Music's Foundation
"Bass So Powerful, You Can Feel It In Your Dental Fillings"
Deep, Deep Bass
Now that my Frankenstein Horns are sounding decent now, I've got to wonder what it would be like if I only had some bass to go with it. With my first wood-working project completed, I felt confident enough to tackle another box right away. Fall and Winter came and went and still no box. I've been pondering the woofer decision all Winter long and went back and forth on cheap vs. good vs. all-powerful-no-holds-barred. Availability and reliability are also factors. After thinking about how painful it would be to cut the MDF, I decided against cheap drivers as it takes just as much effort regardless of the driver, so why not just use something decent. It was a toss up between the NHT 10- and 12-inch from Madisound; the Dayton Titanic 10- and 12-inch from PartsExpress; and the Shiva MKIII 12-inch from AdireAudio. After finding a lot of DIY projects on the net using the Shiva drivers, I was sold as reviews were always favorable and the cost was acceptable at less than $140 (shipping included).
My costs are estimated here:
Shiva driver - Adire Audio - $140
250 Watt, generic, subwoofer plate amp - Parts Express - $130
Dual terminal plate (for dual voice coils) - Parts Express - $5
Black carpet to cover the box (paint looks terrible) - Parts Express $16
3M spray glue for carpet - Parts Express - $9
One sheet of 8x4 MDF - Home Depot - $18
Total cost is roughly $318 (this does not include glue, tools, etc)
Design Considerations
The Shiva white paper (PDF) and applications can be found at the Adire site.
Adire sells their own retail Shiva sub called the Rava. Priced at $399 plus shipping, I was almost tempted to buy it and be done with it all. It's a small box designed for small rooms and home theater. However, my goal was finding the best design and box for tight clean bass that went deep down, really low, and have fun making it. The Rava seemed like it was for the home-theater crowd. Since I already had a plate amp, purchased last fall in anticipation of the "How Low Can You Go" subs, I chose to make the Adire suggested low-Q alignment, sealed-box, as it is designed for "audiophile" use. This application called for a large box of 88.5 liters. It almost deterred me but I felt sound quality was more important than the inconvenient size. I also did something my car-stereo buddy recommended I shouldn't do - I used regular wood glue instead of Liquid Nails. You see, Liquid Nails is thick and because of this it helps seal the box when there are imperfections to the cuts and/or corners of each panel of the box. If you've ever used yellow wood glue you'll know that it doesn't seal anything that doesn't meet squarely. We'll see how this turns out. Also note that I decided not to use screws, either.
Measure Twice, Cut Once
Home Deport cut an 8x4 sheet in half for me length-wise and then at home I cut one 8x2 sheet into a 50-inch piece with 46-inches remaining. I then cut 37-inches from the other 8x2 sheet. I used a circular saw with a straight piece of scrap MDF clamped down as a cutting guide. I made this as square as I could. I then went to the table saw to make the smaller cuts.
Set table saw to 16.5" and cut 5 pieces from 50" and 46" stock. On the 46" piece, save the remaining 13" stock for later.
Set table saw to 18" and cut two pieces from 37" stock
Set table saw to 20.5" and cut three of the 16.5" stock. These are the side panels and internal mid-brace. 16.5" (w) x 20.5" (h) Then cut the 13" scrap piece to get 13x20.5. This will be cut again later.
Set table saw to 22" and cut the two 18" pieces. These are the front and back panels. 18" (w) x 22" (h)
Set table saw to 8" and cut the 13" x 20.5" scrap. This is the rear brace. 8" (w) x 20.5" (h)
Set table saw to 7.75" - cut a piece of scrap bigger than 6" x 8"
Set table saw to 5.75" and cut above piece to desired 5.75" (w) x 7.75 (h). This is the small front brace.
Note: all of the above measurements are found in the Shiva Sealed Box Applications PDF.
Now for the painful part - routing out 13 small 4-inch holes and then one 11-inch for the driver. All of the cutting and routing took me two hours or so. Then I had to spend one hour cleaning up with the shop vac.
Step 1 - Assemble the mid-brace.
Step 2 - Mark down the layout before gluing. I decided to start with the front because I was still waiting for shipment of the terminal plate for the rear.
Step 3 - Top and side panels. You will notice I tried to "caulk" the seams with extra wood glue.
Step 4 - After the first part of the mid-brace had dried (about 2 hours) I then glued the small brace on the other side. Remember to glue it on the 5.75" side.
Step 5 - Once the mid-brace is dry enough to move (I waited overnight) turn the box over on the side panel. This helps you glue the mid-brace and clamp it down. Once it has set (about 2 hours) you can turn it over again and reclamp to make sure the pressure is even.
