How an amp can get underpowered?

ski2xblack

ski2xblack

Audioholic Samurai
@ski2xblack, how do I know what volume level corresponds to what power amount (+/- 3W error margin) for a certain speaker pair?
A pretty good guestimate can be had via tools like this:
Plug the data of the Revels into that and see what you get.

I did, using 85db/w, 10' distance, and 50w, and the results were just under 95db.

That would work fine (for me) in the near field or small room, but ask for the same spl in a larger room involving greater distances and power demands rise exponentially.
 
Last edited:
Mikado463

Mikado463

Audioholic Spartan
You can buy an amp with less power than may be ideal for your speakers and your use, so to me an underpowered amp is just a buying decision.
albeit a poor one !

The Op is all over the place here, he needs to focus on design / function parameters of amplifiers as well as speakers and what any given speaker design demands from an amplifier.

Chris(CPP) gave him a link to the Revel speaker review, wonder if he read it and understood it ?
 
A

adrhc

Junior Audioholic
I already have the link (I read it, it doesn’t help me) but my question is not about the Revel speaker, see my posts
 
Last edited:
A

adrhc

Junior Audioholic
please check my previous large post where I crafted a scenario with 2 possible outcomes one could observe
 
Mikado463

Mikado463

Audioholic Spartan
please check my previous large post where I crafted a scenario with 2 possible outcomes one could observe
and if you look at my post above (#22) and understand the basic knowledge of amplifiers and speakers, 90% of your questions are already answered. It's pretty clear to me that you're having trouble in this area, for the simple fact that you stated Chris's post is 'about speakers and doesn't help' ? Nonsense, it's like peanut butter and jelly, of course they go together !
 
P

PENG

Audioholic Slumlord
please check my previous large post where I crafted a scenario with 2 possible outcomes one could observe
Just to be sure, which post are you referring to? It will also help if you don't mind asking your specific questions again, that you feel have not been answered, because I also thought your questions have been answered already by now.

Be clear, I do want to help, if I have the answers to the specific questions.
 
A

adrhc

Junior Audioholic
Based on previous answers I think that with the below scenario, the one I also posted previously, I'm closer to what I'm searching for.

Let's just suppose that some speakers (2x pair) need 100W for 97db while others need 150W to produce the same 97db. I set the amp to a particular volume level (e.g. 80%) then I test the speakers (in turn) and I expect to have one of these possible observations:

O1. the speakers played at the (approximatively) same noise level (i.e. db amount) whilst they used a very different amount of power; this means 2 things:
- the volume button is not like a pipe valve because, at the same opening level, distinct amounts of energy (aka, substance flowing through the pipe) flow through the pipe
- weird thing: the amp "knew" somehow to allow for more energy to flow through it even though the speakers don't convey to it this information (aka, they don't "ask", directly or indirectly, for the necessary amount of power/energy) - remember that the volume level was set at the same value for both speakers

or O2. the speakers played at very distinct noise levels whilst they used the same amount of power; this means 2 things:
- the volume button is not controlling the volume but the amount of energy that flows through it (which also impacts the volume) hence it behaves like a pipe valve
- weird thing: nothing wrong should happen to the amp or speakers if I open the valve at max (aka, amp's volume button at max) if the speakers are capable of handling more than pipe's max
 
Last edited:
Mikado463

Mikado463

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

PENG

Audioholic Slumlord
PENG, go for it ! this kid's a challenge, his logic and analogies are all over the place and actually makes ones head hurt ............
Thanks, I am very curious about which parts of the answers given so far he doesn't undertand, then I would hopefully know if I, or others could help further.
 
ski2xblack

ski2xblack

Audioholic Samurai
Well, I'm bored at work so I'll play along.

