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[Jeff Woodford]

Centauri wrote on Wed, 15 September 2004 14:39

Jeff NB wrote on Wed, 15 September 2004 19:30 this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth This is not good at all!!  The labs have a much longer path length than the 18s, resulting in all sorts of cancellations at different frequencies.  If you had two stacks, you could run the labs in one stack and the 18s in the other, but not together like this, unless you run the labs to say 80Hz and the 18s above that (where they would work better anyway with the short horn path). Recommend ditch the 18s, add more Labs....

in an idea world i would have 24LABs per side, but as i havwn't built them yet, well thats another story....

the 18's work really well with the labs, the horn length on the 18s is quite long and the way i have the system set up it all works well. there are nodoubt a few frequency problems but i asure you there is plenty of bass.

[Mark Seaton]

Jeff NB wrote on Fri, 17 September 2004 08:29

Centauri wrote on Wed, 15 September 2004 14:39 Jeff NB wrote on Wed, 15 September 2004 19:30 this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth This is not good at all!!  The labs have a much longer path length than the 18s, resulting in all sorts of cancellations at different frequencies.  If you had two stacks, you could run the labs in one stack and the 18s in the other, but not together like this, unless you run the labs to say 80Hz and the 18s above that (where they would work better anyway with the short horn path). Recommend ditch the 18s, add more Labs.... in an idea world i would have 24LABs per side, but as i havwn't built them yet, well thats another story.... the 18's work really well with the labs, the horn length on the 18s is quite long and the way i have the system set up it all works well. there are nodoubt a few frequency problems but i asure you there is plenty of bass.

Those few frequency problems could be what is killing your drivers.  Imagine this...  If you had a pair of LABs together and somehow observed the excursion of the driver when driven as a single unit, vs. a pair together, you would see decreased excursion for more output with a pair vs. the single.  This comes from changing the exit condition of the horn, where adding more, identical boxes effectively devide up the fee space load seen by each.  Now if you were to place the two LABs together, and flip the polarity of one, with the same drive level as before you would see much less output (obvious), but you would also see much greater excursion (possibly not so obvious).  

Unlike in a front loaded box where the box provides the largely dominant air spring and loading on the driver, the horn and its environment are the dominant factors in the LAB.  If you cancel out the front acoustic load, you are reduced to the sealed box loading of the rear chamber (worst/ideal case).  This is almost akin to taking a sealed driver and making a big hole in the box and still driving it with the same signal.  In short, you are killing the designed in excursion limiting.

As others have said, if anything, try running your pictured system as a two way sub section, with a very steep crossover.  If you can measure the response, you want to measure each separately, and see if there are any dips in the response when you add the others.  If there are, do whatever you have to in order to keep them from fighting.