INFO

- about frequency response:
Formulæ are in system.cpp, function response()

- about rectangular ports:
I deduced the function [1.1-log10(x+1.1)*0.35]*circPortLen where x = L/l, from the analysis of Francis Brooke. https://sites.google.com/site/francisaudio69/

- about multiple instance of the same loudspeaker:
Two drivers in series: Re, Le, Sd, Vas and Bl double and the sensitivity is the same as for one driver.
Two drivers in parallel: Re and Le are halved, Sd and Vas double (Bl same as for one driver) and the sensitivity increases by 6dB.
Qes, Qms and Qts don't change for either combination, remaining same as for one driver.

- about Legendre bass-reflex alignment:
Fb = 0.3802 * pow(Qts, 1.0657) * Fs
Vb = 10.728 * pow(Qts, 2.4186) * Vas
(see: https://sites.google.com/site/francisaudio69/5-l-enceinte-acoustique/5-6-comment-calculer-une-enceinte-bass-reflex)

- about Bessel bass-refex alignment:
Fb = 0.3552 * pow(Qts, 0.9649) * Fs
Vb = 8.0707 * pow(Qts, 2.5848) * Vas
(see: same site as above)

- about the Zbinden M4 alignment:
for average baffle:
Volume = (2.68 * Qts - 0.45) * Vas
Tuning frequency = 0.41 * sqrt(1/(Qts*Qts) + 0.97) * Fs
the one above is used in QSpeakers.
for infinite baffle or car application:
Volume = (2.52 * Qts - 0.35) * Vas
Tuning frequency = 0.32 * sqrt(1/(Qts*Qts) + 3.38) * Fs 
(see: http://www.mzbinden.ch/ventedalignments/index.html)