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Amplifier Power: How much do you really need and your system’s dynamic range.

RayDunzl

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I wonder what the frequency spectrum of music is? We know it is music dependent. It also takes more power the lower the freq to get equal loudness with higher ones.

Here's one FFT of music found with a quick search. I could not find the name of the music.

That might represent a moment of music.

You can drag a file onto the RTA window of REW and see the whole tune.

Here is the peak levels of Track 1, Don Fagen - Nightfly

1619370798732.png


Track 1, Daft Punk, RAM

1619370892287.png



Track 1, Beatles, Sgt Pepper

1619370969001.png



Pipe Organ

1619371147526.png


Stravinsky, Rite of Spring, Redwood Symphony

1619371483052.png
 

Ingenieur

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That might represent a moment of music.

You can drag a file onto the RTA window of REW and see the whole tune.

Here is the peak levels of Track 1, Don Fagen - Nightfly

View attachment 126261

Track 1, Daft Punk, RAM

View attachment 126262


Track 1, Beatles, Sgt Pepper

View attachment 126264


Pipe Organ

View attachment 126265

Stravinsky, Rite of Spring, Redwood Symphony

View attachment 126266
So based on area under the curve using the high freq low level as basis average freq is 600-1000 Hz in each case?
 

RayDunzl

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Belker

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Woa. What do you mean by "struggles"? I have 8R 91db jbl speakers and was just about to place an order for purifi eigentakt rated 200w into 8 thinking it's more than enough..
ET400 being 200 w is a bit of a stretch. More like 130 before distorsion skyrockets.
 

RayDunzl

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So based on area under the curve using the high freq low level as basis average freq is 600-1000 Hz in each case?

There is a tendency for music, as is usually mastered to follow this curve, in my opinion:

1619372351970.png


Occasionally there will be a little more bass, occasionally the rolloff doesn't start at 1000Hz, all tunes are different.

But the above represents what is typically seen for peak values.

Only a pure tone (no harmonics, no other instruments) could rise to 0dBfs. -20dBfs is a typical limit for all frequencies when more than one plays simultaneously.

Carla Bley, Wrong Key Donkey

1619372727287.png
 

audiofooled

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There is a tendency for music, as is usually mastered to follow this curve, in my opinion:

View attachment 126268

Occasionally there will be a little more bass, occasionally the rolloff doesn't start at 1000Hz, all tunes are different.

But the above represents what is typically seen for peak values.

Only a pure tone (no harmonics, no other instruments) could rise to 0dBfs. -20dBfs is a typical limit for all frequencies when more than one plays simultaneously.

Carla Bley, Wrong Key Donkey

View attachment 126270

That looks just about right. Perhaps someone "In the know" could elaborate how much power is required for these transients in the bass region. I mean these complex waveforms containing what looks like instantaneous frequency peaks anywhere in between low 30's up to 100's or so. This baffles me a lot because I cannot determine what's going on. When listening to music real time, on the FFT it shows this "tsunami" peak of wide range of bass frequencies. On the listening position it is perceived as a sum of this, all at once. Subjectively it hits chest cavity resonance and the rest of the body in an instant when played loud enough. Also, subjectively, I can imagine it discharges quite a lot of power in a very, very short interval. Anyone?

I mean, if this peak hits this -20, dBFS, and you like to listen 85 db SPL average, 10 watts per channel are never gonna cut it, not even a 100, right? How demanding on the amplifier is this?

EDIT: I know it all depends on speaker sensitivity, impedance, etc. But this "bass burst" sure must suck more power than just a narrower peak at about 40 Hz?
 
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Pegwill

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Hi

Would a contributing factor also be the thickness of the speaker wire? To thin and it would not pass sufficient power not sure if to thick would be a problem, except what would to thick look like? Not sure about the thickness of the cables internal to the amp as they are generally very short in comparison.

Just my thoughts

Regards

William
 

Spkrdctr

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Yep, just use a warble tone (wobble) at 30Hz and use the SPL meter on C and A weighing. There should be a 40dB difference.

What about using a non-warble tone? I don't have a warbler but I'd like to do the test if appropriate.
 

Frgirard

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So the air pressure is oscillated 2/sec or 2 Hz.
Isn't that what a speaker does?
Causes a pressure variation?
What is the wavelength of a 2/sec air pressure variation?
The pressure part define the wave.
The wave length is the velocity part of the wave. The velocity part can not exist without the pressure part.

A mic at 1 cm of a sealed speaker able to 20Hz, you will measure 20 Hz
If you will have a speaker able to 2Hz, this is the same thing
In an headphones the velocity part does not exist. In car the velocity part concern mid and high frequencies.

The link between room lenght and wave length is an audiophile myth.
The room has a room gain and without room gain no bass with spl.
this room gain can extend the low frequency performance.
At home i have been a kh 810 18Hz at - 3dB. With the room gain 15 dB at 0dB for a cal level of 80 Hz.
A beautiful curve but inaudible.
 
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amirm

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My Purifi amp struggles driving my 86dB / 6Ohm speakers while playing large orchestral music. All this since I implemented Dirac Live! Waiting for the 1kW Purifi ...
Indeed. Dirac aggressively attempts to fill in the dips and causes the amp to run out of juice. I had to move up from the Purifi to my 400 watt ML amp and even there, it almost ran out of power!
 

