RT-2 Horn sub, building it

[Elbert]

For those interested, here come the plans for the RT-2 Horn together with pictures from the build.

Hopefully this can be useful, or at least provide some general DIY inspiration.

First we start with the plans.

All text is in Swedish, but the measurementas and drawings should nevertheless be self explanatory, at least to some extent!

[Elbert]

The next scan shows another section of the horn plus some details for specaialy shaped parts.

Follow these cutting plans and the cutting list, and you will be ready to start.

Bear in mind that there is a lot of parts to cut, so unless you got a good place to work and time to spare, I'd seriously consider getting the parts cut by a shop. I spent MANY hours doing it my self, admittedly having underestimated the effort and precision required, and I also ended up having to adjust almost every single piece during the build.

Remember that any leaks in the horn will be detrimental to the result, so everything will have to be made to fit properly.

[Elbert]

One of the first things I did, was to cut out the driver hole in item 4, fit M6 press-in nuts, and check that it all lined up properly. Obviously not that easy to to at a later stage, and if those nuts are properly mounted in the first place, final driver assembly in to the horn is a breeze.


Tip:

If you wish to use a 13" driver (like the SEAS 33F-WB I ended up using), it is a good idea to make this baffle plate a little higher than the specified 318mm.

This just means that the baffle extends a bit further don in to the slot connecting the main rear closed chamber and the foot chamber, which is no problem.

Since I didn't make this provision, I'll have to sandwich an intermediate baffle between the SEAS13" and the original baffle plate in order to get a full sealing surface agaisn the face of the driver.

[Elbert]

The next thing I did was to build the triangular foot. The internals of this foot forms part of the enclosed driver chamber and the triangular external forms part of the geometry for the final horn expansion below the main "box" of the horn.

The simplest way to do this proved to be assembling the front and the rear wall of the foot to the floor of the foot, ensuring a nice 90 degree angle, and then to adjust and fit the angled sides last.

The foot will later on be attached to the floor of the horn before too much of the internal structure is put in place.

The foot was carefully filled, sanded and given many coatings of silk-mat paint.

As you will see from the enclosed image, some left-overs were used for additional bracing of the foot.

[AKN]

Hi Elbert.

Great, please continue....

Long time since I built this horn, a great reminder.

One thing I remember as a potential improvement is to strengthen the backside (inner mouth) with a brace in the middle. The backside is the (only?) weak part in this construction. Of course, this brace should not be larger than it is still possible to access the driver.

[Elbert]

Glad to hear you find it interesting Anders!

Good point about the rear panel/horn mouth being a possible concern regarding stiffness, might well put some bracing there, certainly can't hurt!

I'll have to do this a bit at the time, compressing photos etc...

Now, assuming all the cutting is done away with, time to mark up where the innards go and to pre-drill screw holes in the bottom and top. Not pre-drilling the holes will make assembly near impossible as to opposed to a pleasant and rewarding activity.

I drilled the bottom plate first, then simply used it as a drilling template for the top, worked surprisingly well!

[Elbert]

A special twist I did was to cut a hole in one of the rear corners of the bottom plate, just behind where one of the 45. deg. corner "deflectors" will go.

I then routed a channel over to the area where the inner closed chamber will eventually be.

The purpose behind this, was to make a path for some heavy duty wiring to be drawn to the rear of the horn, the result will be shown later on in the build.

[Elbert]

Now it's time to start putting things together, always nice after all that tedious cutting, drilling and marking.

Now, unless you got the cutting done properly at a shop, all parts will have some sides which are straighter and better than others.

Identifying these and using them as datums during the build is a good idea.

If you start by joining straight edges against straight edges, you will at least get a straight and angular starting point, less than perfect edges joined up,subsequently can then be filled and/ or adjusted.

I started by using the bottom plate as a flat surface, then I selected my "best" side, placing the straightest bottom edge down and the straightest side-edge facing forwards. Just loose, no glue or screws yet!

[Elbert]

Next step is to join the front to the side previously lined up.

Same again, take the best of the front/rear panels, best long edge down and straightest side against the side panel.

Line up and glue + screw.

You should now have an L-shaped section sitting square on the bottom panel.

[Elbert]

Now we are ready to join the Side-front assembly to the bottom.

Carefully move the side-front assembly a bit inwards on the bottom panel, then apply glue to where it will eventually join up.

make sure that the area of the bottom panel where the pre-drilled screw holes for the front and the side are is overhanging the table or worksurface you are using.

Again carefully, lift the side-front assembly and set it down on the glue trying to get the panels as square as possible against the edges of the bottom panel.

Carefully slide the assembly in position so that the end side of the side panel is square on the corner of the bottom panel and its side.

Enter the first screw for the side panel closest to the corner, do not fully tighten. check and adjust as the remaining side panel screws are entered and done semi-tight.

do a final check for straightness and tighten the screws properly.
Some glue should be issuing from the joint, thereby verifying a properly sealing glue joint.

Now you can start the same process with the front panel.
Again, start entering screws from the corner and outwards, making continuous checks along the way.

At the end of this process you will have a starting point which is angular and straight in 3 dimensions, thereby giving you a good datum structure to adjust everything else agaisnt. And if you, like me, did the cutting your self, some adjustments will be inevitable as you go along.