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Single SI HT 18 build

32291 Views 72 Replies 26 Participants Last post by  Billy13
Hey. Thought I'd make a build thread of my new sub beings that I like reading them and maybe others do too. This is my second DIY speaker project, but I'm far from being much good at it. Im still learning woodworking and about as far from an engineer as you can get. I've been reading threads here and elsewhere for quite awhile now and have learned a lot. This is a great forum.

So I picked up an SI HT 18 on preorder, seemed like a good deal. I've modeled all of the 15's and 18's in my price range and decided on a single 18 in a sealed box. I know I lose some SPL down low compared to ported, but the simplicity of the build as well as knowing how a sealed box in this room sounds steered me in this direction. Im replacing an old Velodyne F-1200 which did surprisingly well. I think I'm fortunate to have some nice room gain here.

I went with a box with outside dimensions of 34"h X 24"w X 21.75"d. Using .75" thick mdf sandwiched to .75" plywood for sides and back. Double .75" mdf for top and bottom. Baffle is 2 layers of .75" ply plus a .75" layer of mdf for the front. All bracing is double .75" mdf. After calculating the bracing volume I end up with about 5.75 cubic feet inside. I know its probably overkill and will be heavy, but my design philosophy is if its worth building, its worth overbuilding.:T

Now for some pics.

Beer and power tools.
Tool Machine Toolroom Wood shaper Table saw

Gluing the baffle
Workbench Wood Table woodworking Tool accessory

ply from home depot. Had to squeeze a bunch of glue in and clamp up.
Wood Plywood Table Furniture Hardwood

Workbench Wood Machine Table Tool

Gluing in bracing
Workbench Wood Table Plywood Furniture

White Architecture Black-and-white Line Monochrome

Machine Machine tool Photography


Metalworking hand tool

Black-and-white Monochrome Machine Monochrome photography Photography

White Black Black-and-white Monochrome photography Monochrome

More pics to come.
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Great work! I approve of the beer philosophy. Looks like it will be a solid box, you must have made a lot of dust with all of those routed edges!
I just love the last three pics in B/W! I say print them big and hang 'em in your HT.

Okay, okay, the build looks nice too...
That's your idea of not knowing how to do work with wood?!? I can't wait to see what you build when you feel otherwise... :yikes:

BTW; keep some of that beer handy. You'll need it to bribe a friend to help you move that beast. :D
Gorgeous ply and great looking build so far. Looks like a labor of love there. :T
Still learning woodworking, huh? It looks like you have a pretty good handle on it... :D Nice work so far, I'm looking forward to your build progress. :T
Love how you doubled up on the bracing. I used a single layer interlocking in mine and its not as "dead" as I thought it was going to be.
Thanks for the kind words everyone. I think the key for me is to take it slow. As much as I want to hear the end result I really just enjoy making things. Im already thinking about some new mains and a new center. The mains Im using were my first DIY speaker project and I think they turned out good, but they were designed more for music. In heavy duty HT use they could use more power handling, they would make great surrounds though.
Still gluing up the bracing
Wood Plywood Table Furniture Workbench

Vehicle Black-and-white Automotive exterior Photography Car

Getting there. Im surprised so far with the fit. Im using a $300 table saw and a circular saw, not exactly the best tools for accuracy. Still, I've had no major problems.
Wood Scale model Architecture Plywood Furniture

Gluing up the other side panel.
Furniture Table Wood Machine Plywood

From the back. I used titebond III for all the bracing on to one side and the top(along with lots of 2.5" deck screws) because it was easy to use, but for the other side I used Locite PL fast grab premium. That stuff is like concrete, but I thought it would fill any slight cracks better. Im happy the way it worked, theres a nice bead on all inside seams, though I'll probably still go over everything with caulking just in case.
Furniture Table Workbench Wood Plywood

I'll try to get the back on tomorrow, maybe get some caulking in.

