The Open Source Monkey Coffin repository

The Monkey Coffin Loudspeaker is an open source loudspeaker design, which is being developed by members of the diyAudio community. Full details of the Monkey Coffin Loudspeaker project can be found at the corresponding diyAudio thead. The idea of this page is to keep the central information and measurement data of the Monkey Coffin in a somewhat organized way. The development of the Monkey Coffin does not come for free. We would greatly appreciate your financial support. Important note: DIYers may profit from this open-source project for their own private purposes, for example by building and enjoying a copy of the Open Source Monkey Coffin speaker. Please do not use the information developed in this open source project on a larger scale (for example by selling speakers based on the Open Source Monkey Coffin design or substantial parts of it) without written permission.


CAD drawing of the first prototype (version 20181219):

Monkey Coffin enclosure version 20181219

Monkey Coffin enclosure version 20181219


Woofer (FaitalPRO 12PR320):

  • FaitalPRO 12PR320 factory datasheet: PDF
  • Impedance in free air was measured at cold and warm ambient temperatures (approximately 10°C and 30°C) to show the effect of the variation of the compliance of the suspension. Raw data (cold): FRD file Raw data (warm): FRD file Faital_impedance_warm_cold
  • Thiele Small parameters (determined from above free-air impedance curves and added mass measurement; mean values from “cold” and “warm” measurements): fs = 43.1 Hz, Qes = 0.44, Qms = 8.2, Qts = 0.42, Mms = 50.8 g, Cms = 0.27 mm/N, Vas = 91.1 L
  • Distortion tests: harmonic_distortion_FaitalPRO_12PR320gedlee_distortion_FaitalPRO_12PR320

Midrange (Volt VM752 / 8Ω)

  • Volt VM752 / 8Ω factory datasheet: PDF
  • Impedance in free air Raw data: FRD file Volt_VM752_impedance
  • Thiele Small parameters (determined from above free-air impedance curve): fs = 386 Hz, Qes =  0.75, Qms =  10.7, Qts =  0.70, efficiency (2.83 Vrms, 1 m) = 93.5 dB-SPL

Tweeter: The choice of the tweeter is not yet finalized. We are currently looking at the Scan-Speak R2904/7000 in a waveguide.

System analysis

Crossover filters

  • First x-over design in diyAudio post 119. This is a purely hypothetical concept study based on published driver data, assuming Satori TW29BN as tweeter.
    Monkey Box Schematic LR4 500 - 2500 HzMonkey Box SPL and targets LR4 500 - 2500 Hz

Bass-reflex tuning (woofer in 20181219 box):

  • Measurement shows cone excursion minimum occurs between 34 Hz and 35 Hz
  • Impedance Raw data: FRD file impedance_Faital_12PR320_20181219Box
  • Nearfield SPL Separate SPL measurement of woofer and port is not possible due to acoustic crosstalk. Combined woofer and port output was therefore measured following the method described in the Klippel Application Note AN39. The artefacts at 65 Hz, 130 Hz and 260 Hz are due to room modes. Raw data: FRD filenearfield_box20181219_klippelAN39

Acoustic centers, time alignment:

  • The “driver depth” is defined as the distance of the joint of the voice coil to the baffle plane. The depths are follows:
    • Scan-Speak R2904/7000 in modified WG148 waveguide: 20 mm
    • Volt VM752: 28 mm
    • Faital 12PR320:
  • Measured relative acoustic centers (“AC”, see here):
    • AC of Scan-Speak R2904/7000 in a modified Visaton WG148 is 10 mm behind the AC of the Volt VM752.
    • AC of Faital 12PR320 is 39 mm behind the AC of the Volt VM752.

Acoustic far-field measurements:

  • Single drivers measured with microphone at 1 m distance from the baffle, on-axis and horizontal off-axis at 0°, ±15°, ±30°, ±45°, ±60°, ±75°, ±90° (Faital 12PR320, Volt VM752, Scan-Speak R2904/7000 in WG148). Raw data files (TMD and FRD): ZIP archive

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