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I need some clarification on amp power please. I keep seeing web sites refer to doubling of amp power to gain a 3dB increase in loudness. If that is the case, then going from a 100 watt amp to a 200 watt shouldn't be that much of a difference, right? So any amp around 125 watts or 150 watts isn't really all that different from a "lowly" 100 watt amp?I'm trying to figure out why I would spend money on a new amplifier in the 200 watt range, when something around 125 watts "theoretically" is close the same. Is there another reason? Bigger amps are a lot heavier and a lot costlier which I want to avoid. At what point is it enough?
BTW, I bring this up because I have a 100 watt A/V receiver with 7 channels. I know from reading other forums that it is not near that with all channels driven. I'll be purchasing some new speakers of which are a lowly 85dB sensitive and about 4-6 Ohm. I know most receivers have an issue with this, hence my desire to bump it up a little with a separate amp. But would I need to get a 200 watt amp? Or just a better a 100 watt amp to handle the less sensitive speakers?
Robert
Follow Ups:
A 3db increase is twice the power, but not twice as loud. The ear is non-linear. Physiologists have devised a scale of loudness, which rank-orders sound from soft to loud on units of sones. The physical quantity measured is the sound pressure level. One thousand Hz is used as a reference frequency (where the ear is most sensitive), at a sound pressure level of 40 db above the threshold of hearing (0.0002 microbar). This level is refered to as 1 sone. Doubling the loudness is equal to 2 sones. The result was that for the ear to percieve a doubling in loudness, it takes a 10db change in sound pressure. So, it would take 10 times the amplifier power to be percieved as twice as loud, assuming the loudspeakers could handle to increase of 10db. So, you are right. doubling your power from 100 to 200 watts wont make much of a diffference. Long live horn loudspeakers!!
All's well in what you say except that the human ear does not have its highest sensitivity at 1KHz. That frequency was chosen as a reference (0dB) by Bell Labs before they did their population testing many decades ago. The maximum sensitivity is in the range of 3000-3500Hz and is due to the resonant characteristics of the external auditory meatus (outer ear canal) which is the acoustical equivalent of a stopped tube. As a result, the auditory threshhold in that range is about -6 to -10dB referred to 1KHz.
Oh no, someone was actually paying attention! You are correct, depending on the loudness level being used. At 40db (re 0.0002ubar), the Fletcher-Munson curves have 1kHz at almost the same sensitivity as the 3-4kHz region (within 1 db). These were the curves I used for reference. However, other studies give different sensitivity curves. The curves derived by Churcher and King show the greatest sensitivity (at 40db) at 2.5kHz, being about 2db greater than at 1kHz. The curves derived by Robinson and Dadson (free field) show the greatest variation, showing the greatest sensitivity at about 4kHz, and being about 8db more sensitive (again, at a 40 db level). Overall, all of the curves show the same general trends, and these were the basis for the equal loudness contours.
Thanks for keeping me honest!
> > > bump it up a little with a separate amp < < <85dB sensitivity at 4 Ohm? You'd better be prepared to bump it up a lot! Those babies are juice suckers and 200 watts per channel is not near enough for any sound level approaching realistic. Are you sure those specs are correct? 85dB and 4 Ohms? Seriously, I can't recall ever seeing numbers that bad.
> > > At what point is it enough? < < <
I have over 6,000 watts on tap. That's continuous watts -- not peak. I seriously doubt I will ever need it, but you never know.
:-)
Yes, I really fucked that one up, didn't I? Got the power and loudness screwed up. Sorry about that...For my penance, I promise to read a copy of Sound&Vision and not laugh, cringe or vomit.
...101 strings, or barry manilow.;o)
IIRC, it takes twice the power to gain 3dbs, and 10 dbs is twice as loud. 90 is twice as loud as 80 and takes a *lot* more power. 100 is twice as loud as 90 and requires tremendous power. With inefficient speakers, that is.For me to hit 100 requires about... oh, 2 to 4 watts :D
With some Inifnities I had in the past, to hit 100 you needed something like 300 watts.
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