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Passive Phone Speaker[8/4 · 2ft · 5-Pack]
One pack. One build. All 5 boards used. • Makes 5 phone speakers
Shop Black Walnut 8/4 · 2ft Pack Shop All Speciesselect 2' Lengths / 4-6"
How it goes together
Black Walnut
Hard Maple
Cherry
White Oak
Red Oak
Ash
Hickory
Ambrosia Maple
Sapele*
Padauk*
Purpleheart*
*Exotic — not available for shipment to US customers.
A solid hardwood block that makes your phone louder with no batteries, no cables and no Bluetooth. The phone stands in a slot on top. Its bottom speaker fires down into a hidden chamber, and a flared horn throws the sound out the front. Each board makes one speaker from two layers glued face to face, so one pack makes five — great desk gifts.
Quick Build — for experienced woodworkers
| Part | Qty | From | S4S size | S2S size |
|---|---|---|---|---|
| Layers (top and bottom) | 10 | Boards 1–5, two each | 10" × 4" × 1¾" | 10" × 3½" × 1¾" |
| Glued block | 5 | Two layers face to face | 10" × 4" × 3½" | 10" × 3½" × 3½" |
Block: two layers face-glued, long grain to long grain. The chamber is drilled into both glue faces before glue-up, so nothing shows on top but the slot.
Sound path: phone slot ½" × 1" deep × 3¾" long, back wall 1" from the back → 1¼" chamber 2" deep → horn bored from the front (2" mouth 1" deep, then 1½").
Feet: felt pads under the corners.
Finished size: S4S 10" L × 4" D × 3½" H · S2S 10" × 3½" × 3½". Fits phones up to about 3⅝" wide and ½" thick in their case.
Before You Start
Shopping List
- 1 lumber pack — 8/4 · 2ft (S4S or S2S)
- Wood glue (Titebond II or III)
- Self-adhesive felt pads (20)
- Sandpaper 120 / 180 / 220
- Finish: wipe-on oil, hardwax oil or water-based poly
Tools
- Saw for crosscuts (mitre saw or circular saw with a speed square) — with a stop block
- Drill press with a fence and stop block
- Forstner bits: ½", 1¼", 1½" and 2"
- Chisel, or a router with a ½" straight bit and edge guide
- 2–4 bar clamps, 6" or longer
- Tape measure, combination square, pencil
- Random-orbit sander or sanding block
- S2S only: jointer, straight-line rip jig or hand plane
S4S or S2S? S4S boards arrive flat and square on all four sides — cut and build. S2S boards have rough edges you straighten first. No jointer? Choose S4S.
Our sizing assumptions: ⅛" per saw cut · S4S boards 1¾" × 4", ¼" to square an end · S2S boards trimmed ½" each end and ¼" off each rough edge (3½" clean); we plan S2S at 1¾" thick · sizes drawn for the narrowest board in the pack. Wider boards give you a bigger offcut or a wider part — never a shortage.
Step-by-Step
S4S Lumber Pack
Surfaced 4 sides — no jointing
- 1 One board, one speaker. Each board makes one speaker from two layers. Keep each pair together and pick the best face for the top.
- 2 Cut the layers. Square one end. Clamp a stop block at 10" and cut two pieces from every board — 10 layers. You need 20⅛" per board.
- 3 Mark the sound hole. Stack each pair with the ends and back edges flush. Mark the back edge of both. On the glue face of each layer, mark a centre point 5" from the end and 1¼" in from the back edge.
- 4 Drill the chamber before glue-up. On a drill press, use a fence and stop block so every hole lands in the same spot. Drill a 1¼" Forstner hole 1¼" deep into the glue face of the bottom layer, and ¾" deep into the glue face of the top layer. Don't go deeper — the bottom layer needs its floor.
- 5 Glue up. Spread glue on the glue faces, keeping it away from the holes. Line up the ends and back edges so the two holes meet, and clamp. This is a face-to-face, long-grain joint. Leave it overnight, then sand the sides flush.
- 6 Cut the phone slot. On the top, lay out a slot ½" wide and 3¾" long, centred on the length, with its back wall 1" from the back face. Cut it 1" deep: a row of overlapping ½" Forstner holes cleaned up with a chisel, or a router with a straight bit, edge guide and stop blocks. The bottom of the slot opens into the chamber.
- 7 Bore the horn. Lay the block on its back on the drill press. Mark the centre of the front face, 1½" up from the bottom. Drill a 2" Forstner hole 1" deep. Change to a 1½" Forstner on the same centre and drill until it breaks into the chamber — about 2¾" from the front face. Go slowly and clamp the block.
- 8 Test it. Blow out the dust and stand your phone in the slot, speaker end down. Play music. If the phone is tight in its case, widen the slot a little with sandpaper on a stick.
