Recently, I have been working on a small desktop monitor that makes use of very inexpensive components. This monitor was designed to meet the requirements of my specific desk, room and listening position, so do bear that in mind should you find yourself interested in replicating it.
The requirements were as follows.
- Shallow, inert cabinet which could sit flush with my monitors which matching the appearance of my ash desk.
- Ruler flat response down to 80Hz.
- Ideally suited to a 2.1 configuration.
- High SPL capability with minimal distortion products above 700Hz (both harmonic and amplitude modulated)
- Wide but not necessarily perfectly smooth directivity.
- Very inexpensive.
With these criteria in mind, I drew simple plans for a suitable cabinet.
The total depth is a mere 100mm, which corresponds to the amount of clearance between the surface of my primary display and the rear wall.
Next, I selected the drivers and materials. The objective here was to locate drivers which would deliver the best possible measured performance at the lowest possible price while fulfilling the wide directivity requirement. Eventually, I settled upon the following.
- 2x Dayton Audio ND13 (13mm Tweeter) - $20
- 2x Tectonic TEBM35C10-4 (35mm Midrange) - $34
- 2x Dayton Audio TCP-115-4 (100mm Bass Midwoofer) - $29
- 1x MDF sheet (18mm) - $20
- 1x Ash sheet (30mm) - $20
- 1x Wood veneer sheet - $7
Total cost for two monitors (excluding DSP/amplification): $130
The cabinet material is MDF but I chose to make use of real 30mm ash for the front baffle. This eliminated the need for a front veneer and enabled me to created sealed rear chambers for both the midrange and tweeter without compromising cabinet volume for the bass midwoofer.
I then set about cutting and assembling the cabinets.
With the cabinets assembled, I performed a quick test fit of the drivers and began implementing a simple DSP crossover via my JAB5s, correcting driver responses as necessary.
I wanted to cross the ND13 as low as possible, without running into excursion limits resulting from its high Fs. This will suffice for now but as we shall soon see, 4.5KHz is quite conservative with the current 24dB/oct filters.
There are still a few things to finalize (BMR mount print, 6-pin DIN, router flush trip, veneer, staining) before this project is complete but it is coming together quite nicely. On-axis is currently ruler flat to 80Hz, which aligns perfectly with my calculations for this cabinet.
Distortion performance is also excellent above 700Hz, approaching -60dB at 86dB SPL in the most critical portions of the band. Below 700Hz is much cleaner than this measurement indicates but there are several very loud desk and equipment resonances down there, so much of that can be disregarded.
I do not yet have a proper CEA2034A spin for these monitors but preliminary off-axis measurements (disregard actual frequency response) indicate very reasonable behavior up to 70 degrees off-axis.
That's all for now! Further updates as I complete the remaining work.
