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Old 11th June 2004, 12:05 AM   #1
valnar is offline valnar  United States
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Default Good amp minimum for 85dB speaker?

I'm moving from 90dB speakers in my home theater to 85dB speakers. I do not have them yet, but I only have a 100 watt x7 receiver. As most of us know, this undoubtably is less than 100 watts when all channels are driven.

So I want to supplement it with a separate amp. What is a good minimum I should look for with average volume level listening?

-Robert
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Old 11th June 2004, 12:24 AM   #2
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I understand what you're getting at, but without knowing more about what you think an average listening level is, how big a room, and how hard you were pushing your speakers with your original reciever, it's not simple to make a recommendation that has any true value.

But think about this- you're nearly 6 dB lower in sensitivity if the number's you're quoting are correct (for sensitivity- keep in mind many manufacturer's over state their specs, and some (not many) are realisitc. So, you might only have a 3dB difference to actually deal with...

Examples of speakers that are notoriously on the low efficiency side are Magnplanar's, for example. They really do best with well designed solid state amps in the 150 watt and higher category.

Most of the sensitivity loss in a lot of "box" speakers comes from the baffle step compensation. Though many standard midwoofersand tweeters are around 89-90 dB for 1 watt at 1 meter, after you apply baffle compensation for 4 pi radiation, this may drop between 3-5 dB, depending on the voicing.

That 85 dB sensitive speaker will need 128 watts to hit 106 dB peak at 1 meter. That may correspond with average levels of 85-95 dB, depending on the kind of music. Allow for two speakers, but fall off with distance, and 150-200 watt seems like the right ball park. There are many good options in that range.

Now, if they're real tanks as regards power handling, and you have a big room, and like wide dynamic range, then more power may be justifiable. I never seem to run out of gas with my Aragon Palladium monoblocks, which are balanced differential, about 100 watts class A at 8 ohms, and clip at about 550-600 watts @ 8 ohms. But they are overkill most of the time.

~Jon
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Old 11th June 2004, 01:01 AM   #3
valnar is offline valnar  United States
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85dB is typical for me on movie soundtracks, and I listen to audio usually less. Without going to room size and distance, let's just assume that remains constant (medium-large room, nevertheless)

If I listen to my 90dB efficient speakers with my 100 watt "receiver" amp, and want to get the equivalent volume out of a seperate amp (still 5 or 7 multichannel), then what would I need?

Robert
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Old 11th June 2004, 12:03 PM   #4
sreten is online now sreten  United Kingdom
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In simplistic terms you need 320w per channel to make up the difference.

I suggest you try your new speakers with your amplifier, it should be fine,
IMO not many 85dB/W speakers can handle more than say 150W cleanly.

sreten.
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Old 11th June 2004, 12:21 PM   #5
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You need at least a good 100w amp.
Seriously, much more important than power is the outpup current of the amp.
Do you realize that 1000 watts of power is just the double of 100 watts in terms of power output?
You'll always have to re-adjust the levels of the speakers on your receiver.
What you have to bother is not the volume, but if the amp drives the speakers properly, and that shows even at low volume, with an untight, flappy bass that spoils everything, midband, treble...
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Old 11th June 2004, 01:03 PM   #6
valnar is offline valnar  United States
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Quote:
Do you realize that 1000 watts of power is just the double of 100 watts in terms of power output?
That's a good point. Why all the hoopla about 125 watt vs 200 watt amps? Aren't they pretty close in the end based on that fact? Should manufacturers be making 1000 watt amps in that sense?

I guess that's why I get confused when somebody says a 75 watt amp may not be enough, but 100 or 125 is much better. Or 200. It sounds like all peanuts based on the science.

Thanks,
Robert
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Old 11th June 2004, 02:41 PM   #7
MikeB is offline MikeB  Germany
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Quote:
Originally posted by valnar


That's a good point. Why all the hoopla about 125 watt vs 200 watt amps? Aren't they pretty close in the end based on that fact? Should manufacturers be making 1000 watt amps in that sense?

I guess that's why I get confused when somebody says a 75 watt amp may not be enough, but 100 or 125 is much better. Or 200. It sounds like all peanuts based on the science.

Thanks,
Robert

Somehow you are right, the difference between 75Watt and 100Watt
is peanuts regarding the pure soundlevels...
Its a fact, that you need 10 times the watts for doubling the soundlevel.
But mostly the Amps with some more watts can deliver significantly
more current (with ease), what is in my opinion more important.

Michael
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