Skyline diffuser plans: from panel size to a cut list
A skyline diffuser is a grid of square blocks of different heights glued to a backer. Planning one comes down to four questions: how many cells fit, how tall each block is, how many sticks to buy, and where each block goes. This guide answers them for a 24 × 24 in panel of 2x2 lumber, worked out with the diffuser calculator.
1. How many cells
Use the stock's actual size, not the nominal one: a 2x2 is about 1.5 in square. A 24 in panel then holds 24 ÷ 1.5 = 16 cells across and 16 down, 256 in all. A quadratic residue pattern with N = 7 repeats every 7 cells, so 16 cells are 2 whole periods plus 2 extra; the calculator tells you when the panel is not whole periods and what size would be.
2. How tall each block is
The height codes follow (m² + n²) mod 7 over each 7 × 7 block of cells (m and n count the rows and columns), so there are seven codes, 0 to 6, arranged symmetrically. Code 0 is an empty cell. The heights are the codes times (deepest block ÷ 6); with an 8 in deepest block the step is 1.333 in (≈ 1 5/16″). For this panel:
| Code | Height | Cells | Pieces to cut (5% spare) |
|---|---|---|---|
| 0 | empty | 4 | – |
| 1 | 1.333 in (≈ 1 5/16″) | 41 | 44 |
| 2 | 2.667 in (≈ 2 11/16″) | 36 | 38 |
| 3 | 4.000 in (4″) | 40 | 42 |
| 4 | 5.333 in (≈ 5 5/16″) | 45 | 48 |
| 5 | 6.667 in (≈ 6 11/16″) | 40 | 42 |
| 6 | 8.000 in (8″) | 50 | 53 |
That is 252 blocks (4 cells stay empty) and about 101.4 ft of 2x2 before kerf and spare. The why behind the sequence, and how depth relates to frequency, is in the QRD diffuser design guide.
3. How many sticks to buy
Every saw cut turns a kerf of wood into dust, and short offcuts at the end of each stick are wasted, so the total length is not enough on its own. The calculator packs the pieces onto 8 ft sticks with a 1/8 in kerf: 14 sticks, which is also the theoretical minimum. The plan groups sticks that are cut identically:
| Sticks | Cut from each | Offcut |
|---|---|---|
| 4 | 11 × 8.000 in (8″), 1 × 5.333 in (≈ 5 5/16″) | 1.167 in (≈ 1 3/16″) |
| 2 | 14 × 6.667 in (≈ 6 11/16″) | 0.917 in (≈ 15/16″) |
| 2 | 17 × 5.333 in (≈ 5 5/16″), 1 × 2.667 in (≈ 2 11/16″) | 0.417 in (≈ 7/16″) |
| 1 | 9 × 8.000 in (8″), 3 × 6.667 in (≈ 6 11/16″), 1 × 1.333 in (≈ 1 5/16″) | 1.042 in (≈ 1 1/16″) |
| 1 | 11 × 6.667 in (≈ 6 11/16″), 3 × 5.333 in (≈ 5 5/16″), 1 × 4.000 in (4″) | 0.792 in (≈ 13/16″) |
| 1 | 7 × 5.333 in (≈ 5 5/16″), 14 × 4.000 in (4″) | 0.042 in (≈ 1/16″) |
| 1 | 23 × 4.000 in (4″) | 1.125 in (1 1/8″) |
| 1 | 4 × 4.000 in (4″), 28 × 2.667 in (≈ 2 11/16″), 1 × 1.333 in (≈ 1 5/16″) | 0.000 in (0″) |
| 1 | 8 × 2.667 in (≈ 2 11/16″), 42 × 1.333 in (≈ 1 5/16″) | 12.417 in (≈ 12 7/16″) |
The blocks weigh about 47 lb in pine, before the backer and frame, which matters for how you hang the panel. Set a stop block on the saw for each height and cut all pieces of one height together.
4. Where each block goes
The glue map below is the front view, row A at the top; each number is a height code. Print it at full size from the calculator's build sheet and lay it on the backer, or mark a grid on the backer and copy the codes.
Change the panel size, stock, depth or sequence and the counts, cut plan and glue map update. The build sheet PDF has all three on paper.
Open this 24 in skyline plan in the calculatorBuild order
- Cut a backer to the panel size (thin plywood or MDF) and, if you want a clean edge, a frame as deep as the tallest block.
- Cut all the pieces, one height at a time, against a stop block. Sand or chamfer the cut ends lightly.
- Sort the pieces by code, then glue them to the backer following the map, row by row, keeping the grid square.
- Finish (paint, stain or oil) after the glue is dry, or pre-finish the sticks before cutting if you want each block a different colour.
- Hang it with a French cleat or a rated hanger suitable for the weight; a full panel of solid blocks is heavier than it looks.
Smaller blocks
Smaller cells scatter higher frequencies more evenly but mean many more cuts. The same 24 in panel in 3/4 in stock, 4 in deep, has 1024 cells and 1053 pieces from 27 sticks, against 267 pieces here. Open the 3/4 in version to compare.
The acoustic figures the calculator shows are textbook estimates from the geometry, not measurements. A skyline diffuser works best on a rear or side wall with a few feet of distance to the listener.