RT-2 Horn sub, building it - diyAudio
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Old 31st January 2009, 07:22 PM   #1
Elbert is offline Elbert  Norway
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Default RT-2 Horn sub, building it

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!
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Old 31st January 2009, 07:33 PM   #2
Elbert is offline Elbert  Norway
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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.
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Old 31st January 2009, 07:43 PM   #3
Elbert is offline Elbert  Norway
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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.
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Old 31st January 2009, 07:53 PM   #4
Elbert is offline Elbert  Norway
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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.
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Old 3rd February 2009, 05:22 PM   #5
AKN is offline AKN  Sweden
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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.
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Old 3rd February 2009, 07:27 PM   #6
Elbert is offline Elbert  Norway
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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!
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Old 3rd February 2009, 07:36 PM   #7
Elbert is offline Elbert  Norway
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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.
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Old 3rd February 2009, 07:52 PM   #8
Elbert is offline Elbert  Norway
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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!
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Old 3rd February 2009, 08:10 PM   #9
Elbert is offline Elbert  Norway
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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.
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Old 3rd February 2009, 08:26 PM   #10
Elbert is offline Elbert  Norway
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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.
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Old 3rd February 2009, 08:42 PM   #11
Elbert is offline Elbert  Norway
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Eager to get on, you can now start with the first triangular section that forms part of the horn throat.

This is item 21 (2x) in the build plan, originally cut from a square piece of wood.

I found it easier to make these items out of MDF rather than finding the right piece of wood and cleaving it precisely diagonally.

This piece can just be glued in place without screwing.
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Old 3rd February 2009, 08:53 PM   #12
Elbert is offline Elbert  Norway
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Now it's time to get the first segment/bracing section in to place. (item 12)

Now, here I did a slight twist again, I actually made this in 3 pieces, one central straight piece, and the two angled pieces separately.

This was easier to cut and trim than one big piece, and it also made tapering of the ends easier.

As you will see from the picture, i rounded off the edges of the central piece facing the driver. Probably doesn't mater but it looks nice!

Note that lines for alignment were measured and drawn on the front panel and holes pre-drilled for this segment as well.
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Old 3rd February 2009, 08:56 PM   #13
Elbert is offline Elbert  Norway
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Then the second triangular section can go in.
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Old 3rd February 2009, 09:04 PM   #14
Elbert is offline Elbert  Norway
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To complete the assembly of the first sectioning segment, the two angled parts of item 12 i made separately, goes in.

I got a very nice, allmost aerofoil shaped, taper on these.
First i maked the centerline on the edges and the starting of the taper.
Then I used a grater (is that the right terminology?) to roughly shape the taper.

After that it was very quick to use an orbital sander to smooth and blend the profile.
Placing the two segment parallel to each other made it easy to get a similar profile on both. it is of course important that the horn is symmetrical.

I finished off by giving the tapered segments a coating of light filler and a final sanding, a cosmetic irrelevance I just couldn't resist!

Bear in mind that it is very important to get the widths and angles for these pieces spot on as it will dictate the geometry of the horn folding.
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Old 3rd February 2009, 10:47 PM   #15
AKN is offline AKN  Sweden
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Hi,

Good instructions.

So far in your instructions, I made the same construction choices as you, except the cable channel. My speaker terminals were instead located in the triangular foot.
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Old 3rd February 2009, 11:51 PM   #16
Ivo is offline Ivo  Netherlands
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Very nice project!
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Old 24th February 2009, 06:34 PM   #17
AKN is offline AKN  Sweden
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Hi,
Elbert.
No more? ;-)
You did such fine start in with this tread, please continue. I for one and Iím sure a lot of others want to see the rest of your build.

How do you perceive the sound of this horn today, now when some time have passed?
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Old 8th March 2009, 03:21 PM   #18
Elbert is offline Elbert  Norway
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Sorry, been rather busy lately!

Anyway, got a few more pics to post, can't leave a job half done can we?

Well, here one of the corner "deflectors" is put in to place, just glued and held in place..
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Old 8th March 2009, 03:28 PM   #19
Elbert is offline Elbert  Norway
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Here you can see how I've started to radius the different angles by adding some filler.

Probably not that necessary, but assuming that the initial section of the horn should be as smooth as possible, it shouldn't hurt either.
But it was a lot more work than anticipated!
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Old 8th March 2009, 03:42 PM   #20
Elbert is offline Elbert  Norway
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Now that the front and the sides have been assembled and the first parts of the internal horn structure is in place, the next step is to fit the baffle.

As you can see, the baffle actually protrudes through the hole in the bottom of the horn. This rectangular hole will eventually lead in to the triangular foot once that is mounted to the underside of the horn.

This allows part of the driver to protrude in to the rectangular slot, something which is necessary if the diameter of the driver exceeds the 30 cm internal height of the horn.

If you intend to use a "large" 12" driver or even a 13" driver, you may have to make the baffle a little bit larger so that it actually protrudes through and past the rectangular opening.
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Old 8th March 2009, 03:46 PM   #21
Elbert is offline Elbert  Norway
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A "full-figure" shot showing the assembly so far..
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Old 8th March 2009, 03:50 PM   #22
Elbert is offline Elbert  Norway
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A good time to check that the driver fits..
This is the Eminence Deltamax Pro I originally planned to use, which turned out to be a less than ideal choice..
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Old 8th March 2009, 03:53 PM   #23
Elbert is offline Elbert  Norway
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And from another angle, this is looking at what will be the front of the horn.
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Old 8th March 2009, 03:57 PM   #24
Elbert is offline Elbert  Norway
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Now the second set of dividers go in. Holes are pre-drilled in the sides and the correct height and position drawn up in the inside of the sides.
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Old 8th March 2009, 04:05 PM   #25
Elbert is offline Elbert  Norway
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Now is a good time to assemble the bottom triangular foot before the whole thing becomes to ungainly.

Again, make sure that screw-holes are pre-drilled.

Turn the horn assembly up side down and apply liberal amounts of glue where the foot will go, better to wipe off some excess afterward than getting an air leak here. (you have of course marked out the position beforehand)
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