Wattage Required for Equal Output at All Frequencies

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The power requirements are not only different for different music, but for different cabinet frequency response.
For instance, a sealed cabinet with a response 10 dB down at 30 Hz could be equalized flat using 10 times the power at 30 Hz than at 60 Hz, while another design that is flat to 30 and the same sensitivity at 60 Hz would use 1/10 the power at 30 Hz.

If you look at a musical spectrum that is 10 dB more bass heavy (say the difference between folk and hip-hop) and different cabinet designs, the difference could be 100 times, the folk music with an efficient cabinet would use 1 watt while the hip-hop with a sealed cabinet uses 100 watts.

The simplest way I can explain my question is:

A full range amplifier sees a 2000Hz signal and amplifies it accordingly just as it would to a 20Hz signal. BUT, how does it KNOW how to amplify each frequency I mentioned by WHAT AMOUNT in order to keep the amplification between +/-1dB or +/-3dB over that 2000Hz to 20Hz range????

Amplifiers always state someting like: 20Hz to 20kHz +/-3dB. So, the manufacturer must have done testing that proves its output wattage at any specified frequency is within +/-3dB, right?

I want to know the electrical (not driver in an enclosure) equation behind those tests.
 
Don't shoot me if I'm wrong.

Byt my guesstimate would be that they measure output/frequency using dummy loads, I've done this before, but I cannot answer for mass producers or other diy'ers. Dummy loads of maybe 4ohm, then moving up to 8ohm to check for difference.

Most speakers have a given sensitivity pr voltage, NOT wattage. The ideal Amplifier is stupid, it amplifies everything just the same amount. The difference would be the load the speaker presents, in passive filters, and nominal impedance over the passband. A woofer needs more current because it may be 12ohm at 150hz, but it may be under 5 at 30hz (frequencies mentioned are just examples, but impedance generally lowers with frequency on most common drivers).

Does it make any sense?

Edit:
I am just saying as mentioned before in this thread, the impedance of the drivers passband is what determines the power needed. So I would say, determine where to cross over the driver, calculate how much power the driver would need average over the specified range, then double it (3db) to allow for variations like temperature/short peaks and so on. Just like a sub should have + 3 to 6db for it's range, because the impedance will dip well below the rated impedance, demanding more current from the amplifier.
 
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A full range amplifier sees a 2000Hz signal and amplifies it accordingly just as it would to a 20Hz signal.
The equations are much easier for a resistive load and/or a single test tone, but I'm not sure I can accept the above premise outright. If 2kHz is at 0dB but 20Hz is -3dB, then 20Hz is only half the power of 2kHz. That appears to be a 50% error in this context(?). For a strictly flat response between aHz and bHz, the frequencies are amplified equally, and the amplifier isn't the wiser. The circuit designer may be, though.
I admit I'm not completely un-confused by the question.
 
The equations are much easier for a resistive load and/or a single test tone, but I'm not sure I can accept the above premise outright. If 2kHz is at 0dB but 20Hz is -3dB, then 20Hz is only half the power of 2kHz. That appears to be a 50% error in this context(?). For a strictly flat response between aHz and bHz, the frequencies are amplified equally, and the amplifier isn't the wiser. The circuit designer may be, though.
I admit I'm not completely un-confused by the question.

I agree, dummy loads in labs are one thing.

2,83V/8ohm = ~1w, but this changes over the entire spectrum with all drivers I've seen. Ohms law is the governing factor for power vs frequency.
 
Look at the xmax curve of any driver. Someone said above that for every octave lower in frequency a driver has to move four times as far (if I recall correctly).

The lower in frequency a signal goes, the more mechanical energy it requires to couple the electrical signal to the air.

The math is really beyond me, but it is observable that at some point the sound ceases to be heard and is felt. This is an indication of the mechanical energy in play. I think the answer to your question lays in graphs of human hearing sensitivity and transducer frequency dependent efficiency.

The more bass extension one wants, because of the mechanical limitations and inefficiencies and increased energy needed to reproduce lower frequencies, you will need more power, since everything else ceases to be equal.

(Love your sig Kaffiman ;) )
 
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You mentioned spectrum power. Long ago (1998?), I wrote a C program that did windowed FFT's on any track/song from my CD collection
Very cool! That should be interesting to see what it finds.

I've done it the lazy man's way, with DSP hardware. I set a DCX2496 into 2-way or 3-way crossover mode and moved the crossover points around until I saw the VU meters lighting up the same on each section. Easy with 2-way, not so fast or easy with 3-way.

The equal energy points shifted a bit depending on the signal or musical style. I never did write anything down, but it would not be hard to do again. Having software do it for you and run thru a stack of music files would be cool research. :up:
 
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Hip-Hop is pretty bass heavy. Not like dubstep, tho.
Compare below the track "The Wall" (left) with "Kill You" by Eminem (right)
This gives you a good idea of the tonal balance. Floyd goes lower, but is not as pumped up in the bass.
 

