Major 7th most consonant in small octave?

Question

I noticed when playing on my electronic keyboard that the major 7th is most consonant in the small octave and it gets more dissonant in high octaves and low octaves.

This is weird because most chords get more consonant as you go up octaves.

I know it has to do with the B but why is it more dissonant in the 3rd octave(which is where most chords are consonant) than in the small octave? I mean a Minor-Major 7th has that B also and it is more consonant in higher octaves.

Could it be that since it is a major chord with a major 7th interval that there are 3 overtone series overlapping, one based on C, one based on E, and another based on G and that with 3 overtone series it is more consonant in the small octave?

Or could it be that I just hear it more often in that octave and so think that it is more consonant?

Answer 1

More dissonant in higher octaves would contradict the Plomp-Levelt consonance findings†, so may be a psychological effect, or perhaps due to the specific instrument being used? Here's an equal temperament major 7th in a few different octaves run through Plomp-Levelt:

% perl -MMusic::Tension::PlompLevelt -E '$t=Music::Tension::PlompLevelt->new; for $c (1..10) { say $t->pitches($c*12, $c*12+11) }'
12.2352335799632
7.29340027827011
4.26858749912013
2.78161912423053
2.05878602184421
1.58544807903736
1.25480969644524
1.05392509195799
0.944315385270656
0.887495122387742
% 

Lower octaves per this calculation are more dissonant, and the dissonance tails off in higher octaves.

† R. Plomp and W. J. M. Levelt, Tonal consonance and critical bandwidth, J. Acoust. Soc. Amer. 38 (4) (1965), 548-560.