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Topic: Amp power and current (Read 52857 times) previous topic - next topic
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Amp power and current

Reply #175 –
Quote from: xnor on
You are confusing several things here, Rich B.

Higher power handling capabilities simply tells you that the speaker can take more power without taking damage. That's it.


Generally agreed.

However, there are a  lot of specsmanship and non-standard rating methodologies in use.

It is possible that the alleged higher power handling capabilities are imaginary or hype.

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Higher sensitivity tells you that for a given voltage (therefore power), the speaker will produce higher sound pressure. This is usually specified in dB SPL. (SPL specifies the reference for the dB)


This is yet another number that can and is fudged any number of ways.

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Increasing voltage (therefore power) does increase sound pressure produced by the speaker. You can specify both ratios (higher power : lower power, or higher sound pressure : lower sound pressure) with dB.


Another possible target of imagination, fudging or hype.

"Common Sense" physical evidence can be highly misleading.

The alleged issue of vibration in audio gear can be used to justify using a 1/4" thick sheet of steel plate as the top or bottom of the chassis...  Putting transformers in neat looking heavy drawn steel enclosures sure looks neat in the chassis photographs...

Larger boxes, more and/or larger drivers can be meaningless because the big controlling factor there is Xmax and that number is rarely available.

Amp power and current

Reply #176 –
Quote from: Rich B on
He said not to mistake more power for more SPL.


Quite correctly pointing out that they are not the same thing.

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I said that if you double the power you get more SPL.


That does not mean that power and SPL are the same thing.

And double the power of what?

That is why I said that you didn't provide enough context.

Amp power and current

Reply #177 –
Quote
Quite correctly pointing out that they are not the same thing.


But if you apply more power then the SPL goes up. How can you talk about volume or SPL without discussing power? A byproduct of more power is more SPL. So again, I don't see how you can not talk about more volume/spl when more power is involved.

Amp power and current

Reply #178 –
Quote from: Rich B on
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Quite correctly pointing out that they are not the same thing.


But if you apply more power then the SPL goes up.


To a point, and oh by the way the SQ goes down.

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How can you talk about volume or SPL without discussing power?


How can you talk about volume or SPL without mentioning loudspeaker efficiency and nonlinear distortion?



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A byproduct of more power is more SPL.


Only if efficiency remains the same, the speaker is capable of linearly transforming power into SPL and the listener's ears remain linear and comfortable.

None of those are givens, not one of them!

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So again, I don't see how you can not talk about more volume/spl when more power is involved.


I think this is the second or third time the following has been mentioned on this thread just lately: More power can only effectively increase SPL if loudspeaker efficiency remains the same, the speaker is capable of linearly transforming the additional power into SPL and the listener's ears remain linear and comfortable. No, nine, nichts, not one of those things is a given.  Not one!

Amp power and current

Reply #179 –
Quote from: Rich B on
But if you apply more power then the SPL goes up.


I assume what you are saying is "if I increase the power actually going into the loudspeaker, the SPL goes up". Generally, yes, but as speakers get warmer from the applied power, their efficiency goes down.

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How can you talk about volume or SPL without discussing power?


By talking about volume without discussing power.

I guess part of the problem is that you are not very good at expressing yourself precisely. Note I had to ask "double the power of what?" in my previous message, and you didn't reply.

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So again, I don't see how you can not talk about more volume/spl when more power is involved.


Please, go back and read what I wrote. And assume I actually meant what I wrote. Literally.

There is a difference between "talk about X" and "X and Y are the same thing".

To use your phrasing, you can't talk about breathing without talking about air. That doesn't mean air and breathing are the same thing.

Might sound like nit picking to you, but engineering is all about making sure not too many nits clog the wheels. Science is worse.

Amp power and current

Reply #180 –
Quote
I assume what you are saying is "if I increase the power actually going into the loudspeaker, the SPL goes up". Generally, yes, but as speakers get warmer from the applied power, their efficiency goes down.


Yes, sorry, I meant power going into a speaker. I assumed that was a given.

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I guess part of the problem is that you are not very good at expressing yourself precisely. Note I had to ask "double the power of what?" in my previous message, and you didn't reply


Double the wattage, like going from 10 watts to 20 watts, equals 3 dB increase in SPL. Yes, I probably am not good at expressing myself clearly.

Amp power and current

Reply #181 –
Quote
Only if efficiency remains the same, the speaker is capable of linearly transforming power into SPL and the listener's ears remain linear and comfortable.


Why must efficiency remain the same? If I input 1W into any efficiency speaker, and double the power, or triple the power, the SPL will go up. Going from 1-2 watts, or 2-4 watts, or 10-20 watts. Why wouldn't this apply regardless of efficiency? I'm not talking about 150 watts, or 300 watts, 500 watts. I'm using small numbers here.

Amp power and current

Reply #182 –
Quote from: Rich B on
Yes, sorry, I meant power going into a speaker. I assumed that was a given.


