[1] gregorio, quite accurate corrections, and I agree. Only maybe about level vs volume maximizing difference doesn't look clear, and about the power, I said that 350mW isn't enough for AC/DC drive that means peak ability(700mW), of course, AVG power I can get 2x more
[2] BTW, do you think it is bad idea to add classical compressor cell into the DSP chain of HPA(where are already parametric EQs, Fletcher-Munson loudness curves, bass/treble sliders)?
1. Yes, I agree that I wasn't clear about "physical power" and used it to mean the physical, acoustic SPL energy rather than electrical power. That's because electrical power is effectively arbitrary relative to SPL and it's SPL that we hear and that can cause hearing damage, which you obviously already know. For example 350mW maybe plenty to provide high SPLs with some IEMs but under other conditions (say a large cinema for example) even 10,000W may not be enough to provide the same SPLs. So I was going on the stated peak and RMS SPL energy rather than the wattage of the signal being fed to your transducers. I also agree that I wasn't particularly clear about level vs volume, which is because it's far more complex than it appears. The conscious process of determining volume/loudness appears trivially easy, it requires pretty much no conscious effort or thought, we just automatically know that something is louder or quieter than something else. The fact that all humans (without severely impaired hearing) can achieve loudness determination so easily implies that volume/loudness is a simple, objective property but actually that's not the case, it's actually a "perception" rather than a property and a rather complex process. You're obviously aware there's another variable at play beyond just differences in SPL, as you've mentioned F/M loudness contours, however there's still more variables at play beyond these two. For example, without exception (as far as I'm aware), a louder version of the same naturally occurring sound not only has a higher SPL but also a higher number and balance of harmonics. A shout has both a higher level and more harmonics than normal speaking, the same for a drum hit harder or an acoustic instrument played louder and our brains/perception uses both of these properties in it's determination of volume/loudness. So, if we take say a drum hit (or just about any other sound), artificially add some harmonics to it, adjust the level so it has the same SPL energy as the original hit and then compare the two, the one with the added harmonics will sound louder or, if we take a shout and reduce it's level to the same as normal speech, it still sounds louder. There's also the variable of context; a lower SPL sound can be perceived as louder than the same sound with a higher level depending on what precedes the sound. Additionally, there's the the variable of acoustic size/distance; even compensating for the loss of SPL due to distance, sound with the same SPL in a larger room will be perceived as quieter than the same sound (at the same SPL) in a smaller room. There's also the variable of duration; a short duration sound will be perceived as quieter than the same sound, at the same SPL but with a longer duration. And finally, all these variables interact, so adding more of one of these variables might not increase the perception of loudness depending on say the context. Maximising loudness is therefore significantly different to just maximising level, as maximising loudness will take all (or at least more) of these other variables into account. Incidentally, this is also why I have some objections to the characterisation of the "loudness wars", which isn't just an issue of compression/limiting but also of these other variables.
2. Firstly, I'm not sure what you mean by "classical compressor", do you mean a classic "coloured" compressor or the sort of clean compressor usually preferred in classical music production? If it's the former, then personally I would consider it a "bad idea" as you are "colouring" a recording which already has exactly the amount of that type of colouration desired by the artists (musicians and engineers). In other words, by using a coloured "classic" compressor you are not only changing the fidelity of the intended relative levels (RMS, Crest Factor, difference between quieter and louder sections) but also changing the fidelity of the colouration (intended frequency content, distortion, etc.). However, ultimately it's a matter of personal preference, some people prefer the colouration of using tubes for example. Secondly, are you saying that you are applying Fletcher/Munson loudness curves (or the inverse, to compensate for them)? If so, that's a mistake IMO. Mixes/Masters are created by engineers who are human, who, along with all other humans, have FM loudness contours themselves and therefore, the FM loudness contours are already built-into the released recordings. And, I'm not just talking about a single contour. Typically during mastering, a song will be played back at different levels and the amount of bass and treble set at a compromise level, which would usually err towards having a bit too much bass at higher playback levels. So, unless you're playing back music at especially low levels (in which case adding some extra bass might be a good idea) then I personally wouldn't apply any compensation for FM curves as you're effectively compensating what has already been compensated! Thirdly, it also depends where in the chain you insert the compressor: The input signal to the compressor will be different if the compressor is inserted into the chain before say the EQ than if it's inserted after the EQ and therefore the characteristics of the compression will be different. Where in the chain to place the compressor is a common question from student engineers but there's no right or wrong answer, it depends on the signal/song (and the desired outcome), what might be best for one signal/song might be worse for another and so the best advice we can give to students is to try both ways around and build experience of what difference it makes.
Again, personally I think it's all a "bad idea"! I personally am after the highest fidelity I can get and therefore the only EQ or any other sort of DSP I would ever add is to compensate for some freq response weakness of my particular transducers/listening room acoustics and even then, only in relatively small amounts. If I couldn't get the power required to drive my transducers to the SPL I desired, I would get a more powerful amp rather than effectively mangling the recording to get more RMS into the amp (and volume out) but with the caveat that the "SPL I desire" does not present a significant risk of damaging my hearing. Given the choice though, many audiophiles (and other consumers) would choose their own subjective preferences over high fidelity, that's their choice and not such a "bad idea" (for them), providing of course they're not risking hearing damage.
G