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Old 12th January 2013, 05:21 PM   #1
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Question Myth Busters: 1000W amp is only twice as loud as a 100W amp

I read this
Myth #1 "When driving a perfect loudspeaker a 1000W amp is only twice as loud as a 100W amp. When driving a real loudspeaker that suffers from thermal and mechanical power compression a 1000W amp will be less than twice as loud as a 100W amp, probably only about twice as loud as a 50W amp at best."

On the website
Barefaced Bass - Mythbusters #1 - amplifiers

I think this is incorrect as 1000w will sound twice as loud as 500w.
Reason Double to power and you get almost 3db gain

Are they incorrect ?
Or they conclusions are wrong

about the Myth 3 also i am unsure
Myth #3 - If your amp isn't powerful enough you risk blowing your speakers through underpowering.
Truth #3 - You will never blow woofers or mid-bass drivers, i.e. the 8"/10"/12"/15"/18" speakers found in a bass cab, because your amp isn't powerful enough.

My version of truth- you dont risk blowing but burning it with clipping
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Old 12th January 2013, 05:23 PM   #2
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Well, thermal compresson depends on the driver used.
Regarding myth number three, if the driver is underpowered the voice coil will be fried by the DC current so...
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Old 12th January 2013, 05:33 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Doubling the power certainly does not sound twice as loud.

The Bel (10dB) is known in telephone systems to sound
approximately twice as loud for any given level change.

However the bass end of hifi and the F&M curves of
the bass end means a 100W amplifier sounds more
than twice "as loud" as a 10W amplifier, probably
about 3 times, certainly not 10 times as loud.

rgds, sreten.

People are poor judges of relative sound levels, why the
F&M curves are equal loudness only, normalised to 10dB
steps at 1KHz. There is very little information on peoples
perception of relative absolute levels with frequency.
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Last edited by sreten; 12th January 2013 at 05:50 PM.
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Old 12th January 2013, 05:36 PM   #4
FE3T is offline FE3T  Norway
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If i remember correct a 3db gain is what you need notice a gain in loudness, so i guess 10db are what you need to get twice as loud. and a 10db gain needs 10 times the wattage, so to me 1. are correct if you discard thermal compression and such.
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Old 12th January 2013, 05:44 PM   #5
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Twice the power is 3dB, 50 watts to 100 watts = 3db which is what you need to notice a change. you need 10db to sound twice as loud.

so 100 to 200 watts = 3db,
200 to 400 = another 3db or 6db from 100 watts
400 to 800 = another 3db or 9db from 100 watts

so just about 1000 watts = twice as loud as 100 watts.

Yes power compression reduces a drivers output requiring more input power to = the same acoustic output power. so 10 times the power is a rough figure. not exactly literal.
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Old 12th January 2013, 05:55 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

10dB = "twice as loud" is a very rough approximation.

And clearly wrong for subwoofers and the bass end in general.

rgds, sreten.

1dB is noticeable level change. 3dB is clearly significant level change.
Apparent effect varies with frequency and / or signal spectrum.
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Last edited by sreten; 12th January 2013 at 06:00 PM.
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Old 12th January 2013, 07:15 PM   #7
JMFahey is offline JMFahey  Argentina
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Agree and add: I quickly scanned through what's said in that site.
Found it a mixture of true, hearsay and wrong, plus a springling of "maybe, but irrelevant".
Read it and draw your own conclusions, but don't consider it Revealed Truth or something.
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Old 12th January 2013, 07:21 PM   #8
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If i am putting double the power in a sub then i would expect it to sound twice as loud.
How can that sub cheat and eat up all the extra double and give me only little more loudness
10db= 10 times the power, it should be 10 times loud

dB: What is a decibel?
Play, broadnoise decreasing by 3db steps

Update: Aprox
Doubling of the volume (loudness) 10 dB
Doubling the sound pressure (voltage) 6 dB.
Doubling of acoustic power (sound intensity) 3 dB.

Is a three dB difference in sound twice as loud
Loudness volume doubling sound level change factor of perceived loudness formula calculate power level noise levels volume logarithm dependence three four fold loudness sound - by what factor does level decrease dependence comparison decibel levels 3
How loud is twice as loud - Page 3 - TalkBass Forums

if i have 2 volts reading on multimeter
then i double the amplitude i see 4 volts
but it seems loudness is different from power and amplitude

Last edited by Amit_112dB; 12th January 2013 at 07:34 PM.
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Old 12th January 2013, 07:32 PM   #9
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Welcome to logarithmic scales.
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Old 12th January 2013, 07:33 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Amit_112dB View Post
So you all are correct
1000W amp is only twice as loud as a 100W amp
Hi,

Except it depends, on the spectrum the music has.

rgds, sreten.

Make a recording with various level jumps, say 3, 6, and 10dB
and decide for yourself. Try a bass heavy recording versus
say just guitar and vocals to see its not very clearcut.
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