Interesting point,
but what about major chords that sound louder and also subjectively preferred than single note; this example I am talking about use of synthesizers and sustained waveform note/s that ensure same sound levels, example of the A Major Chord is 440.00Hz, 554.37Hz, and 659.25hz.
This also raises that subjective preference involving complex sounds (timbres and related harmonics) is probably more than just distortion.
One genre that relies a fair amount on this and shows the trend is dance music.
Cheers
Orb
Just in case some wondering how critical bandwidth affects the perception of my A Chord example, here are the cut off points relating to the bands.
This is one reason (not the only one when it comes to complex sounds and instruments' notes) why the chord will sound louder than the individual note as three combined notes in a chord is enough to go across a critical band, for the notes to be masked/same level they would need to be within same band.
Here is a rough guide as it pertains noted as Barks bands given in Hertz as work done by Zwicker; 0, 100, 200, 300, 400, 510, 630, 770, 920, 1080, 1270, 1480, 1720, 2000, 2320, 2700, 3150, 3700, 4400, 5300, 6400, 7700, 9500, 12000, and 15500.
Also another is by Rossing using center frequency with associated critical bandwidth, both in Hz; Center 100 and Critical 90, Center 200 and critical 90, Center 500 and critical 110, center 1000 and critical 280, center 2000 and critical 700, center 5000 and critical 1200).
Rossing's shows threshold for the changes to critical bandwidth, so please appreciate center can be changed to be applicable to all frequencies one may hear and use the right critical.
So playing an A chord will be perceived as louder to the single note.
I am using the example to show how it works on note-chords, but it is also applicable to all that is recorded/played back and what we hear.
As I mentioned earlier while this is physiological, there are also other cognitive possibilities that also can influence perceived loudness (such as the piano study and awareness of cues for say key being hit hard/soft).
Cheers
Orb