Several of us pointed out things it could have meant, such as rated power.

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Double the wattage, like going from 10 watts to 20 watts, equals 3 dB increase in SPL.


As I and others have pointed out, not always.

What you are stating is that there is a linear relationship. That is different from "is the same as". And as we keep pointing out, the relationship is not even linear in all cases.

Amp power and current

Reply #183 –
Consider this:


Look at the right graph, the upper three lines:
black = 85 dB SPL
green = 90 dB SPL
blue = 95 dB SPL

.. at least, that is what the speaker should produce (let's say at 200 Hz) given the supplied voltage. But, surprise, surprise, it doesn't!


Now look at the lower three lines (the SPL of harmonic distortion products). Compare the distance between lines of the same color.
at 100 Hz
black = -30 dB = 3%
green = -25 dB = 5.6%
blue = -20 dB = 10%

(Obviously, this speaker has a much more serious problem around 900 Hz, where distortion reaches 60%)
"I hear it when I see it."

Amp power and current

Reply #184 –
Quote from: xnor on
Look at the right graph, the upper three lines:
black = 85 dB SPL
green = 90 dB SPL
blue = 95 dB SPL

.. at least, that is what the speaker should produce (let's say at 200 Hz) given the supplied voltage. But, surprise, surprise, it doesn't!


Now look at the lower three lines (the SPL of harmonic distortion products). Compare the distance between lines of the same color.
at 100 Hz
black = -30 dB = 3%
green = -25 dB = 5.6%
blue = -20 dB = 10%

(Obviously, this speaker has a much more serious problem around 900 Hz, where distortion reaches 60%)


Great example of how nonlinear speakers can be.

But at $130/pr with fancy Bluetooth electronics, what should we expect?

To add perspective here is a THD @ 90 dB SPL measurement for the very modest (< $100 ea) Primus P162:



and to show what much more money can buy you, the $1500/pr Revel F12:





Amp power and current

Reply #185 –
Yeah I deliberately picked the worst example I could find quickly.

Regarding the images you posted, I hope we can agree that there's of course more to speaker performance than just a single THD plot. (I'm not saying that either speaker is better or worse, because as we've seen before, expensive speakers can be crap too.)
"I hear it when I see it."

Amp power and current

Reply #186 –
So just to put this thread to bed :

1. The power to the load is not defined by the rated power of the amp
2. The power to the load is defined by the voltage applied across the speaker terminals, the speaker efficiency and the speaker impedance
3. Thermal rating has nothing to do with sound quality at all. It is just a rating to tell one how close or far one is from overheating their speaker
4. The current through the load is defined by the load, not the amp, so it doesn't matter how large or how high current the amp is, so long as the amp is not clipping.

Is that about it?

Edit :

5. If an amp must supply 15 watts to hit a specific SPL in a room with a specific speaker, then whether the amp can supply 80 watts or 200 watts, the current to the load, will remain the same, at the same voltage, at 15 watts.

Both amps are constrained by Ohms Law to supply the same power to the load, at the same voltage. Unless one exceeded the amps capabilities.

Amp power and current

Reply #187 –
Quote from: Rich B on
So just to put this thread to bed :

1. The power to the load is not defined by the rated power of the amp
2. The power to the load is defined by the voltage applied across the speaker terminals, the speaker efficiency and the speaker impedance
3. Thermal rating has nothing to do with sound quality at all. It is just a rating to tell one how close or far one is from overheating their speaker
4. The current through the load is defined by the load, not the amp, so it doesn't matter how large or how high current the amp is, so long as the amp is not clipping.

Is that about it?

Edit :

5. If an amp must supply 15 watts to hit a specific SPL in a room with a specific speaker, then whether the amp can supply 80 watts or 200 watts, the current to the load, will remain the same, at the same voltage, at 15 watts.

Both amps are constrained by Ohms Law to supply the same power to the load, at the same voltage. Unless one exceeded the amps capabilities.



Looks like 5 relevant, true statements to me.

Amp power and current

Reply #189 –
Quote from: Rich B on
1. The power to the load is not defined by the rated power of the amp
2. The power to the load is defined by the voltage applied across the speaker terminals, the speaker efficiency and the speaker impedance
3. Thermal rating has nothing to do with sound quality at all. It is just a rating to tell one how close or far one is from overheating their speaker
4. The current through the load is defined by the load, not the amp, so it doesn't matter how large or how high current the amp is, so long as the amp is not clipping.
5. If an amp must supply 15 watts to hit a specific SPL in a room with a specific speaker, then whether the amp can supply 80 watts or 200 watts, the current to the load, will remain the same, at the same voltage, at 15 watts.
Both amps are constrained by Ohms Law to supply the same power to the load, at the same voltage. Unless one exceeded the amps capabilities.


