amplifier power versus frequency

[Israel]

well this one is maybe a confusing one (at least to me)

I've heard that in the full 20-20khz frequency there is unequal power i remember to have heard /read somewhere that the bass frequencies (20-300 hz) claim up to 70% of the power and there the last octave of the scale just claim as little as 5% maybe less.

true?? false?? myth?? misconception?? if it is true there is a table or something or perhaps a math formula or law to that??

sorry if it is a dumb but in part, you started all by making myself understand the sound and how it really works.

thanks for read this

[Bill Fitzmaurice]

On average power density drops by 3dB (halves) with each one octave increase in frequency.

[Bas Gooiker]

I don't know if i understand your question correctly, but amplifiers output varies over the freq band. The power specs that most manifacturers write are based on 1khz. The actual power at <100hz can sometimes be much lower.

Example:
Carvin DCM2500, rated 4ohm 900WPC @ 1K (where most mfgs take readings)
In actuality:
20hz-408WPC
1k-795WPC
20k-1024W

While it's not lying by much at 1k, look at the real sub reading!

You get other random results-
Lab gruppen fp6400, rated 4ohm 2300WPC @ 1k
20hz- 1327W
1k- 2310W
20k- 648W

QSC PL6.0 PFC, rated 4ohm 2600WPC @1k
20hz- 2289
1k- 2549
20k- 2890

Hope this answers your question, if not i misunderstood.

[Israel]

thanks Bill and Bas.,
i think it is more like what bill says, Bas i think you got how the rms figures are calculated. the main reason for my question is that i got a push talk with my nemesis in audio related matters (dont worry we are great friends) on about using full range speakers versus using sub+tops and why sub+tops seems to sound like a more powerful system i ended up saying how power is wasted on a full range setup.

now deeping in, that's one of the reasons why you should double your sub power (at least) and by the way cutting the extra grease on the low end maybe because a 200w per side top will maximize that power (calculating 30hz hp sub 120hz sub\top crossing you should 2x to 4x the low section) uff if it is the way it goes it is quite unfair eh??

[byacey]

Any reasonable quality amplifier will be flat across the spectrum as far as power output. You might experience a little bit of power supply sag when run full bore into a load, but generally the output voltage will be constant 20Hz to 20KHz.

What does change is the power spectral density requirements of the transducers across the audio band to reproduce what we perceive as flat frequency response. As frequency goes up, the power density of the spectrum increases within a set time period compared to bass frequencies. Because more energy is packed into the same period of time, less power is required to reproduce higher frequencies. This is the reason we use pink noise for a random measurement source signal, it contains equal power density across the audio spectrum.

[byacey]

I don't know if i understand your question correctly, but amplifiers output varies over the freq band. The power specs that most manifacturers write are based on 1khz. The actual power at <100hz can sometimes be much lower.

Example:
Carvin DCM2500, rated 4ohm 900WPC @ 1K (where most mfgs take readings)
In actuality:
20hz-408WPC
1k-795WPC
20k-1024W

While it's not lying by much at 1k, look at the real sub reading!

You get other random results-
Lab gruppen fp6400, rated 4ohm 2300WPC @ 1k
20hz- 1327W
1k- 2310W
20k- 648W

QSC PL6.0 PFC, rated 4ohm 2600WPC @1k
20hz- 2289
1k- 2549
20k- 2890

Hope this answers your question, if not i misunderstood.

There's something wrong with these numbers. In the hundreds of power amps I have tested, (with the exception of some tube amplifiers) given a steady 120V line voltage, and the amp driving a resistive dummy load just before clipping, they are pretty flat across the entire spectrum within a 1 or 2 dB.

[Israel]

Any reasonable quality amplifier will be flat across the spectrum as far as power output. You might experience a little bit of power supply sag when run full bore into a load, but generally the output voltage will be constant 20Hz to 20KHz.

What does change is the power spectral density requirements of the transducers across the audio band to reproduce what we perceive as flat frequency response. As frequency goes up, the power density of the spectrum increases within a set time period compared to bass frequencies. Because more energy is packed into the same period of time, less power is required to reproduce higher frequencies. This is the reason we use pink noise for a random measurement source signal, it contains equal power density across the audio spectrum.

+1 that is a reasonable and very factible explanation. thanks

[Israel]

I don't know if i understand your question correctly, but amplifiers output varies over the freq band. The power specs that most manifacturers write are based on 1khz. The actual power at <100hz can sometimes be much lower.

Example:
Carvin DCM2500, rated 4ohm 900WPC @ 1K (where most mfgs take readings)
In actuality:
20hz-408WPC
1k-795WPC
20k-1024W

While it's not lying by much at 1k, look at the real sub reading!

You get other random results-
Lab gruppen fp6400, rated 4ohm 2300WPC @ 1k
20hz- 1327W
1k- 2310W
20k- 648W

QSC PL6.0 PFC, rated 4ohm 2600WPC @1k
20hz- 2289
1k- 2549
20k- 2890

Hope this answers your question, if not i misunderstood.

There's something wrong with these numbers. In the hundreds of power amps I have tested, (with the exception of some tube amplifiers) given a steady 120V line voltage, and the amp driving a resistive dummy load just before clipping, they are pretty flat across the entire spectrum within a 1 or 2 dB.

I dont rely on watts anymore. we are talking here of measures with a steady dummy load but speakers are so dynamic that you can not expect they sound the same at any two separate moments, events ,even the same setup do not sound the same on different places thats why i still reccurring to this and some other forums, cause there are some things that you can expect or explain

[Bill Fitzmaurice]

This is the reason we use pink noise for a random measurement source signal, it contains equal power density across the audio spectrum.

We use pink noise because its power density drops by 3dB with each octave increase in frequency, just like audio content. White noise has constant power density.

[byacey]

I didn't word that correctly; read: Equal energy across the audio spectrum ( octave by octave).