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Old 5th March 2009, 03:15 PM   #1
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Default Internally Curved Austin Horn

In researching the Austin, I came across a comment by RonC concerning rounded corners in a folded horn. After much discussion of epoxy and bondo, Ron said he just used a piece of floor tile. Actually, free samples of floor tiles. I'm assuming he's talking about synthetic floor tile that is flexible and has an adhesive back.
If rounding corners is that easy, shouldn't this be incorporated in most designs?

A question: We know long wavelength sound reflects less than high frequency. Why do some long waves follow the horn and others undoubtedly pass through the cabinet material.? It seems that when low frequencies encounter a material it is absorbed, reflected and/or passed through. What do we know about possible building materials when it comes to these properties?
Don
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Old 5th March 2009, 05:32 PM   #2
Aengus is offline Aengus  Canada
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Quote:
Originally posted by dzzmiller

If rounding corners is that easy, shouldn't this be incorporated in most designs?
Hi Don

You'll get lots more knowledgeable answers from others on this forum (Ron and Scottmoose for a start, I'd expect), but here's I'll stick this in here to bump the thread and hope it gets noticed by the ones who do know.

My understanding is that in BLHs and BVRs there is some advantage in sharp corners, in that they tend to be more or less invisible to low-frequencies, but help to suppress the higher-frequecies. And since it's the lows that we're trying to reinforce, this is desirable.

Your other question - about long waves following the horn - interests me as well. I think it may be an error to say that long waves are "passed through" - as I envisage it, the only way this can happen is for the long wave to vibrate the material and start a new wave front on the other side. If the wall was completely rigid, no waves would pass through. (Note that I'm using "horn" loosely here, just to mean an expanding path of some sort)

As to how they follow, I imagine an expanding bubble of pressure (the wavefront); as long as it is longer than the width of the horn at a given point, it will tend to expand along the centre-line of the horn even if there are curves or folds. Think of an air bubble in a vertical underwater tube, and then the tube curves - the bubble should still follow.

Whether any of this is at all accurate, I have no idea - I'm pulling on my flameproof suit as I speak, to prepare for gentle correction at the hands of fellow forum-members.

Regards.

Aengus
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Old 5th March 2009, 07:20 PM   #3
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Default Re: Internally Curved Austin Horn

Quote:
Originally posted by dzzmiller
others undoubtedly pass through the cabinet material.?
If you get a cabinet wall resonating at a specific frequency, the cabinet walls become more or less transparent to sound at that frequency.

dave
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Old 5th March 2009, 07:51 PM   #4
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...ergo, you want to ensure that the natural resonance frequency of a panel is well outside (above or below) the operating BW of the cabinet in question.

The bubble analogy is actually pretty good. Not far off from Voigt's take on things really. A line that expands toward the terminus sufficiently to cause a transition toward 1/2 wavelength behaviour is a horn BTW; no looseness apologies needed.

Smooth / constant expansion provides maximum efficiency for a given horn profile -of course, whether you actually want maximum efficiency is another matter. The comments about bends / edges are quite correct.
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Old 5th March 2009, 08:23 PM   #5
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There natural resonance frequency and damping , right. So we want a very stiff box, that perhaps has a resonance above 20khz, and is highly dampened?

The curve in folded horns. In an old post RonC stated that curves when changing angles sound better. We know in fluids that a square bend causes turbulence and decreases flow.

Since my first post I've found that many of the Austin builders added circular turns. So back to my original question, is it meaningful to do if it's easy to do? I could make a curve faster than cutting all the pieces for the step turns in the Changs.

Also, what about the CC? Is there an optimal shape?
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Old 5th March 2009, 08:26 PM   #6
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So to understand this, do you want a smooth horn path? Lately it seems that guys that have access to CNC machines are going for the layered look. So is it worth doing a smooth horn path or is the standard horn path out of straight panels just as good. The reason I ask is I am wanting to build the Dallas II speakers. I have had some 206e drivers sitting hear for a while. I modeled the speaker from the plans on Dave's site and there was only one dimension I was missing to have everything match the dimensions from the plans. I guessed on it and I think I have come close but anyway I also created a curve in the model to show a smooth horn path. I was going to build it using this smooth path. So I guess I am asking if its worth it to do the smooth path or if the path using straight edges is as good.

John
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Old 5th March 2009, 08:26 PM   #7
mp9 is offline mp9  United States
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we had this discussion on another thread, it's good to read more opinions on the subject.
Quote:
Originally posted by mp9
i had asked what i think to be about the same question on a.a., to quote Bill Fitzmaurice's answer:
"Curved bends are required if your intent is to extend the usable response of the horn to 800Hz or more. But since the bandwidth of a rearloader is at least two octaves shy of that goal curves are unnecessary".
http://db.audioasylum.com/cgi/m.mpl?...hlight=166es-r

Quote:
Originally posted by ronc
The smooth bends have nothing to do with extended range. It has to do with efficency and wave front distortion.

I have yet to see a pipeline have square changes in direction, there are 90 degree smooth elbows. The difference between a fluid and air is density of the mass. If you dont think air is dense then hold your hand out the window at 100 mph.Now as it changes from a slug to a wave ,things change.

In a square turn the wavefront (as it rounds the bend) first expands, then compresses then expands again then compresses again. Anytime you compress a slug of air you convert some of the energy to heat which is a loss of efficency.

Anyway a BLH is nothing more than a high tuned BR with a big ole expanding vent that depends on TL and horn action.
ron
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Old 5th March 2009, 08:39 PM   #8
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Quote:
Since my first post I've found that many of the Austin builders added circular turns. So back to my original question, is it meaningful to do if it's easy to do? I could make a curve faster than cutting all the pieces for the step turns in the Changs.
No, I designed them the way I did for a reason. I didn't realise the Chang boxes had many turns... which were you thinking of?

Quote:
Also, what about the CC? Is there an optimal shape?
Yes. What you see on the plans. Again, they're the way they are for a reason. Anything else would require a complete redesign.
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Old 5th March 2009, 09:16 PM   #9
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I thought the Austin was a Ron C design????
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Old 5th March 2009, 09:21 PM   #10
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It is. Sorry, misinterpreted your last sentence. This is what happens when you try to do 4 things at once. Dave (or any of the moderators), could you junk the last 3 posts to prevent confusion?
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