new box help

[Andrew Storlie]

so ive built alot of nice boxes but never got into the 4th and 6th order stuff, and i want to, i just got a good deal on a mint 12" alpine type x and i wanna experiment with it...

can someone help me learn how to design 4th and 6th order boxes. or kinda show me how its done and then i can learn by doing it. more or less how tuning goes and how box size effect it all

pictures are always helpful, and links

thanks

[DLHgn]

I can't really give you any help but try downloading and playing with hornsrep. It's a really powerful, and free, program that can simulate those kinds of enclosures but, be warned, it has a pretty steep learning curve.

[Andrew Storlie]

I can't really give you any help but try downloading and playing with hornsrep. It's a really powerful, and free, program that can simulate those kinds of enclosures but, be warned, it has a pretty steep learning curve.

I learn really fast so ill grab it and figure it out

[Triticum Agricolam]

WinISD can model 4th order and parallel tuned 6th order boxes. HornResp can do 4th, and both series and parallel tuned 6th order enclosures. HornResp is tremendously powerful, but its not something you can just sit down and figure out in 30 minutes. There are some really good how-to guides though, here is one: http://www.hometheatershack.com/forums/diy-subwoofers-general-discussion/36532-hornresp-dum-hmm-everyone.html

That how-to guide is a bit outdated and doesn't include how to do series-tuned 6th order or 8th order designs, which are newer features to HornResp, it will teach you the basics though, which is hard part.

In all cases, bandpass boxes are significantly more complicated than the ported boxes people are more familiar with, especially series-tuned 6th order boxes.

To get you started on 4th order designs, here are my thoughts. A lot of people try to really over-simplify bandpass box design, this leads to shortcuts like using "ratios" that will often bite you in the ass. In my opinion, acoustic modeling software (WinISD, BassBoxPro, TermPro, HornResp, etc) is a must for bandpass box design. Otherwise you are just taking shots in the dark, you may be know which direction you are shooting towards, but without software you can't see where you are hitting until the box is complete. It takes some experience to use the software well and to know how to interpret the results, but this still a whole lot better than trial and error. To get you started here is my general philosophy on bandpass box design, I'm happy to help you with any of this if you need:

First start with the rear chamber. The rear chamber determines what output you are going to get and controls cone excursion below the tuning frequency of the front chamber. The bigger you make the rear chamber, the more low end output you will get and the lower your sealed resonant frequency will be, but as you make it bigger your cone excursion goes up too. It's a balancing act to try to make the rear chamber as big as you can to get the most output, but without having it be so big your subs destroy themselves the first time you play a low note at war volume. The manufactured recommended sealed box size is a decent starting point for rear chamber sizing, but you still need to check and see what you get.

The front chamber size determines what output you will get around the tuning frequency. The bigger you make it the more output you get, however you only get output over a limited frequency range. Make the front chamber too big and you get a one-note-wonder. Just how big you should make it depends on the parameters of your subs. Some subs will give you wider bandwidth than others will using the same size front chamber. Subs with lower QTS and/or Vas will be more peaky than subs with higher QTS and/or Vas, this will make some subs inappropriate for 4th order bandpass box usage. Just how peaky you want the output to be depends on your personal goals and listening tastes. Everything is a trade off.

When it comes to the tuning of the front chamber you can move the tuning around a bit to get the frequency response you want, but generally you will get best performance with it being near the sealed chamber resonance, this is another reason why its a good idea to keep an eye on your sealed chamber resonance when sizing your rear chamber. Its a good idea to make your front chamber port adjustable so you can tweak the tuning a bit when you get it in the vehicle. Tuning frequency on paper doesn't always work out to what you get in practice and you may want to shift your passband up or down a bit to fit your listening tastes.

In terms of port area for the front chamber, you need to have a lot. All of the output has to come out of that port, so you don't want to lose output to air resistance due to an undersized port. At 30+ m/sec you can lose half, or more, of your output to port compression I try to keep port velocity under 20 m/sec if at all possible, though it may not always be. Depending on how much power is going to be used, this can require ports as big as 1/2 the cone area.