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Author Topic: Adding extra subs to church installed system - placement?  (Read 9086 times)

Tim McCulloch

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Re: Adding extra subs to church installed system - placement?
« Reply #10 on: February 29, 2012, 01:02:11 pm »

As long as your install subs and the tannoys are both front loaded bass reflex boxes they should play fairly nice together without serious delay issues. The easiest and therefore the first thing you should try is as you thought, stacking the tannoys on top of (or next too) the installed subs so that they couple acoustically. You will instantly hear an increase in low end. If you do NOT hear an increase, it will be on to plan B. Good luck!
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John Penkala

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Re: Adding extra subs to church installed system - placement?
« Reply #11 on: February 29, 2012, 04:36:57 pm »

In our church (seats 750) we have two 18 inch subs on either side of the room in installed cabinets.  We also own two more 18 inch subs in mobile cabinets with castors (Tannoy).  I also have some spare amps.  I want more low end punch for our contemporary worship services.  How can I use the spare amps, my existing mobile Tannoy subs and "add" them to my church system?  I can bridge signal from the existing system to the other amps I think and get speaker cables to connect them.  Question is where do I put the portable subs?  My installed subs do not move.  I could put the Tannoy on top of installed subs or next to them or someplace else altogether.  I also have existing digital delay units at my disposal.  Have been reading about swapping polarity and adding delay to get a sort of "array" approach though I do NOT have room to place subs one in front of the other.  Thoughts or advice?

Steve,
         I'll echo what the others have said about mixing unlike subs. It is hard enough to get subs of the same model to play together well. They will have different frequency and phase characteristics. You can do more harm than good. You could accidentally put that attitional sub energy on the stage while causing nulls in the audience. Remember, a 100hz wavelength is 11.3ft and a 60hz is 18.8 ft. These wavelengths are much longer than say 500hz (2.26ft). They will add and subtract much more evidently than mid-hi frequencies, that is provided your top boxes are deployed in the space properly. You have to have an understanding of the problem before you try a solution. The approach should be to optimize what you have first. There are ways to optimize a system with measurement equipment like Smaart and SIM. This can be tough even for the experienced. Before I added anything, I would look at the cabling from the console to the speaker, making sure there are no polarity reversals, etc. Then I would listen to the system for coverage making a note of any hotspots or nulls. Go on stage as well and listen. Sometimes a couple of milliseconds of delay on the quiet side sub is all it takes. Sometimes not. 
     A few years ago I got a call from a sound company to do a "post mortem". The sound company had a rig out at a festival when a certain knowledgeable FOH engineer who mixes for his wife, at sound check mentioned to the onsite tech that the subs weren't right. The subs were McCauley's version of an SB1000. As he increased volume on the system the subs got to a certain level and didn't keep up with the rest of the system. I get to the shop and the owner says that 1 driver in each double 18 box was blown. I knew right away what it was.........the onsite guys had wired them with NL2 cable and not NL4. Only one driver was getting power! One of the opening acts had pushed the rig to what should have been an acceptable level resulting in blowing the 1 driver in each box that was getting power.
     Wouldn't it be funny if you found a wall patch or a drive line wired out of polarity was the problem?!

     On the bright side, if you have access to the space, you can experiment.  You can add the subs, play with their positioning, and learn by trial and error. I'm not trying to take the wind out of your sails. I just want you to get a better understanding of the conditions you're trying to correct.

JP
« Last Edit: February 29, 2012, 09:25:47 pm by John Penkala »
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duane massey

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Re: Adding extra subs to church installed system - placement?
« Reply #12 on: February 29, 2012, 06:30:16 pm »

Experiment. Use those flaps of skin on either side of your head. If you can't get what you want, then go to plan B, with checkbook in hand.
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Duane Massey
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Steve Carpenter

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Re: Adding extra subs to church installed system - placement?
« Reply #13 on: March 01, 2012, 10:20:04 am »

Experiment. Use those flaps of skin on either side of your head. If you can't get what you want, then go to plan B, with checkbook in hand.

JP -  Thanks for the thoughts and anecdote.  I'll try & keep all of that in mind.  I don't have access to analytical computer tools but good reminders on wavelength, etc.  I'll listen extra carefully as you suggest.

