End Fire with two subs

[Marc Brule]

I've read some threads on cardioid and end fire configurations. I have only two subs to work with (Community VLF double 18's) that will be install under a church stage. My thinking was to place one at the very front edge and the other spaced back for 1/4 wave @63 Hz. Stage is 3 feet high and subs are 22" high (laying on sides)

Questions are:

1) Which would be more suitable: delayed front in phase or delayed rear inverted phase (end fire vs cardioid)?
2) How much of the front of the stage should be breathable to achieve cancellation/summing?

Any other advice is welcome.

Thanks,

 

[Caleb Dueck]

Re: End Fire with two subs

How about sand/brick/cheap mass of some sort for a bunker, to physically keep the sound from going back under the stage, and to keep them from physically coupling to the stage (vibration)?

 

[Chris Nixon]

Re: End Fire with two subs

I've read some threads on cardioid and end fire configurations.

Questions are:

1) Which would be more suitable: delayed front in phase or delayed rear inverted phase (end fire vs cardioid)?
2) How much of the front of the stage should be breathable to achieve cancellation/summing?

Any other advice is welcome.

If you're going to be creating a sub array the differences between polarity and phase are important, as you'll possibly be dealing with both of them simultaneously.

Total Pro Audio | Phase or Polarity?

If you want to experiment with different configurations you can use this.

DDT Software | Danley Sound Labs, Inc.

It will let you set up virtual microphones to look at the frequency response in different parts of the sound field. It doesn't have your particular subs in it but should give a good general idea of what different set-ups will do.



Chris

 

[Caleb Dueck]

Re: End Fire with two subs

The parts I was keying in on are 'under the stage' and 'install'. If it were free air, especially with a larger quantity of subs, then some sort of end fire would work great. Under a stage, with only 2 subs - I'd rather go the bunker route.

 

[Brad Weber]

Re: End Fire with two subs

I've read some threads on cardioid and end fire configurations. I have only two subs to work with (Community VLF double 18's) that will be install under a church stage. My thinking was to place one at the very front edge and the other spaced back for 1/4 wave @63 Hz. Stage is 3 feet high and subs are 22" high (laying on sides)

What is your reason for considering a directional subwoofer array, are you trying to get more directionality or on-axis output, reduce the levels behind the subs or what?

I believe that a similar discussion occurred in the past and the general consensus was that the subs being under the stage would be a major factor as you would get not just the direct sound of the two boxes interacting but also all the indirect reflections from nearby surfaces, the effects of the boundary above, loading if not fully open, etc. Between that and having just two boxes, I'm not sure you would get much benefit and I agree with Caleb that it may be better to build an enclosure under the stage and group the two subs together in that enclosure.

 

[Craig Hauber]

Re: End Fire with two subs

The parts I was keying in on are 'under the stage' and 'install'. If it were free air, especially with a larger quantity of subs, then some sort of end fire would work great. Under a stage, with only 2 subs - I'd rather go the bunker route.

Did a church once that had a cinderblock stage structure with the deck made of poured concrete over corrugated steel. We flushed the subs to the front and caulked around them. When in the crawlspace behind you couldn't tell the subs were even on! There was also no vibration whatsoever on stage.

 

[Ivan Beaver]

Re: End Fire with two subs

The parts I was keying in on are 'under the stage' and 'install'. If it were free air, especially with a larger quantity of subs, then some sort of end fire would work great. Under a stage, with only 2 subs - I'd rather go the bunker route.

Exactly.

Directional subs work great when they have "room" to work. Under a stage is NOT one of those cases.

I always specify the subs be put in a "bunker" when they have to go under the stage on an install.

I specify at a minimum 2 layers of 5/8" sheetrock with overlapping seams-glued and screwed-NOT nailed. This is on ALL sides (INCLUDING the top)-except the bottom.

 

[Brad Weber]

Re: End Fire with two subs

I specify at a minimum 2 layers of 5/8" sheetrock with overlapping seams-glued and screwed-NOT nailed. This is on ALL sides (INCLUDING the top)-except the bottom.

And maybe the bottom, if you have a trap room, pit or similar then under stage subs may be extending into those spaces in which case you want to create a complete enclosure, preferably with some way to get access to install the subs and service them if needed.

 

[Marc Brule]

Re: End Fire with two subs

My main goal is to reduce sound under/behind the stage. I need 180 degrees in front for coverage. Stage is wood - 5/8" plywood on wood framing. Tiled concrete floor. I could make the whole front OT stage (40 feet) breathable with metal grille. What I'm hearing is that enclosing the subs from the side and behind would be more effective than end firing them?

My guess would be that pairing them side by side would couple them without significant loss to the sides and the subs would ultimately only be accessible from the front.

Thoughts?

thanks for the great input.

Marc

 

[Marc Brule]

Re: End Fire with two subs

If you're going to be creating a sub array the differences between polarity and phase are important, as you'll possibly be dealing with both of them simultaneously.

Total Pro Audio | Phase or Polarity?

If you want to experiment with different configurations you can use this.

DDT Software | Danley Sound Labs, Inc.

It will let you set up virtual microphones to look at the frequency response in different parts of the sound field. It doesn't have your particular subs in it but should give a good general idea of what different set-ups will do.



Chris

Great resources! Thanks.

 

[Grant Conklin]

Re: End Fire with two subs

How about sand/brick/cheap mass of some sort for a bunker, to physically keep the sound from going back under the stage, and to keep them from physically coupling to the stage (vibration)?

Hey Caleb,
I've heard you talk about this before, and I was just thinking about it the other day. Could you elaborate on the construction of said bunker? I get the mass wall thing, but I'm not remembering how sand is employed.
Thanks,
Grant

 

[Caleb Dueck]

Re: End Fire with two subs

Hey Caleb,
I've heard you talk about this before, and I was just thinking about it the other day. Could you elaborate on the construction of said bunker? I get the mass wall thing, but I'm not remembering how sand is employed.
Thanks,
Grant

A big sandbox ... with plenty of little Tonka trucks ... and a remote control bulldozer

One I helped with recently, the cavities were larger than the subs. The stage surface was opened, the free air between the subs and the cavity walls/top was packed with sand bags, and the stage surface was closed. It's not as rigid as concrete, but there isn't free air, and a few hundred pounds of sand doesn't move that much.

 

[Rob Timmerman]

Re: End Fire with two subs

Hey Caleb,
I've heard you talk about this before, and I was just thinking about it the other day. Could you elaborate on the construction of said bunker? I get the mass wall thing, but I'm not remembering how sand is employed.
Thanks,
Grant

The goal is to eliminate any paths for sound to travel except out the front. This means walls stiff/heavy enough so as to not vibrate, and no air paths.