The reason I say I'm just learning woodworking is that my grandfather was a master woodworker. My use of butt joints and screws as clamping would have appalled him. He was highly skilled at joinery. Dovetails and stuff that barely needed glue. I doubt he ever used MDF in his life. I also doubt he could have imagined someone wanting an 18" 900 watt high excursion subwoofer in their home. I have no doubt though he could have crafted it with much more skill than I could ever dream of.
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I bet your grandfather would have whittled one out of hickory if he wanted to, and if he's like mine was, would be proud that you are building it instead of taking the easy path. The build looks awesome so far, enjoy it because it will be over before you know it!
For the bracing I started by cutting all pieces slightly oversized as its really hard to cut them exact in the first place, also its hard to keep the glue super clean on the edges. After they dry I then trim them on all sides on the table saw to the exact sizes. Then I just used a jig saw to cut out the middle to the desired shape, then used a plunge router with a 1\2" round over bit for all the inside edges. I glued them in in stages so that I could maintain square using clamps where possible and 2.5 inch deck screws everywhere else. First I clamp the brace in place with no glue, then drill pilot holes for the screws, screw in the screws, then pull them out and take off the clamps. I then apply glue to the brace then reinsert the screws, this pulls them back nicely to where they should be. Then I reapply the clamps. Rinse and repeat for all brace pieces.

Got the back on today. I forgot to take a pic until it was on and I had it caulked up. Yeah, I got a little carried away with the caulking.
Wood Architecture Furniture Plywood

Wood Furniture Plywood Shelf Box

Thats all I got done today as I had some work to do as well as watch my Broncos lose in double overtime.:sad:
I plan on cutting the baffle tomorrow.
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Merriam Webster defines "inert" as Code Reds subwoofer cabinet... :T
Lol jman. Yeah its a bit ungainly. I moved it from the table to the floor at the point when I didnt think I could get it there on my own. That was before the last side and the back. I forgot to mention that I got one other thing done today, I weighed it. 135 lbs without baffle or driver.:coocoo: Not as bad as I thought though. My plan is to have a friend help me just get it up the little 3 inch step from my garage onto the main level of the house. From there Im hoping to use furniture sliders to get it in to place as its ceramic tile all the way.
Nothing wrong with over built. Nothing wrong at all.
A wool blanket would also work wonders. I have had to do the same with many of my monsters. Just me here to move things so you use what you can. Looks awesome again. Love the thick bracing.
Worked on the baffle today. First I clamped all 3 pieces together then drilled pilot holes and screwed in screws without glue for attaching the outside mdf piece to the inside plywood pieces that I had already glued together. I then routed out the woofer holes using the same center pivot point.

Since my model 200 Jasper jig only goes up to 18 3/16" I had to do some modding to get it to the 18 5/8" needed for the outside baffle cut.
Text Font Metal

Getting set up
Floor Flooring Metal

Floor Wire Flooring Machine Electrical wiring

This is the outside baffle piece cut out. I removed it from the inside pieces as this cut out is bigger than the hole that I will cut out of the the rest of the baffle.
Wood Plywood Floor Circle Concrete

This is the 2 layered plywood inner baffle cut out and set on the box. Note the ring around the hole. I got the previous cut just a hair too deep. No big deal though.
Wood Plywood

This is with the outside piece laid on.
Wood Plywood Machine

Architecture Circle Window

Test fit. I went with 16 5/8" for the inside cut.
Audio equipment Loudspeaker Subwoofer Technology Auto part

Fits perfect
Wood Automotive wheel system Wood stain Table Furniture

With the outside piece on.
Audio equipment Technology Wood Machine Gas

Loudspeaker Audio equipment Subwoofer Car subwoofer Technology

Loudspeaker Audio equipment Car subwoofer Subwoofer Computer speaker

Loudspeaker Audio equipment Subwoofer Car subwoofer Computer speaker

Im thinking of using a 1/8" roundover bit on the outside cutout. Then I need to decide whether to use t-nuts or just screws to attach the woofer. In another thread I asked for opinions on this and got some good advice. I ordered a 1/4" heavy duty t-nut kit from parts express so I have it if I go that way, but it definitely adds another step to the build. After I get that done I'll drill holes for the binding posts, give it a good vac job, add poly fill, then glue on the baffle. I wish I didnt have to work tomorrow.
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I had to cut a hole in my brand new Jasper jig too, and I'm glad you posted the photo of the vac hose on the router since I have the same router and couldn't figure out how to hook mine up
The vacuum attachment on this plunge base really works well, I recently did some fixed base routing and the mdf dust is incredible.
I used 1/4" round over to start on my edge and ended up using 13mm instead. Tell us how yours goes.
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