Duane - At this point I think I'll do as you suggest.  I have lots of access to the space and equipment so I'll experiment and use my ears and an SPL meter initially to see how it all sounds.  I can work with rehearsals live as well and see if I can get a better overall sound.  Thanks very much to all for your patience with me and good practical advice. 
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Tim Padrick

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Re: Adding extra subs to church installed system - placement?
« Reply #14 on: March 01, 2012, 11:48:47 pm »

An ounce of experimentation is worth a pound of conjecture.  Try 'em here, try 'em there, and see what you get.
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Scott Carneval

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Re: Adding extra subs to church installed system - placement?
« Reply #15 on: March 02, 2012, 12:29:13 am »

Since no one else pointed this out I guess I will...M7CL, XTA, Crest, all of that tells me you have a very expensive, high quality system that was most likely designed, installed, and configured by someone who knew what they were doing.  Why on earth do you feel it necessary to tamper with it?  If you want to add a pair of subs, call the contractor and explain what you would like to do.  It might cost more up front, but I promise it will sound better in the end and save you money in the long run if you let them handle it. 

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brian maddox

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Re: Adding extra subs to church installed system - placement?
« Reply #16 on: March 02, 2012, 08:17:41 am »

...a certain knowledgeable FOH engineer who mixes for his wife...

now who on earth could you be referring to...  :)  i suspect said mystery man wouldn't mind this phrase on his business cards...

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Brad Weber

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Re: Adding extra subs to church installed system - placement?
« Reply #17 on: March 05, 2012, 07:42:11 am »

Thanks for replying, I'll try to do better at providing information.  We have a digital M7CL48 board sending signal to an XTA DSP which provides EQ, delay and crossover.  We use all Crest FA901 amplifiers (see attached) for driving a first arc of Tannoy 12 inch two way speakers.  8 across L-R-L-R etc. and a delayed arc for 8 more smaller Makie two way speakers.  We have two 18 inch subs with mono signal on either side of the stage.  The right sub seems to have a small amount of hum.  I am exploring whether or not there would be improvement in the low end by adding two more Tannoy 18 inch subs I have with two more FA901 amplifiers.  Looking for low end punch I guess might mean Thud or punch.  Clearly if I experiment with sound by doubling my sub woofer drivers I will be looking for more sound below the Crossover setting (I think it is at 110 but not positive).  In any case, I wanted to use my ears as the ultimate measure of success so was looking for suggestions on placement and now I could use some validation on cabling the signal input to the two new amps I am proposing.
I agree with Scott that this sounds like a rather complex system, especially for a 750 seat church, however we have no idea how well the system fits the room or what the actual speaker models are and the use of Tannoys for the main system in conjunction with Mackies for the delay ring is a bit unusual.  The four L/R pairs in each of two rings with just two subs located left and right seems to mean that potentially everyone hears a different combination of left and right mains and left and right subs with no two people hearing the same thing and some possibly being quite different.

Before you go modifying the system you may want to first document all the equipment models, how everything is wired and the settings for the processor.  If it was a professional installation then such documentation should have been provided, although it may have been 'misplaced' at some point.

I think it is important back to Dick's question of what you are really trying to do.  'Punch' could relate to and be affected by many things.  Best case, adding the two extra subs would give you 3-6dB more sub level but is that added level alone really addressing the problem?  Again, we don't know all the products involved but I am not surprised that two single 18" subs would have difficulty keeping up with 8 mains and 8 fills.  At the same time I would also guess that right around crossover frequency, which is apparently unknown, you might have all sorts of interesting interactions going on between the subs and mains and between the multiple mains.  And that is not even considering the potential effect of the XTA processor settings or any settings on the M7CL or the sub locations or the room itself.  It makes sense to establish the goals before addressing how to implement a solution.

I checked my existing sub signal input and noticed the input comes from the XTA via XLR single connection to the first sub amp which is setup in Bridge mode.  I see the installer used spade connections to get signal to the second amp but he dropped the ground on the second amp which is in the same rack.

I am proposing adding two more identical amps and thought I could just add more spade connections to deliver signal to the two additional amps which would be in the adjacent rack (not the same rail).  I tried that with one amp and got more hum on the existing subs so either I have a bad amp or a ground problem I am not handling properly.  I am attaching pictures of the two existing amps to show the signal wire connections and then one picture of the speaker connections in bridge mode.
How did you wire between the two amps?  Did you also drop shield at the input of the second amp?
« Last Edit: March 05, 2012, 01:39:00 pm by Brad Weber »
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brian maddox

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Re: Adding extra subs to church installed system - placement?
« Reply #18 on: March 05, 2012, 10:35:18 am »

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brian maddox
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Re: Adding extra subs to church installed system - placement?
« Reply #18 on: March 05, 2012, 10:35:18 am »


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