I'm designing my first speaker, a simple 2 way MT, and I’m currently looking into various cabinet styles. How might one best control baffle diffraction effects? There are two good free programs out there: Edge and Baffle Diffraction Simulator (BDS). I’ve been trying out various baffle designs to see what looks good. I’m new to all this so I’ll post my findings in hopes that it’s useful to some other newbies out there. For those who are experts, I suspect there is nothing new here (if I have everything correct). Of course, I don’t claim to know what I’m doing, YMMV, etc.
Effects of baffle diffraction on the speaker’s apparent output:
If we take a regular floor standing 2 way MT speaker with sharp edges, we see a diffraction pattern like this:
Image not available
Ugly, eh? Lots of variability, ups and downs. It might not sound so great with certain frequencies boosted, others far down relative to the boosted ones.
Change the shape of the cabinet, let’s say we use 5 sides rather than 4, adding chamfered (or faceted) edges, and offsetting the drivers from the center line will have a cabinet looking like this:
Image not available
It’s ugly, but we can fix that part later (see below). But look at how much smoother the baffle diffraction effects are:
Image not available
Smooooth. Almost soothing, when compared to the 4 sided sharp edged cabinet.
The software:
Of the two programs, Edge and BDS, they each seem to have strengths and weaknesses- near as I can tell from not much experience using either program. Edge is easier to use and quicker. It has more variability in the baffle shapes you can use. But there does not seem to be a way to change the edge treatments. BDS takes longer to manipulate and looks to be more precise, with the ability to change numbers exactly, not just by dragging thigns with the mouse. BDS has fewer shape choices, but does have the ability to treat the edges with chafers and roundovers.
Some things I learned from the simulations:
I was trying to find situations with smoother plots and minimal deviation from peaks to troughs.
-A wider baffle with a chamfer (facet) is better than a narrow baffle with sharp edges
-A chamfered edge is better than a rounded over edge (I’m still trying to understand this one fully)
-A rounded over edge is better than a sharp edge
-A 1.5” chamfer is better than a 0.75” chamfer
-A straight baffle is better than one that is slanted 5 degrees, which is better than 10 degrees
-A 5 sided (like shown at top) or 6 sided (like the remaining front after Jon cut facets in his M8ta’s) baffle is better than a rectangular 4 sided baffle. (Note the typical tweeter at top, woofer below configuration)
-There seems to be not much difference between 5 versus 6 sided
-Offset drivers help a fair amount versus centering them in the middle of the baffle- according to BDS. Edge seems to show less of a difference.
-Any of these indiviual changes seem to make small differences. The two different plots shown above are the two extreme cases I found- from the ugliest to the prettiest plots. So getting smooth plots seems to be a combination of many small effects.
Conclusions- What I will incorporate into my cabinets:
From what I found above, it looks like I’ll be using a wide baffle (due to 1.5” double thickness to minimize resonances/vibrations) with multiple (3 or 4) layers of BB plywood on the front baffle. In a rectuangluar box. But cut the 1.5" facets out to make the desired 6 sided part of the baffle. The 6 sides will be prettier than the 5 in the figure above. I’ll also offset the drivers from the center.
A question:
Sharp edges are bad for baffle edge diffraction. Chamfered edges are better, but they still have flat edges. So I would think the best thing to do is chamfer the edges. And then sand all the sharp facet edges smooth. Almost a gentle roundover of the chamfered edges Does that sound like a good idea?
So there you go. A new guy trying to learn about cabinet design. I hope it’s helpful to someone.
-Jon
Effects of baffle diffraction on the speaker’s apparent output:
If we take a regular floor standing 2 way MT speaker with sharp edges, we see a diffraction pattern like this:
Image not available
Ugly, eh? Lots of variability, ups and downs. It might not sound so great with certain frequencies boosted, others far down relative to the boosted ones.
Change the shape of the cabinet, let’s say we use 5 sides rather than 4, adding chamfered (or faceted) edges, and offsetting the drivers from the center line will have a cabinet looking like this:
Image not available
It’s ugly, but we can fix that part later (see below). But look at how much smoother the baffle diffraction effects are:
Image not available
Smooooth. Almost soothing, when compared to the 4 sided sharp edged cabinet.
The software:
Of the two programs, Edge and BDS, they each seem to have strengths and weaknesses- near as I can tell from not much experience using either program. Edge is easier to use and quicker. It has more variability in the baffle shapes you can use. But there does not seem to be a way to change the edge treatments. BDS takes longer to manipulate and looks to be more precise, with the ability to change numbers exactly, not just by dragging thigns with the mouse. BDS has fewer shape choices, but does have the ability to treat the edges with chafers and roundovers.
Some things I learned from the simulations:
I was trying to find situations with smoother plots and minimal deviation from peaks to troughs.
-A wider baffle with a chamfer (facet) is better than a narrow baffle with sharp edges
-A chamfered edge is better than a rounded over edge (I’m still trying to understand this one fully)
-A rounded over edge is better than a sharp edge
-A 1.5” chamfer is better than a 0.75” chamfer
-A straight baffle is better than one that is slanted 5 degrees, which is better than 10 degrees
-A 5 sided (like shown at top) or 6 sided (like the remaining front after Jon cut facets in his M8ta’s) baffle is better than a rectangular 4 sided baffle. (Note the typical tweeter at top, woofer below configuration)
-There seems to be not much difference between 5 versus 6 sided
-Offset drivers help a fair amount versus centering them in the middle of the baffle- according to BDS. Edge seems to show less of a difference.
-Any of these indiviual changes seem to make small differences. The two different plots shown above are the two extreme cases I found- from the ugliest to the prettiest plots. So getting smooth plots seems to be a combination of many small effects.
Conclusions- What I will incorporate into my cabinets:
From what I found above, it looks like I’ll be using a wide baffle (due to 1.5” double thickness to minimize resonances/vibrations) with multiple (3 or 4) layers of BB plywood on the front baffle. In a rectuangluar box. But cut the 1.5" facets out to make the desired 6 sided part of the baffle. The 6 sides will be prettier than the 5 in the figure above. I’ll also offset the drivers from the center.
A question:
Sharp edges are bad for baffle edge diffraction. Chamfered edges are better, but they still have flat edges. So I would think the best thing to do is chamfer the edges. And then sand all the sharp facet edges smooth. Almost a gentle roundover of the chamfered edges Does that sound like a good idea?
So there you go. A new guy trying to learn about cabinet design. I hope it’s helpful to someone.
-Jon
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