outdoor even - sizing equipment (particularly subwoofer)

[Sydney]

Re: outdoor even - sizing equipment (particularly subwoofer)

Always a compromise...
What was the distance between the sub below and the main ( on pole ) above?
Looks to be about 8' of the ground

[ryanbouma]

Re: outdoor even - sizing equipment (particularly subwoofer)

Woofer CTC spacing was probably a little less, maybe 7 feet. The poles weren't very long. XO was set to 120hz LR4. Integration was good, in fact had a bit to much sound power there I think. No measuring was done though. Overall the bass was "fun" bass. I ran it a tad hot overall. For the folks in the power alley, they would have been feeling. I was offset just to the fringe of the alley, but closer to the band than the spectators. Had a lot of heat on the bass. And in the nulls it was really weak. The kick drum and low tom dominated the bass. The bass guitar was kept more in sync with the rest of the mix. And the bottom of the keyboard also. Overall for what we had to work with, it was fun and sounded great.

I used DIY speaker on the keyboard and drummer monitor. They were like "what the heck are these things" :D They had dual 12" celestion ftr12-3070c woofers and a SEOS12 DNA-360 top. Use a pretty basic 1700hz XO. The drummer asked for kick drum in his monitor! With a 50hz tuning, it handled it like a champ

I'm rambling.

[Sydney]

Re: outdoor even - sizing equipment (particularly subwoofer)

All in all it worked out...
The question about the 7 foot CTC was prompted by the compromise and resulting issues of having main up in the air for better dispersion and bass bins down on the ground.
As separation distance increases summation decreases
7' is equal to the 1/2 wavelength of 80Hz the spacing creates uneven summation at an around that frequency.
In my experience that distance benefited from some sort of a fix ( a polarity reversal or perhaps delay )

[ryanbouma]

Re: outdoor even - sizing equipment (particularly subwoofer)

I figured that's what you were getting at. I was worried about that. But the summation seemed fine. At least I couldn't hear a problem. The JBLs couldn't quite handle my initial 100hz XO. Being outdoors I figured the vertical summation wouldn't be much of an issue, provided we were still within 1/4 wavelength. Reversing polarity would have created a null, I'm sure. I don't think you can fix a physical separation problem with polarity or delay. You have to reduce the physical separation no?

[Sydney]

Re: outdoor even - sizing equipment (particularly subwoofer)

... Reversing polarity would have created a null, I'm sure. I don't think you can fix a physical separation problem with polarity or delay. You have to reduce the physical separation no?

Ideally as little physical separation as possible.
However I'm sure you have seen large set ups where the mains were a much greater distance of separation than 7' and the issues were addressed somewhat with delay.
Note distance from flown line arrays and ground subs here.

Of course there are limits to how far the separation distance can be stretched and the reduced efficacy of the delay as distance increases.
Bob McCarthy discusses in detail in his book ( Sound System design ) on the section on Summation.
Anecdotally: I've experimented with polarity reversal at such separation distance and it improved the bass by reversing the existing null caused by the separation.
This is not un-similar to the techniques/guidelines for making sub arrays directional and similar to tricks that other bands ( The Grateful Dead for instance ) tried to direct summation and propagation.

[Brian Steele]

Re: outdoor even - sizing equipment (particularly subwoofer)

I wonder if a third sub placed at the center and delayed wrt the side subs could have served to reduce the "power alley" effect and at the same time not overwhelm your band with bass?

[wg_ski]

Re: outdoor even - sizing equipment (particularly subwoofer)

It would probably still overwhelm the band. The problem is that they're not on an elevated stage that you can put subs under. When I'm DJing most high school gyms I put the sub cluster off to one side (the one opposite me). I've even seen dummy subs used so the audience doesn't know it's only coming from one side. Unfortunately, this requires 80Hz-capable mains.

[Sydney]

Re: outdoor even - sizing equipment (particularly subwoofer)

Yeah It's a big compromise playing in an area selected versus one designed for performance.
One of the things I would have tried ( circumstances permitting ) would be to set up a Cardioid Sub array.

[ryanbouma]

Re: outdoor even - sizing equipment (particularly subwoofer)

I've even seen dummy subs used so the audience doesn't know it's only coming from one side. Unfortunately, this requires 80Hz-capable mains.

I seriously considered this LOL. Even played around with the idea for 5 or 10 minutes during setup. I felt it put all the bass to one side and as you mentioned, the mains didn't interact quite as well it seemed. Ultimately I think I was compelled to use both because I had dragged those 250lb beasts there and the organizers paid the $50 rental for each. I felt both had to be turned on. Haha, stupid reason ya, but oh well. I think sometimes as a sound guy we hear all the problems, but the audience just cares about the sunshine, the music, the people, the dancing, etc. In this case it was a success. The organizers (both the church and the town) were happy with how everything turned out. Not just the sound quality. So I think it was a success.

[Sydney]

Re: outdoor even - sizing equipment (particularly subwoofer)

...Ultimately I think I was compelled to use both because I had dragged those 250lb beasts there and the organizers paid the $50 rental for each. I felt both had to be turned on. ...

Similarly:
If you can get to page 84 of the book Sound System Design and Optimization: There is a Perspectives anecdote by Dave Revel in which " there was significant pressure from the client to use ALL the rented resources". Dave waited until dinner break and unplugged 2 of the 3 speakers. He received complements on the improved sound. "Not a single person could identify the reason for the improvement." ;)

[ryanbouma]

Re: outdoor even - sizing equipment (particularly subwoofer)

Haha, ya, that's exactly it. I shoulda just turned one off during intermission just to see if people would have said anything. I bet you're right people would thought it improved.