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Author Topic: Adding Subs to Round Venue  (Read 6011 times)

John Oliphant2

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Adding Subs to Round Venue
« on: March 30, 2015, 11:32:26 AM »

I’m upgrading my PA at a Native American dance arena, and want to add subs this spring. The venue is a round gazebo, basically an octagon roof with eight big wooden joists at the perimeter and a dirt floor. The gazebo is about 40 feet in diameter, then 50 feet of grass, then bleachers all around. 

We currently have four JBL CBT 70J/E, pointed 90 degrees apart, driven by a pair of Crown CDi 4000’s.

Either powered or passive subs work, haven’t decided yet. My limitation is that the subs I use need to be relatively small to be unobtrusive. I plan to put the subs directly under the CBT70’s. I don't need a huge thump I just need some low end.

My big concern at this moment, from reading around the forum, is what it’s going to sound like inside that gazebo with four subs on the perimeter. Is there a certain sub design I should choose or avoid to prevent the players inside the gazebo from vibrating into a pulp?  ;D

I’ve been looking at the JBL PRX718XLF, and also read some great stuff about the Danley TH115, but the Danley’s are probably too big for my stage.  Is the THmini worth considering?

FWIW, I have a XTi 6002 available for power, and roughly $5k budget.
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Ivan Beaver

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Re: Adding Subs to Round Venue
« Reply #1 on: March 30, 2015, 01:05:35 PM »

I’m upgrading my PA at a Native American dance arena, and want to add subs this spring. The venue is a round gazebo, basically an octagon roof with eight big wooden joists at the perimeter and a dirt floor. The gazebo is about 40 feet in diameter, then 50 feet of grass, then bleachers all around. 

We currently have four JBL CBT 70J/E, pointed 90 degrees apart, driven by a pair of Crown CDi 4000’s.

Either powered or passive subs work, haven’t decided yet. My limitation is that the subs I use need to be relatively small to be unobtrusive. I plan to put the subs directly under the CBT70’s. I don't need a huge thump I just need some low end.

My big concern at this moment, from reading around the forum, is what it’s going to sound like inside that gazebo with four subs on the perimeter. Is there a certain sub design I should choose or avoid to prevent the players inside the gazebo from vibrating into a pulp?  ;D

I’ve been looking at the JBL PRX718XLF, and also read some great stuff about the Danley TH115, but the Danley’s are probably too big for my stage.  Is the THmini worth considering?

FWIW, I have a XTi 6002 available for power, and roughly $5k budget.
The first couple of questions I have (since I am not familiar with the "sound requirements" of this type of event) are: How loud does it need to go and how low does it need to go?

Without that information-it is hard to suggest any product.

For some style the subs only need to be as loud as the mains and for other styles the subs need to be at least 20dB (or more) louder.

That makes for a HUGE difference in the amount  of or type of sub needed.

I am also confused as to where you plan on placing the subs.  You said under the mains-and another place you said on the perimeter?

I "assume" (hope) you plan on putting the main in the center facing out.

But the subs cannot be under the mains and on the perimeter at the same time.

Some explanation would help
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Ivan Beaver
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John Oliphant2

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Re: Adding Subs to Round Venue
« Reply #2 on: March 30, 2015, 01:48:35 PM »

The first couple of questions I have (since I am not familiar with the "sound requirements" of this type of event) are: How loud does it need to go and how low does it need to go?

Without that information-it is hard to suggest any product.

For some style the subs only need to be as loud as the mains and for other styles the subs need to be at least 20dB (or more) louder.

That makes for a HUGE difference in the amount  of or type of sub needed.

I am also confused as to where you plan on placing the subs.  You said under the mains-and another place you said on the perimeter?

I "assume" (hope) you plan on putting the main in the center facing out.

But the subs cannot be under the mains and on the perimeter at the same time.

Some explanation would help

Sorry for the confusion. I plan to place the subs under the mains. I guess I was referring to the perimeter of the octagonal gazebo, which is where the mains are located. So, subs located at the four poles, North South East West, facing out, each about 15-20 feet from the center.

This is tribal drum music. Here's a rough recording:
https://www.youtube.com/watch?v=m85gq2MS2m0

I've attached a photo of the venue. You can see the mains hanging on the gazebo. (That is not the mixer I use, lol)

The SPL next to the drums is impressive, but I don't need to reproduce all of that. This isn't concert volume, it's moderate or a little loud, and at the FOH I can have a conversation with no trouble. With better balance I think I can reduce the volume so the dancers don't go deaf as they pass the mains.

