Originally Posted by TMcG
Are you looking for the column to be the same depth for it's full height? If not, you could have a deeper column base up to your chair rail height for the smoothing sub and then keep a thinner upper column.
This is a good idea.
If you needed a little extra depth this could work and look good.
Originally Posted by HopefulFred
Is the change you're considering in treatment depth? I think 6" for treatments would be pretty close to ideal. Then a 16" deep column would stand out 10" and look right. Of course, there's no rule about that - the column could end up flush with the treatment and still look very good, IMO.
Regarding the output from smoothing subs: I have a few thoughts here, which might be half-baked, so prepare a few grains of salt. In a room with perfect walls (zero transmission - perfect reflection) the null from a single driver located at a room boundary would be a perfect notch, where SPL goes to zero at one line across the room. If an additional sub is at the opposite wall, the measured SPL at that location should be equal to every other position ( I think, but again, this might be half baked), assuming the subs are identical. If the second sub were good for half the output of the first, I think the notch should be reduced to being only -3dB - so that's pretty good. Obviously a theoretical perfect room doesn't exist, so expect some smearing in space, time, and frequency. (Speaking of that, can you put a small sub in there and check out your modal response as is? There's lots to learn at this stage, with the basic shell complete.)
I just don't see why anything other than identical subs should be considered, when flexibility, phase, and output are all taken into account. I'm sure I haven't supported that statement enough to be persuasive, but there you have it: I favor symmetry in all aspects of subwoofer system design. Maybe that's naive or ill-informed, but that's what I'm doing - but sealed, which I think will be a lot more forgiving that horns.
A local friend of mine I know in real life is HAA, ISF, Cedia, THX, ..etc.. Certified and has taken Dennis Classes and also traveled out to the THX ranch for some trainings; He explained this to me once: In an ideal scenario you'd actually have 4 subs, one in each corner, and two on the floor and two on the ceiling. This would produce the best result.
Placement of subs can fix a lot of issues, so can a properly designed room. Smoothing subs are a good tool to use for sure, but not a requirement. And with a properly designed bass horn you won't necessarily have better or worse response at the LP than a sealed sub. The only certain is you would have more bass and lower distortion within the design intentions assuming it was designed right. You'd also need a lot less watts to get that. I think around here there is a prevailing assumption that sealed is better simply because they are easy to calibrate, have good extension, easiest to build, and take the least amount of space. This is all true, and obviously has some serious benefits too. But, the one thing sealed isn't great at is output so while they are a great solution for a smaller space they become much worse solution for bigger spaces.
There is a reason why Metallica uses bass horns at their show and not sealed subs. There is a reason why most of the IMAX theaters have Danely bass horns installed in them. It's because in bigger spaces they work better, and in situation where you want good output they are the best choice. The problem with bass horns isn't that they are hard to calibrate really, it's more just the WAF factor they are big, and difficult and expensive to build and design. Ported subs are out of phase 180 degrees at port tune, sealed are not- and horns are 90 degrees out of phase. Mixing them can be a tad bit tricky but it's not impossible. There is a bunch of guys in the DIY section running mixes with good results validated with measurements and I have read a couple threads where even Dennis calibrated some sealed smoothing subs with some ported cabs and said the results were very good.
Room nodes and response are tough to really account for 100% in the design phase because just moving the sub off the wall or closer can change things, and it's not always as perfect as it seems in theory when you actually measure the room. Things can be different so really the best way is to plan the room the best you can according to theory and then measure the final results to calibrate. I'm not sure JPA would know the full importance of some of this stuff until he has subs in his room, but either way it's all fixable for a great result with any kind of sub and even a mix of them.
I think that an 80Hz null would occur if the radiating plane is 3.5 feet from the wall. With most subs that wouldn't be a problem. If a sub was so large that the baffle was that far away from the wall the simple cure is to aim it at the wall I think. More subs in more locations has a natural effect of smoothing response so probably the best solution is to have more than just one subwoofer and to locate the subwoofers properly. If you can get some subs on the side of the room and back of the room that will do a great job at evening out the response. The way subwoofers interact with a room are usually dependent on their placement in the room, and moving them or placing them in a different spot can get a different result. But having a bunch in different spots has a way of averaging out things. JPA can you do a sub in the back to counteract the sub in the front ? That's a great option for you. It won't necessarily alleviate your need to calibrate but my guess is it would minimize it and have a positive effect at your bass response at LP.