4th order blow through sub question

[fordpride]

Gotcha. Thanks

[Triticum Agricolam]

Here is how I do it. 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. It takes some experience to use the software well and to know how to interpret the results, but this is where other people can help point you in the right direction. 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. Depending on how much power is going to be used, this can require ports as big as 1/2 the cone area.

[fordpride]

Out of the software that you mentioned which one would you recommend for a first timer?

[Triticum Agricolam]

WinISD is probably the easiest, and is free. Make sure you get the newest version though, you can get it here: http://www.linearteam.org/download/winisd-07x.exe

[fordpride]

All your help is much appreciated

[island boyeee]

TA, great info on the 4th order BP! I'm just starting to consider this as an option for my "SQL" build. I used to build stereos for pure mayhem many years ago, and am finally trying to finish the stereo build for my race/weekend car (06 Subaru WRX sedan). I definitely want loud, but this time with quality in mind.

I had planned to do 2 ported boxes for some 12" RE Audio SE (now SE-X...) subs. I currently have 2 fiberglass/MDF rear facing boxes I built, but I think I want to scrap them and build something that fires into the cabin, and seal off the trunk (these cars are made of tin, I would have to reinforce the entire trunk/lid).

Unfortunately, finding adequate room to fire 2 12's and the ports into the back seat opening is proving near impossible for a good design. So, I'm considering moving to one beefier 12 (probably the RE Audio SXX) and using my ~3+ cu. ft. to do it right. Or, I started wondering if a 4th order BP might be for me.

Thoughts on this? Kind of thread jacking, but I figure this would be good info for the OP.