« Last Edit: March 30, 2015, 01:54:04 PM by John Oliphant2 »
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Tim McCulloch

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Re: Adding Subs to Round Venue
« Reply #3 on: March 30, 2015, 02:05:53 PM »

Model a circular placement in Meyer's MAPP, using the 650 sub.  You'll see some interesting things happen, most of them you won't like.
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Corey Scogin

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Re: Adding Subs to Round Venue
« Reply #4 on: March 30, 2015, 02:11:59 PM »

Model a circular placement in Meyer's MAPP, using the 650 sub.  You'll see some interesting things happen, most of them you won't like.

Definitely model it yourself to see.  Here's a quick one from the Danley Direct software (using TH118's but the principle is the same) modeled at 63Hz.  The smaller square approximates your gazebo, the larger approximates the grass area.  The first image is with a sub below each main.  The 2nd is with the subs clustered in the center.  Red = loud, blue = quiet.
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John Oliphant2

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Re: Adding Subs to Round Venue
« Reply #5 on: March 30, 2015, 02:28:03 PM »

Definitely model it yourself to see.  Here's a quick one from the Danley Direct software (using TH118's but the principle is the same) modeled at 63Hz.  The smaller square approximates your gazebo, the larger approximates the grass area.  The first image is with a sub below each main.  The 2nd is with the subs clustered in the center.  Red = loud, blue = quiet.

I'm afraid to ask what black represents... ???
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Ivan Beaver

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Re: Adding Subs to Round Venue
« Reply #6 on: March 30, 2015, 05:19:15 PM »

I'm afraid to ask what black represents... ???
LOUD!!!!!!!!!!!!
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Jerome Malsack

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Re: Adding Subs to Round Venue
« Reply #7 on: March 30, 2015, 07:59:26 PM »

Looking at the four speakers  top, bottom, left and right. 

I wounder because of the wave length if there will be both phase and other issues.

Starting on the top  and move one speaker 90 degrees left and same frequency and then the opposite speaker bottom and distance 180 from the speaker  so Yeah the physics comes to play based on frequency and distances.  Did the program take this into account on the screen and model ?

There will be sound at the center and phase ??  But this will all be dependent on the distance / frequency.  I feel the closer the subs are placed to each other the better you sub will sound and the easier it will be to run. 
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Tim McCulloch

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Re: Adding Subs to Round Venue
« Reply #8 on: March 30, 2015, 09:40:19 PM »

Looking at the four speakers  top, bottom, left and right. 

I wounder because of the wave length if there will be both phase and other issues.

Starting on the top  and move one speaker 90 degrees left and same frequency and then the opposite speaker bottom and distance 180 from the speaker  so Yeah the physics comes to play based on frequency and distances.  Did the program take this into account on the screen and model ?

There will be sound at the center and phase ??  But this will all be dependent on the distance / frequency.  I feel the closer the subs are placed to each other the better you sub will sound and the easier it will be to run.

In the 2 examples Cory posted you can see that the maximum LF spl is right where the drum is.  Considering the reflective cone of the gazebo roof and I think you'll have a recipe for sonic problems if you create a confluence of sub frequencies.

The pattern you see in Cory's first example is a matter of physical spacing between the subs and the center frequency being modeled.  Even if there were some kind of time-domain issue with the subs that does not show in the prediction, from a general physics standpoint the coverage shown is validly represented.
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Luke Geis

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Re: Adding Subs to Round Venue
« Reply #9 on: March 30, 2015, 11:21:04 PM »

You have a challenge on your hands, that is for sure. The ideal thing would be to keep the subs in one spot that would be of equal distance from all the other speakers. That means lots of subs right where you don't want them. The other practical approach would be to place them next to each speaker, but that will leave you with comb filtering and sporadic coverage and still leave a bit of sub energy where the drums are. So there is no two ways around that.

Looking at the venue though you have entry ways. If you can line things up so that the nulls are pointed more to the opening between the grandstands you can at least utilize the energy. You have to do models at several frequencies to see how it may act. Sadly, as much as I would rather have the subs centralized, placing them next to the other speakers seems it may be the best option.
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Re: Adding Subs to Round Venue
« Reply #9 on: March 30, 2015, 11:21:04 PM »


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