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Author Topic: Subwoofer Location Discussion  (Read 4079 times)

David Haile

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Subwoofer Location Discussion
« on: September 28, 2004, 11:09:24 am »

We're designing a new 350-seat nearly traditional chapel-style peaked roof sanctuary.  The sound consultants have spec'd two 18" subs in the wall on the floor on either side of the wide stage.  This puts the subs about 50' apart.  I think it will be a comb filtering nightmare so I'm pursuing alternate locations.

The easiest location is on the wall behind the stage on the outer edges of the stage - puts the speakers 35-40' apart.  Better, but not perfect.  Any closer together and they start getting behind microphone locations.

The other location is on top of the wall behind the stage - maybe 9'-10' above the stage.  Coverage would have to be controlled to keep the output out of the front center mic, but all the other mic locations should be OK.  I can also just roll off the front center mic at 150Hz.  The two main speakers are on a truss just above and in front of the stage, about 16' off the ground and 16' apart.  I'm thinking this location for the subs with a slight delay on the mains will be my best choice.  I worry about the lack of a floor next to the subs.

The wall behind the stage is angled on either side with an 8' hold in the middle where it goes back to a full height rock wall that contains a cross and a window way up high.

Thoughts?
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Tim Padrick

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Re: Subwoofer Location Discussion
« Reply #1 on: September 28, 2004, 09:49:30 pm »

Subs split: bad.  A big power alley and lots of dead spots.

Behind the stage: Very bad.  You'll have to delay the tops so much (to get them in time with the subs) that (time wise) the system will be behind the mics.  This will make house's spill very bothersome to those on stage.   (My system is all front loaded.  To get the tops aligned to the subs requires a delay of 12.5 feet.)

On the truss: good.  Not as good as being centered on the floor, but the next best thing.

(Also make sure that having the tops centered and splayed would not be a better option than having them split.

(For links to articles on The Power Alley and Boundary Cancellation, go to http://www.padrick.net/LiveSound/SubwooferInfo.htm )

David Haile

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Re: Subwoofer Location Discussion
« Reply #2 on: September 29, 2004, 12:28:56 am »

I just looked at the drawings again tonight.  The place where I want to put the subs is in a wall 7 to 8 feet above the floor of the stage.  They will be behind and above vocalists who will probably be 10' from that same wall.  My main speakers are full range - down to 50Hz.  I hope to keep the subs 80Hz or lower.  Please tell me why this won't work!  This is the Only Place in the room where I can locate subs less than 45' apart.

The band is not in the coverage of the subs - just a few vocalists on one side assuming we stay with the same configuration that we presently use.  I can move the vocalists if I have to.  This location puts the speakers about 14' apart (that's a guess) and only 8' behind and 10' lower than the main speakers.  The room is 35' high at the center with the main speakers at 16' to 18' high mounted on a truss that is open in the middle.  A center cluster just won't work and subs on the trusses is not an option.

I know it isn't ideal, but we're not a 110db rockin' church nor are we an organ-centric traditional church.  We're in the middle and we've designed a sanctuary with a more traditional look than the usual box modern church.  I'm 100% behind the design - just trying to plan speaker locations so we can host Audio Adrenaline when they are touring the smaller churches in Colorado.  Smile
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Tom Young

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Re: Subwoofer Location Discussion
« Reply #3 on: September 29, 2004, 05:49:29 pm »

I wouldn't worry too much about combfiltering at subwoofer frequencies, which vary from 11 ft (at 100Hz) to 37.75 ft (at 30Hz) and tend to couple togther rather nicely.  A 50' spread will yield a comb filter first/primary peak 20Hz and the first null at 10Hz (well below your subwoofer operating range). You MAY have problematic standing waves, however, depending on the room dimensions.

The LAST thing you should do is move the subs behind microphone positions and so far out of alignment with the rest of the system.  You also should try to keep the subs near to the floor and/or walls, as this provides additional "free" gain.

If you really are unsure, once your sanctuary is open and running try the subs in several positions  and then install them once you've decided where they sound best.
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Tom Young, Church Sound section moderator
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Al Limberg

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Re: Subwoofer Location Discussion
« Reply #4 on: September 29, 2004, 06:19:11 pm »

Purely as an exercise in throwing a couple other thoughts into the mix, if the subs were run from an aux, placing behind vocal mics wouldn't be a problem (altho that certainly doesn't solve the time alignment problem - then again, you might even get away with placing them at floor level then getting the 'free' output available from coupling).  Another thought - why not place both subs on the same side?  Since you aren't a high volume sort of church, they aren't apt to draw attention to themselves due to high output and it solves the power alley/cancellation dilemma. Thought number 3 - send Tom a round trip airline ticket or a set of prints along with a blankish sorta check and let a pro handle it. ?;o)

Al  
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David Haile

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Re: Subwoofer Location Discussion
« Reply #5 on: September 29, 2004, 06:23:40 pm »

???  Don't worry about it?  Isn't this one of the big Gotcha's in system design?  Please explain.

