Slot Port Box Calc
DIY Slot-Port Enclosure Calculator
Enclosure Dimensions
Thickness of the enclosure walls; subtracted twice from each dimension. Common values: 0.75" (3/4" MDF), 1.0" (dual-layer), 1.5" (competition builds).
Butt joints: panels overlap at corners. Rabbet/dado: panels interlock (reduces visible edges). Miter: 45° cuts at corners. This affects cut sheet dimensions.
Internal Adjustments
When "Sub Up" is selected, the internal height shrinks by 0.75″ (basket clearance); when "Sub Back" is selected, the internal depth shrinks by 0.75″.
Number of extra baffle layers beyond the first (0 = single, 1 = double, 2 = triple).
• With Sub Back, these are front baffle layers.
• With Sub Up, these are top panel layers (top pieces).
Each extra baffle adds one wall-thickness layer to the baffle stack and is subtracted from net airspace.
• With Sub Back, these are front baffle layers.
• With Sub Up, these are top panel layers (top pieces).
Each extra baffle adds one wall-thickness layer to the baffle stack and is subtracted from net airspace.
Number of port boundaries shared with box walls (0-3). Flanged ends add more effective length than free ends. 3 = typical L-shaped slot port sharing top, bottom, and one side.
Internal bracing volume in cubic feet. Window braces, dowels, corner braces. Subtract from net airspace.
Subwoofer Info
Effective total baffle stack thickness (auto-calculated from Wall Thickness and Extra Baffles). Used for cutout volume and extra baffle displacement.
Volume displaced by the woofer motor and frame (manufacturer spec). If blank, a typical value is auto-filled based on woofer size.
Diameter of the woofer mounting hole. The cylinder of air in this cutout is added back to net volume since the woofer occupies that space above the baffle plane.
One-way linear excursion from manufacturer spec. Used to calculate displacement volume for port velocity. If unknown, typical values: budget subs 8-12mm, mid-tier 12-18mm, SPL subs 20-40mm+.
Port & Tuning Details
Internal width of the port slot opening. For slot ports, this is typically the narrower dimension.
Internal height of the port slot opening. For full-height slot ports, this equals internal box height.
Physical centerline length of the port from inside the box to the exit. For L-shaped ports, measure along the centerline of the path.
Thickness of internal port walls (dividers). Affects port volume displacement and generates cut pieces in the cut sheet.
Results
Gross Internal Volume: TBD cu ft
Net Airspace: TBD cu ft
More info
Net airspace = Gross internal volume + cutout volume − woofer displacement − port displacement − bracing − extra baffles.
Tuning Frequency: TBD Hz
More info
Calculated using: Fb = (c / 2π) × √(Av / (Vb × Leff))
Where Leff = physical length + end corrections. For rectangular ports, end corrections use hydraulic diameter: Dh = 2×(H×W)/(H+W). Flanged ends add 0.85×√(π×Dh²/4), free ends add 0.6×√(π×Dh²/4).
Where Leff = physical length + end corrections. For rectangular ports, end corrections use hydraulic diameter: Dh = 2×(H×W)/(H+W). Flanged ends add 0.85×√(π×Dh²/4), free ends add 0.6×√(π×Dh²/4).
Port Velocity: TBD m/s
More info
Peak port air velocity at tuning frequency. Formula: Vp = (Sd × Xmax × 2π × Fb) / Av
Guidelines: <17 m/s = optimal, 17-25 m/s = acceptable, 25-34 m/s = audible noise likely, >34 m/s = severe compression/chuffing.
Guidelines: <17 m/s = optimal, 17-25 m/s = acceptable, 25-34 m/s = audible noise likely, >34 m/s = severe compression/chuffing.
Port Area per Cube: TBD in²/ft³
More info
Ratio of port cross-sectional area to net enclosure volume. Higher = less compression. Guidelines: 12-16 in²/ft³ = typical, 16-20 in²/ft³ = recommended for SPL, <12 in²/ft³ = may limit output.
ft³ per sub: TBD cu ft
Effective Port Length: TBD in
More info
Physical port length plus end corrections based on common walls. This is the acoustically effective length used in tuning calculations.
Cut Sheet
All dimensions in inches (Width × Height). Material thickness: 0.75"