How an amp can get underpowered?

[PENG]

Thank you all for taking the time to read my long response to the OP's questions. Aside from typos, if I had made any mistakes in such a long post (and that is quite possible, even as I tried to avoid using too much numerical/calculated examples), I would welcome any feedback; and would make the necessary corrections.

 

[MrBoat]

I just noticed you may not have gotten the answer to this question.

When you said "the amp volume/power button", did you mean the volume dial on a preamplifier, or an integrated amplifier? Power amplifiers typically don't have volume control, some do have knobs for gain adjustments, those are not the same as volume control.

If so, then I would assume you are talking about using our PC's output to control your preamplifier, or the preamp inputs of an integrated amplifier.

In that case, if you set the volume output of the PC (computer) too low, your integrated amp, or power amp, will likely to be in what you call "under power" scenario for your speakers, unless your speakers are super sensitive and you sit very close to them.

If you se the PC volume to 100%, then your preamp, or integrated amp, will be able to do their best to give you all it can do in terms of maximum output power for your speakers. In a setup like this, I would typically set my PC output to 90 or 100%, and use my preamp to control the "volume". I hope this help answering your question, if you are still bother, please ask again, with more specifics.

I used to set my pc at 100% volume and control the AVR output with the remote but got tired of messing with batteries for said remote. Now I set the amp (in my case an old Denon AVR) that's hooked up to my pc to less as a form of protection on some speakers I hook up to it, and control the output from the volume + - on the pc keyboard instead.

I also control the subs and dsp from the desktop as well. I have noticed no audible difference doing it this way as far as sound quality is concerned after having done it both ways. This way, I can sound level and control everything on the fly from one place. This helps me adjust without volume normalization having to be included in some software like when playing CDs from the same system. I have always used EQ/tone controls on the fly since I started listening to music on my own.

 

[adrhc]

I think now I know why you are having trouble understanding the answers given to your questions, so I will try a different approach this time. Instead just telling you we need more information, I will start by explaining why your question cannot be answered without some of the missing information. And let me do it in point form so you can ask questions on the specific points if necessary.

1) How loud, in dB a speaker can produce depends on at least the following info
a) The sensitivity of the speaker, usually given in X dB/2.83 V/m
b) The distance your ears are from the speaker.
c) The voltage applied to the speaker input terminals, that depends on the signal level to the preamp, and the volume control scale, and gain of the preamp.
d) Nominal impedance of the speaker.

a) X dB/2.83V/m means the speaker will produce X dB, X could be any number such as the 97 dB you used, and 2.83 V is the voltage applied to the speaker terminals, by the power amplifier.

Impedance is also an important factor. You keep referring to watts instead of voltage. You are not alone on this though, as most people do like to stick with watts, unfortunately. EEs, physicists, amp designers will likely prefer to use voltage and current, instead of power, though all 3 are related.

Take a look of a simple example to demonstrate why you need to know the impedances, in order to give your question a meaningful answer, albeit still a simplified one.

In the above scenario/calculations, we assumed the impedance of the two speakers you used in your questions are the same, such as 8 ohms, but if speaker B is 4 ohms, then the voltage it needs for the amp to output 150 W would actually be lower than that required for the amp to output 100 W into speaker A, and as you must know by now, that would be another reason for the volume positions to be different for the two speakers to produce 97 dB. If you want to see some calculations, I can do that, in the meantime you can also play around with the following online calculators, one was posted earlier.

Crown Audio - Professional Power Amplifiers | English
Peak SPL Calculator (hometheaterengineering.com)

Conclusions:

A) You can see that by coming up with the different sensitivity numbers that ski2xblack mentioned, we can satisfy your example of using the two speakers, both produces the same 97 dB spl, yet one needs 100 W and the other needs 150 W. You can also see that we have to make quite a few assumptions, that is, it needs more than what you provided in your question, and without making the assumed sensitivity and nominal impedance, we could not answer your question in a meaningful way.
B) At the same volume position, of the preamp, the power amp output voltage will be the same, so the two speakers used in your example question will not produce the same spl of 97 dB, but they will produce 97 dB at different volume positions.
C) All of the above are simplified, just to make it easier to understand the basic concepts.



Not really like that, it may be better to stay away from such mechanical analogy. It should be easier enough to understand that the volume control controls the voltage input to the power amp, and that in turn affects, that is, controls the output voltage of the power amp. The output voltage of the power amp will then drive current into the speaker load, and you can calculate the current flow using Ohm's law, that is V=IR, or I = V/R, where V is the voltage in volts, I is the current in amperes and R is the resistance in ohms.

