4th order band pass wall

audionoob1234

CarAudio.com Newbie
Hi I’m a little confused on how to design a 4th order if it’s as a wall, I want to do 2 18s in a little truck with a topper. You can walk through the cab since it is cut out so it’s kinda like a van what ratio should I try to get and what tuning I want to be windy from the port but also have a good range of frequencies it can play.
 
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Hi I’m a little confused on how to design a 4th order if it’s as a wall, I want to do 2 18s in a little truck with a topper. You can walk through the cab since it is cut out so it’s kinda like a van what ratio should I try to get and what tuning I want to be windy from the port but also have a good range of frequencies it can play.
Could you please clarify your question about designing a 4th order enclosure for your system?
 
My old 4th order wall with 2 18s. Sealed section on bottom. Ported on top.


4th.jpg



4th 2.jpg
 
How do you calculate the port on a wall like that?
I'd make sure your subs are compatible in a 4th 1st. An Ebp under 60 is what I'd look for, once designing starts I'd size the sealed side for goals. 40-48hz can yield huge extension depending on driver and ratio. Other than that just tune to rear chamber resonance. I've designed scores of 4ths and everything I said above is either a big consideration or rule of thumb. 4ths have tradeoffs at times and it usually manifests in power handling. Be sure to put the magnet side of the sub in the vented side man so you can smell coils burning before the subs pop and back off.
As far as sizing the port 50-70% sd is a good rule depending on driver capabilities. I use 100ft/sec port velocity as my upper limit and up to 120ft/sec if port ratio is low. That said Aeroports can perform well above that velocity but designing with an Aero 150ft/sec is a good rule of thumb. A 1:1 ratio port is about as efficient as you'll get but an Aeroport is less wall plus decreased turbulence and that equates into output... boundary layer and laminar airfow and all that stuff.
Either way you go modeling is a must for finding resonance, inputting power applied and tailoring response while keeping excursion and velocities in check.

Real modeling
 
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How do you calculate the port on a wall like that?
Calculate the available cubic feet you have to work with. Subtract the thickness of wood being used for the 7 to 8 panels. Most enclosures are made with 0.75" (19.05mm or 1.905cm) wood.

7 panels = the port is the length of the panel thickness.

8 panels = the port is longer than the panel thickness and you are using 3 of the 6 sides of the enclosure as the port.
 
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audionoob1234

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