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...
