Amplifier power / question for the EE's

[Dimitrov]

Hi there,

For this example, assume a fixed SPL. Let's assume you have 2 solid-state amps. One is rated to deliver 100 watts, another 300 watts. If you listen at a fixed SPL, still well below the limits of the 100 watt amp and change amplifiers to the more powerful 300 watt model, the voltage/current into the load remains the same? Or does anything change?

The reason I'm asking is because I had a friend who told me his B&W speakers "like" power. But I can't wrap my head around that. Speakers react to voltage - assuming fixed SPL in both cases, the voltage and current to the load must remain the same surely according to Ohms Law?

The speaker won't "see" the extra power unless you apply a higher voltage. Am I right here? Or is there something I'm missing here?

 

[Mad_Economist]

While rated power is not significant here, there is a case where, for a constant input level to both amplifiers and equal gain for both, you'd still see a change: if the output impedance of the amplifiers meaningfully differed. In this case, the voltage "seen" by the speakers could increase for the amplifier with lower Zout, with a proportionate rise in SPL (although this would likely not be constant with respect to frequency). This is not very likely, however, as solid state power amplifiers typically have very low output impedance relative to the impedance of the load (the speakers).

An additional case where a 100W and 300W amp could theoretically differ audibly would be if the distortion of the lower-rated amplifier was a particularly audible sort - let's say something with a lot of high order harmonics relative to the lower order, more masked stuff - and its distortion rose substantially before it was near its maximum rated power. I would call this unlikely as well, however, since you don't see many amplifiers with that sort of distortion behavior (that is, both particularly audible distortion, and a lot of it long before clipping) - I actually can't think of one off the top of my head.

In general, I think it's often a wild goose chase to try to put these sorts of comments into a technical context (and often not appreciated by the people making them). There could be something we don't know about happening with your friend's B&W speakers and his two power amps, of course - but I would put a higher bet on your friend liking the extra power than the speakers

 

[Dimitrov]

Yeah, but when my friend makes comments like that I don't believe he means what he says - they "like" power - it's not as if he is using the rated power of the amp.

I think he assumes that simply changing the rated power will make the speaker sound better but rated power is just potential. The speaker doesn't "see" potential right? Unless you turn the volume up to the point where the lesser amp runs out of steam, the extra juice won't be detected by the speaker. It's just unused power.

That's my point. Will the speaker react any differently by virtue of simply raising the maximum (potential) power? Hence the requirement that the voltages applied are identical - SPL identical with both 100W and 300W power amp. Will the speaker use any more power using the bigger amp with assuming same applied voltage into the load?

Or do speakers have advanced circuitry built-in where they can somehow sense how much unused power is available across from their terminals and "feel" better as a result? I'm not the EE, but that idea just sounds preposterous to me.

 

[Mad_Economist]

Will the speaker use any more power using the bigger amp with assuming same applied voltage into the load?

Possibly, depending on your views on whether "cause more power to be used" is equal to "use more power" and the efficiencies of the amplifiers in question. You may not see more voltage over the speakers, but you might well see more heat in the room But...

Will the speaker react any differently by virtue of simply raising the maximum (potential) power?

While I suspect that this is rhetorical, the answer is, of course, no.

Or do speakers have advanced circuitry built-in where they can somehow sense how much unused power is available across from their terminals and "feel" better as a result?

That would have to be some pretty damn clever circuitry, given that even humans can't always quite agree on how much unused power something has - does the B&W only sound better if the amplifier can manage 300W in the FTC test, or will 300W peak for a period of a second do for keeping it happy?

 

[Theo]

Isn't the power rating refering to the current intensity the amp is able to provide? I guess your friend listens to loud music? Then when voltage is getting high enough, the 300W amp will be able to provide current distortion free when the 100W can't... So, there will be a difference when SPL gets high. I suppose, not so much at low volume.
If the speaker has a sensitivity of 88dB @1W, then the SPL @100W would be 108dB and the SPL @300W would be 112dB. Not much of a difference. To me 100dB SPL is loud enough, anyway...

 

[solderdude]

An amplifier is a (limited) voltage source with a current limit. voltage x current = Wattage.
It is usually rated in watts for a certain impedance under certain conditions.
How much Watts is dissipated in the speaker thus depends on its impedance and the supplied voltage.

A speaker does not 'want' nor 'demand or ask' power nor does it have any 'sensing' technology in there at all.
It draws power from a voltage source (the amplifier) which must be able to supply enough current belonging to that voltage.
The amplifier just has to deliver a voltage and the speaker draws current depending on its impedance (which varies per frequency)
The condition thus is: voltage and current must be enough for that speaker with its efficiency and impedance.

When using ineffiecient speakers it is quite possible to reach 100W peaks when listening loud.
Impedances can drop below the rated value and amps may be current limited.

