Cardioid Subwoofer Setups

  1. #1 by Mark Norgren on 01-14-2018
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    Cardioid Subwoofer Setups

    Just finished reading a great article, new to me at least, and would like to try this for our next couple of shows.

    http://www.fohonline.com/ci/31-tech-...er-setups.html

    1. Place one sub about a quarter-wavelength behind the main sub.
    2. Reverse the polarity of this rear “cancellation” sub.
    3. Delay the cancellation sub by about a quarter wavelength (4 to 5 ms)
    4. Turn down the cancellation sub by about 3 dB.

    Our PA contains 4 QSC KW181's,subs, so I should be able to set this up. We also use a M32R and a DL32 stage box that will sit on stage. This particular stage is about 20 feel deep. I'm a bit confused as to how far to place the cancellation sub behind the front facing one? Maybe I'm reading this wrong. Is the cancellation be caused by the delay sent to the cancellation sub? Can you stack the subs? A bit confused, not a sound engineer, just a guitar hack!

    Can someone walk me through the routing , sub placement, delay, and wiring from the stage box? I really appreciate your help! Thanks and really looking forward to going this a try!
  2. #2 by Mark Norgren on 01-14-2018
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    Our Current Scene

    If you care to look or make suggestions, this is our current scene.

    Kevin Maxwell was a gent and helped me out a ton! Thanks Kevin if you are out there!
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  3. #3 by Mark Norgren on 01-14-2018
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    Routing

    How about this?

    I found an Output Delay menu under routing. I went ahead and assigned mix bus 11 and 12 for the delayed subs. I used 5ms of delay and was pleasantly surprised to see that it told me 5.6 feet! Under each of the mix busses, I pushed the levels up to 0 db to each of my channels that will send sub frequencies.

    Not sure how I will control the levels of the delayed subs? I think I might need to use these like an aux feed sub, just not sure how they will work with the mains getting levels from the main fader?

    Can I use a DCA to control the levels?

    Kind of fun trying to figure this one out. As you can tell, I'm still a guitar nerd at heart!
  4. #4 by Paul Vannatto on 01-14-2018
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    Hi Mark,

    I had a look at your scene. Why not use the M/C bus. Send what you want to this bus and set the Setup, Config, M/C depends on Main L/R.

    For routing, simply assign both outputs 11 and 12 to the M/C, then go to the Output delay screen and delay the desired output (11 or 12) that feeds the reverse sub.

    If you want to just send all Main L/R to these subs (not my preference), then send the Main L/R to a matrix, then assign that matrix to the Outputs 11 and 12 and set the delays accordingly.

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  5. #5 by Mark Norgren on 01-15-2018
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    New Scene

    Paul,
    You lost me. I guess I'm not sure on the routing piece. Please take a look at this new scene and let me know what you think. Feel free to make changes and send it back if you want. I really appreciate your help!
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  6. #6 by Craig Fowler on 01-15-2018
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    Cancellation happens because the subs are omni directional. The idea is that the sound traveling out of the front sub also travels out the back of the sub (because it's omni directional,) and reaches and sums with the sound coming out of the other sub. If you can get the right polarity inversion\delay\placement, you can make it such that the waves from both subs intersect when they're exactly 180degrees out of phase with each other. If they're exactly 180degrees out in a specific spot (behind the front sub,) when they sum, they'll sum to a null (0,) ie cancellation in that spot. This means you get bass in front of the sub, but not much behind it (under\firing back at the stage.) As a bonus, the sound emanating from the rear sub (because it's also omni-directional) can arrive in-phase with the sound from the front sub in front of the front sub, meaning you actually get a bit of a boost to sub level out in front, which is good. You end up with less bass on stage, which is good for all sorts of reasons. As you've gone from an omni directional LF output to an output with a null at the back, you've essentially made the sub array's output pattern cardioid, hence "cardioid sub." Yes, you can stack them. Do two stacks of 2. The subs on the bottom of each stack (these will be your "cancellation subs") pointing towards the stage (I know it seems counter-intuative that to get rid of bass on the stage you point the subs at the stage, but the polarity inversion and delay will fix that.) The subs on top should point toward the audience.

    Your scene is a bit of a mess. I see you've got some vox channels routed straight to LR, some to a drum monitor group which is then routed to LR, and some to the group+LR. Andy's monitor is also set to output pre-fader (and is fed to LR?,) so his bus master won't have any effect on what he hears. You've also got the drum monitor routed to LR. That aside...

    To get maximum rejection (and minimum lobing (power alley if you space the subs out)) I'd mono-cluster all 4 subs in the centre of the front edge of the stage, run them aux fed (that's what the console's M\C bus is there for,) then use the console's own processing (or ideally dedicated speaker management) to deal with the polarity\delay\xo\eq\level for tops and subs.

