What The .........?

It has been a long time since I have done a project, so let's get started, shall we?

This project will involve three of these:



and one of these



and a lot of this



all wrapped up in a nice wrapper.


I started cutting wood today, and using my DowelMax to help line things up once glue-up happens. This will be large, so I will need everything lined up quickly and easily once glued. The wood is 23 3/4" x 48", and I am not cutting them down, just to give you an idea.

I got the dowel holes drilled into the four sides



Then did a test run



It lined up perfectly.

Progress will be slow, but I will keep it updated. Next issue is to cut 19 1/4" holes......the Jasper Jig isn't big enough....darn.

It's already looking like a proper coffin.Just doing a test run to make sure everything fits and lines up well.

Stay tuned

Those are 21" PR's from Kevin Haskins. I don't recall if they were called Exodus or Maelstrom or ???

6th order bandpass, and YES!

First off--if you don't know yet, this is a blatant rip-off of Mark Seaton's BMF design he did for that audio-company-who-shall-not-be-named many years ago. His design used a 15" driver with 18" PRs. Mine will use an 18" driver with 21" PRs. It's a VBMF! Mark knows how to design a sub, so the BMF was as compact as you could make it, and looked great. I don't know how to design a sub, so I made mine oversized so that I could add something solid to the insides if the volumes turned out to be too great, especially in the front chamber. Building it will be much easier than messing with the weights on the PRs and the volumes of the chambers.

Second--damn you Menards for no longer carrying baltic birch. I picked up this "Tigerply" that also has 13 layers in the 3/4" ply. Make that 13 layers of crap. Luckily I will be wrapping the whole thing in MDF so it will hide my shame.

Third--The Jasper Jig goes to 18 15/16" and I needed 19 1/4" for the PRs. What to do? Drill another hole in your Jasper Jig, of course! I just measured out 9 5/8" from the bit and drilled my own hole with the drill press and a 1/8" bit. Drilled like butter. The pic shows my test drilling--I had to go out further for the final hole.


Once the jig was done, I got all the driver holes routed and mocked up the box.



Next up, bracing

I got some work done in the last few days--I can't glue it up all at once, so a few pieces at a time. Got the outsides glued up.



Got the inner mount for for the 5100 installed after drilling for the screws and installing the gasket. Added some bracing as well.




Still trying to figure out the rest of the bracing. Should be able to pop the top on soon, then laminate the whole thing with 1/2" MDF.

Slow progress, but progress nonetheless. I got all the bracing done using a mix of ply scraps, Baltic Birch scraps, PL Premium, Titebond, pocket screws, etc.



Once all the bracing was set, I popped the top on, which went on perfectly since I had set it up to use dowels previously. I used Bowclamps to go across the spots where there was cross bracing. They worked fantastic.



Once this cures, I can go ahead and install the drivers and get to testing the different weights on the PR's. When that is set, I will pull the drivers out, laminate the entire box with 1/2" MDF, and either paint or veneer. I have set the big PR's into their cutouts--they are just ridiculously large!

There are several reasons I use the MDF. I like the surface better than this crappy ply for either painting or veneering. It adds rigidity. It seals. It countersinks the drivers.

Slow but steady progress here. Getting the last of the MDF layered on. Let me reiterate that what is known as TigerPly is the most evil ply made by man. I was so happy to see the last of it disappear beneath the MDF. It truly is garbage.




Had to make a circle cutting jig to make the 21 1/4" cut outs for the PRs, and that worked perfectly.




I have the lead shot to use as weight in the PRs. Washers are just too unwieldy to work with. They would stick out a long way and it would take a ton of them to get the job done. I will mess with weight using the lead shot, then gorilla glue the shot in permanently when I settle on an exact weight.
I also ordered a gallon of Duratex as that is good enough for my dark theater, and this thing is too huge to veneer affordably.

I do not have any washers from the mass kit. I bought these off of someone else and there were no washers included. All I have is a bolt and nuts/lock washers for each one. I bought some large fender washers and they were not very heavy--it would have taken a ton to load the PRs. I do not know the max weight on these. I have tried to get Kevin Haskins to answer questions, but no luck so far. I was just going to wing it. I will have to revisit my model now that it's time to test the drivers. If I recall correctly, I was going to add ~1800g to the rears and only 400 or so to the front.

A couple coats of Duratex and it's now time to load the box with drivers.



The final volumes turned out to be about 10.2 cf for the rear chamber, and 2.8cf for the front chamber. That front chamber will need some solid filler to reduce the chamber volume to up the tuning point. My model abilities are limited. I was using WinISD with three different models going at once. I was using 2 PR models, one for each chamber, and a model for a 6th order bandpass. I made all volumes the same, and would change tuning points on the PR models and see how it affected a 6th order bandpass model. It is very crude but gives me a rough idea of how the entire box will perform with all the outputs combined. I am going to start out with about 2000g on the rear PR's, tuning at ~18Hz, and 400g on the front PR, with a volume of ~1.5cf, and tuning at ~56Hz. It's a start at least. I am not sure how I will measure and sum the three outputs from the PR's(any tips Ricci?), but one step at a time.

Here is the 5100 all snugged in to its resting spot as seen through the front chamber



If I left the front chamber at its current volume, the tune on the front chamber would be way low, somewhere in the low 40's. So, I needed to remove some volume from that front chamber. Foam to the rescue!



I think I can beat down to the volume to somewhere near 1.5cf with this combo. With 400g on the PR, that would push my front chamber tune to ~57Hz and make for a pretty combination with the rear chamber 17 Hz tune

Measuring out the lead shot



My trusty old scale from my veterinarian days keeps coming in handy!

I think I am going to bag the bolts and washers completely and just Gorilla Glue the shot into place. The inserts are kind of crooked, don't look all that sturdy, and my MDF rings I made as giant washers can't go in very well since the inserts are set in at odd angles, which makes the bolts skewed. Uggh.

DONE!

Not without drama and trauma, but it is at least all assembled. It turns out that the round tube where the weights screw in will hold exactly 1870 grams of lead shot plus the gorilla glue to keep it in place. Oh, and gorilla glue foams up far more than I remember! It was a fountain held in check with duct tape. This what the rear PR's looked like when it had all cured.



The front PR only had 400g of lead shot added, so I used way too much gorilla glue and let it foam as much as it wanted.




Somehow, there is a stray piece of shot rolling around in a dust cap or somewhere else close by. I am hoping it wedges itself in somewhere and is never heard from again. Murphy's Law would counter that and say that it will shake and rattle and bother me forever more.

Here is the final product in its home. Those are 15" LMS5400's in the background to give you an idea of scale.



Tonight I will get it hooked up and at least fire it up for a listen and leak check.

Crazy amounts of high quality bass. That's my first impression after listening to some multichannel Talking Heads. I only had a few minutes, but it made for a huge grin on my face. This was using this single sub in my theater where I normally have EIGHT subs going! Measurements to come when I can....