This question is spurred by my likely purchase of JBL CBT 70J-1 for listening at the far end of a very long room. To be paired with a subwoofer in the corner to fill in the low end. And also someone's thread of some stunningly lovely line source speakers made out of umpteen small drivers with like aluminum face plate.
Anyway, a line source in theory is making a wave expanding in a planar fashion instead of part-spherically, thus the SPL falling off as 1/distance instead of 1/distance^2. Usually you can't have a line source subwoofer because to get the planar effect the line length has to be more than or approaching or something the bass wavelength which is super long. OK, too bad, so sad. But suppose in my 8' ceiling American room, I stack 8x12" in the corner. Now the airflow is kind of "constrained" by the floor and ceiling so has to expand in a planar sort of way. YAY! There's my plane wave subwoofer to match by plane wave mains.
But there's trouble in Paradise! It's too big...what if I use only 7x12"? 6? 5? 4? At the long wavelengths it doesn't seem you'd need the subs literally touching, or that you could reduce from 16x6" (hard to get to go low) to 8x6" etc. How much space can you leave between? What if you put the woofers on different faces of the tall enclosure? What if you wrapped the vertical array with a kind of snail to make a huge vertical bass horn feeding planar into the room?
Really the low frequencies in a room are more complex in time and the 1/distance concept not applicable like at the higher frequencies but at least as a "wave launch" kind of idea I wonder when is a bass line source no longer a line source...
Anyway, a line source in theory is making a wave expanding in a planar fashion instead of part-spherically, thus the SPL falling off as 1/distance instead of 1/distance^2. Usually you can't have a line source subwoofer because to get the planar effect the line length has to be more than or approaching or something the bass wavelength which is super long. OK, too bad, so sad. But suppose in my 8' ceiling American room, I stack 8x12" in the corner. Now the airflow is kind of "constrained" by the floor and ceiling so has to expand in a planar sort of way. YAY! There's my plane wave subwoofer to match by plane wave mains.
But there's trouble in Paradise! It's too big...what if I use only 7x12"? 6? 5? 4? At the long wavelengths it doesn't seem you'd need the subs literally touching, or that you could reduce from 16x6" (hard to get to go low) to 8x6" etc. How much space can you leave between? What if you put the woofers on different faces of the tall enclosure? What if you wrapped the vertical array with a kind of snail to make a huge vertical bass horn feeding planar into the room?
Really the low frequencies in a room are more complex in time and the 1/distance concept not applicable like at the higher frequencies but at least as a "wave launch" kind of idea I wonder when is a bass line source no longer a line source...
Stay close to one boundary.
It is only 8 feet.
Floor or roof, pick one
Assuming most don't mount to the ceiling pointing straight down.
Too high from one boundary...The largest is always the roof or ceiling.
Add one more boundary a wall you get the classic " Bass dip"
With 8 foot room typically dont want a woofer much higher than 28 to 30 inches.
Close as possible to the floor even better. Corner loaded even easier.
Now you eliminate any distance from the walls as well.
Down low in a corner, facing up all done.
Yine aways are just junk vertical with millions of excuses to explain why junk vertical is ideal.
Waste of time for non directional frequencies. Waste of time for directional ones especially
It is only 8 feet.
Floor or roof, pick one
Assuming most don't mount to the ceiling pointing straight down.
Too high from one boundary...The largest is always the roof or ceiling.
Add one more boundary a wall you get the classic " Bass dip"
With 8 foot room typically dont want a woofer much higher than 28 to 30 inches.
Close as possible to the floor even better. Corner loaded even easier.
Now you eliminate any distance from the walls as well.
Down low in a corner, facing up all done.
Yine aways are just junk vertical with millions of excuses to explain why junk vertical is ideal.
Waste of time for non directional frequencies. Waste of time for directional ones especially
Just a quick FWIW that when you're in the room's modal region, the line array stuff isn't really a factor. As you move away from the source, you'll find the sound might actually get louder. The -3dB/2d thing will only apply outdoors with a very tall subwoofer, or in a room with only a (very solid) ceiling and floor.
Chris
Chris
Yes, the "rollout" of sound pressure is more complex. On the other hand though it seems to me the "spread" of pressure over time should be different from a line source the entire height of a corner instead of the point of a corner. On the other other hand 8 feet is the wavelength of 140 Hz so at very low frequencies that would not seem to matter.*
Is there actually some kind of simulation available to do that kind of modeling?
*then again since the CBT J70-1 I am contemplating don't go super low, those upper bass frequencies could well be very relevant.
wavelengths are too long and the modal response too unpredictable to simulate.......you have to start taking into account how the walls, floor and ceiling are built too.
4 stand alone subs.....one of them out of phase 180.......you have to experiment which one......smoothest in room bass response you'll ever experience
4 stand alone subs.....one of them out of phase 180.......you have to experiment which one......smoothest in room bass response you'll ever experience