osmcdoc
Documentation for the Open Source Monkey Coffin Loudspeaker
picture by mbrennwa, 6.12.2019
The Open Source Monkey Coffin Loudspeaker
Notes and Disclaimers
The Open Source Monkey Coffin (OSMC) loudspeaker was developed in an “open-source project” in the diyAudio forum. The aim of this documentation is to provide the OSMC design to DIYers for their own private purposes, for example to build a copy of the OSMC. Do not use the information developed in this project on a larger scale without written permission (for example by selling speakers based on the OSMC design or substantial parts of it).
The OSMC development was financially supported by diyAudio members LORD-SANSUI, Paul Vancluysen, George Wright, KaffiMann, Charles Bueche, zimmer64, John Barbor, mbrennwa, and other anonymous members. Thank you!
Overview
The design targets for the OSMC were defined as follows:
- The OSMC must be straight forward to make for DIY novices.
- The box format should follow the “large monitor” format, sometimes also referred to as “monkey coffin” (hence the name). The internal volume should not be larger than 60–80 L. The enclosure must be a simple rectangular box which is easy enough to make on a kitchen table.
- The OSMC should be “amplifier friendly”. It should work well with small amplifiers like the popular Amp-Camp-Amp, tube amps, etc.
- The OSMC should be a three way loudspeaker.
- Keeping part costs low is not of paramount priority. If the right parts cost a lot of money and there are no cheaper equivalents, it’s okay to use those parts in the design.
- The loudpseaker efficiency was targeted to 92 dB−SPL at 1 m and 2.83 V input voltage, with a bass extension to 45 Hz (−3 dB). Note that, given the constraints of the box size, this can only be achieved if mechnical losses within the loudspeaker system were virtually zero, which is nearly impossible in real-world loudspeakers. However, these targets still provided useful guidelines for the design process.
- The impedance curve must not exhibit any sharp peaks or dips, and the OSMC should qualify as an “8 Ω speaker”.