XPRESS SPEAKER DIY-1

X-onken Xpress - 4

"I saw the angel in the marble and carved until I set him free. " -- Michelangelo

Carving something with your own hands is easy -- once you have a clear picture of it in your mind. I am reminded of Sakuma San meditating for days in his cafe, until the circuit concept of his amplifier gets etched clearly in his mind. The rest is merely giving shape to what you saw in your mind. So the first step before embarking on the X-onken build is to get the concept clearly etched in your mind. Ready? Put on the imagination cap.

Onken - Top View

We need to get a 'picture' of our micro-Onken build. Study the various Onken photographs and the excellent sketches of Hiraga from L'Audiophile that introduced the Onkens to the western world. Be warned though -- no need to be scared by the measurements! They are substantial, as they are of the giant "Sumo" Onken, not our little 'baby' X-onken. First, check out the view from the top. On both sides we find the Onken port panels. The rear low frequency radiation from the speaker driver travels thorugh the narrow Onken ports on the sides to emerge in the front, reinforcing the front radiation. This naturally raises the efficiency of the speaker.

Onken Speaker 
( Hiraga - L'Audiophile )

Please also note that as we are using a full range driver, the rear radiation will contain all the MF and HF elements, and these need to be absorbed fully, so that only the LF radiation is left to travel out through the Onken ports. For this purpose the inside of the box is lined with half inch or three-quarter inch thick jute felt or cotton felt. It is to be noted that only the inside walls of the cabinet are lined thus -- there is NO absorbent filling inside the box, unlike in conventional speakers. It is important that nothing obstructs the free flow of air through the Onken ports.

Now take a look at the Onken port side panels. They are twin walled and consist of an outer panel, four small battens (in our case) spaced equally, and cut from the same half inch thick board that we are using for the cabinet, form three long and narrow Onken ports from the back to the front, and an inner panel. These are labelled as Onken-out, Onken-in, and battens in the cutting guide. These port panels will be what we build first, and they are to be done with some care and accuracy.

The 'baby' X-onkens are just 15 inches tall. Minus the top and bottom panels, it is all of 14 inches tall. The cabinet sides are assembled first from 14 inch tall panels, and then the top and bottom are stuck on, and then the cabinets are "finished". That is the order of the build.

Have the cutting guide before you. Both the boxes can be made out of half of a standard size 8' x 4' panel. It is advisable to first cut two pieces from the 4 x 4 board measuring 14 inches (plus) width. This could be cut into all the Onken port panels (x8 pieces) and the two front panels. From the remainder, mark and cut the two back panels and the top and bottom panels (x4 pieces). What remains are the battens -- note that they are less than one inch wide. It is also advisable to label the panels as they are cut -- particularly the Onken port outside and inside panels.

Panel Cutting Guide

While making cuts, make sure that the dimensions are a mm or two more than specified. After cutting, same-sized panels should be clamped together and using the Try square and rough emery cloth (50 grit first, and 150 grit later) wrapped on a piece of (multi!) wood, make sure that they are "fair and square". This is a step that cannot be hurried as the "squareness" of the cabinet depends on this.

Assembly Tips

Cutting the multi-wood panels with the box knife has to be practised a bit -- it is not about using force, but one of technique -- start the cut along the straight-edge with the blade upright and using uniform pressure. Once the cut is made, it is easy to repeatedly score along the cut a few times until the knife cuts through. Always use a scrap board below the cut line to buffer the sharp knife. Be very, very careful with sharp tools, and wear cut-resistant gloves. With practice, you should be able to make almost perfect right-angled cuts. Check with the try square and correct both the panel size, corner right angles and edge right angles meticulously. It pays to do that, so that your final assembly will be painless and FAST! (Mind you, this is the XPRESS Blog!)

Another step where some extra care is needed is while sticking panels together with PVC solvent cement. Normally (minimum) glue is applied to both the mating surfaces and then the panels are held together for say, ten seconds, and left to dry with a weight on it for a few hours. It is likely that the panels might slip out of alignment when pressure is applied. The easy solution for that is to first pin them together with ordinary pins or very thin nails driven just a little into the boards. Then pull the panels apart, and THEN apply the glue and bring them together, the pins preserving the alignment, and then put them under a weight. After the joints are bone dry, pull out the pins.

A Finished X-onken

At each stage, wherever necessary, check measurements and right angles and correct with the emery block.

So start by cutting all the panels, and correcting them and getting ready for assembly. This will take some time (it should!), and once things are ready, the final assembly will be a breeze -- believe me!

Do share your build pictures of all the stages, your experiences, tips and comments so that other builders will benefit.

Here is to a successful, easy, Xpress build!!

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