You have described two pairs of speakers with different sensitivities. Of course they will produce different spls using the same volume setting. (Similarly, if you wanted to match spls, the more sensitive speaker will require a lower volume setting.) The speakers don't "know" or "ask" for anything. It's you who controls the volume knob, not the speakers. So, using your given conditions, you would hear what you describe in scenario O2, but the conclusions you want to draw are just incorrect/incoherent. Also, turning the volume to 80% of max will most likely take you well beyond the amps safe, linear range.
 
A

adrhc

Junior Audioholic
Of course they will produce different spls using the same volume setting.
This is a surprising fact for me because I initially thought the volume button allows me to request the desired audio volume level, e.g. 64db, then the amp is supposed to work with the speakers the technical details of fulfilling my request.
 
Last edited:
Mikado463

Mikado463

Audioholic Spartan
This is a surprising fact for me because I initially thought the volume button allows me to request the desired audio volume level, e.g. 64db, then the amp is supposed to work with the speakers the technical details of fulfilling my request.
ahhh, there ya go, step one !
 
ski2xblack

ski2xblack

Audioholic Samurai
Yeah, a db scale volume control can be pretty accurate, but only after calibration (e.g. running Audyssey, etc, or doing measurements and tweaking trims manually), but without such calibration they are rather arbitrary.
 
A

adrhc

Junior Audioholic
O2. weird thing: nothing wrong should happen to the amp or speakers if I open the valve at max (aka, amp's volume button at max) if the speakers are capable of handling more than pipe's max
well, now I have to think at a scenario which to help me highlight my misunderstanding on the above remaining part; I guess it should be something that includes the concept of “signal”, mentioned in one of the previous posts
 
P

PENG

Audioholic Slumlord
Let's just suppose that some speakers (2x pair) need 100W for 97db while others need 150W to produce the same 97db. I set the amp to a particular volume level (e.g. 80%) then I test the speakers (in turn) and I expect to have one of these possible observations:

O1. the speakers played at the (approximatively) same noise level (i.e. db amount) whilst they used a very different amount of power; this means 2 things:
- the volume button is not like a pipe valve because, at the same opening level, distinct amounts of energy (aka, substance flowing through the pipe) flow through the pipe
- weird thing: the amp "knew" somehow to allow for more energy to flow through it even though the speakers don't convey to it this information (aka, they don't "ask", directly or indirectly, for the necessary amount of power/energy) - remember that the volume level was set at the same value for both speakers
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.

or O2. the speakers played at very distinct noise levels whilst they used the same amount of power; this means 2 things:
- the volume button is not controlling the volume but the amount of energy that flows through it (which also impacts the volume) hence it behaves like a pipe valve
- weird thing: nothing wrong should happen to the amp or speakers if I open the valve at max (aka, amp's volume button at max) if the speakers are capable of handling more than pipe's max
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...
 
Last edited:
ski2xblack

ski2xblack

Audioholic Samurai
That's a banger of a post, @PENG quite thorough!

@adrhc read that, and read it again. In fact reread all of PENG's posts until the tetris pieces of understanding fall into place.
O2. weird thing: nothing wrong should happen to the amp or speakers if I open the valve at max (aka, amp's volume button at max) if the speakers are capable of handling more than pipe's max
well, now I have to think at a scenario which to help me highlight my misunderstanding on the above remaining part; I guess it should be something that includes the concept of “signal”, mentioned in one of the previous posts
That's not totally bonkers, as it happens all the time. The vast majority of consumer power amps lack any sort of gain (input sensitivity) controls. They're pegged at 100% all the time, the gain is what it is and that is what you get. Alas, their input sensitivities are often low enough, and preout voltages potentially high enough (if you turn it up to eleven), to possibly land you in clipping territory.
 
Last edited:
lovinthehd

lovinthehd

Audioholic Jedi
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....
 
P

PENG

Audioholic Slumlord
Another thing that bothers me is whether the amp can get underpowered if I only change the volume to 100% from my computer (initially set to 10%) while not rotating/switching the amp volume/power button; does the volume change from the computer have any effect?
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.
 
newsletter

  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
Top