Audiophiles are as passionate as car enthusiasts when it comes to tweaks that will squeeze the last ounce of performance out of their gear. The problem is that tweaks usually cost money. Sometimes they cost a lot of money.
Your mission, if you choose to accept this project, is to challenge your inner creative, add a little performance to your high end audio or home theater system on the cheap and feel that “Do It Yourself” pride that goes along with it.
The platform we’re building is finished in Goncalno Alves (which is also sold as Tigerwood). This wood species is hard, heavy and dense. Its smooth grain is characterized by stripes and swirls alternating from cream to golden brown to black. It’s also weather and insect resistant which makes it a popular choice for high end flooring and outdoor patio decking. We chose it because we have a matching custom equipment rack also made of Goncalno Alves.
The isolation platform is a double box design using a ¾’ plywood sub-box encased in an exotic hardwood outer box. This significantly cuts down the material costs (premium hardwoods are expensive) and waste. Veneering is a popular choice among woodworkers because of the cost savings, but a veneer is too thin and would probably crack and split over time due to the stress caused by excessive weight and temperature changes.
There are many other beautiful domestic and exotic hardwoods, which are heavy and dense. Some other good wood choices would be Cherry, Oak, Maple, Purplehaert or Bubinga. If you don’t own or have access to a bandsaw, you can opt to get the millwork done at a local woodshop or cabinet maker.
Kudos to my colleague Oz Martinez of Let There Be Sound, a high end audio-video boutique in Plantation, Florida for supplying the vintage Krell KST 100 stereo amplifier pictured in this article.
List of required materials and tools.
- 1 ½ x 6 ¼ x 48 inch Goncalno Alves hardwood board – about $30
- 1 2x4 sheet Birch Plywood - $13
- Handful of 1 ¼ inch course thread drywall screws - $2
- Bottle of premium woodworkers glue - $7
- 1 Bag of dried play sand - $6
- Quart semi-gloss spar urethane wood finish - $9
- 2 foot length of 4x4 wood post material - $5
- Few sheets of 150 and 220 grit sandpaper - $4
- 4 aerospace grade aluminum spinning tops - $24 (We’ll tell ya where to buy later.)
- Small tube latex caulking - $3
- Pack of 1 ½ inch self-stick felt furniture pads - $3
- Bandsaw (for re-sawing)
- Electric planer
- Electric sander
- Drill or screw gun
- 3/8 inch drill bit
- 3 four inch foam brushes
- Substitute Goncalno Alves with a different exotic or domestic hardwood
- Biscuit joiner
Before you start, remember the woodworker’s creed: measure twice, cut once.
After deciding on the final size of the project (ours is 18 ½ x 16 ½ x 6), we start out by squaring and re-sawing the Goncalno Alves board with the bandsaw into about ¼ inch thick pieces of Goncalno Alves thin-wood. Again. This cuts down the cost of the project without sacrificing performance.
The finished width of the thin-wood is 6”. This is important, as it will dictate the maximum height for the construction of the sub-box, which will be smaller than the Goncalno Alves outer box.
Construct the sub-box with the birch plywood by cutting lengths of the birch that will yield the correct sub-box height. Taking into account the 11/16 thickness of the sub-box top and bottom covers and the ¼ inch for the Goncalno Alves thin-wood top, our width is 4 3/8 inches. Then cut and miter the birch into four lengths -- two 18 inch pieces and two 16 inch pieces.
Since the final weight of the project is about 50 pounds, join the mitered ends using at least one joiner biscuit in each corner. Coat each end of the joints with a film of woodworker's glue, clamp and let it set for a few hours.
Though not as strong as a miter joint, you can also use a simpler butt joint, but be aware of your final sub-box length and width. For the butt joint method, your glue up should include attaching the corners with 2 of the course drywall screws for each corner. Remember, either method must yield a perfectly square box.
Cutting the lengths slightly smaller than the 18 and 16 inch sizes eliminates possible gaps in the construction of the final outer box. The outer box thin-wood can be sanded back to the correct sub-box size during the final assembly using the 150 grit sandpaper.
With the leftover birch plywood sheet, cut off an 18 x 16 inch piece for the sub-box bottom and attach it with a film of woodworkers glue and 8 of the drywall screws (two per side). Sand back the bottom evenly to match the box length and width if necessary.
Take your 4 x 4 wood post and miter cut a piece off the entire length of the board. It will look like a long triangle. Then take the long triangle and cut off four 4 3/8 inch pieces. Attach the triangles inside the box to the four corners using glue and one drywall screw on the outside corners of the box. Then line all the inside corners and joints with a bead of caulk. Finally, seal the wood on the inside of the box with a coat of spar urethane like you see in the picture at left.
