Building 2x18" boxes...

[Jakob]

When building this type of box, what do You need to take into consideration? I'm not thinking of bracing or dimensions since this kind of information is available in the tech. docs. I was more thinking of things like:
1) Will placing the 2 woofers as close together as possible yield a better sonic result?
2) What hight from the floor should the drivers be located on?
...and so on.

Anyone with 2x18" boxes for home use with any info regarding this or other facts they feel should be mentioned?

Thanks!

[1audiohack]

What I have been thinking about and have yet to model or try and test is to what extent you can tune the in room response of subs by driver separation. If the drivers are on the same plane mounted 3.5' on center from each other they should achieve the mutual coupling boost at about 80 Hz and down right? So if they are placed 9.5' apart they should couple and boost at about 30 Hz and down. That could be a nice tuning tool if they really behave that way in an acoustically small room.

[Eaulive]

What I have been thinking about and have yet to model or try and test is to what extent you can tune the in room response of subs by driver separation. If the drivers are on the same plane mounted 3.5" on center from each other they should achieve the mutual coupling boost at about 80 Hz and down right? So if they are placed 9.5" apart they should couple and boost at about 30 Hz and down. That could be a nice tuning tool if they really behave that way in an acoustically small room.

Where do you get these numbers from? I would like to understand the physics behind this.
(Not trying to argue, just curious )

[Lee in Montreal]

9.5" for 30Hz coupling. Did you mean 9.5' (114" or 2.9m) ?
Trying to figure out how to mount two 18" drivers 9.5" apart...
Or is it at a 9.5" distance difference from the listener? So, a 9.5" delay.

[1audiohack]

I corrected the inch / foot errors in my last post, thanks Lee.

Eaulive, that's Barry math and theory. A couple of years ago when our little world slowed way down we compacted our fab shop into our machine shop and eliminated one of our 13,500 square foot buildings. It was dead empty for a couple of weeks before the lease ran out. I have never worked in an acoustically large room before and at 390,000 cubic feet it truly meets Manfred Schroeder's definition of a large room for very wide range music and with five concrete surfaces it was also a truly statistically reverberant space.

I set up a small system on a pallet that I could move around with the forklift and went about experimenting with placement, ETC and RT60 measurements and what ever else I could pull off after work.

I had six 2235's in separate boxes that I set together in every way I could think of, in a pile, ports together, ports apart, in a line facing up, facing out, all together and spread apart.

With TEF in a room with the first hard reflection at 75 feet away, it was also pretty easy to gate and get 1/4 space frequency measurements. One of the observations was that I could change the shape of the frequency response curve by equally spacing the subs out along the wall. I did not have the time to work this to what I would dare call conclusive, but there is something there. I need to try it 1/4 space outdoors. The other issue is in many small rooms we are working in the pressure zone at very low frequencies, at that point not much matters. There is so much to know and so little time.

[JBL 4645]

I did not have the time to work this to what I would dare call conclusive, but there is something there. I need to try it 1/4 space outdoors. The other issue is in many small rooms we are working in the pressure zone at very low frequencies, at that point not much matters. There is so much to know and so little time.

^^^That was very thorough Barry. Cool post!

Did you not also try inside this hanger or what ever infinitely baffled sub bass by making a false wall at one end and stacking all the JBL behind it?


The 2235 that's the 15" JBL down to 20Hz.

[Eaulive]

I corrected the inch / foot errors in my last post, thanks Lee.

Ah... that makes more sense to me now

With TEF in a room with the first hard reflection at 75 feet away, it was also pretty easy to gate and get 1/4 space frequency measurements. One of the observations was that I could change the shape of the frequency response curve by equally spacing the subs out along the wall. I did not have the time to work this to what I would dare call conclusive, but there is something there. I need to try it 1/4 space outdoors. The other issue is in many small rooms we are working in the pressure zone at very low frequencies, at that point not much matters. There is so much to know and so little time.

Interesting, we do the same things with antennas to modify the pattern. Basically the total energy is the same, the apparent "gain" is due to the stretching of the pattern in a given direction at a given frequency, It's probably the same with accoustic waves.

I remember fooling a little with LF steering by carefully placing and delaying multiple subs.

Thanks for sharing your experience.

[badman]

Ah... that makes more sense to me now


Interesting, we do the same things with antennas to modify the pattern. Basically the total energy is the same, the apparent "gain" is due to the stretching of the pattern in a given direction at a given frequency, It's probably the same with accoustic waves.

I remember fooling a little with LF steering by carefully placing and delaying multiple subs.

Thanks for sharing your experience.

The mutliple locations will simply have lobed summation when they're acoustically significantly apart- easy to manipulate for one position, a little harder with multiple positions. And as you add more subs, you add more averaging- read, less lobe control.

Sure it's fun to play with but seems purely acaemic, for use in sound reproduction.