Speaker loads are typically reactive, that is, it has resistance, capacitive reactance, and inductive reactance, the complex formula is Z (impedance) = R (resistance)+jXL (inductive reactance)-j/XC (capacitance reactance), X is the frequency dependent variable, X = 2*pi*f (f is frequency in Hz).

Comprehensive Impedance Formula Guide for Electrical Engineers - Keysight Technologies

More on the volume control question you previously asked:

To answer your previous question about volume control's relationship to at what point the power amp run out of stream, we would have to know the volume scale, the gain of the preamplifier, and the maximum output voltage of the preamplifier into a given load impedance. That gets easier if you can pick out a specific preamp, or integrated amp, and a power amp, and we can use the Revel speaker you previously mentioned.

Basically, you seem clearly understand the point that if the volume is set to maximum, then there isn't anything else you can do to push the speaker further, except if you can increase the input signal to the preamp, and the preamp can handle the increased voltage, then you can push further. Chances are though, as others mentioned, at normal source signal levels (example: CDP, BDP, tuner), most preamps and integrated amps will be well into their clipping zone, therefore distortions will be sky high, as you approach even 50%, let alone 80% or maximum. Then again, we should not generalize, but should consider each individual case based on the specifications of the preamp. Otherwise, as you alluded, to, we are dealing with hypothetical scenarios, that's fine but imo, it could get misleading easily and quickly, if not careful...

I understand well 1a and 1b; I feel like I have an enough understand of 1d; I stated from the start that I'm not using a preamp so I'm not sure how to understand 1c. I understand that many variables are influencing the outcome that's why I would rather consider the simplest case (that's why I specified the same ohms impedance in my example, though I'm not sure is possible), where the differences are only the smallest set that still allows for a speakers pair to play well in the scenario I previously presented whilst the other pair to underpower the amp.

Because the preamp is used a lot in your explanation, and I don't intend to use one, I'm sorry, I'm not able to follow it.

I'm using no preamp, I connect my computer with optical wire directly to the amp which is, I guess, an integrated amp; as an example let's consider this to be the amp: https://europe.yamaha.com/en/products/audio_visual/hifi_components/a-s701/index.html.

 

[adrhc]

I just noticed you may not have gotten the answer to this question.

When you said "the amp volume/power button", did you mean the volume dial on a preamplifier, or an integrated amplifier? Power amplifiers typically don't have volume control, some do have knobs for gain adjustments, those are not the same as volume control.

If so, then I would assume you are talking about using our PC's output to control your preamplifier, or the preamp inputs of an integrated amplifier.

In that case, if you set the volume output of the PC (computer) too low, your integrated amp, or power amp, will likely to be in what you call "under power" scenario for your speakers, unless your speakers are super sensitive and you sit very close to them.

If you se the PC volume to 100%, then your preamp, or integrated amp, will be able to do their best to give you all it can do in terms of maximum output power for your speakers. In a setup like this, I would typically set my PC output to 90 or 100%, and use my preamp to control the "volume". I hope this help answering your question, if you are still bother, please ask again, with more specifics.

I'm talking about the kind of volume button like the one present in e.g. https://europe.yamaha.com/en/products/audio_visual/hifi_components/a-s701/index.html.

 

[adrhc]

That would be a magic volume knob that automatically calibrates different speakers (let alone the distance to your sear) to the same apparent loudness just by setting it at one point on the dial....

I agree with you now but it's not so obvious; one can assume that the devices (amp & speakers) are able to negotiate all technical details to solve user's request; e.g. modern phones do negotiate with the modern chargers various charging aspects to reduce the charging time as much as possible or to delay it, based on your charging habits, such that exactly at the proper moment for you the phone to be completely charged.

 

[adrhc]

I used to set my pc at 100% volume and control the AVR output with the remote but got tired of messing with batteries for said remote. Now I set the amp (in my case an old Denon AVR) that's hooked up to my pc to less as a form of protection on some speakers I hook up to it, and control the output from the volume + - on the pc keyboard instead.

I also control the subs and dsp from the desktop as well. I have noticed no audible difference doing it this way as far as sound quality is concerned after having done it both ways. This way, I can sound level and control everything on the fly from one place. This helps me adjust without volume normalization having to be included in some software like when playing CDs from the same system. I have always used EQ/tone controls on the fly since I started listening to music on my own.

I intend to do the same but I ask the questions I ask because I'm curious about how things work though still at a shallow level of understanding; I feel like it gonna help me in a way.

