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Since adding subwoofers to the system, it might require to roll off the low end of the main speaker (example high pass filter at 95hz), this means the main speaker is no longer needed to responsible under 95hz.
Normally my main speaker required 100w tube amplifier for optimum performance to fulfill 87db sensitivity of the main speakers.
As the speaker no needed to handle under 95 cycle once handover to the subwoofer , rumor has it that the main speaker required less power to drive, let's say 25% as used to, this meant at least 25w. Is that really true?
"Since adding subwoofers to the system, it might require to roll off the low end of the main speaker (example high pass filter at 95hz), this means the main speaker is no longer needed to responsible under 95hz."
"Is that really true?"
You didn't say what your main speakers are, but, in general, what you say/ask is on the right track.
There are multiple issues to consider in your post.
Firstly, to be clear, where you cross over from the main to the sub doesn't happen "suddenly" at a particular frequency. The chosen frequency is the transition point. Both the main and the sub will still be reproducing sound below and above that frequency.
So, whether it's 95 Hz, 50 Hz or 150 Hz, there is overlap between the drivers' output. This overlap is an important concern which affects (not 'effects') the overall sound quality.
Secondly, rolling off the low end of the main speakers improves their performance and their amplifier's performance, because of the reduced excursion requirements and power/current demands.
Thirdly, many speaker manufacturers offer products which are intentionally inadequate in the bass end, for economic and marketing purposes. Some people don't care about great low end, but also want a "nice" sound capable of more-or-less high output levels. Other people want a nice speaker which they can afford without the low end, and add it later. Etc.
The concept of the typical "subwoofer" for home hi-fi is mostly marketing. There's a cross between hi-fi and "almost" hi-fi. Hi-fi includes frequencies down to the range of 40 Hz or lower. Woofers should include that range adequately. "Subwoofers" need only come into play below there. But, selling "hi-fi" speakers for $2K to $15K+, and still needing subwoofers as an add-on is misleading.
It depends on what you listen to and what kinds of music stresses your system now.
Perceived loudness is determined by the midrange frequencies. High-pass filtering the main speakers won't affect that, so your system won't play any louder, except maybe in the bass.
If bass heavy music (dubstep etc.) is what causes you to hit your system's limits, then you might be able to use a smaller amp if you high-pass the mains. But if you're more of a jazz or classical listener, or even mainstream pop & rock, I suspect you will still need the power you have now.
With a solid-state power amp, the output voltage is independent of the load (for all practical purposes). In that situation one would still need the same voltage swing in the mid-band to achieve the same playback SPL, and therefore the same power.
Tube amps are a bit different in that they not only typically have higher output impedances, but usually also have various taps on the output transformer to achieve maximum power transfer. But that is a can of worms. When I had a Dyna Stereo 70, it sounded best with the output tubes strapped for triode operation. This dropped the output power almost exactly in half. Further, no matter what loudspeakers I used, it always sounded best when using the 4 ohm tap, which delivered the most current and had the lowest output impedance. One had to choose between musical magic and musical energy - it wasn't possible to have your cake and eat it too.
Strictly my personal opinion, prone to error, and not necessarily those of my employer or various tube manual authors.
If you roll off the mains (some don't, including myself) your main amps will see less of a load, thus you could do with smaller amps.
I see no issue with rolling off your mains, so long as the xover is well designed/made, and the xover point is suitable. If running one sub I generally prefer a much lower xover point, say around 40Hz (I run dual subs at around this point). Also, I would not remove your amp and buy a 25% lesser powered amp based on this fact, as the actual volume required doesn't directly equate to watts generated. So maybe now you can get away with a 90 WPC amp...?
Now the reverse of that, is you've removed the bass, which is the most demanding on the amp.
Do you already have a 100W tube amp? If so, and you're happy with the match/sound, I wouldn't rush out to get a smaller amp. Just me maybe...
I have 100w amps on the speakers. Assume adding the subwoofer with 95hz cutoff, I would like to give 35w push pull amp a try. I want to see the possibility
The subwoofer I want to try is Bag End and it's crossover is fixed at 95hz.
In my system, i Also high pass the main speakers, but at a frequency above that of the low pass to the sub. Sub crosses about 40 to 45hz while the high pass to the main speakers is 50 to 55hz.
The 'gap' is filled in since neither filter is 'brick wall' and either 24 or 12 db/octave.
You are being VERY optimistic about how much power you will 'save'. The 50:50 power distribution point is roughly 350hz.
How do you intend to mediate the crossover?
Too much is never enough
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