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SQ-50 cutting of parts:

Building material: Fibreboard (particle board), thickness 15 - 16mm (5/8”).
15 - 16mm / 5/8'' might seem thin, but as there is no point anywhere on the cabinet further away from an edge than about 10 cm / 4”, this is more than enough to avoid audiable vibrations.
For the same reason, simple fibreboard is enough for high quality sound.
Even if most DIY loudspeaker sites recommend MDF board, we don´t anymore. We and a few of our customers have done extensive comparisons, and the inexpensive coarse particle board sounds much better. Using MDF is OK, but you will get a softer, less precise bass response, and maybe also more resonance in the mid-range.

First of all: Notice that all parts are 250mm / 9.9'' in at least one direction. This makes the cutting easy and quick.
Begin by cutting the fibre board into nine 250mm / 9.9'' wide lengths. Then shorten them so you get the following:

First, before changing the saw adjustment, cut one length into four equally wide (250mm / 9.9'') parts (top/bottom parts).

Then adjust the saw to make...

Four parts 1060mm / 41.7'' long (Sidewall parts)

Two parts 1018mm / 40.1” long (Front parts)

Two parts 1008mm / 39.7'' long (Back parts)

Two parts 40mm / 1.6'' wide (Bass vent parts)

Start by cutting holes in the front parts (1018mm / 40.1'') for the loudspeakers (see drawing below).

One 150mm hole for the woofer and one 86mm hole for the tweeter.
On the back part drill two holes for the cable connectors (2 x 5mm / 0.2'')

Assembling the cabinet with recessed front:

Put one side part on a table, and then glue the other parts onto this:

First glue the top part, because its place is so obvious: Edge-to-edge with the side part on three sides (front-top-back).

Then glue the front, recessed 10mm / 0.4'' from the front edge of the sidewall.

After this, the back part, vent part and the bottom part, in that order.

When glueing the bottom part make sure that the vent opening is 10mm / 0.4'' high. This is important. The distance to the bottom edge of the sidewall is not important at all. Thus, if the sidewalls are not 100% perfectly cut it doesn´t matter. As the sidewalls are about 10mm / 0.4'' longer than the front, you always get the bottom part above the floor, and that is the important thing, not how much.

Tip: You can put a pair of R03 / AAA batteries inside the vent while the glue cures. They have just the right diameter (10mm)! A normal CD cover also is 10 mm thick.

Assembling the cabinet with flat front:

The same as above, except for recessing the back part 10mm / 0.4'' from the rear edge of the side part and the front part edge-to-edge with the front edge. (See the right drawing below)

When all these parts are glued onto the sidewall, you put the dampening material into the box.

Use one of the following, they all work well:

Standard dampening: 300g/square meter (9 oz / square yard) polyester wool mat (about 30mm / 1.2'' thick) glued onto all inner surfaces except (or including, it really doesn´t matter much) the front. Keep a few centimeters (an inch or so) free from the inside vent opening. See the drawings.
Alternative 1: As above, but use ordinary needle-felt carpet instead of polyester wool mat.
Alternative 2: Make about 1kg / 35-40 oz of polyester wool fluffy, and simply fill half of it in each cabinet.
Warning: Do not use mineral wool! Fine particles may loosen, find their way into the speaker magnet system and destroy it.

Finally, glue the second side part onto the rest.

What glue?
Ordinary glue for wood (white glue), which takes a few hours to cure is probably the most common glue for joining wooden parts. But during the curing period you have to keep the wooden parts in place. You can use nails which can be removed afterwards, for example.

You can also use contact glue. It is a rubber glue that is spread on both surfaces to be joined, then you wait 5-10 minutes, and then join the parts. The glue will then fix the parts immediately, so you can´t do any adjustments afterwards. However, if you are careful and put glue on all surfaces to be put together, you can build the cabinet in less than half an hour.

If the SQ-50´s are built according to these plans, and fit with the original speaker kit (SQ-50E) you can expect a sound quality which very closely resembles the sound you get in high-quality studio headphones. Pure and clean, and with a bass response deep down into the subbass range.

The sound of these speakers is so close to the original signal that we dare to recommend them for close-field listening in small music studios (where 107 dB SPL is enough).

However, the purpose of the speaker design was originally to make it suitable for home use. It is deliberately made high-and-narrow.
High enough to get the speaker elements up to a lever where ordinary furniture doesn´t get in the way. A footprint small enough to make the speaker easy to place in medium-sized rooms.

Please notice that a side-tuned ported cabinet like this puts very high demands on the speakers elements. The TS parameters are crucial. Even small deviations result in a degradation of sound quality. Fortunately the original speaker kit is not very expensive.
Click here for more info about the original SQ-50E kit.

Click here for another interesting speaker design – the VH-1 Voigt horn!