Hide a Speaker in a Log

I found this log on a hike in Vermont many years ago. I liked it so much that I threw it over my shoulder and took it home. Until now it was just an interesting thing standing in the corner. It’s time to do something more with it. Looking through my piles of stuff, I decided to put a pair of old car speakers inside the hollow of the log and set the whole thing on a stable base. Naturally the speakers should be bluetooth, as amplifier boards, like this one, make it so easy to do.

I started with a vague idea of what I wanted: a stable, simple, heavy base that would support a structure housing the speakers on either end and the bluetooth amp board inside. And the log would fit over the whole structure and rest on the base. The plan was to hide as much of the structure and innards as possible, leaving the log unchanged.

As a cheapskate, I set out to use as much of the stuff I already had and purchase as little as possible.

I considered putting some LED lighting in it, but then I came to my senses. The last thing I need is one more thing in my living room with an obnoxious LED staring at me. Enough already, electronics designers!

Here is the list of materials I ended up using.

Reclaimed / recycled Materials:

Log, reclaimed from the wilds of the Northeast Kingdom

Speakers, reclaimed from my trusty old truck

Wall wart power supply, reclaimed from some old device (can’t remember what)

Threaded rod, reclaimed from old unfinished projects

Melamine board, recycled from an old busted treadmill

Metal mesh, reclaimed from an unused shelf thing in the garage

Aluminum angle, recycled form old projects

Wire, recycled from many old devices

Some plywood and foam scraps from other projects

Rubber, from an an old bike inner tube

Caulk

Glue, tape, and various hardware I’ve had laying around

Scrap wood for feet along with some felt pads

New materials:

Dayton Audio KAB-250A 2x50W Class D Audio Amplifier Board with Bluetooth 4.0, from Parts Express for about $40

Sakrete 5000 plus, 80 lbs from Lowes for about $7

PVC pipe and fittings, from Lowes for about $10 total

A barrel connector to match the power supply, from Amazon for about $4

An On/Off floor switch, from Amazon for about $7

I started out by making sure the speakers would fit in the cavity of the log. Then I took one of the them to the store with me in search of a good material to use as a housing. In the plumbing section, I found that the speaker fit perfectly in the end of a PVC 3” coupling. So I bought 2 of them and a 2 foot section of pipe to match.

Confirming that the bluetooth amp would fit inside the pipe, I ordered one. When it arrived, I wired it up to the speakers and power supply and made sure it worked as planned.

Using a small plywood circle cut to the inner diameter of the pipe and a piece of foam slightly larger, I isolated each end of the pipe’s cavity for each speaker. Running the 2 wires for power through the pipe wall, I was able to wire up the the rest, hot glue the speakers onto the couplings, and press fit it all together.

(Stand by for a wiring diagram.)

By putting the speaker tube in the log, I could plan out some dimensions. I figured that to keep the thing hidden in the log it would need to be 10” above the base. With the threaded rod and some aluminum angle I could make legs that would attach to the sides of the pipe and hold the thing above the base.

Concrete was the obvious solution to the problem of making a custom, heavy base. I used a piece of melamine from an old broken treadmill to make a mold that was 18” square and 3” tall. I sealed up the seams with caulk. Using the legs mounted to the pipe to know where, I placed some dowels, which are slightly bigger than the legs, through the mold and wrapped them in packing tape so the concrete wouldn’t stick to them. To make room for the power wires, I taped a hot glue stick to one of the dowels.

I mixed up the concrete and filled the mold half way up and put the metal mesh on top. I then finished filling the mold and let it cure a couple days.

After removing the base from the mold, I was able to pound out the dowels leaving the holes to mount the structure.

Finally, I made up some simple feet with scrape wood and felt pads to protect the floor. Each foot needed to be adjusted independently by adding layers to level out the base, due to the uneven surface of the bottom. When I was happy with the leveling, I glued the feet on with some caulk (to make it easy to remove if I need to change the approach).

Wires were installed for the power down one of the legs and through the hole left by the hot glue stick and out the back side. The barrel connector went on the end of that wire and an on/off floor switch was installed too.

I moved the whole thing up to its final location. That base is quite heavy. By propping the base up on a couple of 4” tall blocks, I was able to install the structure through the holes in the base and snug them up with washers and rubber washers I made using old inner tube (not too tight, don’t want to crush the hole walls). Finally, and with a little help from a friend, I tipped the base and structure on one of it’s edges and slid the log over the structure and stood her up right.