Box Volume VS Cabin Volume

[squeak12 10+ year member]

Which is more important. I know to a point each is. Im looking into doing some competing in a street class(no wall, stays in cargo area). I have a late 80s Blazer that I can use and the dimensions in it are 36 x 36 x 15 to stay below the window, I think. Or I could use my daily driver which is a 97 Expedition and I have around 48 x 48 x 17 to work with. My main concern is that I have enough box volume but without sacrificing the SPL due to too much cabin volume. Not sure on the sub size yet, but it will be a quad .7 MT with a 20.1 probably.

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[helotaxi 5,000+ posts]

Figure out where the cabin gain will peak in the vehicle. Plan the enclosure acordingly to maximize the cabin gain. Determine sub size based on what will work best in the space you have with the tuning you need.

That's my understanding of it all anyway, but I don't compete...

 

[amartin_72]

Figure out where the cabin gain will peak in the vehicle. Plan the enclosure acordingly to maximize the cabin gain.

Care to explain how this is done?

 

[CHIT0WNZHUSTLA 10+ year member]

blazer > expediditon

 

[helotaxi 5,000+ posts]

Block off the approximate volume to be occupied by the enclosure. Get a test box (needs to be sealed to minimize impedance rise) and a test sub and place them in the approximate location of the sub enclosure. With Db meter in hand (just a basic Radio Shack model will work you don't need to get too loud for this test) play test tones of each frequency at the same volume and see where it peaks. You have now just plotted your car's cabin gain.