4th Order Box Build / Tuning Help!

[SubieSPL_Maniac 10+ year member]

Ok so I'm planning on building my first 4th order band pass. It's going to be in a trunk with the port coming through the rear deck. I've done some research but I'm open for any suggestions and could also be completely wrong.

I am getting a 12" soundqubed HDS3 for my brother.. the sealed section is going be 0.75 and the ported section about 1.5 without the port. The sub will be inverted (the magnet and basket in the ported section).

My plan is to create a square or rectangular port depending on the tuning! I will probably make it removable so I can change out ports.

This is where I get confused, I read the higher I tune the port, the lower it will play?!? can anyone help me with this. AND should the port be wider for more air movement? I want it to play well at about 32hz. Any suggestions are welcome!

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[SubieSPL_Maniac 10+ year member]

nobody??

 

[brian84corvette 10+ year member]

well i was going to add that the math seems small. .75 for sealed to me would be 3x for ported side once you take away displacment from sub and port... so maby id be trying to design that with 2.25 on the ported side.... otherwise i dont see the advantage of using 4th order unless you want to take gain from the box... cause at 2:1 ratio a ported box is just as loud as a 4th and alot less complicated to do.

 

[dbjunior 10+ year member]

You need to build sealed side to get the boxes sealed,reaonants around,45-47hz then tune the ported side to the sealed frequency you will want to use half the sd for port area and larger the ported side the better i like a 3to1 one or 4to1 ratio. Tuning at 46hz will play into the high 20's with ease 32 will be very loud so ignore the fact its tuned high

 

[Kangaroux 5,000+ posts]

For my obsidian OA-12 I did 1 cube sealed / 2.5 ported, and that's net volume which includes space for the sub and the port. The port was about 45 in^2 and tuned to 40hz. If 32 is the lowest you want to go you can tune it to about 45hz, though don't tune it too high because your low end will drop off pretty steep.

I suggest getting an 8" sonotube/concrete form from home depot/lowes and using that as your port. That's 50 in^2 and you can make a large port to start out with and keep cutting it down until you get a sound that is good. If you go this route, just note that if you don't attach some sort of flare to the end of the sonotube you will get a lot of noise from the high velocity air not having a smooth entrance/exit.

 

[SubieSPL_Maniac 10+ year member]

thanks.. Im going to increase the sealed section to about 1cft, and the ported side to 2.25 I guess. And ill tune it to 40hz