Nedro and others, let me point out another reason that the D accordion
might have been right for the early cajun singers.
Cajun men were, in general, smaller
than their grandchildren and great grand children are now at a comparable age.
A cursory study of the anatomy and physiology of the larynx, vocal cords,
and would suggest that the resultant smaller structures in smaller men would
change the acoustic properties of the resonating chamber. A smaller
larynx would naturally create a higher pitch.
John, your scientific analysis holds water. Small fellows with high voices. Tours of the River Road plantations near New Orleans point out that the French Caucasians were quite small, possibly 6 or 7 inches shorter than the present norm.
250 years of gumbo, boudin, and jambalaya have doubtless contributed to the dimensional assimilation of the Cajuns.