow the tiny speaker up, if you happen to turn the volume knob way high up.

and you can safely connect a 0.25 watt amp to a 2kw speaker. (given the amplifier can drive the impedance presented by the speaker) even if you turn the volume knob all the way up it would have no issues.

so then how are things like this are choosen ?
speakers have a so-called efficiency.
it is mesured in soundpressure level at 1 meter distance, with the speaker driven by 1 watt of power. (there is a nother unit for this, taking a drive voltage instead of power but we shall now skip that part)

so, You figure out the sound pressure level You would desire, then look up the efficiency of the given speaker. then You can work out how many watts of power you would need to get the desired maximum sound pressure level. then, you can take a look at the powerhandling of the given speaker. will it be able to handle the required power input or not. this is a graph, as powerhandling is freqvency dependant.
and there you have it.
if the driver can handle it, and does not impose an impedance that can not be driven by a given amplifier, and the power requirements can be statisfied by the amplifier, then the speaker was choosen correctly.
in practice i personally shoot for some overhead.
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Old 4th February 2015, 07:46 PM   #3
infinia is offline infinia  United States
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design the speakers 1st, they are the most important. in-fact they should be the no 1 priority of the total system budget. the nice thing about LM3886 is they can be made to work well in active crossovers. There are some well known commercial 2way active monitors that do this. The older model Behringer Truth uses 2xLM3886 bridged for the bass /mid and a single LM3886 for the horn loaded dome tweeter. edit > not sure about the newer ones.
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
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Old 4th February 2015, 10:02 PM   #4
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Thank you very much, that made things much clearer
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