Step 6 - Now glue the side panel. This is where you will know if your cuts are good. For me, the side panel was coming out about 1/16". I had two options: plane down the mid-brace, or sand down the mid-brace. I chose neither and decided to add more glue and let things be. When the box is carpeted no one will know the difference unless they run there hands down the edges. Performance shouldn't suffer as long as the brace does its job of keeping vibrations down to a minimal and the glue holds.
Step 7 - Once the bottom panel is in place, make sure the boards will meet the rear panel flush. If not, sand and use putty if needed. Allow the putty to dry and then sand before gluing on the rear panel. If it looks bad, use lots of Liquid Nails as it will fill in your cracks. My boards looked ok so I just sanded it a little and used a lot of wood glue. At this late stage, if you have any doubt about your board meeting flush against each other, my recommendation is to spend the big bucks (~$2.50) for the Liquid Nails. Otherwise, all of this hard work would be for nothing!
Step 8 - My bottom plate looks ok, but I ran out of clamps in step 7 so there's doubt in my mind... and you know what I said before! Out with the Liquid Nails to caulk all of the inside seams. This won't hold the box together but it will keep it air tight, which is what we want or the bass will suffer. I reached in from the front baffle hole and from the rear and used my fingers to apply as the caulk gun was too big to reach inside the cabinet. I probably wouldn't have had to do this if I only had one or two more 36" clamps for step 7. I also noticed that my middle brace was 1/16" or 1/32" shorter than the side walls so Liquid Nails is used to fill the gap.
Step 9 - Measure the terminal plate and mark the cut lines on the wood panel before drilling the starter holes for the jig saw.
Step 10 - Once the terminal plate fits properly, glue the rear panel in place. I usually wait one day for Liquid Nails to dry before sanding.
Step 11 - Clean off the surfaces with a moist towel and then move the box to a clean surface to dry. Since the carpet color I chose is jet black, I decided to do the gluing inside the house to keep away from the saw dust. Starting from the bottom (where no one will look), I wrap the woofer from bottom to front to top to rear to bottom, allowing each side to dry before moving on. I use a spare piece of MDF as a squeegee to help get out air pockets and stretch the carpet evenly. I cut the edges with a simple utility knife. The sides are done last. If the seems aren't tight, you might see the MDF at the corners. To hide the imperfections use a black marker or some black, auto touch-up paint to dab on. No one will know.
Step 12 - Once the box is covered and dry, you can solder on the speaker cable to the terminal plate. I used four pieces of CAT-5 cable and some black wood screws purchased from Parts Express to mount the terminal plate. I chose dual binding posts so that I could operate the driver at 4 ohms. If I should make another one, I can just connect one pair of posts for 8 ohm operation. I drilled pilot holes to help mount the plate, and it is optional to caulk the plate so no air escapes. However, this is quite permanent when using Liquid Nails.
Step 13 - The plans called for 16-ounces, or 1-lb, of poly-fill. I had some Acousta-Stuf in stock so used that to stuff the back chambers and placed some directly behind the driver.
June 3, 2003
The driver did not fit perfectly into the 11-inch hole, so I forced it as much as I could to test the sound. At the moment, I have a sensitivity mismatch between the sub and horns. The sub needs a lot more juice to get its mojo running nicely while the horns takes very little power for high output. So, I guess I will have to build that tube amp sooner than I thought. As a quick test of the sub's capabilities, I turned off the main amp and just raised the volume on my 5687 preamp to push the sub a bit. I heard too much info from 80-hertz on up! After checking the plate amp's specs, I confirmed that the default crossover slope for this model (purchased from PartsExpress) is 12db. I recommend you get a plate amp with a 24db slope. Another thing I noticed was it didn't go too deep in the bass. This somewhat confirms my evaluation of the 5687 preamp... it doesn't go as low as a solid state or passive preamp. I may try another tube type in the preamp or just go solid state, depending on cost, and just use tube amps for the warmth... this is up in the air. I may also get an active crossover to manipulate the slope and bass frequencies as I think a small amount of delay would be in order... the horns seem too dynamic or fast for the sub.
The carpet treatment didn't work out and I will be tearing it off, sanding the box, and re-routing that driver hole sometime in the future. So out goes the subwoofer, for now anyway (sorry, no pics as it is butt ugly).
September 20, 2003
The peeled the carpet off and put on one coat of primer. I will sand down and put on one more coat of primer before sanding again and spraying gloss black. The primer is the cheapest I could find (oil-based) since MDF soaks up paint.
More to come...
