Originally Posted by recon440

-Theoretically, let's say I have equal responses (current ported box vs. 4th order). Will firing it off the rear deck be louder than having the woofers firing from the same plane as the B-pillars (woofers are 10cm away from rear seats with twin slot ports between the seats). That's my main motivation in trying out the 4th order.

Originally Posted by cxa0897

I would make several simplifying assumptions to keep things sane.. Treat the subs as a point source, and take the freq response of the box with a mic right there In front of it. Then I would just place a mic where the listening point would be using the same sweep and find the difference in responses. That's the vehicles transfer function. This can be done with the existing box or something simpler like a sealed box which should be a lot flatterThat convolved with the half space enclosure response should give a pretty good result, assuming everything is accurately measured. Trying to play around with three dimensions would be horrifying. I just don't think it'd be worthwhile

Originally Posted by Fallen

I've tried using LEAP (comercial software), and with it you can do basic geometry like you mentioned. And then you can specify the position of the mic, for the response at a given point.

One of the issues with the geometry approach, is the cabin is leaky. And it's difficult to measure the leakiness. You can make estimates.

Anyways I'm terrible at convolutions to be honest. If I'm not mistaken you just need to add the transfer function of the enclosure with the transfer function of the cabin. You could convolve the impulse response of the enclosure with the input and then convolve that with the cabins impulse response to get the transfer function of the whole system. If I remember right.

Originally Posted by recon440

-Is there software that can model/predict the spatial response at a particular point in an echoic environment? ie. What I have in mind would to input a simplified geometric model of the vehicle environment (measure the width and height of cabin, length between A,B,C pillars, slope of windshields and depth of dash/rear deck). I'd like to see happens when I convolve the transfer function of this environment with the anechoic response of the speaker box set from a certain point in space.

Originally Posted by cxa0897

loading off the window will certainly not gain 9 dbz, but i would expect it to make some improvement. loading off the window should help, as well as having some gain from having the port directly inside the cabin

Originally Posted by 666WMD

That all this with a handful of salt, I'm new to 4ths and am basing my thoughts on observations more than knowledge of how they actually work.

Good thing you covered your ass on this one because...

That's a pitiful response from the 4th, which might be the subs themselves, but try dropping the sealed side down to 1.5cuft and bump up the ported side as much as you can, at least to a 2:1 ratio.

wrong. there is no reason to go 2:1 or more unless you are designing it just for spl. Im fairly certain Jud explained this one to you, but the sealed portion controls the lower end of the response, and the ported section controls the upper end of the response. the response he has there is nearly identical to the ported box, far from pitiful.

55hz is kinda high for a 4th as well, perhaps bring it down in 2-3hz increments until the gain levels out. I would think 45-50hz would be better.

wrong. this depends entirely on what the objective is. this tuning freq is the upper cut off. a 4th with a port tuning of 45 will drop off shortly after that, making the mids take up a large portion of the upper bass. on the opposite end, a 4th with a tuning of 80 hz could be used to have the response extend much further, at the cost of some efficiency. remember theres an efficiency/bandwith compromise. as one increases, the other decreases. 4ths are very, very versatile, and the cut off should be determined by where the mids cut off.

Even the sealed box seems to have a poor response, dropping that a whole cube might give a wider response.

wrong. dropping the volume on the sealed box would decrease the low end extension. increasing it would increase the extension.

Loading off the window might gain you something, but you'd probably have to angle the mouth so as to not choke it with a lesser distance from the edge of the rear seat to the window than the distance across the depth of the port mouth.