The phrase used by that person is simply wrong. He should say:
My speakers are inefficient and needs more power than some other speakers to make it 'sing'.

edit: was crossposting with other members it seems ...

 

[Dimitrov]

An amplifier is a (limited) voltage source with a current limit. voltage x current = Wattage.
It is usually rated in watts for a certain impedance under certain conditions.
How much Watts is dissipated in the speaker thus depends on its impedance and the supplied voltage.

A speaker does not 'want' nor 'demand or ask' power nor does it have any 'sensing' technology in there at all.
It draws power from a voltage source which must be able to supply enough current.
The amplifier just has to deliver a voltage and the speaker draws current depending on its impedance (which varies per frequency)
The condition thus is: voltage and current must be enough for that speaker with its efficiency and impedance.

When using ineffiecient speakers it is quite possible to reach 100W peaks when listening loud.
Impedances can drop below the rated value and amps may be current limited.

The phrase used by that person is simply wrong. He should say:
My speakers are inefficient and needs more power than some other speakers to make it 'sing'.

edit: was crossposting with other members it seems ...

Right. Clipping is not a factor here in this example - so if equal voltage applied between 100 watt (rated) and 300 watt (rated), the current into the load cannot be any different is what I gather to be the correct answer.

The point here is that if the comparison was apples to apples (and they usually NEVER are) then whether the amp had twice or 10 times the current capacity compared to a lesser amp wouldn't affect that speaker if both are still operating well below their limits. It wouldn't perform any better, sound any better or feel any better at lower levels, where the lesser amps aren't close to clipping.

That's basically what I wanted to know. I get the feeling there are people out there that actually believe that this is true.

Of course if listening loud things can change quickly, but I wanted to eliminate that just to understand if changing the quota for power in and of itself would change speaker behaviour.

 

[solderdude]

Both amps can still 'sound' different (to someone) but would have nothing to do with 'power' in such a case but could be distortion, output impedance, FR related (as a technical reason) or some kind of personal bias that lets him believe such is the case.

When someone has the experience, or thought, the higher (or lower) powered amp sounds 'better' to them then most people will draw the conclusion that it must be the Wattage.

 

[Dimitrov]

Both amps can still 'sound' different (to someone) but would have nothing to do with 'power' in such a case but could be distortion, output impedance, FR related (as a technical reason) or some kind of personal bias that lets him believe such is the case.

When someone has the experience, or thought, the higher (or lower) powered amp sounds 'better' to them then most people will draw the conclusion that it must be the Wattage.

If you recall I started a thread a few weeks back on power amps over this belief. After doing research into various makes and models I noted the gain can vary significantly from model to model even if one keeps their volume position the same and this alone could account for the "difference" (I mean improvement) that is routinely reported.

Of course expectation bias is always a possibility, but a 3-4 dB difference in gain from one model to another is a significant enough difference that it could sound different (I mean better). But the same effect could be obtained by simply raising the volume on the lesser amp! Which makes me think that people are just swapping amps around and hearing gain differences, which is pointless IMO. Such a vicious cycle, spending money on things when it's possible their past amp had the same "qualities" but poorly set up and compared.

 

[Pluto]

I had a friend who told me his B&W speakers "like" power

By virtue of Ohm's Law, a given output voltage has to be ‘supported’ by the ability of the amplifier to supply sufficient current to satisfy I=V/R. Of course, it's not really as simple as this because, when it comes to audio, it ain't DC and R is not entirely resistive in nature. But the amplifier has to deal with the idea that the required current is approximately proportional to the applied voltage and inversely proportional to the actual load presented by the speaker, however bizarre that load happens to be at the instant in question.

 

[solderdude]

Higher power amps usually have a higher gain as they need to supply a higher output voltage from the same source.
Though this isn't always the case.
There are lower power amps with higher gains (as they may be designed for lower input voltages).

So the gain MAY be a reason I certainly would not call it a rule. So a higher power rating may or may not have a higher gain.
Also most people use integrated amps and in such a case the volume 'position' can also induce strong suggestions a certain amp does not have enough power when in fact they just need more gain or have a volpot with a different characteristic.

There are many reasons why people think certain ways about audio related stuff.
Rarely this is based on real knowledge about this though.
Most audiophiles just have an opinion or regurgitate whatever, to them reliable, info they find on the web.

 

[solderdude]

But the amplifier has to deal with the idea that the required current is approximately proportional to the applied voltage and inversely proportional to the actual load presented by the speaker, however bizarre that load happens to be at the instant in question.

The amplifier merely needs to be able to deliver or disspate the current drawn and generated by the speaker regardless of its output voltage.
With high capacitive loads ( or inductive) the currents may be out of phase with the applied voltage (by the amp).
A speaker can have several capacitive and inductive impedances at different frequencies.
The amp does not expect a current proportionally to the output voltage.
Though most speaker amps may only have been designed and tested with resistive loads.

