Lumina 100 audiophile loudspeaker building description
The loudspeaker design and building directions presented below were published in good faith. Nevertheless the publisher assumes no liability either for the accuracy of information contained herein or for any loss or damages arising from the use of these pieces of information.
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THIS IS PRELIMINARY DESIGN INFORMATION!
The Lumina 100 loudspeaker has not been built yet. The plans are based on manufacturer data, and simulation with measurement data of similar drivers, therefore the crossover may need fine tuning. The first builder of this loudspeaker may get free help from the designer. Further information: help for DIY speaker builders.
Please keep to the plan exactly!
It's expediential to have the enclosure prepared by a joiner owning a CNC machine. It's rather difficult to make the countersinks for the speaker baskets at home. Of course it can be made using a router, provided you have the proper router bits, and a circle cutting jig. The internal edge of the midwoofer cutouts must be chamfered, at approx. 10 mm depth, as exemplified in the next image.
PVA wood glue, D3 type is recommended for gluing.
The internal cross braces are 22x70 mm and 22x110 mm cross sectional MDF elements according to plan.
Cover the internal walls of the enclosure with elastic adhesive that sticks to wood, using a notched trowel, in approximately 2.5 mm thickness. For example, the Mapei Adesilex G19 or a similar high-viscosity adhesive that dries to a rubber-like layer, can be used. If you are unsure, first test the glue on a piece of MDF. Fill the cabinet evenly with 60 dkg pillow stuffing material such as polyester pillow fill or long-fibre wool.
As this is a low distortion loudspeaker, I highly recommend the use of gold plated speaker terminals. Douglas Self in his Audio Power Amplifier Design Handbook wrote that ferromagnetic speaker connectors cause well measurable distortion when a sufficiently low distortion amplifier signal is passed through them. While measuring amplifiers, I myself have not discovered this problem, therefore I can't affirm his observation, and I don't think that brass or gold plated brass speaker connectors are necessary. Anyway, I have not specified the terminal, you may use a connector tray with gold plated terminals or gold plated binding posts, brass or steel as you like, provided that they are long enough to reach across the 22 mm thick MDF back panel.
The crossover can expediently be mounted on the bottom panel of the cabinet. For this purpose the bottom panel of the cabinet must be made removable. Components with 5% tolerance are recommended. The best solution for fastening components seems to be cable ties. Tie them to a thin (e.g. 5 mm thick) HDF plate and screw that plate to the inside of the cabinet. I haven't made a component layout or PCB plan, just solder components together across their leads or with suitable cables, wherever the leads are not long enough.
Adding the R3, C5 components is optional, but I recommend including them. C5 is specified as a 250V capacitor but in addition to being rated at least at 250V, another important parameter is that it should be able to withstand at least 10VAC RMS at 1 MHz. For example, Wima FKP2 250V capacitors are suitable. Please consult the data sheet of the capacitor you intend to use. R3 should be low inductance type, e.g. metal oxide or metal film. 120 Ohms is an approximate value only. The value of R3 can be adjusted more accurately depending on the exact geometry and dielectric of the speaker cable by using the following calculator. Add 5% to the value of characteristic impedance provided by the calculator and choose the nearest standard E24 resistor value!
All inductors are air core, except for the lower midwoofer. Don't fasten coils with ferromagnetic metal screws (e.g. steel), because they may cause some distortion. To prevent crosstalk, place coils at least 10 cm away from each other or - if they are closer - direct their axes perpendicular and skewed:
The hard-to-come-by capacitor values can be attained by connecting more common values in parallel. By parallel connection, the capacitances are summed. In the circuit diagram of the crossover, the shown voltage of capacitors is the minimum suitable rating, you can also use capacitors with higher withstanding voltage. I recommend the 400V DC rated Jantzen Superior Z-Caps for C1 and the Standard Z-Caps for the other capacitors in the crossover.
Copper speaker cable of at least 0.75 mm2 cross-section or CCAW speaker cable of at least 1 mm2 cross-section is recommended.
It is recommended to install spikes into the base of the cabinet.