1. Yes.

2. To be strict, voltage and impedance only.
(Efficiency tells you how good the speaker is at converting electrical into sound power. When you operate the speaker near the max. levels, the voice coil will heat up increasing speaker impedance. So the amount of power the speakers draws for a given voltage will go down. That's known as power compression.)

3. I'd call it power handling and due to the above effect (power compression), sound quality will actually suffer if you operate the speaker at this limit.

4. Yes. (I wouldn't say an "amp is high current", but "an amp that has high current output capabilities". The load draws current as needed.)

5. Yes.
(Although in some rare cases the amp has a high output impedance, which will result in the output voltage varying a bit with the impedance of the load. )
"I hear it when I see it."

Amp power and current

Reply #190 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
So just to put this thread to bed :

1. The power to the load is not defined by the rated power of the amp
2. The power to the load is defined by the voltage applied across the speaker terminals, the speaker efficiency and the speaker impedance
3. Thermal rating has nothing to do with sound quality at all. It is just a rating to tell one how close or far one is from overheating their speaker
4. The current through the load is defined by the load, not the amp, so it doesn't matter how large or how high current the amp is, so long as the amp is not clipping.

Is that about it?

Edit :

5. If an amp must supply 15 watts to hit a specific SPL in a room with a specific speaker, then whether the amp can supply 80 watts or 200 watts, the current to the load, will remain the same, at the same voltage, at 15 watts.

Both amps are constrained by Ohms Law to supply the same power to the load, at the same voltage. Unless one exceeded the amps capabilities.



Looks like 5 relevant, true statements to me.


Xnor is right. (2) contains a superfluous element, efficiency. Efficiency speaks to how loud, but it has nothing to do with power delivered.

Amp power and current

Reply #191 –
Thanks for the explanation. I'm trying to change the way I think about things and will try to express myself better in future to avoid any misunderstandings.

Amp power and current

Reply #192 –
Quote from: Rich B on
Thanks for the explanation. I'm trying to change the way I think about things and will try to express myself better in future to avoid any misunderstandings.


I think it is interesting to see how thinking about power amps in a correct technical way as opposed to the usual audiophile myths affects equipment choices.

The audiophile myth is that a more powerful amp will always sound more powerful and therefore better. That puts the purchasers on an everlasting treadmill of amplifier upgrades because there is never enough power.

The technical facts are that once you have enough power to avoid audible distortion, which in modern times means avoid clipping, you don't need to worry about obtaining a more powerful amplifier.

Amp power and current

Reply #194 –
Quote from: julf on
Quote from: Arnold B. Krueger on
you don't need to worry about obtaining a more powerful amplifier.


As long as it goes to 11...



Interestingly enough I was just reviewing some old AES papers and found a reference to Fielder stating that the average TV listener's preferred SPL is about 70 dB.  Yup, the same Fielder that one of our more vocal posters refers to all the time in his critiques of the CD format.

Amp power and current

Reply #195 –
So in order for one to use the rated power of the amplifier, the amp would need to be supplying the maximum voltage it can supply, and this depends on the volume, and also on the dynamic range of the signal?

If I turn the volume all the way, that doesn't guarantee anything. I imagine the signal would need to have a very high crest factor, so the peaks would demand more voltage from the amp.

Amp power and current

Reply #196 –
Quote from: Rich B on
So in order for one to use the rated power of the amplifier, the amp would need to be supplying the maximum voltage it can supply


To be precise, the amp would need to be supplying the maximum power it can supply. Depending on the load impedance, the amp might be voltage limited or current limited.
Your statement is only true if the load impedance is high enough that the amp is voltage limited.

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and this depends on the volume, and also on the dynamic range of the signal?


Are we talking about peak power or average power?

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If I turn the volume all the way, that doesn't guarantee anything. I imagine the signal would need to have a very high crest factor, so the peaks would demand more voltage from the amp.


Not really. The highest sustained power output would probably be with a square wave, with a crest factor of 1 (0 dB).

Amp power and current

Reply #197 –
I'm just trying to understand what would be required in order for a given amp that has a given rated power to exploit that rated power. And you are saying that is load dependent?

I'm sure earlier you said more power = more voltage. But maybe I misread what you meant.

Amp power and current

Reply #198 –
About the power handling, so if you approach the power handling limits of any speaker, distortion both linear and nonlinear tends to increase. What about mechanical non-linearities?

Amp power and current

Reply #199 –
Quote from: Rich B on
I'm just trying to understand what would be required in order for a given amp that has a given rated power to exploit that rated power. And you are saying that is load dependent?


Yes. I am pretty sure we have stated that a number of times. Power is voltage * current. Current depends on load (and voltage). According to Ohm's law, current is voltage divided by resistance.
If you combine those two formulas, you get Power = voltage * current = voltage * voltage / resistance. So power is proportional to the square of the voltage, and inversely proportional to load resistance.

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I'm sure earlier you said more power = more voltage. But maybe I misread what you meant.


I did. Power is proportional to the square of the voltage, and inversely proportional to load resistance.