Boundary Cancellation

[Bryan Cox]

I've read all I could find on boundary cancellation and there's something I don't understand.

The rules of boundary cancellation say to place your subs a certain distance from a wall to raise the effected frequency above the crossover point so the band pass isn't altered. But how do perpendicular walls affect this? If you were setting up in an area that had perpendicular walls, say, 15' on either side of a subwoofer, would those walls alter frequencies in addition to the parallel wall the sub is aligned with? Would one need to calculate the distance from all walls to determine which frequencies would be cancelled?

[Bill Fitzmaurice]

The same rules apply, so either have the subs very close to or as far as possible from those walls.

[Bryan Cox]

The same rules apply, so either have the subs very close to or as far as possible from those walls.

I thought you might say that, Bill. But it occurs to me that if we take all things into account we could use ceiling height and walls as an advantage.

[Bill Fitzmaurice]

Yes, you can. If you're less than 1/4 wavelength from both the rear and side wall you're for all intents and purposes corner loaded. We don't think about the ceiling, since all rooms have them, but it also adds to the spatial loading compared to outdoors. Ceiling cancellations tend not to be a problem, since they tend to be either around 8 feet or a lot higher.

[Bryan Cox]

Yes, you can. If you're less than 1/4 wavelength from both the rear and side wall you're for all intents and purposes corner loaded. We don't think about the ceiling, since all rooms have them, but it also adds to the spatial loading compared to outdoors. Ceiling cancellations tend not to be a problem, since they tend to be either around 8 feet or a lot higher.

Yeah I read in one article that the average 8' ceiling will add a slight bump at around 70 Hz. I downloaded the distance tables I found and I think those will be useful in the future.

I see now why it's best to test outdoors. No boundaries to worry about. Luckily, the aircraft hangars I test in have 25' ceilings. That'd create a ~22 Hz bump which is below my crossover point so I should be good. If not, I'll just place the subs at ~14' from a wall to cancel it.

[Grant Bunter]

That'd create a ~22 Hz bump which is below my crossover point so I should be good. If not, I'll just place the subs at ~14' from a wall to cancel it.

22Hz is also more than 1 octave down from your preferred sub(s) High Pass point of 50Hz. If you're using a LR48 (48dB/octave) slope, that means 22 Hz is at least -24dB compared to 50hz.
So, don't even worry about it.

Just stick with the "prime directive" in the sub sticky and never place cabs within 2 to 8 feet of a boundary...

[Bryan Cox]

Thanks, Bruce. That's easier to remember than what I was attempting.

[Grant Bunter]

Thanks, Bruce. That's easier to remember than what I was attempting.

Bruce? Nah.
Bruce is that tall Texan fella.
I'm a short wheel based Aussie...

[Bryan Cox]

Thanks, Bruce. That's easier to remember than what I was attempting.

Bruce? Nah.
Bruce is that tall Texan fella.
I'm a short wheel based Aussie...

Oh crap, I'm sorry Grant! I'll be sure to be more careful in the future.

[AntonZ]

Don't sweat it Bryan, he's short and far away

[Bryan Cox]

Don't sweat it Bryan, he's short and far away

[Bill Fitzmaurice]

Bruce is that tall Texan fella.

Maybe. Texan men say that everything is bigger in Texas. Texan women disagree.

[Bryan Cox]

Bruce is that tall Texan fella.

Maybe. Texan men say that everything is bigger in Texas. Texan women disagree.

Hence the big trucks.

[Seth]

Hence the big trucks.

[Bruce Weldy]

Bruce is that tall Texan fella.

Maybe. Texan men say that everything is bigger in Texas. Texan women disagree.

Not true! My wife insists my belly is way too big.....and getting bigger every day.