sub in/under stage.

[chetorch]

hello all! i've got a question, just need a general answer.

does placeing a subwoofer under the stage affect the FOH mix or monitoring in any negative way? our stage is basically hollow, about 16' wide and 12' deep.

[waynehoskins]

Recessing subs in the front of the stage is pretty common. The stage does, however, need to be tall enough. That usually means two or maybe even two and a half feet.

[darsmith]

We have a pair of dual 18" subs that were under the stage. Along came a new sound tech and he moved them out onto the platform. I can't tell any difference, but they sure take up a lot of room on the stage. The new sound guy moved on (on the road promoting a band) and I would like to see them put back under the platform. Our room acoustics are not the best, so maybe that's why I did not notice any appreciable difference to moving them up onto the platform. I think the crossover is set at about 120 Hz, so directional sound is not a problem.

[[Director] drew ryan]

THe short answer is it depends. What is your stage made of? If it is concrete, you will only notice a small difference on stage. If it is wood, you have just made a very large resonant chamber and your musicians will notice it a lot. You may even be able to get more sub in the room.

Subs are usualy placed under the stage so that they can sit next to eachother. By doing this you get a coupling effect of the subs and will have a 3dB increase over the sum of the 2 subs if they are spread apart. You also don't get in to as much cancelation of waves as the waves are generated from the same spot.

[cmchamp]

To supliment what Drew said. When subs are separated - you present a power alley in the center of the room - the line of simetry between the two - and then cancellations along the rest of the room. When subs are coupled together - depending on their design - not only can you get a 3dB increase due to coupling, but you also can have frequency extension lower due to a longer length creating the wave.
As Drew said, when you have a wood stage, it will most likely not be dense enough to not resonate. This resonance will be noticeable as well as be transmitted up the mic stands into the microphones.
C

[chetorch]

yeah our stage is wood and high enough. thanks all for all the great info!

as for the mix going into the sub, we have had to work with our mixer and what we could work out (because all the a/v things are done by volunteers) was that the sub mix comes from one of the auxilury sends. is this ok? I don't know much about crossovers, I guess I'll have to look into it, but will this work for now?

[waynehoskins]

You really want a crossover. Avoid feeding the subs full-range if you can.

There's debate in the audio community as to whether subs should be aux-fed or taken from main mix. I'm not a fan of aux-fed subs myself.

Crossover is very simple, main stereo mix (usually after the graph) goes in, everything below the crossover frequency comes out one set of jacks, everything above comes out another. The more formal (but never-used) name is "frequency dividing network".

So main left and right go into the crossover, and out from that you get left sub, left top, right sub, right top. Usually crossed over somewhere around 80, and of course with enough power behind the subs.

[brenthomer]

1. We just pulled our subs out from under the stage. We hated them there.

2. We put them on the stage and the musicians loved them. they felt a lot more "presence" that way, and we had a nicer sound in the house. I think the big problem with them under the stage on the floor was a bass wave needs a lot of room to fully form, and we didn't get a nice sound until towards the back of the sanctuary.

3. We removed the house feed to the subs and stuck them on an aux (via crossover). ohhh...it is soooo much nicer (for us). I think that is b/c our room is a big ice cube made of concrete.

[cw4u]

We drive our subs from our dbx DriveRack. We used to feed it via a aux send, decided to run it from our dbx. It works well for me, but I don't have access to the driverack, so I can't boost the subs any. (I like a lot of bass)

Our two subs are put on ground level on stage right and left. It works well, but not powerful enough for me.

[MediaGuy]

Ours are under the stage on either side. We just hosted a concert last weekend, who brought in their own equipment and had the same model of JBL subs that we have. They placed them on the floor in front of the stage (center, where ours are left/right), and I heard no noticeable difference - except the volume: They peaked out at 110db.

[asimmons32]

I have looked into flying our subs above the stage. Right now we have L/R subs under the stage set about 15 feet apart. They work fine but have the "power alley" effect in the center of the room as MC Champ has stated above. The front of our stage is round or has a curve to it so I cannot set them together. I will be exploring the possibility of fling the subs up above the stage. I have read that the bass response is smother if they are flown. Has anyone flown their subs and could expand on this?

[Brad Weber]

Originally Posted by brenthomer

2. We put them on the stage and the musicians loved them. they felt a lot more "presence" that way, and we had a nicer sound in the house. I think the big problem with them under the stage on the floor was a bass wave needs a lot of room to fully form, and we didn't get a nice sound until towards the back of the sanctuary.

Not to nit pick but the concept that low frequencies need space to 'form' is a common misconception. There could be a number of reasons for what you experienced, but it is not a result of needing some distance for a wave to 'form'.