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

[fortyquid]

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

[Timn8ter]

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.

[Volenti]

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.

[Mos Fetish]

That sounds suspiciously like a flattened sphere...?

[5th element]

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

[Timn8ter]

Originally posted by Mos Fetish
That sounds suspiciously like a flattened sphere...?

Kinda like this?

[LineSource]

For traditional monopole speakers, the B&W tapered-tube enlosures look like very good physics.

[fortyquid]

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....

[7V]

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?

[bradley]

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?