I have bought a DIY 2 way speaker kit (Seas Indunne) and cant figure out how many watts I need out of a channel to drive it.

It uses a woofer that is rated for 80 watts long term/250 watts short term and a tweeter that is rated for 55 watts long term/150 watts short term

  • 2
    \$\begingroup\$ Those are the ratings the speakers can handle without cooking themselves, to actually listen to music comfortably, assuming you're in a normal sized room you only really need a handful of watts. A 10W amplifier would probably be ample. \$\endgroup\$
    – Colin
    Dec 21, 2016 at 7:39
  • \$\begingroup\$ so does my tweeter limit the entire 2way setup to 55 watts continuous max? \$\endgroup\$ Dec 21, 2016 at 8:26
  • \$\begingroup\$ The tweeter uses less than half the spectrum so your limitation will be woofer power. \$\endgroup\$ Dec 21, 2016 at 8:38
  • \$\begingroup\$ isnt the spectrum 0 - 20,000 Hz? The XO on this setup is 2,600 Hz. Isn't the tweeter working on a majority of the spectrum? \$\endgroup\$ Dec 21, 2016 at 8:41
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    \$\begingroup\$ no.. use log(f) or count octaves.. Sensitivity is 85dB @ 1W @ 1m but if you like normal TV sound a few watts is typical, but if you have the space and like bass 100Watts is better \$\endgroup\$ Dec 21, 2016 at 8:57

1 Answer 1


It depends on how you intend to listen to your system, how you decide on the listening level, and where you play it. Obviously you may tend to play it louder in an open space or hall, than in a living room.

There is a school of thought that says the amplifier power capability should either be a bit more, or a lot less, than the speakers. This assumes you sometimes set the listening level by turning it up until you hear distortion, and then back off.

If the speakers limit by distorting, as the suspension runs out of linear travel, you would hope that you are still within the thermal rating of the voice coils. Turn it down then, and all is good.

If the amplifier is slightly smaller than the speakers, then you might be tempted to turn it up until the amplifier limits by hitting the rails. That generates a whole slew of high harmonics at the full power of the amplifier that pass straight through the crossover to the tweeter. By the time you've spotted the distortion it's already too late, kentucky fried tweeter. If the amplifier is a lot smaller than the speakers, then the tweeter should be able to handle this abuse.

Big 'system' amplifiers often have soft limiting, that turns the wick down automatically while still short of clipping to avoid this problem, whether a smaller domestic one would is another matter.


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