Re: 4th order bandpass enclosure help
If you're going for SPL in a 4th order you don't want tuning that low. In the low to mid 40s would be better for both your goals and your subs, as they will not play well at low frequencies without a shite tone af air behind them.
If you want to do it right, I would recommend downloading WinISD Beta and modeling the subs in a number of different boxes. If you can find a curve you like on that program, then build it.
But just trying different volumes at random or relying on rules of thumb ratios that do not take into account the characteristics of the individual drivers is the reason why 4th and 6th order enclosures have the reputation of being hard to design.
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