Calculating Cone Excursion in DCR Sub

[elambert]

As I understand it, in a DCR type of alignment for a subwoofer you have 2 tuning points, the original point and one 1 octave higher.

I am looking at rebuilding the box for my Quatro and was interested in the DCR to help control overexcusion in a lower tuned cabinet. My question is how can you calculate excusion to design the box with the two tuning points?

I really need to buy a bigger badder sub, but that is not in the $$$ cards right now.

TIA
Ethan

[kelticwizard]

Assuming the excursion of the cone at the upper tuning point is reduced the same as the lower excursion point, the excursion at the upper point should be abut 25% the excursion of the lower tuning point.

Therefore, the excursion around your lower tuning point should be your concern.

the excursion of the lower tuning point will not be affected by the DCR. Below the lower tuning frequency, the woofer's excursion will rise just as fast as with the single tuned box.

In short, the DCR is not the answer for overexcursion in a bass reflex cabinet. However, it willl cut down on excursion higher up the line.

Take two identically sized cabs with two identical woofers.

Box A is a single tuned reflex correctly tuned to 40 Hz.

Box B is a Double tuned reflex, same woofer, tuned to 40 Hz and 80 Hz.

Below 40 Hz, the excursion of Box A and Box B is identical.

Between 40 and 60 Hz, the excursion of Box A and Box B is identical, or very close.

Between 60 Hz and 160 Hz, the excursion of Box B will less, at points much less, than Box A.

Remember, the lower you go, the more excursion you need. At 40 Hz, you need four times the excursion as you do at 80 Hz, (if SPL remains the same).