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Amplifiers always state someting like: 20Hz to 20kHz +/-3dB. So, the manufacturer must have done testing that proves its output wattage at any specified frequency is within +/-3dB, right?

I want to know the electrical (not driver in an enclosure) equation behind those tests.

This kind of question is better asked in one of the amplifier forums, but I will take a stab at it here.

The typical amplifier is a gain stage at it's simplest. This just scales up the input voltage by some factor like 30x, and provides means to supply large currents that are needed to drive loudspeaker drivers.

For certain reasons, it is good practice to "roll off" the voltage gain of the amplifier at the low and high frequency extremes. In general, the voltage gain curve (essentially the same as the frequency response) is "flat" in the middle (the audio band) and rolls off below and above that. There aren't otherwise frequency anomalies like peaks and valleys in the frequency response, typically. This level of information is probably seen as too "engineering mumbo jumbo" to the marketing department, and wrapping that up in to a little spec like 20-20kHz +/-3dB makes them much happier, so that is what you see. When you see that kind of spec, think "the drooping of the frequency response at 20Hz and 20kHz must be less than 3dB". Otherwise you will be reading through all sorts of charts and such, and the average consumer has no basis with which to interpret this kind of information, so it's not offered.

One other point... As another poster mentioned, most specs (if not all) are obtained into resistive loads. Everyone knows that a loudspeaker load has inductive and capacitive aspects to it. How to standardize testing into complex loads is not really established, although I recently read about a simulated loudspeaker circuit that Stereophile used to test amplifier distortion. I'm not sure that this would change the frequency response, but possibly the distortion performance and maximum output power level depending on the phase angle of the load. This is just speculation on my part, however.

-Charlie
 
Hip-Hop is pretty bass heavy. Not like dubstep, tho.
Compare below the track "The Wall" (left) with "Kill You" by Eminem (right)
This gives you a good idea of the tonal balance. Floyd goes lower, but is not as pumped up in the bass.

My greatest appologies, for some reason I was thinking about Dark side of the Moon when I said the wall. In any event, I agree with what you're saying. I'd be interested to see...or even participate in what it takes to gather this information.

I've got about 70,000 tracks in my music collection. For reference, the track I was thinking of in my original comment was "Speak to Me" from Pink Floyd's Dark side of the Moon, which has a pretty viceral heartbeat sound..which I find very, very fun to play extremely loud.
 

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This kind of question is better asked in one of the amplifier forums, but I will take a stab at it here.

The typical amplifier is a gain stage at it's simplest. This just scales up the input voltage by some factor like 30x, and provides means to supply large currents that are needed to drive loudspeaker drivers.

For certain reasons, it is good practice to "roll off" the voltage gain of the amplifier at the low and high frequency extremes. In general, the voltage gain curve (essentially the same as the frequency response) is "flat" in the middle (the audio band) and rolls off below and above that. There aren't otherwise frequency anomalies like peaks and valleys in the frequency response, typically. This level of information is probably seen as too "engineering mumbo jumbo" to the marketing department, and wrapping that up in to a little spec like 20-20kHz +/-3dB makes them much happier, so that is what you see. When you see that kind of spec, think "the drooping of the frequency response at 20Hz and 20kHz must be less than 3dB". Otherwise you will be reading through all sorts of charts and such, and the average consumer has no basis with which to interpret this kind of information, so it's not offered.

One other point... As another poster mentioned, most specs (if not all) are obtained into resistive loads. Everyone knows that a loudspeaker load has inductive and capacitive aspects to it. How to standardize testing into complex loads is not really established, although I recently read about a simulated loudspeaker circuit that Stereophile used to test amplifier distortion. I'm not sure that this would change the frequency response, but possibly the distortion performance and maximum output power level depending on the phase angle of the load. This is just speculation on my part, however.

-Charlie

Well, an amplifier into a speaker represents such a complex load, but we can overcome that with brutish amplifiers and large, bristling power supplies. I'd suspect that the difficulty of driving strange loads can be answered by simply having an amplifier that's built like a firefighter.
 
Cool, thanks. FWIW, the equal energy point of "Brick in the Wall" is about 300 Hz and the rap track maybe 280 Hz. An octave or more below that of pink noise. Unless I measured wrong.

Right. Equal energy aside though, we should be wary of tracks that seem benign, but at some point become absolutely brutal.

Case in point, BT's Go(d)t. It's a 10 minute track, but if you look at the last few minutes of it, he changes the bass drum thump so that it's absolutely outrageous.

If you were to look at the track in "average" format it would look like a fairly standard EDM track, however the latter half of it will pop woofers out of their coil gaps if not handled with care.
 

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