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Apr 08 2014

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Horny Ribbon, Standard Tool Set

{{ Update: 2014-04-09:   After some listening tests, the results were pleasing. But I noticed that the main “thrust” of the sound wave, the SPL pressure level, is kind of like “focused” directly in front of the horn.  Mind you, Now I am talking about horizontal dispersion.  The vertical “issue” has sort of resolved itself .. by itself.  So, started wondering about what can I do about the “horizontal” issue …. Looking at the contraption, and then comparing with some other designs as published on the net, it became immediately obvious, that the ANGLE is too sharp.  So what can I do about it ?

Luckily, the angled inserts, the boards, are loose, so I can freely manipulate them. So here is what I did: I simply partially “pulled” them out of that boxed frame, and made the angle much much wider. Something like 90 degrees now. The side effect of this is that the “entrance”, the neck, or “entry” into the slit is now “hidden” within the whole rectangular box, together with the whole ribbon tweeter actually. It shifted forward and is now completely enclosed within the outline of the box.

So now, I have a HALF_Horn of sorts:   the first half of the horn has an angled “right” side, an angled “left” side, and a flat “ceiling” as well as a flat “floor”.  But then, the “extended” part of the horn consists only of the  angled “right” side, an angled “left” side, but it has no “ceiling” and no “floor” whatsoever.  Just the angled vertical boards protruding from the box frame.

It works.

The “horizontal dispersion issue” is successfully alleviated and resolved with this modification

/ Update }}

 

Greetings,

Just to expand a bit, on that super sonic ribbon tweeter that I purchased as an addition to the recently completed DIY speakers, the ones that I am currently using in my audio setup …

P1110310 b P1110301 b

As I started glueing together the individual pieces of wood, which have been precision cut, as a service, for the price of peanuts, at the wood cutting services department of LEROY MERLIN construction market, I had an interim phase, in which I had the basic square box outline already glued together. ….. I was left with just two additional boards so as to close up the box, the front  panel and back panel of the box ….

And then …. a moment of reflection ….

P1110302 b P1110304 b

… a change of plans.  Yet another crazy idea.

What if I try to use these boards in a different manner ?

The width of the original board, the one that was cut to pieces ( and obviously sourced from the “staircase finishings and fixtures” department), I thought:

Maybe, … just maybe, they would fit inside the box.

What if I try to “slide” them into the box ?

So as to create a resemblance of a horn tunnel ?

Indeed, they did fit.  A very tight and precision fit.

I prepared a very coarse setup. Put the boards in, and made a make-shift  HORN out of them.

A horn tunnel, one that that shall acoustically “load” the ribbon, whereby the ribbon would now be placed at the very back of the box, or horn setup, if you prefer.

P1110305 b P1110306 b

There was a bit of experimenting and fiddling, especially with setting a “good” initial width of the “input” slit of the horn, the one touching the ribbon tweeter, and setting the angle of those two angled boards inside of the outer box.  And then, suddenly, VOILA !!!

The sound is superb. Don’t touch or change it.  Simply perfect. As photographed.

It turns out that the “input” slit should be even narrower than the original “Output” slit of the ribbon tweeter. After some experimental fine-tuning, I came up with the temporary setup as can be seen on the photos.

P1110309 b P1110315 b

The back side of the tunnel needed to be masked by some small piece of anything, because the height of the box is larger than the height of the tweeter. So I took a small picture from the adjacent wall.

P1110313 b

Now, the thing is – with this setup, I shall need an extra board, from the back side, as a mounting surface for the ribbon tweeter. But that is no problem. Will simply fetch yet some additional wood from the market, cut accordingly to this particular need.

P1110312 b P1110311 b

Obviously, as this is a make-shift setup, The tweeter is not fully centered, on the vertical axis, with respect to the horn tunnel.  It is simply sitting on the box of matches.

P1110300 b

So I started wondering that I shall need to cut out a “centered” opening within the back support board, the one that the tweeter shall be mounted to.

