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[Kevin Maxwell]

Acoustic problem – Subwoofer cancellation in the Booth.

I worked with a sound company on an install of a newly built venue (nightclub/bar) that has live bands and also dance music (DJ). I don’t have the measurements of the venue. I am supposed to go there tomorrow and I plan on taking some measurements. The owner had it built with the (DJ/Live Mix) booth into the house right wall. I think it is about 30’ from the edge on the stage. It is partially sticking out into the room (maybe about 2 feet) so you can see the stage to your right. And it is about 2 to 3 feet above the dance floor. They didn’t listen when told not to build the Booth that way.

There are 4 powered subwoofers under the stage. The problem is the sound for the subs gets significantly reduced in the booth and it is most noticeable with what a DJ plays. In the room the bottom end is A LOT louder than in the Booth. I found that if I position myself in the back left corner on the Booth I can hear the subs much better. I think that corner is causing the cancellation in the Booth. One day when testing some of the setup in the room I stacked some boxes in that corner to see if would affect the sound but it didn’t seem to break up the cancellation. Also that corner is at the top of the stairs to the Booth so I can’t take up much room there. I was thinking of trying a Sono Tube stuffed with some insulation stuffed inside of it and placing that in the corner. They come in 4foot lengths and a bunch of different diameters. I just remembered while writing this that I have 2 - 2’x4’ (I think it is 2”thick) acoustic panels made from Fiberglass duct board that are framed and covered with speaker cloth. I am going to bring them tomorrow and play around with placement and see if that makes any difference.

I have worked with a very high end acoustic consulting firm on a couple of projects and someone there would probably know the answer to this problem. But they are VERY expensive and this Venue owner would never pay what they would charge. I just put in a call to an acoustic consultant that is probably more reasonably priced to see if he makes house calls. He is located not too far away from this place.

Does anyone with experience with thus kind of situation have any recommendations?

[John Roberts {JR}]

How about a microphone out in the room to monitor SPL? Feed that mic to a RTA.

Having less bass in the sound booth sounds like a possible benefit.

JR

[Tim McCulloch]

How about a microphone out in the room to monitor SPL? Feed that mic to a RTA.

Having less bass in the sound booth sounds like a possible benefit.

JR

Kevin's description is giving me a Marty McCann flashback, JR.  His tech note about subwoofer placement relative to boundary surfaces.

I'm thinking the protruding part of the booth, 2-3 feet above the floor, is creating a phase cancellation that is transmitted structurally into the booth, which also has its own resonance(s).

@Kevin - yeah, this is one of those "doc, it hurts when I do *this*" and doc says "then don't don that."  The correction for the problem the club owner created will be expensive.  Not correcting it will be expensive in subwoofer repair costs and neighbor complaints.  If the DJ can't FEEL the LF, he/she/they are gonna turn it up, guaranteed.

[John Roberts {JR}]

Kevin's description is giving me a Marty McCann flashback, JR.  His tech note about subwoofer placement relative to boundary surfaces.

I'm thinking the protruding part of the booth, 2-3 feet above the floor, is creating a phase cancellation that is transmitted structurally into the booth, which also has its own resonance(s).

@Kevin - yeah, this is one of those "doc, it hurts when I do *this*" and doc says "then don't don that."  The correction for the problem the club owner created will be expensive.  Not correcting it will be expensive in subwoofer repair costs and neighbor complaints.  If the DJ can't FEEL the LF, he/she/they are gonna turn it up, guaranteed.

Do they still make those bass seat shakers?  Maybe have the DJ sit on an extra sub facing up with a seat cover. [/joke]

JR

[Helge A Bentsen]

Put a sub in the booth?

[Caleb Dueck]

Kevin's description is giving me a Marty McCann flashback, JR.  His tech note about subwoofer placement relative to boundary surfaces.

I'm thinking the protruding part of the booth, 2-3 feet above the floor, is creating a phase cancellation that is transmitted structurally into the booth, which also has its own resonance(s).

This is my first thought as well, followed by horizontal pattern collapse due to the subs, I assume, being spaced horizontally under the stage.  This is a great example why going against audio recommendations to save money rarely saves money - and often costs a whole lot more to fix.  I've had this conversation with owners too many times.

[Rob Timmerman]

Do they still make those bass seat shakers?  Maybe have the DJ sit on an extra sub facing up with a seat cover. [/joke]

JR

As it sounds like the booth is elevated, bolting a shaker (the Buttkicker units are still available for sale and not especially expensive) to the booth floor might actually be a reasonable solution here.

[Paul G. OBrien]

The location of low frequency nodes (which includes cancellations nulls) indoors are a product of the sound wavelengths in question and the subwoofer and listening positions. One of those 3 has to change to affect the nulls, sound absorbing materials can dampen a buildup but that has no effect on a null.

