Acoustic Panel Fabrication Guide

Absorption Panel Fabrication

Wall-mounted fabric-wrapped rockwool panels are the primary absorption treatment. They reduce flutter echo, control early reflections, and lower RT60 to design targets.

The standard absorption panel is a fabric-wrapped rockwool slab on an MDF backer board, mounted with a 25mm air gap behind. This air gap improves low-frequency absorption by allowing the rockwool to act as a velocity absorber.

Step-by-Step Fabrication

1. Cut MDF backer: 1200 × 600 × 18mm. Sand all edges smooth to prevent fabric snagging. Mark impaling clip positions on the back face: 150mm from each edge, spaced evenly (4 clip positions).
2. Cut Rockwool RWA45: 1200 × 600 × 50mm slab using a long bread knife or electric carving knife. Cut on a flat surface with a straight edge guide. Wear N95 mask + nitrile gloves — mineral wool fibres are irritating to skin and lungs.
3. Cut acoustic fabric: 1400 × 800mm (100mm overlap on all four sides). Ensure the fabric is acoustically transparent (see fabric selection callout below).
4. Lay fabric face-down on a clean, flat surface. Center the rockwool slab on the fabric, then place the MDF backer on top of the rockwool (MDF back face up).
5. Pull fabric tight over edges. Staple to MDF back using T50 staples at 40mm spacing. Start at the center of each edge, then work toward corners. Pull firmly but evenly — no wrinkles on the face. Fabric must be smooth and taut.
6. Fold corners like gift-wrapping: fold one side over first, then fold the adjacent side over it to create a neat hospital corner. Staple through the fold.
7. Trim excess fabric with scissors. Ensure no raw edges protrude beyond the MDF backer perimeter.
8. Install 4 impaling clips on MDF back at the marked positions (150mm from each edge). Screw each clip plate using the supplied screws. Prongs point outward (away from MDF).
9. Mark wall positions. Use a laser level to mark panel center points on the wall at the target layout height. Install Z-clips or impaling clip receivers on the wall with a 25mm spacer behind for the air gap.
10. Press panel onto clips. Align the panel backer over the wall receivers and press firmly. The impaling prongs engage the clip receivers. Verify 25mm air gap with a spacer block at the top and bottom edges.

Same construction as the standard panel, but positioned at first reflection points on the Control Room side walls. These are the most important panels in the mixing room — they prevent early reflections from coloring the stereo image at the listening position.

Same construction as the standard panel but with 2 × 50mm rockwool slabs stacked (total 100mm depth). Used in the VO Live room where 70% wall coverage is specified and maximum absorption at low frequencies is needed.

The fabric covering MUST be acoustically transparent. If it blocks airflow, the panel will reflect sound instead of absorbing it, defeating its purpose entirely.

Bass Trap Fabrication

Corner-mounted bass traps are essential for controlling low-frequency room modes. Sound pressure is highest in corners — placing dense absorbers there is the most effective use of treatment material. Each trap runs floor-to-acoustic-ceiling (2750mm).

Step-by-Step Fabrication

1. Cut two strips of 18mm plywood: 300mm × 2750mm each. These are the two side panels that press into the corner walls. Sand edges smooth.
2. Join the two strips at 90° along one long edge using a continuous piano hinge (2750mm) or wood screws + wood glue at 200mm spacing. The piano hinge allows angle adjustment to fit the corner exactly.
3. Cut 5 triangular plywood shelves: right-triangle with 280 × 280mm legs. These internal shelves hold the rockwool packing in place.
4. Screw shelves into the two side panels at 0mm, 550mm, 1100mm, 1650mm, and 2200mm from the bottom. Use #8 × 40mm wood screws, 3 per shelf per side.
5. Pack each section with Rockwool RWA45 (45 kg/m³, 150mm). Cut triangular pieces to match the shelf shape. Pack firmly but do NOT compress — compression reduces air spaces and lowers absorption performance.
6. Cut acoustic fabric to cover the entire open hypotenuse face: approximately 450mm wide × 2800mm tall (50mm overlap top and bottom).
7. Staple fabric to side panel edges, pulling taut. Start at center height, work outward toward top and bottom. Use T50 staples at 40mm spacing.
8. Fit trap into corner. Press the two plywood sides flat against the corner walls. The piano hinge at the corner vertex allows the trap to conform to any corner angle variations.
9. Secure with L-brackets: 2 at top (screwed to ceiling grid framing or concrete slab with anchors), 2 at bottom (screwed to float floor substrate). Use neoprene washers between brackets and wall surfaces to prevent rigid bridging.
10. Seal gaps between trap side edges and wall surfaces with a bead of acoustic sealant (Tremco or equivalent). No gaps should allow sound to bypass the trap.

Bass traps use Rockwool RWA45 at 45 kg/m³, 150mm — more than double the density of standard panel rockwool. This dramatically improves low-frequency absorption:

QRD Diffuser Fabrication

Quadratic Residue Diffusers scatter sound energy evenly across the room instead of absorbing it. They are used on the Control Room rear wall to prevent flutter echo while keeping the room “live” for accurate mixing. This maintains the natural spaciousness that a dead rear wall would destroy.

A QRD panel has a series of wells (slots) at specific depths calculated from a prime number sequence. Each well depth scatters a different frequency band. Together, the wells produce uniform sound diffusion across a wide bandwidth.

