how does the port effect sub box?

I understand that port size determines what Htz it is tuned to.

What determines how many Htz to tune to though? 30? 35? 38? 40? What is the effect if the Htz tune if tweaked a little bit either way?

My preliminary plan to is build a ported box for (2) 8s under the driver's side rear seat of my 99 Silverado extended cab. I should be able to get around 1.5 cubic feet with out too much difficulty. I wanted to go with (2) 8s because they can both be forward firing instead of upfiring into the seat bottom.

Is a ported box generally louder than a sealed box?

1) The target tuning frequency is determined by the system designer based on two main criteria.  First are the T/S parameters of the driver being used and where it operates best.  Second is the intended purpose of the system.  In an SPL comp vehicle, the tuning frequency is optimized to create the highest possible sound pressure peak in the vehicle.  This requires extensive testing and calculation to find the perfect resonant spot in the vehicle/woofer/enclosure system, and is often much higher than what would be used in a music system, such as 58Hz.  In a music or SQ system, the designer wants the flattest possible output with the largest frequency response range, often resulting in low tuning near or below the Fs of the driver.  So to answer your question, the tuning frequency is calculated based on the parts of each system and what you need it to do.

2)  Ported enclosures need to be assembled carefully and precisely to hit the desired tuning frequency.  An error of a few percent can shift the tuning in often undesirable ways.

3) All else being equal. a ported enclosure is generally louder than a sealed enclosure around the tuning frequency, but not necessarily louder elsewhere in the pass band.

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Thanks.

Any thoughts on why there aren't many people using 8 inch subwoofers? I'm guessing that given the same amp they will make less sound?

I measured and won't be able to get both 8s in a single ported box under the driver's side of the rear seat. I think I'll make 2 seperate ported boxes, one under each side. I think another benifit to making sperate boxes is on each side I will have more than enough room for a ported box.

Should the port and speaker both fire forward?

What would happen if the box is bigger than required by .15 to .2 cubic feet?

8-inch woofers are a fine solution for a limited space installation.  Just don't expect huge boom from them.  As far as making a .2 cuft error in enclosure volume, you can tell what will happen if you model it.  In general, using a port designed for one enclosure volume in another that is 0.2 cuft  larger will shift the tuning frequency upwards.  How much up it goes depends on the size of the enclosure and the size of the port.Support the12volt.com

I think I've decided on Infinity 860w 8 inch subs. They fit in my budget and are 250 watts RMS.

Are there any good free ware programs to design / model a sub box?

i dont know af any software that you can get free.  there is software out there, but it is rather expensive.  The12volt does have calculators though.  they are very helpful.  here is the link.     https://www.the12volt.com/caraudio/boxes.aspIf your cousin is such a good installer, and he will install anything for a 6 pack; why are you talking to me?

kaztheminotaur wrote: Are there any good free ware programs to design / model a sub box?

Try WinISD  https://www.the12volt.com/installbay/forum_posts.asp~TID~74558~PN~1

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