What about mounting them in the walls on the end of the stage and reducing the distance between the speakers by 10'?  No mic's will ever be there because the stage angles into the wall at that point.

I suspect I don't need more gain on the low frequencies.  Our system designer/consultant guy says the room is small enough and our subs big enough that we would be fine with only one if there was a place to mount it in the center.

It might be possible to do as you suggest and try out the subs in a couple of different locations.  I have to do this after the walls and electrical and before the carpet and pews are installed.  That's in April!
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David Haile

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Re: Subwoofer Location Discussion
« Reply #6 on: September 29, 2004, 06:36:12 pm »

Al Limberg wrote on Wed, 29 September 2004 23:19

Purely as an exercise in throwing a couple other thoughts into the mix, if the subs were run from an aux, placing behind vocal mics wouldn't be a problem (altho that certainly doesn't solve the time alignment problem - then again, you might even get away with placing them at floor level then getting the 'free' output available from coupling).  Another thought - why not place both subs on the same side?  Since you aren't a high volume sort of church, they aren't apt to draw attention to themselves due to high output and it solves the power alley/cancellation dilemma. Thought number 3 - send Tom a round trip airline ticket or a set of prints along with a blankish sorta check and let a pro handle it. ?;o) Al


3 - I would happily hire Tom except we already have a consultant who recommends the same thing - one sub per side - 50' apart.  I'm trying to figure out if there's another way to do it.

2 - Two subs on one side?  That is weird.  I might as well put them in the back above the entrance if I'm going to do them on one side.

1 - Time Alignment?  Why is my proposed 10' below/10' back solution (with a small delay on the mains) any worse than having the subs 16' below and 16' to the right of the mains?  At least the speakers would be almost vertically aligned if not horizontally.

DWH
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Karl P(eterson)

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Re: Subwoofer Location Discussion
« Reply #7 on: September 29, 2004, 10:33:47 pm »

1. The time alingment is (mostly) for the Y axis (linear distance in deapth) thus, side to side and up and down does not matter anywhere near as much as deapth. 10 down 10 back is MUCH worse than 16 down 16 over

2. Two subs on one side is not weird, and you could put them in the back if you wanted, but it would be a bit weird as some people would be able to localize the bass as coming from behind them. In truth I would take putting both on one side over one on each side and long before i stuck them up behind the performers in any way or shape.

3. If the only option is one on each side, it isn't the best, but it works, better than up behind the performers.

Karl P
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David Haile

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Re: Subwoofer Location Discussion
« Reply #8 on: September 30, 2004, 02:45:35 pm »

Tom Young wrote on Wed, 29 September 2004 22:49

I wouldn't worry too much about combfiltering at subwoofer frequencies, which vary from 11 ft (at 100Hz) to 37.75 ft (at 30Hz) and tend to couple togther rather nicely.  A 50' spread will yield a comb filter first/primary peak 20Hz and the first null at 10Hz (well below your subwoofer operating range).


Hey - I found your article on using Aux for subs!  OK - I believe you.  I'll have them run it with the big spread between the subs.  The place where I wanted to move them is always available if I want to try it in the future.
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Mike Sveda

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Re: Subwoofer Location Discussion
« Reply #9 on: September 30, 2004, 04:35:32 pm »

Can the subs be out in the open and then be closer together? Our 4 subs are sitting right out on the floor on either side of the alter steps. 4 EAW SB250 boxes for all too see.  Nobody pays any attention, jsut 4 big black boxes on the floor....
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David Haile

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Re: Subwoofer Location Discussion
« Reply #10 on: September 30, 2004, 05:27:32 pm »

Does that work in your Mom's church?  It would be odd - these things are 25" cubes.  Mom would not approve, but Mom hates our music (true).

Maybe I could put a cushion on it and call it a foot rest, or put a back on it and Viola, it is a chair.  I could put large eyes on them - God is watching you.
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Mike Sveda

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Re: Subwoofer Location Discussion
« Reply #11 on: October 01, 2004, 01:29:22 pm »

Here's a pic of our sub locations:

http://img90.exs.cx/img90/5882/129933344ccdEON_ph.jpg

Do you have a pic of your church?
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David Haile

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Re: Subwoofer Location Discussion
« Reply #12 on: October 01, 2004, 11:33:10 pm »

We're still in the design/layout phase of our new sanctuary.  I'm not jumping the gun because we're breaking ground in about one month, the whole sanctuary is on a concrete slab, all wiring and A/C will be in conduits in the concrete.  The concrete will be poured by Thanksgiving!

Now that I've seen it, I think I like that idea of a movable sub.  I'll have them frame the original spots, run the wire to those locations, then close it up and put a speaker connector on the wall.  That way I can try all sorts of options and still keep the option open of putting them in the wall.

Do I need the frog, lunch timer, and coffee thermos?
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