If in the same box with a woofer and two equal passive drives (in vertical in the same column with 20 grams of added weight each) I move 10 grams from the upper drive (the one closer to the woofer) to the bottom driver, the Fb is still the same or change?
(To be clear, before: +20g & +20g; after: +10g & +30g)
(To be clear, before: +20g & +20g; after: +10g & +30g)
So the lower passive would go down in resonant frequency with the larger weight, while the upper one would go up. But also the Q of the resonance would change, the one with the lighter weight would become less pronounced, while the one with the now heavier mass would become more.
If you're looking to "broaden" the resonant point at which the passives become effective, maybe a bit less than a +/- 50% weight change?
If you're looking to "broaden" the resonant point at which the passives become effective, maybe a bit less than a +/- 50% weight change?
I suppose it is similar to having different ports in a vented box. The passive radiators don't have two different resonances, but the whole system has one resonance. Chances are, the system resonance will not change much (it will, however, also very much depending on the existing mms of the resonators), but the passive resonators' excursion will be different (heavier one -> more excursion). I would not recommend to do it, why would you?
higher mass PR will introduce more distorsion and compression due to higher excursion. Also, this PR will age more quickly.
higher mass PR will introduce more distorsion and compression due to higher excursion. Also, this PR will age more quickly.
In theory, there should not be any difference between theory and practice, but in practice, there is.
It is fine saying that it only one resonant system, but the ports are located at different points in the box and therefore in theory would act on different volumes/mass/velocity of air and internal box resonances. The general feeling is that the passive radiator location doesn't matter and yet, I have found that it does: the closer to the woofer the better to reproduce higher and heavier resonances.
I did several tests, listening for classical piano: the most realistic (but not the cleanest) is if the upper passive radiator is tuned at 50hz and the lower tuned at 38hz with double added mass weight. In this case I would prefer realism, than just using the same weight at 44hz for both.