    Assuming no dedicated speaker management:

    Channels with useful LF content (kick, bass etc) routed to the M\C bus at unity, and also assigned to LR. M\C depends on LR in Setup>Config. Channels without useful LF content (eg vox, guitars) assigned to LR (not M\C.)

    M\C master and LR master up to unity (you can use the M\C master to offset the subs from the tops to balance things out, and use the mainLR fader to control the overall level of the whole PA.)

    M\C bus routed to a matrix (at unity, post-fader.) The matrix will be for the "cancellation" (bottom) subs. Mtx master fader set at -3dB (this is the -3dB cut the article mentioned.)

    Depending on what the subs do with a full range signal, where their XO is, and how your tops integrate with that, you might want to use the eq on the M\C bus to knock off the HF, so the M\C bus\matrix is only outputting the LF you want from the sockets.

    Assuming no daisy-chaining of speakers:

    Set up 2x outputs to be fed from the M\C bus, which will feed your front (top) subs. Set up another 2x outputs to be fed from the cancellation matrix, and invert their polarity (this is where you apply the polarity inversion setting from the article.) These outputs will feed the cancellation (bottom) subs. Then go into the output delay settings and delay those cancellation subs' outputs (the delay setting mentioned in the article.)

    ^That gets you your cardioid setup. Leave the polarity switches and the gain levels on the subs themselves alone: the console is doing polarity inversion and the -3dB cut. Just use the gain pots on the subs to get the subs loud enough for the venue with your gain structure. They should be set at the same level on all the subs.

    Route mainL and mainR to another 2 analogue outputs, leave them as normal in terms of polarity and delay. You can use the mainLR's eq to knock off the bottom end if your tops are not built to integrate nicely with the subs in terms of XO. If you want you can then add whatever delay you need to all outputs (but don't forget the extra few ms on the cancellation subs to maintain the cardioid output) to align the whole PA to the backline.

    HTH

    Last edited by Craig Fowler; 01-15-2018 at 06:18 AM.
  7. #7 by Kevin Maxwell on 01-15-2018
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    - Mark Norgren wrote View Post
    If you care to look or make suggestions, this is our current scene.

    Kevin Maxwell was a gent and helped me out a ton! Thanks Kevin if you are out there!

    You are welcome. I am still around.

    I see that you posted this in the Midas and the Behringer forums and it looks like you have gotten more answers on the Midas forum. You might find that you will get more answers if you read and then post over on the http://forums.prosoundweb.com/index.php . Look for the section about subwoofers. And I am sure that you know that not all subs are created equal.

    It depends on the reason for doing the Cardioid subs as to what might work for you or if you should even try it. From what I have read when using the same number of subs but changed to a cardioid configuration you will get less and different sound out front, besides some cancelation in the back. I have wanted to play around with the different sub configurations and see what the results are. If you are having a problem with the subs impacting on stage too much, then that is one reason to try cardioid. If your problem is uneven coverage in the house I don’t think that is the solution you want.

    The problem with most sound systems is the left right stacks of speakers with the tops and the subs. This separates the subs and creates the uneven coverage and it usually results in a really hot spot (for the sub content) upstage center. One small trick but not a real solution is to slightly delay the subs on one side of the stage. With this you will be able to change where the peaks and nulls are. I did that in one church because we couldn’t change anything about the sub placement but it changed where the problems were in the room. It didn’t fix it but it moved it to places that weren’t as critical. I think I have even tried just changing the level of one side in relation to the other and get a similar affect.

    As others have said it is better if you can lineup the subs across the front of the stage. If the stage allows for that. Or just put all the subs on one side of the stage. I convinced a small church that had 2 QSC subs (I think they have a 12 in each one) to put both of them on one side in the front. They now have much more even coverage then when they were split and in general it is very hard to hear that the sub is only coming from one side. It is a bit of a one note sub though. It depends a lot on what the setup will allow. I work for one company that I would really like to stack the subs across the front of the stage but we use then on the left and right to stack the main speakers on. So that is out for now.

    I was helping out at an event where the sound company brought 4 or 6 cardioid subs and put them across the front of the stage, the stage was high enough and I think they may have even been under the stage. This was outdoors. These subs had (I think it was) 6 speakers in each one to make them cardioid. When testing things I walked around and was surprised at the control of the bottom end it was mostly just covering the seating area, it fell off a lot to the sides. I don’t remember if I had a chance to walk behind everything. We did set off a car alarm on a car that was about 200feet away when testing. They were self-powered, big heavy and expensive.

    So to do cardioid or not, it depends.
  8. #8 by Mark Norgren on 4 Weeks Ago
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    Not Cardioid, Reverse Delay?

