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designing box understanding slope


d2freak82

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I'm designing a box, I've been building boxes for many years, although I've only punched in the size and port in the past to determine the box I build. I'm trying to better understand the dynamics behind it.

I have bass box pro at home, but I'm using WinISD at the moment, I've posted a screen shot to help. I have a filter LPF @ 80hz,  my box is going to be 4-4.5ft^3   I used triticum's spreadsheet to determine my min port area is 39in^2 with 53in^2 as optimal. For argument sake as I haven't decided on box dimensions yet I put my port as 15x3 (WinISD automatically gave me a length of 17.68). 

From what I've read my f3 is my fall off points at -3db. I'm trying to figure out what type of slope I'm looking for! Now from what I'm starting to understand (I changed the low pass filter to 70hz after the screen shot) the peak above -3db on both the high and low side are my window of well played or best frequencies for the sub. With my new filter that gives me a nice window between 29hz and 76hz before it receives a big fall out.  I could be wayyy off here,  could anyone help me understand this? What am I looking for with this slope ? 

If needed I'm running an old school Orion HCCA15d2 with 1000watts rms @1ohm

 

box slope.jpg

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the only thing you are missing is that in car response is going to be vastly different than what WinISD shows since it does not account for the cars affect on the sound wave. You will most likely see a bigger hump around 40 Hz and will be able to play a little lower.

 

Also since you are using winISD you can check that you have enough port area by checking port velocity.

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