Using A Lower Wattage Amp For Mains With A Powered Subwoofer

Wise members,

Looking at buying some Ohm Walsh floor standing speakers.  Read many reviews stating that they need much power, the more the better - even beyond what they are rated.  If I get their new Beta line with 500 watt powered internal subwoofers, I was told that less amp power is needed.  Why does a powered subwoofer reduce the needed amp power?  Is his because most of the speaker driver motion is for the low frequencies and they are what consumes the power?  Trying to understand the physics behind this and also if the advice that I have received is correct.

Also, what wattage Amp should I target?  Looking at the Ohm Acoustic's F-5015s.

Thanks in advance
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If you follow Elizabeth's good advice and contact the manufacturer, two things I suggest that you ask are (a)what is the crossover point between the powered section of the speaker and the unpowered section (i.e., at what frequency does that occur); and (b)what are the slopes of the crossover circuit (e.g., 6 or 12 or 18 db/octave). Neither of those things appears to be specified for the F-5015 at the Ohm website.

I've read that as a very rough rule of thumb most music tends to have approximately equal amounts of energy above and below about 350 Hz. That makes sense to me, although obviously that figure will vary significantly from recording to recording and from moment to moment. But generally speaking if the crossover point is significantly less than 350 Hz the unpowered section of the speaker would typically have to be supplied with more power than the speaker's internal amplifier is supplying to the powered section of the speaker. And if the crossover point is significantly higher than 350 Hz the speaker's internal amplifier would typically be supplying more power than the external amp.

And the steeper the crossover slopes are (e.g., 18 or 24 db/octave rather than 6 or 12 db/octave) the more the power capability of the external amp that is necessary could be reduced.


-- Al
It means that at the very least, the amp will see a high load (100 Ohms or more) where the subwoofer frequencies are. This can help low current amps perform better.

If there is a high pass filter, it will also reduce the voltage swing the amp has to produce, greatly increasing dynamic range. 

Apparently there's no manual posted it yet, so I can't tell you which they are relying on.