    If I hear people correctly, it kind of sounds like I might be better off rear facing, reverse polarity, and delaying two of the four subs? WE don't have the ability to put them all four in front of the stage. I have tried to straighten up a few of the things in the scene. Please remember that my knowledge is limited, yet with your help, I am learning every day. Your patience in much appreciated. I have posted a new scene with some changes to get another look. Thanks so much!

    a. Fixed the monitor sends on Andy and Drums.
    b. Have the delayed subs set up in Bus 11-12, going to M/C
    c. Subs will be stacked, two per side, with one per side rear facing, reverse polarity and delayed?
    d. DCA's straighter out.


    Side question: Can I just hook my MacBook Pro up to the board with a USB DN32 cord? Will the computer control the board real time or is that just a send to the computer? I also want remote control with an iPad, have router already working.
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  9. #9 by Craig Fowler on 4 Weeks Ago
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    Routing>Out1-16:
    Andy's monitor is still outputting pre-fader (it's blue, not pink like the rest.) Well done un-assigning it from LR though.

    Muting\lowering DCA7 will kill a lot more than your FX.

    Some channels you've pushed up in M\C which is good, but they're not actually assigned to the M\C bus. Select the channel, press the "Mono\Centre" button in the "Main Bus" section of the channel strip so it illuminates orange like the "main stereo" button adjacent to it.

    Keep the channels assigned to subs as Kick, Bass, Floor Tom, Keys (if they're electric,) tuba (if you've got one: horns are mentioned,) and playback. You don't need guitars, snares, and rack toms in the subs. You've got some channels pushed up in M\C, some pushed up in bus11\12, and bus11\12 routed to M\C, but no channels routed to M\C or bus11\12. Running channels>bus>M\C is one step more complicated than it needs to be.

    Given you haven't inverted polarity in the out1-16 tab, I assume you're doing that on the subs themselves. Same with the -3dB offset. I don't see any delay dialled in anywhere.

    Fair enough if the venue\stage precludes you from clustering the subs in the centre. You can only do what you can do. It means you'll end up with a power alley (a lobe with lots of bass down the middle of the room, then nulls either side of the lobe, then more lobe and null "alleys" spreading outwards, due to phase cancellations. Clustering the subs (even off to the side, instead of in the middle) would mean more even coverage. If the mix position is centred between the subs, the bass will sound good and you'll balance the tops against that. Move a few metres to the left or right, and the mix will sound top-heavy as the bass has dropped off. If you try to balance subs and tops based on the nulls, then anyone standing in a lobe will think there's too much bass, and intelligibility will suffer.

    If you've got spare channels you could do a Dave Rat solution and run 2 channels for each of the LF instruments. You hard pan them (so you've got KickL and KickR,) and eq them differently, so that they're dissimilar (of course this means running subL and subR instead of using the M\C bus.) When they intersect, their signals are different due to the different eq settings, which means there's nowhere near as much cancellation.

    Yeah, getting even LF coverage s a challenge, especially if you're outdoors. Usually the solution is to throw more subs at it.

    This article explains the problem of having subs on either side of the stage: different areas in FOH are subject to cancellation of different frequencies, so the bass sounds good in some areas and not in others. The further apart the subs are, the more problems there are (which is why clustering them is useful.) Attempting to fix it with delays just moves the good\bad spots around (which can be good if there's an area you don't need to sound as good,) but it doesn't actually solve the problem. This applies regardless of whether the subs are cardioid or not. It might be better to run 4 subs evenly spaced across the front of the stage to minimize the power alley effect and deal with an omni-directional output, rather than spreading them to the edges and running cardioid. It really depends on the stage+venue.

    The DN32 is only for 32x32 audio transport and some midi\clocking etc. You can't control the whole console over it using Edit. What you should be doing is plugging your router into the ethernet socket on the rear of the console, connecting your ipad wirelessly to the router, and connecting the macbook to the router over ethernet\wifi.

    PS, un-assign your RTA mic from LR.

    Last edited by Craig Fowler; 4 Weeks Ago at 07:18 AM.
  10. #10 by Mark Norgren on 4 Weeks Ago
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    Wow!

    Thanks so much Craig for your time an expertise! I am getting more familiar with things as I move through this process.

    a. I am color blind, so the pink blue thing was tough! Good thing my wife was close, so I found that one! Andy's monitor should now be post-fader.

    b. I unassigned some of the channels to the DCA 7, not sure what I was thinking.

    c. I have the delay (.5 ms on Bus 11 &12) set up in the Output Delay section of the Routing Tab. I have Reversed the Polarity on the Output Tab as well. I will reduce the reverse sub 3db on the physical sub itself.

    d. I took a few channels off the LF M/C Busses.

    e. Do you have any suggestions regarding the effects section and how I am using Reverb's and Delay's?

    Again, thanks so much!!

    Other than those, I think it may be close. Surely much better than it was before?
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