But then … Again, I started thinking …

Hmmm ….

Remember that thing that I mentioned about the unevenness of the vertical dispersion when using such a long and narrow ribbon ? The thing about different listening experiences whilst sitting, as opposed to whilst standing in front of the speakers ?

Maybe this OFF-AXIS temporary setup has some off-top merit ?

Just maybe. Why not test it ?

So I prepared for some make-shift listening session.

Hurray !

It turns out, that with this particular, non-centered setup, the vertical unevenness phenomenon is very much relaxed, practically non existent. Unfortunately, I do not know is this a result of the off-axis tweeter location, or a side effect of loading the tweeter with the horn in general.

So now I have a real dilemma: should I mount the tweeter “centrally” with respect to the tunnel, or maybe just mount is with this level of asymmetry, “as it is”, with this highly non – centered alignment ?

You tell me.

Cheers,

Ziggy.

P.S.   One thing that needs to be mentioned here.

Till now, I did not use any finesse tools whatsoever.

The boards were cut to order in the service department of a construction market. The precision and repeatability of the length of the cut pieces is very satisfying. Provided, that prior to cutting, you purposefully get rid of the leading edge of the board, and cut off an initial scrap, say 3mm thick, dispose of it, then ask the guy to set the machine to your target fixed cutting length. By such means you actually can achieve an outstanding precision and repeatability of the size and geometry of the individual pieces that you cut.  I assess that my 12 boards have a length precision of about 0,1 mm, which is great, because I expected the result to be much more lousy than that.

Actually, I took three boards of a size of 1000 x 200 x 16 mm, and cut them into twelve even pieces. Mind you, the cutting saw has a thickness of it’s own, count in something like 3mm or more for the wasting. So, just to be on the safe side, I ordered 4x 245mm pieces to be cut from a single length of 1000 mm of staircase finishing wood. It was a close call, but came out perfectly, with only but a half of a centimeter of scrap at the end.

So, in order to build two such horns, I started off with 3 x 1000 mm boards, cut those into 12 x 245mm, and now have the material to start off with. With the two horns.  What I am now missing is just some two extra bits of wood for the mounting of the back side of the horn, and the tweeter on top of that.

I did not even take my toolbox out of the garage.  So, basically, what I am saying here, is that you do not need to be a “Stradivarius” style, woodwork carpentry genius, so as to construct a horn.  You may say, OK, indeed you can, but the shape of the tunnel is not hyperbolic, quadratic, tractrix, or otherwise. It is a simple flat piece of board. In simple words: it is not “Curved”.

YES. You are very Correct.  Indeed, it IS a crude setup. A simple board. Two angled boards, actually. It is much less than optimal.

It could be better with a certain “shape”, with curves involved. But that would require of me finesse skills in the area of carpentry. An area where I am but only making my first cautious steps here.

But my message is as follows:

There is a difference like between Heaven and Earth, a difference as to how the ribbon performs in the plain vanilla unloaded version, as opposed to as currently loaded with this crude horn setup.

I think that now I shall order two additional pieces of wood, but this time I shall cut each of the standard 1000 x 200 x 16 boards into just two pieces, 495 mm each.  A total of four resulting pieces. Exactly what I need.

Why four ?  Because these will be the vertical inserts, forming the horn tunnel, albeit an extended version thereof, an elongated version, with the vertical panes protruding in front of the whole setup.

This way, the vertical planes of the tunnel, which essentially are the more important ones, will be extending into free space, slightly in front of the setup.

Come to think about it, I could just as well add some topping and some bottom to them, as they shall constitute a sturdy support in their own right.

Things are starting to be looking good.

This is what the full Jensen now looks like (work-in-progress):

P1110316 b P1110322 b P1110320 b P1110319 b P1110318 b P1110317 b

 

Permanent link to this article: http://hiend-audio.com/2014/04/08/horny-ribbon-standard-tool-set/