BBQ Speaker: A Folded Horn Bluetooth Speaker

The goal of this project was to investigate whether we can use a complex, 3D-printed folded horn enclosure to maximize acoustic efficiency and project high sound pressure levels (SPL) from a low-power source.

By pairing dual FaitalPRO full-range drivers with an expanding internal acoustic pathway, this design matches acoustic impedance with free air to maximize output per watt. To handle internal standing-wave pressure spikes without losing energy, the PETG-CF enclosure is sealed with custom TPU gaskets and clamped under high tension using M4 tie-rods to eliminate panel resonance and seam leakage.

For a detailed assembly guide see also our blog post.

Print Settings

For maximum structural rigidity under standing-wave pressure, print all structural parts using rigid, low-resonance material.

Required Quantities:

• PETG-CF: Main enclosure body shells, side panels, internal horn partition blocks (1:1 from CAD).

• TPU 95A: 4x Airtight Sealing Gaskets, 2x Cable Guide Plugs.

Bill of Materials (BOM)

Audio & Power Hardware

• 2x  FaitalPRO 3FE25-4F Drivers

• 1x 10W Bluetooth Amplifier Board with DSP/PEQ & LiPo charger IC

• 2x18650 Li-Ion Batteries

• 1x Dual-cell 18650 Battery Holder

• 1x SPST Switch (for balancing circuit)

• 1x 4.7 Ohm Resistor (0.25 Watt or higher)

• 1x  8mm Loose-Fiber Acoustic Dampening Mat

Mechanical Hardware

• 4x M4 Threaded Rods (cut to size) with matching M4 nuts and washers

• 2x M2.5 Heat-Set Inserts (Amplifier mount)

• 4x M3 Heat-Set Inserts (Battery holder mount)

• 2x M2.5 screws

• 2x M3 screws

• Speaker wire, heat shrink, crimps, self-adhesive rubber feet (optional)

Assembly Overview

1. Driver & Enclosure Prep

• Solder wire leads to the FaitalPRO driver terminals before mounting (access inside the chamber is tight once seated).

• Line internal horn curves and flat sidewalls with the 8mm fiber matting to absorb high-frequency reflection paths and suppress panel resonance.

• Mount the drivers securely to the flat baffling, ensuring the driver sealing ring compresses evenly so the rear chamber is completely airtight.

• Press TPU cable plugs into the partition walls and thread speaker wire through to maintain a sealed chamber.

2. Electronics & Safe Battery Equalization

• Heat-set M2.5 inserts into the amp platform and M3 inserts into the battery rails at ~250°C. Secure the amplifier board and the battery holder using their respective machine screws.

• Safe Parallel Link Setup: Insert two 18650 cells with the switch set to OFF (routing current through the 4.7 Ohm resistor). Measure voltage drop across the resistor with a multimeter. Once the drop falls below 0.1 V, flip the switch to ON to lock the cells into a direct parallel link.

3. Sandwich Stack & Clamping

• Stack components in sequence:

  • Outside Panel

  • TPU Gasket

  • Body with Speaker

  • TPU Gasket

  • Inner Panel with TPU Plug routing the speaker cable

  • Center Ring

  • Inner Panel with electronics mounted and wired to them and a TPU plug routing speaker cable to body

  • TPU Gasket

  • Body with Speaker

  • TPU Gasket

  • Outside Panel

• Pass four M4 threaded rods through the corner channels, add washers, and torque the nuts down incrementally in a diagonal pattern to compress the TPU gaskets evenly.