Due to the ravages of age, I find myself casting about for a more portable rig without sacrificing too much performance. I have a Crown XLS1500 on the way, with which I plan to bi-amp a box leftover from a stillborn project from long ago, but with different drivers than it was designed for. Originally, I was going to put two K110’s in a wedge for a vocal floor monitor, but halted the project when the K110’s were needed elsewhere. The box (pictured) is built except that the baffleboard was never cut nor the vent shelf glued in.
I think I can put a 12” and a 6” in this box, and use it either upright in the backline or as foldback in rehearsal or when DI’d to FOH. I’ve narrowed the drivers down to a 3012HO or 3012LF, and an LA6-CBMR or Alpha-6CBMR (all Eminence). The reason for the latter choices is that I won’t need to expend extra volume for a sub-enclosure. I might also add a pair of Motorola/CTS KSN1005’s, with crossover.
I have an Audioarts 2100A crossover and a 4100 4-band parametic EQ, and I’ll be using a Tech21 RBI pre-amp.
I’ve been looking at the 3012HO and 3012LF with the Jeff Bagby spreadsheet, but I’ve been having a heck of a time ironing out the group delay and the vent air velocity. The main problem I’m having is optimizing the vent design so it will a) produce the “right” Fb, b) be quiet and c) fit in the box without interfering with the drivers. And, of course, d) the vent(s) must be experimentally tunable during assembly.
My idea at present is to cut a new shelf which will go all the way to the back and seal off the main volume, which would then be 44.25 liters gross. I would install two 3” dia. or four 2” dia. straight vent pipes into that shelf, running parallel to the baffle, with the flared ends facing into that rectangular cavity. Here’s where it gets sticky, since using end flares to allow a higher, yet quiet, vent velocity means the pipes must be closer to the drivers (to accommodate the flare flanges), but without the flares (and thus bigger and longer required tubes) there is a question of whether their other ends will be too close to the opposite wall at the correct length.
So I have some questions, if this is not too tedious:
1) How close do calculated vent lengths come to actual lengths when using end flares? Some of the commercial flare/tube kits I have seen are just shy of calculated lengths, but my experience with other builds (long ago) was that the vent tunes at a shorter actual length than predicted. I surmised this was due to end losses making the vent effectively longer (I never used flares).
2) What effect, if any, will the exit cavity shown have on tuned length and duct noise? It measures 21” x 2.5” x 5” (avg) deep.
3) Which would work better in this box, the 3012HO or the 3012LF?
4) What would be the ”right” Fb for an HO in this box? Higher eases the vent length problem, but with 300W available from the XLS1500 I don’t want to exceed xmax at 41.2 Hz (I only play 4-string).
5) Which of the 6” drivers is a better match? I’m thinking maybe the LA6, due to its higher thermal dissipation limit.
6) What’s a good crossover design for adding a couple of KSN1005’s (in series) across the 6”? I’ve seen some circuits, but I’m not sure about the crossover frequency that will be most compatible with these 6” drivers.
7) Is there a detail drawing available somewhere that shows exact dimensions in profile of the 3012’s (needed to determine duct clearance)?
8) What is the intrusion volume of each of these four drivers?
Any help/suggestions appreciated. http://i900.photobucket.com/albums/a...g?t=1362496409 http://i900.photobucket.com/albums/a...g?t=1362496699 http://i900.photobucket.com/albums/a...g?t=1362496646