002 Meno Paradox (pair)
https://cdn.shopify.com/s/files/1/1059/0268/files/Loudspeaker_Kit_Assembly_Instructions.docx?4534604482021983572Meno's Paradox (Learner's paradox): A man cannot search either for what he knows or for what he does not know
A small two way speaker kit with fantastic sound. Easy to build over a couple of evenings or over the weekend. Several options available for the intrepid experimenter.
Features a real wood grain veneered box, in Tasmanian oak, or if you prefer an MDF box is available that is less expensive.
Instructions to assemble the speaker can be downloaded:
Instructions to construct the MDF box (PDF).
Note that the main photo shows a rebated front baffle, this has been changed to a 17 mm veneered front baffle that can be face glued. We would recommend painting it before gluing.
The design brief was to produce
- a small loudspeaker;
- that could be put together with the least number of tools, readily available at a hardware store;
- good sound; and,
- a great price point.
I believe the two hardest things for most speakers to reproduce is bass, and high female vocals. We think that given the size limitations we have delivered on all points in the design brief.
The woofer is essentially a paper cone with the addition of proprietary fibres, probably papyrus as they advertise in data sheets for other drivers. It has a 25mm voice coil, 4.5mm XMax, is built on a plastic frame. It is a nominal 8 Ohms and suits a smallish vented box very nicely. The data sheet is here.
It was chosen because of several reasons:
- It is great value for money;
- It is 8 Ohms. Amplifiers generally perform better into 8 Ohms than 4, exhibiting less distortion and are easier to drive;
- It sounds fantastic,
The tweeter is a fabric dome with a neodymium magnet, good power handling, and a very compact face plate, allowing it to be used in a small box easily. Datasheet is here.
Modelling showed us that a box from about 5 litres to 10 litres would work well. 5 litres with an Fb of 45 Hz provided for an F3 of 75 Hz, a 7 litre box was modelled with an Fb of 55 Hz gave us an F3 of 60 Hz, and a 10 litre box tuned to 54 Hz gave an F3 of 52 Hz but could not be made flat. This was based on the manufacturer’s data.
We went for the mid-point, providing a flat response and better power handling, and headed into the workshop to build a prototype box. Happy with the sound we tweaked it, but essentially kept it to 7 litres.
The box is 17 mm MDF veneered with real Tasmanian oak, no vinyl wrap here. If you purchase the plain MDF box, it is 16 mm with a 17 mm wood veneered MDF baffle.
The external dimensions are 295(H), 180 (W) and 240(D). This gives an internal dimension of around 7.4 litres. The box is small enough and the panels thick enough that no internal bracing is required.
The crossover occurs at 3 kHz. It is a second order crossover with some impedance correction. We tried a resonance peak correction, and found it made little difference. We took out the resonance circuit to simplify the circuit.
We have purposely used electrolytic capacitors, because it saves on cost, which we have passed on and allows you to experiment without having already paid for expensive capacitors in the kit which you end up not using. Electrolytic capacitors are cheap, so if you replace them you really haven’t lost very much. If you want to spend $100 or more on more expensive capacitors, feel free, but this is a cost we would have had to pass on in full, and not all our customers would have wanted that. There is little to be gained from changing the inductors, as these are rated to 100 Watts or so, and the law of diminishing returns will kick in. Also you will have to change the resistances so that the totals are the same.
Below is the schematic. Values will be provided with the instructions which are included with all versions of the kit.
The frequency response is flat (± 2 dB) from 85 H to 20kHz. And ± 3dB from about 60 Hz to 20 kHz.
We will be posting measurements in due course.
You will need:
- Masking tape (green or blue, 50 mm);
- A soldering iron and solder (40-80 watts is probably the ideal, but a smaller iron is ok);
- Holt melt glue, or silicone (hot melt glue is faster);
- PVA glue (clear drying is strong enough and easier to clean);
- Wire strippers;
- A finish for the box. Some of our ideas include spray paint, stain and polyurethane;
- Tools for finishes such as paint brushes and sand paper;
- A 3 mm Allen key, or driver;
- Clamps or weights. Don’t stress if you don’t have clamps, weights will do the job, but you will want 10 + kgs. Some bricks?
What you won’t need: a table saw; a router and numerous router bits; drill, jigsaw, dust collector, a dozen clamps, big work area.
Options include just purchasing the drivers, drivers and crossovers, a complete kit with either a wood veneer box or a plain MDF box, assembly of the crossovers and/or box, and a complete and finished loudspeaker stained and polyurethaned.