[Dave Garoutte]

Our sound booth is the opposite; it's a big bass trap.

[Steve-White]

Put a sub in the booth?

Exactly what I was thinking.  Keep in simple, if the house sounds good and it's a booth issue, then make it a booth solution.

[Tim McCulloch]

Exactly what I was thinking.  Keep in simple, if the house sounds good and it's a booth issue, then make it a booth solution.

If this is a cancellation node, then it's a crap shoot.

[Steve-White]

If this is a cancellation node, then it's a crap shoot.

Easy enough to borrow/rent sub(s) for a little testing.  Doesn't work, no harm no foul.

[Tim McCulloch]

Easy enough to borrow/rent sub(s) for a little testing.  Doesn't work, no harm no foul.

Yep.  In the order of "cost of being wrong", this is among the cheapest.

[Lance Hallmark]

You generally don't want sub from the main PA spilling into the booth, especially if the DJ is mixing. Put a sub in the booth and call it a day. Usually it's the opposite, which is a problem for mixing when there is a delay in the Main subs.

[Ivan Beaver]

Without knowing a bit more details, it sounds like one possible problem is simply room modes.

They are freq dependent areas that are based on the height/width and depth of the room, with the ceiling being generally the dominate mode producer.

If this is the problem (I have seen it numerous times), you have 2 solutions.  Either move the DJ booth or change the physical size of the building.

A local sub in the booth might help, but that could cause problems elsewhere-such as on the dance floor.

The BEST idea is to figure out why the null is there/what is causing it, and attack that.  Or you can take random guesses and hope one of them will work.

[Kevin Maxwell]

Thank you for all of the replies.

We went to the Venue on Saturday and made some adjustments to the DJ part of the system. In the DJ feed in the DSP we reduced the level of the Subwoofer feeds so they are not as accentuated as they had been. There is still some cancellation in the booth but now since the sub level isn’t as overkill on the dance floor as long as the DJ doesn’t crank up the bottom end of their feed, it is more reasonable. Still kicking but not ridiculous.

I had brought a couple of 2’x4’ acoustic panels along to test to see if they would affect the sound in the booth.  I tried placing my acoustic panels in different places in the booth and if I put them on the back wall of the booth the Subs came to life in there a little bit more then without them. So to me it sounds like the sub frequencies are canceling acoustically off the walls in the Booth.

I had placed a call to an acoustic consultant that I have been aware of for years and is known by other friends in the audio business. I am not mentioning his name or his company on purpose. I left a message but he never got back to me. He lives not far from this venue and from looking on his website he seems to be reasonably priced. I think he is semi-retired and doesn’t run the company he started that makes a bunch of different types of acoustic treatments. But I am not sure if the venue Manager/part owner of this venue is in a position to spend more money at the moment. 

To answer some of the comments. The DJ part of this doesn’t have turntables but the DJ can bring them and tie into the system. There really isn’t enough room in the booth to set up the standard DJ coffin that a DJ might bring. So if they setup outside of the booth then they might have a skip problem. I am not a DJ and I try not to work with them so I may be using the wrong terms here.   

The butt kicker or more preferably that type of transducer mounted underneath the Booth right where they stand might help. The chances are they won’t be sitting at all. I have one that attaches to a drum stool for use with an electronic drum set and if set right it works great if set wrong it is an annoying butt massage. I got it when a church stopped using an electronic drum set and went back to acoustic drums. I don’t use it at all.

I am not sure that I would say that the booth design was to save money. I think it was just what the owner wanted and had no idea that it wasn’t the best design. The main owner (there are a few people involved) owns the entire strip where this venue was built. ONE of his restaurants is at the other end of this strip. It is very high end, not the kind of place I go to regularly. But the chef of that restaurant once brought a large amount of a Pasta dish to us for lunch as we were working, it was great. 

There is a speaker that the DJs can use in the booth if they want to. There is no place in the booth for a Subwoofer and I would worry that it would interact with the room subwoofers. Also I don’t think the manger thinks this is enough of a problem to pay for the addition of that. I am worried that a DJ might think there isn’t enough low end and boost it to compensate. I realize that the DJ may not listen to the manager telling them to walk out of the booth and just listen to how it sounds in the room.

I probably should have said at the beginning of all of this that they are not really aware of the sub cancellation in the booth. Their issue was how loud the subs are in the room and complaints from outside the venue because it was so powerful in there. I was the one who was concerned that if the DJ in the Booth doesn’t hear the low end in the Booth that they will try and compensate and boost up the low end making it too loud on the dance floor and everywhere else. After we were done with the changes we made, we cranked the system and I walked outside to listen and I didn’t hear any of the music that we were playing outside of the venue. I didn’t try it with the door open to see what the difference was. 
 
So for now we will see how thing go there (after the changes we made) and deal with them if they have a complaint.

[ProSoundWeb Community]