 

[TLS Guy]

PENG, go for it ! this kid's a challenge, his logic and analogies are all over the place and actually makes ones head hurt ............

That is why I have been avoiding this. He does not realize how complex the interface between an amp and loudspeaker load is.

 

[adrhc]

 

[TLS Guy]

I intend to do the same but I ask the questions I ask because I'm curious about how things work though still at a shallow level of understanding; I feel like it gonna halp me in a way.

Essentially this is much more complex than you think. You need to understand the trigonometry involved in the situation. Essentially a loudspeakers is not even close to a resistive load. In its simplest terms it means that current and voltage increases are separated in time. With loudspeakers the phase angle between voltage and current is prone to swing negative and in some speakers severely so. This is especially prone to happen in the power band in the lower and lower mid frequencies.

So, this creates a problem where an amp is just no able to provide the power that you think it would.

This is because of the concept of apparent power and true power. To cut a long story short, the apparent power at a given moment can be high. So this leads to high demands for current that the amp may not, and often can't meet. So this will cause the amp to distort sooner than you thought it would have. So this power demand is called the apparent power, as this power is given back at a different point in the sound wave. So although there is no increase in the true power over time, the amp has to meet the current demands for the apparent power. On those rocks, there is plenty of misery.

 

[adrhc]

That is why I have been avoiding this. He does not realize how complex the interface between an amp and loudspeaker load is.

I do realize it but I also know that it can't be more complex than general relativity theory which I guess anyone can grasp it today because there are so many helpful explanations available (check YouTube); the science behind it it's crazy and most people can't understand it (me included) but they can understand a good analogy; I guess this is what I need here too.

 

[adrhc]

The thing I understand is that an underpowered amp would send such a signal to the speakers that their tweeter would break. I understand the signal is clipped hence the tweeters will spend more time playing something very stressful for them, enough long to break them. It's as if I would have to keep in my arms a heavy recipient, open at the up-side, filled with some poison which can harm me if I touch it; I might be able to keep it few seconds but left enough time in my arms I'll eventually shake and drop it hence pouring the poison on me.

What I don't understand is why this happens for speakers rated with more watts, compared to the amp rated watts, instead of for those rated with less watts.

 

[lovinthehd]

I agree with you now but it's not so obvious; one can assume that the devices (amp & speakers) are able to negotiate all technical details to solve user's request; e.g. modern phones do negotiate with the modern chargers various charging aspects to reduce the charging time as much as possible or to delay it, based on your charging habits, such that exactly at the proper moment for you the phone to be completely charged.

Actually some modern gear can accommodate such as was pointed out, many avrs have such a setup routine you can run so that your volume is based on the sensitivity of your speakers and the distance to your seat, calibrated with a microphone; 2ch integrated amps generally do not have this feature, tho.

 

[TLS Guy]

I do realize it but I also know that it can't be more complex than general relativity theory which I guess anyone can grasp it today because there are so many helpful explanations available (check YouTube); the science behind it it's crazy and most people can't understand it (me included) but they can understand a good analogy; I guess this is what I need here too.

You ask for the moon, don't you?

I am not going to let you get the better of me though, and I will try this analogy with a bit of English Victorian engineering. So I am going to explain the LEAS water lift at Folkstone that has long been used to get visitors up and down the sea cliff.

So what this lift consists of is two cars on rails, one up and one down. They are connected by a steel hauser on pulleys, and as one car goes up, the other goes down.

The drive is to pump water into a tank in the upper car. When it has sufficient water the upper car starts to descend and the lower car ascend. The water is pumped up the hill by an electric motor, in Victorian times it would have been a steam engine.

Now, obviously the lift has to stop when one is up and the other down to let passengers on and off.

So if the passengers are heavier in the top car, less water is required to pull up the lower car. If on the other hand there are some "porkers" in the lower car, then more water is required. So if the lower car is heavier, more water is required at the top. But if on the way back the lower car is lighter, then the energy required to pump the excess water is given back.

Now obviously the lift has to stop, at each half cycle to let passengers on and off.

However let's have a hypothetical situation where we want to get the cars going smoothly up and down with no delay. In other words a sine wave.

Now let's suppose that we could hypothetically change the load of a lift on a whim, like a loudspeaker load.

Now that would require more water to have to be added to the descending car if the speed was to be maintained. Then if nothing changed more water would have to be let out faster and at the lower end to maintain our perfect sine wave.

