7 inch Aluminium mass adjustable passive radiator.
The Accuton P173 is an adjustable high end passive radiator and is an ideal partner for the C173 range of drive units. Features include an aluminium cone, rigid multi branch chassis and large maximum excursion of ± 5mm.
Adjustable mass tuning is accomplished by adding / removing stainless steel weight discs giving a possible resonance range of between 20Hz - 70Hz.
The stated nominal resonance frequency of the passive radiator is taken at 3mm excursion to give a realistic value.
Here's a formula to calculate the resonant frequency :
Fres= sqrt[1/(Cms corr.) x Mms x 4 pi^2)] with Cms corr.= 1/[(1/Cms) + 1/((Vb/Vas) x Cms)] ... phew! :0)