There are two reasons for adding the triangles to the inside corners. First, it gives added strength to the sub-box. Second, at the end of the project, each triangle will be drilled with a vertical hole to mount the aluminum tops which are used as the cone-shaped feet of the isolation platform. This design also prevents the sand from leaking out.
Now, let’s prepare a sand, sawdust and wood-shavings mixture to fill the sub-box. The sand purchased in plastic bags is very moist and must be dried out. Wet sand would condensate on the inside of the box …never a good thing. After it's dry, put the sand, sawdust and wood shavings in a bucket or other suitable mixing container and mix it by hand.
After it’s mixed, shovel it into the box. Fill the sub-box until you can drag a flat piece of wood over the top of the box without dragging the mixture onto the top edges. You don’t want to have any sand or wood-shavings on the top edges that will prevent a good seal when you glue and screw the sub-box top cover on. To the left is the sand filled sub-box.
With the remaining piece of birch plywood, cut another 18 x 16 inch piece for the top of the box. Glue and screw the box cover to the top of the box. Remember to put a coat of spar urethane on the inside of the box cover before attaching it. Sand back the cover to match the box sides if necessary. You now have a completely sealed, sand-filled sub-box.
Now we can start attaching the Goncalno Alves thin-wood pieces to the sub-box. First, cut three 16 x 6 pieces of thin-wood from the Goncalno Alves boards for the top of the box. Coat the entire sub-box top and the glue side of the thin-wood with a film of woodworker's glue. Then clamp them to the box top, also place a clamp horizontally across the top to pull the edges in tightly… This eliminates any gaps. Let it set for two to three hours, then remove the clamps.
Now cut two more lengths of thin-wood that are slightly longer than 16 inches for the box sides. Coat the sides of the box and the glue side of the thin-wood with a film of woodworkers glue, then clamp and let set for 2 hours.
The thin-wood should be flush with the front and back ends of the sub-box. Sand back flush to the sub-box if necessary.
We’re almost finished constructing the box, but be aware that when cutting the front and back ends of the thin-wood, they need to be at least 18 ½ inches long to account for the extra width added to the sub-box after adding the thin-wood to the sides.
After the cuts are made, apply the glue to the box front and back and the glue up side of the Goncalno Alves. Clamp and let set for a couple of hours. After removing the clamps, sand flush with the sides of the box if necessary.
Sand all the sides, top and bottom of the box with the 220 grit sandpaper. Then wipe the box down using a cotton rag with a tiny bit of mineral spirits to remove all the sawdust. Using a foam brush apply 3 coats of the spar urethane to the top and the fours sides. Remember to let the finish dry and sand the box with 220 grit sandpaper in between coats. We’ll apply finish to the bottom later.
Spar urethane is a better choice than regular polyurethane because high-end audio components like amplifiers can run extremely hot. Spar urethane is very resilient to temperature and moisture changes. That is why it’s used on boat decks.
After letting the third coat dry for about 24 hours, flip the box over onto a hard flat surface covered with a thick soft blanket. With the incredible weight of the project, you don’t want to have any impressions showing up in the finish by laying it on anything coarse.
Since the bottom of the box has the birch plywood face exposed, I used some amber stain before I applied the 2 coats of spar urethane finish. Remember to sand in between coats. Take a look at the picture to the left. This is our isolation platform sans the aluminum mounting cones.
About the aluminum tops used as mounting cones: You can get them from Nickel City Tops. They’re actually sold as high-end toys. Precision made from aircraft grade aluminum, they make a high grade and much cheaper alternative to the mounting cones available at high-end audio salons.
To install the cones, turn the box over and mark four holes 1 5/8 inches in diagonally from the corner of the sub-box. Then using the 3/8 inch drill bit, drill a 1 inch hole into the four pre-marked corners of the bottom of the box.
Then punch a hole through the felt furniture pads and push them down through the stem of the cone. Make sure the adhesive side of the pad isn’t against the top of the cone. Then peel the adhesive backing off the felt pads and install the cones to the holes drilled into the bottom of the box. At the beginning of this step is a shot showing how the cone looks after installation.
Turn the box over, stand back and admire your isolation platform. Allow about 72 hours for the finish to cure before placing the equipment on the platform. The final weight of our exotic high-end isolation platform comes in at a whopping 60 lbs! Combine that with the 55 lb Krell amp and you better make sure you set this up on a termite-free floor.
Rick Contrata is an audiophile and a self-taught woodworker. His projects include humidors, cabinetry, furniture and wood specialty applications using domestic and exotic hardwoods.