Soffit Relections & 5.1 Surround

It is my understanding that the hard front face of the soffit must be perfectly flush with the face of the speaker. Wouldn't this hard surface make a giant unwanted reflection point for the front/rear surround speakers? How would one deal with that? Could I put fiberglass on the front of the soffit at the top like the bottoms generally have? If so, should the wood soffit front still be flush with the speaker, and the fiberglass just stick out past the speaker face? Would that mess up the functioning of the soffit?

the soffit (more correctly baffle, we actually baffle mount speakers but soffit is frequently used...) can have absorption on it and still function for its intended purpose - namely providing a boundary surface for low frequency waves. so if you put mid and high frequency absorption on parts of the front soffit, (and even if there is multiple depths involved) you're unlikely to impact your high frequency response but you also want to consider that any hard/sharp transitions as potential diffraction points which can impact your overall imaging and response. 5.1 soffit mounting takes a lot more care to balance all of those considerations than simply having stereo...

Thanks Glen. Here is a crude sketch up. Ignore the fact that there is no framing for the baffle. Would something like this be OK? More researching is in order as I don't have a good understanding of diffraction and how it would relate to this situation. Could you elaborate if you get a minute?

delete - dupe

if you take a look at some of John's soffit designs, you'll see how the baffle hard surfaces and absorption surfaces work together. in addition, John has provided some drawings of portable surfaces where you can see a number of the absorption panels being integrated with the hard panels to create a good balance. on diffraction - if you look at many speakers you'll notice that the edges are rounded. this allows a smoother transition for the low frequencies to wrap around the speaker. this avoids a diffraction effect on the front edge corners of the cabinet from creating illusionary point sources which could alter your perception of the phantom stereo image as well as potentially create comb filtering and other undesirable effects.

I'm going to try to find those drawings of John's that you were talking about. Hmmm, that's interesting. The Mackie HR-824s that I'll be using do have rounded edges on the side but not the top. So would slightly rounding the edges of the soffit bezel similar to the edges of the Mackies help avoid diffraction?

actually, because the edges are rounded, you probably want to route the inside of the baffle plate so the monitor sits flush - the idea being to reduce any gaps to a couple of millimeters if possible and avoid any potential diffraction effects - so your monitor is effectively on an "infinite baffle" (trademarked term btw...)

OK, that makes alot of sense. Thank you for taking the time to illustrate it! A picture is worth a thousand words. I have a pretty good grasp on the concept now. The one last thing that I'm not 100% on is why build the box around the speaker box itself? I've seen people build soffits/baffles with and without the extra box. I was considering not bothering with that step due to possible heat issues with active monitors as well as saving on material costs and labor time. A big influence in this approach was Kendale's setup- same monitors as mine and no extra box. He has reported great sonic results and has had zero overheating problems. If you get a second could share your opinion on the pros and cons of the additional box?

will this help out?

Ro wrote:

will this help out?

Thanks Ro. Yes, I have read that thread multiple times over the months. I'm assuming you may have been steering me to the "ventilation path" illustrated there to keep the amps cool. I'm aware of that design, I should have mentioned that, sorry. What I didn't see in that thread is anyone weighing in on the positives and negatives of the extra box around the loudspeaker, although there was a little mention that it can be done both ways. What I'm trying to find out is what the benefits of the extra boxes are.