Edge diffraction: large, rounded baffle, or narrow square baffle

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SL would have it that it is better to have a porportionally (to the driver diameter) smaller baffle than a(n objectively) narrower baffle with a smaller woofer. with this in mind, I am wondering which is better to put the five-inch driver on a five-inch baffle (which leaves no room for rounding the baffle edge) or on an eight-inch baffle with a one-and-a-half-inch round-over on each side?
Thanks,
-fortyquid
 
This will be interesting. I don't think this question has been answered, at least, satisfactorily. Common wisdom seems to suggest that a narrow baffle lends itself to better imaging, however, imaging goes hand in hand with accurate FR, therefore, a wider baffle would result in a lower frequency of baffle step compensation taking the BSD network out of the mid-range. I'm looking forward to input from others of more experience. :)
 
From my testing from a few months ago with a 5'' mid in a narrow open baffle (6.5'') compared to the same baffle with the addition of half rounds attached to the sides (used 4'' pvc pipe cut in half lengthwise);

The addition of the half rounds greatly smoothed the spike caused by the baffle step.

but I also believe that the round overs are quite frequency dependant, and that their size should be proportional to the width of the baffle, ie;

The wider the baffle the lower the baffle step frequency therefore the larger the round over radius needs to be to "make a difference" at that frequency.

In short put the largest roundover on the narrowest baffle width that you can.
 
Heh it does to me too sphere :)

Ive got a 5.5" w15cy in an enclosure that allows about four mm either side of the driver in the cabinet, BSC is active as is the whole system and it images really well. The enclosures are not square tho and taper out wider then the front baffle and then go in to a smaller area then the front at the back.

Either way I suppose it wouldnt be hard to make some plastacine round bits and attatch them to the sides and see if it does anything to the sound.

Matt
 
Mos Fetish said:
That sounds suspiciously like a flattened sphere...?
Kinda like this?:)
 

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Thanks for all the posts, guys.
But which is the lesser of the evils a narrow (in the frequency domain) , spiky responce, or a broader, smoother, but more delayed (in the time domain) responce? I am under the impression that, as mentioned above and by Sig.Lin.
http://www.linkwitzlab.com/faq.htm#Q8
that a porportionally narrower baffle will be less obtrusive because of the increasing directionallity of the piston with rising frequency. So I figure the best square-edged baffle is the narrowest possible baffle. But what about the addition of rounded edges to the sides of this smallest-of-all-possible-baffles? According to everything I have read so far this would move the baffle step lower and makes the transition smoother in the frequency domain. But I suspect that this will actually increase the time domain inconsistency at the baffle step....
 
Hi guys

Just popped in on a break from family-time at my in-law's in Germany.

I believe that Volenti's analysis is about right. Fortyquid, your question is a good one. For the sake of building a speaker that could give you years of pleasure, why not build one mock-up with the baffle as narrow as possible and another with the addition of rounded ends (or two of each for testing the stereo imaging). As Volenti says, the diameter must be large enough for the diffraction frequency involved so will be dependent on the baffle width.

I liked Timn8ter's photo. One day, when I get time, I must do something like that. ;)

I hope everyone's having a musical Xmas and wish you all a Happy New Year.

Steve
PS: Bristol Show, anyone?
 
I have little technical background but have always wondered, while reading discussions of baffle step compensation and edge diffraction, what would be the outcome of eliminating the reflectivity of the front baffle surface as much as possible. B&W obviously does away almost entirely with the baffle surface in the photo posted above, but if front baffle diffraction issues are a problem, why aren't drivers surface mounted on more common flat baffles and a layer of very dense felt, say 3/8 to 1/2 inch, applied to the balance of the surface. Wouldn't this make the baffle relatively acoustically transparent?
 
bradley said:
I have little technical background but have always wondered, while reading discussions of baffle step compensation and edge diffraction, what would be the outcome of eliminating the reflectivity of the front baffle surface as much as possible. B&W obviously does away almost entirely with the baffle surface in the photo posted above, but if front baffle diffraction issues are a problem, why aren't drivers surface mounted on more common flat baffles and a layer of very dense felt, say 3/8 to 1/2 inch, applied to the balance of the surface. Wouldn't this make the baffle relatively acoustically transparent?