This fact may* also be a reason for some amps to sound different while measuring the same on a test bench.
In that case the output voltage of the amplifier is not an exact but amplified copy of the input signal and thus is very measurable under certain loads but not under resistive loads.
All speakers have different impedances and different reactive and capacitive behaviour.
There is no single dummy load that is representative for all speakers.

*personal thoughts not knowledge.

 

[PierreV]

Semi anecdotal comment...

I have two pairs of speakers (see profile) almost side by side in the same room. One of them, the focal is rated 92dB (2.83V 1 meter) the vivid is rated 87dB. On the same amplifier, with the same gain, there's a difference, but not as much as expected based on specifications. Anyway... when I did my first methodical comparisons on a 2x100W rated (Linn) amplifier, matching levels at my listening position in REW (both response curves are flattish) I noticed that the focal sounded much less defined in the mid-bass range.

My standard test record was

- a very nice recording btw.

That came as a surprise as I had spent some time listening to both speakers at the dealer and had not noticed any lack of precision from the focal there. So I started investigating a bit and looked at the impedance/frequency curves of both speakers and noticed the focal go significantly lower than the vivid https://www.stereophile.com/content/focal-maestro-utopia-iii-loudspeaker-measurements

Since I had purchased two hypex NCore400 kits I decided to give them a try: focal bass definition problem solved. Putting the hypex on the vivid doesn't seem to improve their mid-bass, but the result is striking as far as the focal are concerned. I switched back and forth quite a few times, matched levels and even did a few DBT with the help of my partner. I should also mention that I don't typically listen at a high SPL and I wasn't particularly stressing the Linn amp in either case... The Linn preamp was used in both cases.

So, I had a theory (which basically was that the Linn amp wasn't able to deliver enough current to the focal in that FR), was lucky enough to be able to test it in the same room, at matched levels with amplifiers that, in theory, were able to deliver more juice at lower impedance. It seems to have worked. But to be honest, I am not sure my theory is correct and don't think I am able to measure the current flow and the speaker's response accurately.

Speaker/Amplifier matching still has its mysteries (at least for me). I'd love to be able to test those high-end, high current reserve but low rated power amplifiers one day.

 

[solderdude]

Current testing on a cable may not be too difficult to do.
Winding a coil around 1 of the wires of a speaker and connect it to a soundcard input (mic sensitivity).
Would need calibration though and probably gives problems at mains frequencies and multiples.
Would do this near the speaker.
One could also use a 0.1 Ohm resistor in series and measure that using a sound card.

On the other channel connect the signal on the wire and attenuate it enough.

Haven't done such tests but assume this works.

 

[PierreV]

Well, am a bit ashamed to say that while I own a decent oscilloscope and several other instruments, I feel a bit out of my depth in classical EE Bits and bytes, logic analyzer, bus protocols I can live with that, wild herds of electrons oscillating frantically, not so much.

Impedance, conductance, reflectance... all these "ance" words trigger reluctance

 

[HammerSandwich]

Or do speakers have advanced circuitry built-in where they can somehow sense how much unused power is available across from their terminals and "feel" better as a result?

Only VERY high-end models have this feature, and it requires exotic cables to function correctly.

 

[Ron Texas]

With low efficiency speakers lots of power is beneficial.

 

[Dimitrov]

With low efficiency speakers lots of power is beneficial.

You mean, CAN be beneficial? If you don't listen loud enough to warrant the extra power then it's all a bit redundant isn't it?

 

[Ron Texas]

You mean, CAN be beneficial? If you don't listen loud enough to warrant the extra power then it's all a bit redundant isn't it?

If you never turn it on, it doesn't matter. Music has a lot of dynamic range, so what appears as low volume can have short bursts requiring lots of power. As Bill Clinton said it depends by what you mean by the word "is". If you want perfect wording, hire a $600 per hour lawyer.

 

[watchnerd]

Hi there,

For this example, assume a fixed SPL. Let's assume you have 2 solid-state amps. One is rated to deliver 100 watts, another 300 watts. If you listen at a fixed SPL, still well below the limits of the 100 watt amp and change amplifiers to the more powerful 300 watt model, the voltage/current into the load remains the same? Or does anything change?

The reason I'm asking is because I had a friend who told me his B&W speakers "like" power. But I can't wrap my head around that. Speakers react to voltage - assuming fixed SPL in both cases, the voltage and current to the load must remain the same surely according to Ohms Law?

The speaker won't "see" the extra power unless you apply a higher voltage. Am I right here? Or is there something I'm missing here?

Does he mean they like high current amps?

Speakers that have loads that either drop really low, or have a lot of tricky impedance phase angles, can be considered 'hard to drive' by amps that don't have much current reserve.

That being said, I've never heard B&W's being especially difficult loads.