Our design: N=7 QRD (7-well pattern), design frequency f₀ = 1000 Hz.

The unit depth is calculated as:

Well width = 800mm / 7 = 114.3mm per well (use 114mm with 0.3mm tolerance at the edges).

Step-by-Step Fabrication

1. Cut MDF back panel: 800 × 800 × 18mm. This is the foundation of the diffuser. Sand edges smooth.
2. Cut 6 MDF fin dividers: each 800mm × 98mm × 9mm thick. These vertical fins create the 7 wells. The fin height equals the maximum well depth (98mm).
3. Cut 7 filler blocks from MDF offcuts. Each filler block is 114mm wide × 800mm long, with varying thicknesses:
   Well 0: 98mm thick (fully filled) • Well 1: 73.5mm • Well 2: 0mm (no filler — full depth) • Well 3: 49mm • Well 4: 49mm • Well 5: 0mm (no filler) • Well 6: 73.5mm
   For non-standard thicknesses (73.5mm), laminate multiple MDF layers and plane/sand to final dimension.
4. Dry-fit assembly on the back panel. Place fins at 114mm intervals. Place filler blocks in each well. Verify all pieces fit flush. Mark positions with pencil lines on the back panel.
5. Glue fins to back panel. Apply PVA wood glue along the bottom edge of each fin and press into position. Use clamps or weights. Ensure fins are perfectly perpendicular to the back panel.
6. Glue filler blocks into wells. Apply glue to bottom face, insert between fins, press against back panel. Clamp the entire assembly and allow 24 hours cure time.
7. Sand the front face flush. Use a belt sander or hand-plane across the fin tops and filler block surfaces. All surfaces that face the room should be smooth.
8. Apply 2 coats of semi-gloss paint (any color). Diffusers do NOT need acoustic fabric — they rely on geometry, not porosity. Paint protects the MDF from moisture and gives a professional finish.
9. Mount using French cleat system on the rear wall. Attach one cleat strip to the panel back, the matching strip to the wall. Hang at ear level seated (~1200mm center height from floor).

The Control Room rear wall is 2.00m wide. Target coverage: 80% = 1.60m.

Mounting Systems

Every treatment element needs a secure, acoustically-appropriate mounting method. The wrong mounting can create rigid bridges that transmit sound through the isolation system, or fail under load and drop panels.

• Installation: Screw the base plate to the wall at the marked position using appropriate wall anchors. Then push the panel backer board onto the prongs — the barbed tips grip the MDF.
• Spacing: 4 clips per 1200 × 600mm panel, positioned 150mm from each edge.
• Load rating: Each clip supports ~3 kg. A standard panel weighs ~4 kg with 4 clips = safe margin (12 kg total capacity vs 4 kg load).
• Air gap: Use a 25mm spacer washer or standoff between the clip plate and the wall to create the required air gap.

• Two-part system: Wall strip and panel strip interlock like a Z shape. The panel hooks over the wall strip and gravity holds it in place.
• Natural air gap: The Z-profile provides a natural ~25mm air gap when mounted, improving low-frequency absorption without additional spacers.
• Preferred for: Double-thickness (100mm) panels, any panel over 5 kg, and installations where a consistent air gap is critical.
• Load capacity: Supports up to 15 kg per 200mm clip pair when anchored into studs or masonry.

• Construction: Cut a 50mm wide plywood strip at 45° on a table saw. This produces two matching pieces — one for the wall, one for the panel.
• Wall piece: Screw to wall with the angled face pointing up (like a shelf). Level is critical — use a spirit level.
• Panel piece: Screw to panel back with the angled face pointing down. The panel hooks over the wall piece.
• Advantages: Very strong (distributes load evenly along the full cleat length), easy to hang and remove, naturally self-aligning.
• Recommended for: QRD diffuser panels which are heavy (~4–5 kg each) and must be removable for future maintenance.

• Method: L-brackets at top and bottom of each bass trap, screwed into wall studs or concrete anchors.
• Isolation requirement: Place a neoprene washer (3mm thick, 40-shore durometer) between the L-bracket and the wall surface. This prevents a rigid bridge that would transmit vibration through the trap into the wall structure.
• Fasteners: #10 × 50mm wood screws into studs, or M8 sleeve anchors into concrete/masonry.
• Bracket positions: 2 at top (50mm from ceiling), 2 at bottom (50mm from floor). Brackets attached to the plywood side panels of the trap.

If a suspended absorption cloud is required above the mixing position (in addition to the standard ceiling tiles), use the following suspension method:

• Suspension: Aircraft cable (1.5mm galvanized steel wire) + turnbuckle at each of the 4 corners of the cloud panel.
• Ceiling attachment: Eye bolts drilled into the structural slab above (through the ceiling tile grid). Use M8 expansion anchors rated for overhead load.
• Adjustable height: Turnbuckles allow fine adjustment. Set the cloud bottom surface to align with the 2750mm acoustic ceiling line.
• Load rating: Each aircraft cable + turnbuckle must be rated for 4× the cloud panel weight. A typical 1200 × 600mm cloud weighs ~5 kg; each cable must be rated for 5 kg minimum (20 kg total for 4 cables vs 5 kg load = 4× safety factor).