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4th order 15 not hitting like its supposed to


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hey guys new to the forum, just built a 4th order with a dayton audio rss390hf 15. i have calculated it in winisd and hornresp and it shows that i should be getting great response from 25 up to about 70 hz. the box is 2 cubes on either side and tuned to 45 hz. i have it in my truck right now and have tha port coming through on the passenger side its a blow through set up. it feels like theres a ton of bass at 28 and below and a bunch around 45 and above but between that there is almost none. i haent put any seals around the cab or bed so maybe all that bass is kinda escaping and just resonating in the bed? i have a cap on and the glass on it is flexing so maybe from 30 to 45 it all goes in the bed and doesnt fill the cab with bass. idk what are youre thoughts on this  do you think sealing up the port to cab will improve the response?

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Like CleanSierra said, how much port area?  How much power are you running?

Sounds like it could be cancelling due to reflections somewhere.  Sealing everything up would be a good thing to try.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

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At a glance, you may want a larger ported section

You'll also want to err on the side of more port area. Particularly if it's only 2" wide 

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Also could you post a sketch or diagram of how everything is laid out?

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The thing is with WinISD, almost no one uses it right. It gives a prediction of a response based on an open air environment. i.e. sitting on the floor in a field. If you design something there, you need to plot cabin gain and integrate that. You'll also need to take into account where it's located in the vehicle and if any surrounding areas can contribute to cancellation or constructive  interference. 

Regarding ports, the whole port velocity thing is garbage. Throw it out. It doesn't take into account the effects of the laminar sublayer - which is where air in the port flowing closer to the surface of the wood moves slower than it does in the middle. It also doesn't take into account the effect of port diameter vs. air velocity. A larger port will allow for a higher air velocity before any audible chuffing occurs. 

Seriously. More port, and a larger ported section. All of your sound output from a 4th comes from the port. Let it breathe. Conceptually, a 4th order is a ported side for output with a sealed side to control the mechanical movement of the cone. You're essentially running a 15" driver in a 2cuft ported box.

Still would like a sketch of the box

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