What's with the sharp edges on speaker boxes these days? - diyAudio
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Old 22nd October 2012, 10:45 PM   #1
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Default What's with the sharp edges on speaker boxes these days?

I'm not talking about chamfered edges. I'm talking about 90 degree sharp edges.

Is it for looks? Is it to cause purposeful diffraction?
It it for ease of veneer application?
What do you guys think?
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Old 22nd October 2012, 10:57 PM   #2
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Let me ask you this: why should someone bother to chamfer the front baffle edges and what effect does that have on sound/frequency response/imaging/ etc.? Answering that question in depth might help you understand why chamfered edges are not all the rage anymore.

-Charlie
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Old 22nd October 2012, 11:11 PM   #3
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Well, Charlie, you could just tell me.
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Old 22nd October 2012, 11:29 PM   #4
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Anyway, it used to be way worse. Speakers would come with trim around the edges. Like this:

http://www.digitaltrends.com/wp-cont...1/klipsch1.jpg
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Old 22nd October 2012, 11:40 PM   #5
jcx is online now jcx  United States
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Dr Geddes seems concerned about box edge diffraction, uses generous radii

I believe he claims due to his listening test results he weights early time delay distortions like baffle edge, mouth diffraction, HOM in horns as more audible defects than many nonlinear/THD distoritons in typical loudspeakers


how about some pointers to threads, reference materal rather than off handed dismissal
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Old 22nd October 2012, 11:48 PM   #6
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Originally Posted by Melo theory View Post
Well, Charlie, you could just tell me.
Knowledge is power, but in order to have a conversation about the info that leads to the knowledge you must first have some basic understanding of the fundamentals. This is the path I am trying to lead you down...

First Google "Olson diffraction" and read the first link from True Audio. What do you think the differences in the graphs are telling you for different shaped boxes?

Let's start there.

-Charlie
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Old 22nd October 2012, 11:48 PM   #7
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I just visited Charlie's web site and he has 3 speaker projects up right now.
1 is 45 degree chamfered
1 is rounded over
1 is a wide baffle with what looks like a sharp edge.
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Old 22nd October 2012, 11:56 PM   #8
SY is offline SY  United States
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I'll say it simply- most chamfers are too small to show a large effect on diffraction. They're more for decoration. You need large chamfers or radii to have a significant effect at midrange and lower treble frequencies. A little felt will have considerably more effect.
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Old 23rd October 2012, 12:15 AM   #9
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I'll say it simply- most chamfers are too small to show a large effect on diffraction. They're more for decoration. You need large chamfers or radii to have a significant effect at midrange and lower treble frequencies. A little felt will have considerably more effect.
OK, now we are getting somewhere. The post above is hitting on the high point of the topic - most people use their router to put a 1/2" 45 degree chamfer or roundover along the edge of the baffle. In theory, this DOES result in smoother frequency response (oooh, aaah!) but in practice it doesn't. Why? The size of the chamfer is inversely related to the frequency above which is has an effect. So the 1/2" roundover can only help things above something like 4000 Hz (guesstimating here). But what is happening at 4000Hz? Only the tweeter is operating and its dispersion is causing that part of the wavefront that is emitted to the side, towards the cabinet edge, to be down in level by maybe 12dB, so any effect is muted at best.

You could make the roundover HUGE so that it is effective at lower frequencies where it will do some good. But making a 4"-6" roundover turns out to be somewhat difficult, although there are some special curved MDF products that can do it. Mostly it just looks stupid.

Why go to all this trouble in the first place? The goal is to smooth out the ripples that tend to occur with rectangular cabinets with sharp edges. Most people want their loudspeaker to have a smooth frequency response without major peaks or dips. But it turns out there are other clever ways to minimize these ripples even if you have perfectly square edges, like playing with the position of the driver on the baffle until the ripples are as low as possible using a diffraction simulator (software). This is what I do (now).

Sure, in the past I had some speakers with rounded or chamfered edges. I didn't build the cabinets. The cabinet maker put these edge reliefs there for cosmetic reasons and because a perfectly square edge is prone to damage, so the edge has to be relieved anyway. But I don't believe that the edge profile has anything to do with the sound or has much impact on the frequency response, it's just there.

I was hoping you (Melo) would get a grain of curiosity about these things. There is lots of physics behind all of this. Just cutting to the answer often leaves out large and sometimes important points about WHY something is the way it is. That is why the journey to the destination is often times more important than the destination itself.

-Charlie
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Old 23rd October 2012, 12:18 AM   #10
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Quote:
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I'll say it simply- most chamfers are too small to show a large effect on diffraction. They're more for decoration. You need large chamfers or radii to have a significant effect at midrange and lower treble frequencies. A little felt will have considerably more effect.
This is a common misconception. Assume a hemispherical wavefront, then consider that the angle of incidence varies the effective size of any edge termination.

This is borne out by one of our local's measures, but I don't remember whose site off the top of my head. He was surprised by the effect of something like 1/2" roundover down near 1200Hz.
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