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The conversion project begins. Dual 15" to dual 21".

post #1 of 18
Thread Starter 
I'm going to be converting these dual 15" loaded cabinets to dual 21" loaded cabinets. They are 11.4ft3 internal per driver, and tuned to 31.7hz. I will be taking the old JBL 15s out of the other cabinet in favor of a pair of Eminence Kilomax 15s until I can convert the second cabinet to 21"s. The objective here is to have 2 dual 21 enclosures that I can use either on thier own or together with the other cabinets. The output capability for the size, and how these fit in the van pack space make it a no-brainer.


RCF 21"(teal) vs JBL 15"(green). The Kilomax 15 models almost the same as the JBL. The difference in output should be no surprise:

Here is the plan:

1. Remove drivers and grilles.
2. Remove fiberglass damping inside the box.
3. Remove t-nuts and any other mounting hardware currently installed in the driver area.
4. Sand front of box to raw wood.
5. Cut a 3/4" plate fit the face of the box.
6. PL the snot out of said plate and glue it to box face.
7. Roundover plate edges.
8. Cut pair of 21" holes.
9 Reconfigure bracing.
10. Rewire cabinet.
11. Paint black(/gasp, what?){maybe}
12. Install drivers.
13. Fashion grilles out of expanded metal sheeting.
14. 4ohm bridge on an Ashly KLR-3200, delivering 3200w per box.
15. Hurt people.

The JBL 15"s are 19.5lbs per, the 21"s 24. The most significant weight addition will be the Piece of 3/4 I graft on to the front of the box. I can and will still be able to move these on my own. I have considered using my low tuned 18" bass cannons with either Zv3 or SI 18s to provide 0-35 and use these 35 up.
post #2 of 18
Thread Starter 
I'm still somewhat on the fence with the driver choice.

The new ceramic version is available, but so is the neo, and I can get 4 of the neos for the same price as the ceramic. They have different recone kits, in simulation the x model takes 2mm less excursion for equivalent output(which could simply be a better driver/cab match), but also claimed to handle 500w more due to new motor venting.

I already have one Neo model that is my favorite 21, and the X is somewhat an unknown quantity. Most likely splitting hairs but there isn't a clear winner with pros and cons each. Still needs some thought, but regardless there will be a pair of 21s.
post #3 of 18
it sure is a shame that those drivers went up 300$ in the past 2 years I have been eyeballing them to make a 2x21 cab for bass guitar. mad.gifmad.gifmad.gif
post #4 of 18
Hey. Sorry I missed you text. I was napping. redface.gif I figure you must be asleep by now.

I'm not sure exactly what you wanted me to model but I tried my best anyway. The frequency response graph is -10dB because it was off the charts at full power from the Ashly. I modeled Xmax at full power. I have no idea what the port sizes are but from the look of it, they look like 4 or 5 inch ports and either way I rendered there will be SEVERE port compression using those.

Let me know what details you'd like to work on and I can redo these.
post #5 of 18
Originally Posted by whiskey_face View Post

it sure is a shame that those drivers went up 300$ in the past 2 years I have been eyeballing them to make a 2x21 cab for bass guitar. mad.gifmad.gifmad.gif

We did that for a while. It was funny and ridiculous at the same time. 2 21sw152's wired to 2 ohms in a 24" cube firing dual opposed on the bottom with an Ampeg 410HE on top. Head was a Crest 8002 with with a Sansamp RBI and a DCX2496. It got old talking about it to bass players who had no clue..."Man what brand is that?", "How many watts is that","My buddy used to play through some EV 15's". My own bass player didn't know much about what he was playing through. The best part about it was anyone who played through it would suddenly get very conscious of their volume and end up with a realistic IOW lower volume than usual instead of bouncing off of the clip limiter in their bass head all night. If you ever saw the clip lights on the Crest with that rig people were getting out of there in a hurry.
post #6 of 18
Thread Starter 
I figure I'll have to address the porting at some point, most likely adding a couple more and lengthening them a bit. I was looking to compare the N and X versions, but I'm locked into the N version.
post #7 of 18
BTW Justin I just stumbled on a sick deal yesterday. Just sick. You'd be proud.
post #8 of 18
Thread Starter 
Started this project today, in preparation for grafting the new plate at the shop tomorrow.

Remove drivers:

Remove fiberglass insulation damping and driver mounting hardware:

Test fit the 21, oops it doesn't fit:

It will fit there after some modification:

This part was a complete bitch. The paint that is on there instead of sanding off nicely has to liquify and practically turn into a paste. Burned a couple of 80 grit belts in the sander. First one is done, on to the other one. Had to put some new winter tires on the van, and it interrupted my progress a bit.

post #9 of 18
Thread Starter 
Both ready to go. The second one sanded down much easier.

post #10 of 18
Thread Starter 
Picked up a sheet of 3/4, 4 tubes of PL, and a notched trowel to complete the graft today. Cut the plates down to size, filled the exiting mounting holes in the old baffle with PL, coated the back of the plate with PL, tacked them down with a couple of brads and clamped it up:

Tomorrow I'll unclamp, hit the edge with a roundover, cut the driver holes and clean out the cabs. Not sure whether to damp yet or not, and not sure if I'll be able to paint by the show Friday where this cab will get it's first run. I am going to be painting alot of things all at once I think. So I may hold off, not sure.
post #11 of 18
Thread Starter 

post #12 of 18
post #13 of 18
Thread Starter 
In process pics.

Trim excess PL, roundover plate, place driver, cut holes, remove waste, remove brace, and blam. Tomorrow is clean thoroughly, rewire, and light one up. I need to figure out a grill solution still.

Test fit driver:

post #14 of 18
post #15 of 18
Thread Starter 
Water pump seized on the van halfway home, had to tow it in. So instead of another driver I get a new radiator and water pump. That is Thursday's project. I have my grille solution figured out, tomorrow is supposed to be clear so I'm hoping to get one of these running and finish prepping the 18s.
post #16 of 18
Thread Starter 
Turns out it was the tensioner pulley. Saved some cash. I have a bunch of pictures to update, but I have to get home first. I'll tease with this, maiden voyage style:

post #17 of 18
Thread Starter 
First I fabricated the grilles. Did something really similar to my adapter plates for the 21 cabs, but a little different this time and cut out the hole and rear mounted the grille so it seems to float with no mounting.

Vacuumed out the inside of the cabinet and made up the wiring. There are 2 8ohm speakers that are parallel for a 4ohm cabinet impedance:

Time for drivers!

And a test run...

Once all is proven good, mounting the grilles:

Next step will be paint. I'm doing up the 18s now and I won't have time to paint these before Friday so it looks like it will have to wait till next week. I still have to fab grilles and wiring for the other cabinet as well. After last nights show I think there might be just a touch of ring to these, I may pop a couple of pillows in there to damp it down a bit.
post #18 of 18
Lookin' good, my friend! smile.gif
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AVS › AVS Forum › Audio › DIY Speakers and Subs › The conversion project begins. Dual 15" to dual 21".