6th order cabs and other stuff

one huge disadvantage--

i have an eminence omega pro 18 inch woofer mounted in a 7.8 cubif foot box. yes its big, yes it goes down to 30 Hz or so. BUT-i neglected to do my research properly. although the design looks good in a speaker design program, i am putting a 5 string bass through it. the driver i chose is not a very good choice for such a large box. im no speaker genius, but i have been lead to believe that it can be hazardous to improperly tune your cabinet, as well as make it too big. if you do this incorrectly, the "cusion" of air behind the cone will not be enough to protect it. hence if i crank the volume through my 18 cab it "farts" a little bit. I will miss having a mosterous (read--cool looking) subwoofer cab, but when i go home from college this weekend, I am going to build a much smaller box for it, in the lines of 3 cubic feet or less. Before you change your cab design, ask yourserlf if its really necessary, because as far as im aware it involves a lot of time and experimentation to get it right, and ask yourself if your driver can handle being in the new situation. I know nothign about 6th order bandpass boxes, but i know if theres not enough air pressure behind the cone, you risk mechanical damage to the driver. please feel to correct me if im wrong anyone, but this is what ive been lead to believe. either way, good luck.

 

Dave,

Check out: http://216.150.71.139/audioinnovation/theories.html

I think a 6th order will be an order of magnitude more difficult to build than the 4th order bandpass. The tuning for both ported chambers will be difficult, and I've found the calculations really don't come close.

I think the correct way to build a 6th order is build two ported boxes of the designed specs, and tune each separately. Once half would be tuned with the rear of the driver facing inward. The other cab would be with the driver mounted externally and front side facing inward.

Once the two halves are correctly designed and tuned with your driver then you would build a second cabinet incorporating both halves. I don't see how you could tune it otherwise, as one would affect the other during tuning.

 

I've been all through the design formulas, and find that port tuning formulas don't get very close to real world tuning. Dunno why, but I don't yet have a full explanation of HOW the formula is derived. If I have that, perhaps I can apply it to what I'm seeing with a DVOM.

I'm winding up with short port lengths than the calculations indicate. Consistently. My 1x15 sub is 5.2 cubic feet net volume, measured to a gnats' butt including each individual piece of bracing. The box is tuned at 31 Hz, but the formula says I have to have 7.8 cubic feet to tune at 31 Hz, when I actually have 5.2 cubic feet.

My 10" project in work now is being done as a preliminary box at 0.71 cubic feet net, with an external port. I'll find the real world tuning for this combination, then add the volume occupied by the external port to the cabinet volume, and it should be an exact match. I'm building four 1x10, so I am willing to build the pilot test box first, just to get the other four correct the first time.

I'm getting tired of hauling around big, heavy stuff.

 

Tufnutz --

No speaker content here, but thanks EVER so much for becoming a Suupporting Member and knocking that doggone annoying hypnotic Demarest avatar off the screen!