The felt will still only be addressing a limited frequency range, most probably to high to prevent baffle step, though it may help a little in other areas.
 
A list of my experience:
Understanding diffraction was the big key to stepping up my designs. Huge.
Felt does help that last bit of tuning in the high treble. Used it for years. So has Vandrstein and he knows far more than I.
Really narrow boxes are difficult to manage the diffraction. (5 inch) Q of the first hump is too low for a simple notch. Slightly wider ( 8 inch) gets you into a range where you can work with the BSC and crossover points to tame it. Sometimes just shifting the midrange up.
I was surprised how much going to 3/4 inch round-over ON ALL 12 EDGES helped over 1/2 just on the baffle.
I have plans to do an oval cylinder with flat angled top and bottom with large radii. About three down on the project list.
 
Even though this is a fairly old thread, I'll throw something into the fray. I built Lynn Olson's Ariela and ME2 speakers some years ago. On his web page, he discusses the audible value of large radii edge round overs. I used my table saw to make tangential cuts and then used a hand plane to finish the rounding over process. It worked very well on the solid walnut corners. I made 1" and 1.25" radii. Lynn says it makes a noticeable improvement, but I haven't done experiments.

It's in the "driver cutouts" section of this page:
The Ariel, Part I

Best,
John
 
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Joined 2008
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But which is the lesser of the evils a narrow (in the frequency domain) , spiky responce, or a broader, smoother, but more delayed (in the time domain) responce?
My opinion, or preference is for the somewhat wider baffle. A narrow baffle with a large radius could fit this category. My reasoning (apart from preferring the sound) is based on a number of factors. There is the increase in our difficulty separating a second source (the diffraction signal) the closer it is in time to the direct sound. Then the reduction in involvement with the baffle at higher frequencies where we seem to be more sensitive to issues like this. A larger baffle can also reduce the number of boundary reflections that require attention by maintaining 2pi directivity.

Perhaps the maintained directivity also plays a part, I'm not sure, it just seems that male voices and other things in that range can sound better weighted.

what would be the outcome of eliminating the reflectivity of the front baffle surface as much as possible.
Sound may travel perpendicular to the driver and across the baffle, but diffraction will thereafter occur only when the baffle changes direction.

It seems to me that if a baffle is held flat only for the dimensions required to get down to the room's Schroeder frequency where the room becomes effectively modal, and our sensitivity to diffraction also happens to fall off, then the point is moot and we have as good as an infinite baffle.
 
Two good references for adding felt to edges with curves of results.

Diffraction Doesn't Have to be a Problem

Stepped Baffle Study

A radiused edge is always to be preferred. Even if the cabinet gets effectively bigger the reflection severity is reduced so the final dimensions become immaterial.

If you want to experiment with edge radiuses (radiii?) you can either bend cardboard and tape it to the edge or shape some styrofoam. Both are equally reflective edges at the frequencies of interest.

David
 
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Joined 2005
A radiused edge is always to be preferred.

I would say yes ...but
there could be 'certain' other factors that makes it a bit more complicated than that

like say, if it means the width goes from internal volume around mid and bass
if narrow baffle, those are already limited

so if you want nice big roundings, you also get a wider box...
and in that case, I might prefer a curved front instead, and forget about the roundings
but tricky
 
I'm just not buying that there is any "goodness" to an inherently narrow baffle. I can see secondary issues having an influence (box volume and internal contours).

In truth, the best width for a sharp edged box is impossible to generalize about. You have to look at the frequency range of the driver involved and the frequency band of the worst reflections (related to driver directivity). Sometimes making it narrower puts the response notches up and that helps. Just as often making it wider and moving the notches down may help. Hard to generalise and you have to look at the individual driver curves and compare to your intended crossover point.

In the end a well radiused edge will reduce reflection level and hence the notch depth. That is aways a good thing.

David S.
 
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