So if we had this cycle and wanted it to stay constant, it only would if the pump could provide enough water pumping it up the hill to keep time. The energy though would be given back as the other car came up.

However if the pump could not keep up, then there would be delay and the cycle would not longer be even and that would be analogous to distortion.

So if the load were to vary, and even though the excess energy of the lift was given back at the top, if the pump could not provide the water quick enough our cycle would no longer be smooth. There would be distortion.

This is the same as an amp not being able to provide the current for the apparent power and causing distortion, even though there is no requirement for more power over time.

 

[MrBoat]

I intend to do the same but I ask the questions I ask because I'm curious about how things work though still at a shallow level of understanding; I feel like it gonna help me in a way.

Best cure for curiosity is to dive in and just do it. Things become a lot more relatable when you can hear the results.

The science is great and all, but this stuff is mostly designed to be easy to use, just following basic common sense and RTFM. Household name brand products will be predictable enough. Things start to go off the rails when you start getting all fruity and eccentric with it.

 

[adrhc]

You ask for the moon, don't you?

I am not going to let you get the better of me though, and I will try this analogy with a bit of English Victorian engineering. So I am going to explain the LEAS water lift at Folkstone that has long been used to get visitors up and down the sea cliff.

So what this lift consists of is two cars on rails, one up and one down. They are connected by a steel hauser on pulleys, and as one car goes up, the other goes down.

The drive is to pump water into a tank in the upper car. When it has sufficient water the upper car starts to descend and the lower car ascend. The water is pumped up the hill by an electric motor, in Victorian times it would have been a steam engine.

Now, obviously the lift has to stop when one is up and the other down to let passengers on and off.

So if the passengers are heavier in the top car, less water is required to pull up the lower car. If on the other hand there are some "porkers" in the lower car, then more water is required. So if the lower car is heavier, more water is required at the top. But if on the way back the lower car is lighter, then the energy required to pump the excess water is given back.

Now obviously the lift has to stop, at each half cycle to let passengers on and off.

However let's have a hypothetical situation where we want to get the cars going smoothly up and down with no delay. In other words a sine wave.

Now let's suppose that we could hypothetically change the load of a lift on a whim, like a loudspeaker load.

Now that would require more water to have to be added to the descending car if the speed was to be maintained. Then if nothing changed more water would have to be let out faster and at the lower end to maintain our perfect sine wave.

So if we had this cycle and wanted it to stay constant, it only would if the pump could provide enough water pumping it up the hill to keep time. The energy though would be given back as the other car came up.

However if the pump could not keep up, then there would be delay and the cycle would not longer be even and that would be analogous to distortion.

So if the load were to vary, and even though the excess energy of the lift was given back at the top, if the pump could not provide the water quick enough our cycle would no longer be smooth. There would be distortion.

This is the same as an amp not being able to provide the current for the apparent power and causing distortion, even though there is no requirement for more power over time.

very nice explanation, thank you!

 

[adrhc]

That seems like a simple system. What is the ONE thing that you are so worried about?

Just the salient ONE thing.

Not having enough power?

I’m curious about how an amp could get underpowered and thus be able to change de amp volume without breaking something; it seems for the moment that in order to determine whether the volume is too high only hearing the speakers would tell me that something is wrong.

 

[lovinthehd]

The way you keep saying how an amp "could get underpowered", like it changes somehow, is odd. It's more that the amp you buy/use is of sufficient power in the first place for your use, or it isn't. Just how loud do you want to listen? Are there particular speakers you're worried about?

 

[adrhc]

while reading various articles I encountered the "underpowered" notion as describing a situation in which an amp can be; that "underpowered" situation I tried to explain to myself because it seemed to me counterintuitive (from a very very high level, user point of view), i.e. something rated with more accepted power (e.g. 300W speakers), aka for me meaning "better/tougher", could break while something accepting less power (e.g. 100W speakers) might go fine with the same amp and same settings for it

PS: at this moment I'm happy with the help received till now and the @TLS Guy's analogy

 

[lovinthehd]

The term is overused, and causes more worry than needed generally IMHO. At some point any amp can be underpowered for a specific situation, the idea is simply to have adequate amplification for your potential situations and not worry about it.

 

[William Lemmerhirt]

Because the preamp is used a lot in your explanation, and I don't intend to use one, I'm sorry, I'm not able to follow it.

I'm using no preamp, I connect my computer with optical wire directly to the amp/URL].

I believe in this case, you can consider the PC to be your preamp. In the same manner, it does the processing, and controls the preout voltage to drive the amp.