Getting Ready for Austin!!!

02Xcape said:

I'm about to pick everything up this weekend... So I'll take pics of the items asap bro... But I have not measured the resonance.. Do u know it by any chance... I'm thinking of tuning the ported box a 55 hz... What do u think should it be lower... Thanks for the advice...

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I have not measured this car for resonance because I don't build SPL systems. In the world of SQ, the goal is deep bass response but FLAT (or musical) response at the full spectrum. For this reason, I often do not port boxes in cars. The cabin gain is so great in a typical vehicle that quite literally the car is acting like a ported box itself in gain structure. In fact, most builds I work on including my own need EQ work to tune OUT the cabin gain, so it plays into the proper response anticipated on a musical system. Cabin gain is measurable...

Take a calibrated mic, and go out to an open field with your sub box and the mic. But the mic 1 meter (3.3 ft) in front of the sub, and play tones (or calibrated white noise), and record the graph on a laptop of what the mic reads. Now, that's your "anechoic" or non-gained response of the sub. It can be a good idea to move the mic to another 1 meter away location, or perhaps 3 or more, if you need to create an average that is more realistic (since there may be peaks) Put the box in the vehicle, this time you can measure with your mic where people's heads are, and play the same sounds and record the response. The difference between these plots is effectively the cabin gain of the vehicle. That stays constant for that vehicle no matter what you put in it, unless you change its shape dramatically.

Another far more simple thing to do is to play a sub known to play flat and pure from a very low frequency up to a high one (say, 10hz to 150hz) without distortion, and mic that at the head location. The peak in response indicates the cabin gain structure, but a little less accurately than doing the outdoor test.

If you are tuning for SPL and SPL alone, it would be a smart idea to find approximately or very accurately the high point of this cabin gain, and then tune the box for it. If you are looking for a "streetable" box that will play loud but sound acceptable for SQ (reasonably flat and very musical), then you are after a totally different box design.

Either way, WinISD Pro is my go-to for box modeling. It is free of course. Try it if you haven't before.

OK if this is strictly for SPL comps, build the biggest box you can, first of all. Build it double-thick, or at the very least use aggressive bracing. Rhino liner won't do squat for flexing. It does a great job at damping but that's not the same. With the box as big as it can be, then you can calculate the right tune. You'll want to use a slot loaded port or some massive PVC piping with roundover tips. Using WinISD here will help you get it spot on. Again, if you post the T/S specs of this particular sub you are using, I can help develop the right box size and port tuning you will need. It is a very precise science when you are talking ported boxes, you have a tolerance of only 4% or so before things get out of tune and tend to sound completely wrong.

The reason you start with the biggest box you can in SPL comps is that you want the box to contribute as much gain as possible. The bigger it is (up to the limit of Infinite Baffle or 3x the VAS spec), the more efficiency the box will have if tuned right.

So, you probably want to take up most of the trunk, right?

Sealed boxes have tolerances of 10% or more, and are better suited to normal or musical sound, or SQ if you prefer.