Venue eq issues.

I knew about boundary cancellation but never got to struggle so much with it until a few months ago: I had to set up a friend's soundsystem as fixed in a venue which is an austrian fort built around 1800, when that happened the town's ground was significantly below the current level because it was basically built on sand and stones so it kept getting lower but, the ground was constantly raised through the years by putting more stable ground components anywhere it could be possible.
Raising the fort was obviously not an option so it is now 1 floor below the street level, that means the soundsystem was installed inside a room with about 1m thick walls which had as much ground behind them as the whole city has.
For the first party the system was actually put up by my friend and here you can see how he placed the speakers. I must warn you that they were mainly placed there for aesthetics and space management purposes though. 



Room is very small, it's around 7m long and you could not hear the bass from the front at all. On the back of the subs though you were literally getting your internals shaken and killed by bass, it would've been cool enough for the peeps standing back there if it didn't hurt their ears when the party was over.

My thought was that the walls being "infinite" due to being underground were making even deep bass bounce tightly and the waves coming back from the wall to the front would cancel whilst the ones on the back were adding up, this was also a problem from the side walls and the ceiling.
My solution was to push the subs as close to the back wall as possible, so that it would give them the most natural position, and measure the exact room length to add it as a long delay on the LMS (I thought that's basically like subtracting the box lenght).
It worked, and now its response is pretty flat for such a room with difficult acoustics interaction.
The perfect setup IMO would've been to put just one stack in the middle with the tops a bit angled and separated but since it is physically impossible here's what I managed to do at best:



As someone already said, placing subs near walls could help but keep in mind it could worsen the situation instead so best way would be to do the invert phase, find the point at which they cancel the most and invert phase again as it was mentioned before.

PS: corners make it all worse, your best bet would be for you to do a single central stack

Edited by Darkstar - 09 August 2015 at 7:02am

Jasonstry wrote: My worst case was just two walls..... http://peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

Nice article, as long as you ignore his mathematics at the end.

...ok then theres way more i need to learn about it....

Does boundary cancellation really appear in such an odd shaped room? I would hazard a guess at the 4m ceilings arent helping as it a half wave of 40hz give or take....

Try running your black box 60-180 and your mid hi in from 180, the overlap with your sub will give you chance to run a 100Hz test tone and have it appear in both cabs, as Robo right points out the horn will have a massive phase shift against a G-sub.

darkus wrote: Robbo wrote: Have you time aligned the G subs with the Black Box 15s as they will cancel bass out due to one cabinet being direct radiating and the other being horn loaded---they are completely out of phase with one another. No I havent, how would I work out what to set it at or just change it and do it by ear.