- 9 Sand and finish. Round or chamfer the outside edges and soften the edges of the slot and horn. Sand 120 → 180 → 220. Wipe on oil or hardwax oil, two coats, keeping finish out of the slot and chamber. Stick felt pads under the corners.
S2S Lumber Pack
Surfaced 2 sides — straighten edges first
- 1 Prep the boards. Trim ½" off each end to remove any end checks. Joint one edge straight, then rip the other edge parallel (¼" off each rough edge is our planning allowance). S2S boards finish 1¾" thick, so screws and some sizes change — use the sizes in this column.
- 2 One board, one speaker. Each board makes one speaker from two layers. Keep each pair together and pick the best face for the top.
- 3 Cut the layers. Square one end. Clamp a stop block at 10" and cut two pieces from every board — 10 layers. You need 20⅛" per board.
- 4 Mark the sound hole. Stack each pair with the ends and back edges flush. Mark the back edge of both. On the glue face of each layer, mark a centre point 5" from the end and 1¼" in from the back edge.
- 5 Drill the chamber before glue-up. On a drill press, use a fence and stop block so every hole lands in the same spot. Drill a 1¼" Forstner hole 1¼" deep into the glue face of the bottom layer, and ¾" deep into the glue face of the top layer. Don't go deeper — the bottom layer needs its floor.
- 6 Glue up. Spread glue on the glue faces, keeping it away from the holes. Line up the ends and back edges so the two holes meet, and clamp. This is a face-to-face, long-grain joint. Leave it overnight, then sand the sides flush.
- 7 Cut the phone slot. On the top, lay out a slot ½" wide and 3¾" long, centred on the length, with its back wall 1" from the back face. Cut it 1" deep: a row of overlapping ½" Forstner holes cleaned up with a chisel, or a router with a straight bit, edge guide and stop blocks. The bottom of the slot opens into the chamber.
- 8 Bore the horn. Lay the block on its back on the drill press. Mark the centre of the front face, 1½" up from the bottom. Drill a 2" Forstner hole 1" deep. Change to a 1½" Forstner on the same centre and drill until it breaks into the chamber — about 2¼" from the front face. Go slowly and clamp the block.
- 9 Test it. Blow out the dust and stand your phone in the slot, speaker end down. Play music. If the phone is tight in its case, widen the slot a little with sandpaper on a stick.
- 10 Sand and finish. Round or chamfer the outside edges and soften the edges of the slot and horn. Sand 120 → 180 → 220. Wipe on oil or hardwax oil, two coats, keeping finish out of the slot and chamber. Stick felt pads under the corners.
How does a passive speaker work? A phone speaker is tiny and its sound spreads out in every direction. The slot and chamber catch that sound and the horn guides it out the front in one direction, a bit like cupping your hands around your mouth. Expect a clear boost in volume and fuller sound — not a powered speaker, but a big step up.
Why drill the chamber before glue-up? Drilling 2" straight down through a ½" slot isn't possible with a 1¼" bit. Drilling each layer from its glue face hides the chamber inside the block and keeps the top clean.
Why step the horn? A horn that gets wider toward the front helps the sound spread out smoothly and get louder. Two Forstner bits are an easy way to make that flare without a lathe.
Make It Yours
- Two-tone: glue a walnut top layer on a maple bottom layer.
- Landscape version: make the slot longer and move it to one end if your phone's speaker fires from the side.
- Desk organizer: drill a few ⅜" holes along the top for pens.
Safety and Care
- Wear eye and hearing protection. Use a push stick for every rip under 4" wide.
- Clamp the block to the drill press table for every Forstner hole. A large bit can grab a loose block and spin it.
- Run the drill press at a slow speed for the 1½" and 2" bits and lift often to clear chips.
- Cut the layers with a stop block on a mitre saw. Keep your hands at least 6" from the blade.
Frequently Asked Questions
Not for S4S boards — they arrive flat and square on all four sides. S2S boards need their edges straightened: a jointer, a table saw with a straight-line jig, or a hand plane all work. No jointer? Choose the S4S pack.
The slot is ½" wide and 3¾" long, which fits most phones in a slim case. Measure your phone in its case before you cut. Make the slot a little longer or wider if you need to.
It works best with phones that have a speaker on the bottom edge, which is most of them. If your phone plays stereo from the top and bottom, the bottom speaker gets the boost.
Hard, dense woods like maple, walnut and cherry give the clearest sound. Choose any species in the pack — the shape matters more than the wood.
Planned offcuts only: the end trim and about 3⅛" (S4S) or 2⅞" (S2S) at the end of each board — enough for a test block to try the Forstner bits on. All 5 boards go into the speakers.
Yes. A 4ft pack makes 10 speakers: cut four layers from each board instead of two.
