Coax4c - studio monitors/speakers

Compact 4" coaxial 3D printed active studio monitors with DSP (only digital input, dsp/amp board limitation). Monitors are sealed design for best transient speed and mid-range monitoring with target Qtc 0.50 (Critically Damped) and compactness. Monitors are designed with dedicated subwoofer in mind (80hz crossover/HPF) so don't expect good response in low frequency range. About monitors aesthetics, its of course inspired by Kef LS speakers and baffle anti-diffraction design. Target of this project was to create professional grade monitors for critical listening and music production.

WinISD:

BOM:

Monitors

• - ~4kg of filament (i used PETG-CF, 5 walls, 30% infill)

• - 2x SB Acoustics SB12PACR25-4-COAX

• - 8m Sommercable SC-NYFAZ 2x0.75mm² (1.7m - amp-monitors, 30cm - terminals-driver)

• - 8pcs Faston F1 female connectors (for driver terminal)

• - 2x4pcs M4 Banana Plug Speaker Terminals (42-43mm, aliexpress)

• - 1-2pcs Alubutyl 35x50cm Vibrofiltr PRO 2.0

• - 1-2pcs 8mm Recycled self-adhesive felt 35x50cm

• - Damping wool (i used Ikea polyester pillow)

• - 5m 2x20 mm foam sealing tape (Monacor MDM-20)

• - 60pcs 5x5mm M3 heat inserts (yeh its a lot :D)

• - 32pcs M3 12mm DIN 912/ISO 4762 screws (front panel)

• - 10pcs M3 14mm DIN 912/ISO 4762 screws (back panel)

• - 8pcs M3 10mm DIN 912/ISO 4762 screws (drivers)

• - 8pcs M3 7mm flat washers (drivers)

Amp + DSP

• - ~300g of filament PETG or ASA (dont use PLA, amp can be hot)

• - 8pcs 5x5mm M3 heat inserts

• - 4pcs 5x4.5mm M3 heat inserts (two inserts location)

• - 5pcs M3 6mm DIN 912/ISO 4762 screws

• - 4pcs M3 30mm DIN 912/ISO 4762 screws

• - 3pcs 15x15mm Alu heatsink (2 for TPA and 1 for RPi)

• - 1pcs FE6930 CLIFF speaker connector

• - 2pcs M2.5 25mm DIN 912/ISO 4762 screws

• - 2pcs M2.5 nuts

• - 4pcs M3 6mm DIN 7991/ISO 10642 screws (top cover)

• - RPi 3 or RPi 4 + SD card

• - 8.5mm 2x20 GPIO extender

• - HiFiBerry Beocreate 4 channel amplifier board (alternative can be cheaper WONDOM JAB5, but its older TDA7498E,so not good as TPA3220 in beocreate)

• - 25V 4-6A PSU brick adapter 5,5/2,1

• - Rocker switch 6A (type MRS-101A-C2-B/B, for hole size 19.2x13mm)

• - 15cm 2x2.5mm² speaker cable (cable for rocker switch. you can use faston F2 conectors and crimping lugs)

• - 8x 8-12cm 2x0.75mm² speaker cable (cables are soldered on speaker connector + heat shrinks, crimping lugs are used for connectors on board side)

• - Toslink optical cable

Final price: ~530 euro (yeah no so cheap, but you get bi-amp and dsp for every channnel, most expensive part is Beocreate 4 channel amp)

HiFiBerryOS settings:

Current problems & todo v1.1:

• - Inverted channel on tweeter - Problem with default DSP profile on HiFiBerryOS ?

• - Optical input automute - i need to create my own DSP profile with Sigma Studio for disabling automute. maybe setup optical output for sub.

• - Create also profile with FIR crossover (336taps-3.5ms delay, crossover fq=2400hz)

Fixed problems (v1.0-1.1)

• - On axis dip in 9.7kHz- Out-of-phase radial reflection at the tweeter-midwoofer cone transition interferes with the tweeter's output. Recommended fix is listening 30 degrees off-axis (measurements 50cm from speakers 30 degrees off-axis)

  • On-axis 9cm from tweeter

  • Off-axis 30 degrees 50cm from tweeter (left channel)

• Uploaded AMP/DSP case for beocreate board. updated BOM for amp.