4th order bandpass boxes

holdinmyown wrote: the bass reflex design is only about 8-10 db higher than that of a plain sealed chamber.

Only? 8-10dB's is dramatic!

First, reducing air velocity is all about having larger port opening space.  Use the program to work with some different port opening sizes while keeping tuning freq where you want it to be.  Also, be sure that you are looking at air velocity within the range of audio frequencies that you will likely be listening to in real life (for example, a high velocity at 20 Hz means nothing...where does it hit at 35 Hz?)

Design your bandpass box with the wisdom that you will be changing it a few times to get what you are looking for in sound and performance.  Meaning this:  experiment with unfinished boxes and design your project so that you may make size changes without having to start from scratch each time.  An experienced designer may find a perfect combination of a particular driver and a particular placement in a particular vehicle....but then find that it doesn't work out quite as well in a different vehicle.  Time and patience are your allies when dealing with bandpass, else you end up with something that sounds no better than a prefab that you can pick up at a store.

If your sealed design is "boosting" a range of frequencies, this is a high Q.  You will see that the rolloff is steep as well.  If there is no peak and the rolloff is gradual, you will note that the Q is likewise lower.  Car audio sealed tends toward high Q for a couple of reasons:  limited space for large enclosures, and the desire for booming bass in today's music climate.  Your bandpass needs a marriage of the sealed side with the vented side to produce the sound you are looking for, so prepare for some experimenting.  In other words, with bandpass there quickly must come a time for hands-on building and forget worrying about  logic and assumptions.

And note also, if you want maximum SPL you will want your target to peak in the 50 to 60 Hz range, not 95 Hz.  Your vehicle resonance plays a huge role in this.

dude your post states 16Hz. & you wanna "step it up" from ported boxes? Here is a quick lesson as to why BP boxes came into being. Size. back in the day, a 12" sub would require about 7 cubic feet of air space for a ported box, & would not perform well sealed with low freq. unless a large box was used, but then power handling was sacrificed. Also, with a BP box, the only sound you hear is the port tuning, you do not hear the distortion coming from the sub, & because of this cheap sub makers started using them to make their cheapy subs sound better....the down side, is you do not hear the sub crying for mercey. 

Now, those BP boxes could be made smaller by sacrificing a smooth responce, for being efficient at 1 freq. or 1 group of freq...& depending on the box, a freq. & it's octave. i.e 40Hz & 80Hz., but there is a lul in the output between those freqs., & the rolloff is quite steep, so 30Hz is prob. 7-10db down from the peak freq. in our 40Hz example

Those that posted above are correct, 80Hz (or around there) is a proper x-over point for a sub, never in a car audio subwoofer application should freqs. above 120hz ever be used. all it does is muddy the sound, make the bass directional, & lowers power handling of the sub.

Here is some solid advice. Post up here what kind of car you have, & maxximum box dimentions you can have, & see what some of us come up with for ya. I would almost bet for output most will make a big slot ported box, & if you want accuracy, most would make a moderate sized sealed.

So, post car, year make model, Amplifier model #, & rated output

Size & model # of sub, as well as how many you are using

& size restrictions

A little more advice, be nice to those you are asking for help, & they will give better answers. Now give an apple to the teacher.....sucka LOL