Ingenieur

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The pressure part define the wave.
The wave length is the velocity part of the wave. The velocity part can not exist without the pressure part.

A mic at 1 cm of a sealed speaker able to 20Hz, you will measure 20 Hz
If you will have a speaker able to 2Hz, this is the same thing
In an headphones the velocity part does not exist. In car the velocity part concern mid and high frequencies.

The link between room lenght and wave length is an audiophile myth.
The room has a room gain and without room gain no bass with spl.
this room gain can extend the low frequency performance.
At home i have been a kh 810 18Hz at - 3dB. With the room gain 15 dB at 0dB for a cal level of 80 Hz.
A beautiful curve but inauble.
Not sure I'd call it a myth.
In a 10 ft. room a sub can vary pressure at 20 Hz, and you will feel it, but not discern a tone.

I did not say a folded/reflected wave would not exist. We were talking about power amplifiers/speakers not headphones. I could see how a headphone basically coupled to the ear could vibrate the drum at any frequency.

If the room is too small you will not get good sounding bass below a geometrically determined threshold.

Driving up a mountain and back down in 10 minutes is a pressure 'wave', starts at relative 0, goes down, then back to 0
1/2 wavelenth
f = 2 x 1 / 600 = 0.0033 Hz

https://www.acousticfields.com/wavelengths-in-our-rooms/
 
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gonzoucab

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Indeed. Dirac aggressively attempts to fill in the dips and causes the amp to run out of juice. I had to move up from the Purifi to my 400 watt ML amp and even there, it almost ran out of power!
Can i ask what amps do you have Ammir?
 

Ingenieur

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63 Hz, ~ 70 dBC instantaneous
~ 15-20 mW on meter? Estimated


Z = cos 8 x 4.1 = 4 Ohm
P = 0.288^2 x 4 = 0.02 W

I would have thought the difference would be greater?
1000 Hz same level
0.01 mW
230 mV
 

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solderdude

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Now measure it on dBA setting which was the whole point.

or better yet... measure music (with lows, not girl & guitar) on 70dBA average and then measure dBC on peak levels.
 

Belker

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Indeed. Dirac aggressively attempts to fill in the dips and causes the amp to run out of juice. I had to move up from the Purifi to my 400 watt ML amp and even there, it almost ran out of power!
Would love to see those MLs on the bench!
 

solderdude

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Hi

Would a contributing factor also be the thickness of the speaker wire? To thin and it would not pass sufficient power not sure if to thick would be a problem, except what would to thick look like? Not sure about the thickness of the cables internal to the amp as they are generally very short in comparison.

Just my thoughts

Regards

William

II would say it would be 1dB difference at the most when the impedance of the speaker goes really low between a thin and thick wire of equal length.
 

solderdude

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What about using a non-warble tone? I don't have a warbler but I'd like to do the test if appropriate.

An alternative is a narrow filtered noise band. 30Hz is asking for room modes so dB levels could easily differ 10dB or so.
 

RayDunzl

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Perhaps someone "In the know" could elaborate how much power is required for these transients in the bass region.

The recording is the driver of power levels, look to the waveform for the initial clues.

The waveform represents the request for voltage from the amplifier by the recording to be applied to the speaker terminals.

As for "bass transients", uh, there aren't any. Bass is slow slow slow.

In the organ piece above, here is the highest voltage request. Ooh... looks like an abrupt change, and hard to reproduce... The clip is about 2 milliseconds in length.

1619383454268.png


Let's call that peak 50V. Loud. 625Watts into 4 ohms load loud.

Now zoom in on that "transient". The dots are sample values, and are 0.000023 seconds apart - 23 microseconds.

1619383613048.png


The slew rate - rate at which an amplifier can change voltage - "Most well designed amplifiers are flat out to 100kHz so in that case you would need a minimum slew rate of about 32V/usec in order to achieve such a wide bandwidth". - https://www.audioholics.com/audio-amplifier/amplifier-slew-rate

So, for this example, assuming 50V peak of the music waveform, might need to move 2 or 3 volts in 23 uS, well below its capability.

There are faster transients, none should really tax a decent amplifier's ability to follow the waveform, if the amplifier's bandwidth exceeds the bandwidth of the musical signal, and it can flow current as demanded by the load at the requested voltage.
 
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Ingenieur

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Now measure it on dBA setting which was the whole point.

or better yet... measure music (with lows, not girl & guitar) on 70dBA average and then measure dBC on peak levels.

I determine the 'point' ;)
dBA 45
I know what was wrong, started working out right after posting and realized I left the sub on! Lol
Without sub
63 Hz ~70 dBC
Calculated P = 0.91^2 x 4.1 cos8 = 0.21 W
Since R = 4 the meter is spot on.

1000 Hz, ~70 dB
0.01 W

0.01 to 0.2 ~ 13 dB W
2 x P = 3 dB SPL
2^13/3 = 20, 20 x 0.01 W = 0.2 W

I previously estimated 0.35 W for 31.5 Hz
1 Oct power ~ 3 dB
So 31.5 Hz or 2 x 0.2 ~ 0.4 W
 

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