ok , i have 2 15'' fi btl's and i want to do a 4th order ....

i cant remember where i read that btl's are not made or not good for 4th order designs ....

its this true?? can somebody explain...

They will work just fine in a 4th order bandpass, while it has a sealed chamber it's also ported, so not the same as all sealed

well i got an email from the guy thats designing me the box...

The Fi BTL is not suitable for 4th order bandpasses (essentially a sealed box with an acoustic low pass filter). It will however work great in a 6th order bandpass(Essentially a ported box with a acoustic low pass filter).

Magenta is a 6TH order bandpass, Cyan is a 4th order bandpass.

As you can see the 6th order bandpass is better with the Fi BTL.

Even if we make the 4th order bandpass into a SPL box, the SPL 6th order bandpass will be louder.

makes sence to me...

i just never heard of btl's not beign suitable for 4th order's...

i keeep learning new stuff everyday

I've seen a lot of people do BTL's in 4th orders down here in FL. I'm not a big fan. They seem to work pretty good for most people but I'd have to agree that a 6th order would be better for it. I've only seen one in a 6th order and it was much more impressive than any of the 4th orders.

6th order is by far the way to go... although exceedingly more complex and intolerant of errors in design. AS the higher the order of enclosure goes, it seems the room for error becomes exponentially smaller.

Everything "works", just how well is why we tend towards certain types of enclosures.

Thanks,

Scott

As Scott said, the 4th and 6th are both equally doable, the 6th (if made correctly) will be far superior to the 4th. The problem is that you need a LOT of volume for a good 6th, and if ur not willing to rebuild the box if its mis-tuned, you may just want to go with a simpler ported design. But hey, if you can do it, I'd love to see another good BtL 6th order

I did a gen 2 BtL 18" in a 6th order for a Chrysler 300 it was a pain in that the design called for the woofer to be installed halfway through the build process, so it was all draped up in plastic for a few days, but man did it pound. Both ports fired into the cabin, it had three plexi windows facing back. I went for a 3:1 volume ratio between the two "halves" of the box, as I've had good luck with that ratio before, but ended closer to 4:1 due to a weird shaped trunk. I was too scared to fiberglass in more volume, as the tuning is soooo finicky

Be thorough, be precise, post pictures

Edited November 26, 201014 yr by SubSam

red panels are removable . Without them, the port area increases, port length decrease, chamber volume increases and the tuning goes up. It will cause 3dB more output from 41Hz to 50Hz or so.

im hoping to start building the box next week... ill deff post pictures because im sure ill have a lot of more questions...