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How to run a center PA channel?

Discussion in 'Sound, Music, and Intercom' started by Wolfgang, Nov 23, 2008.

  1. Wolfgang

    Wolfgang Member

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    So this year, I've been trying to get our in-house pa up to spec (it was really in pretty bad condition). Started off with getting the feedback frequencies more or less tuned out and it finally wired in stereo, which brings me to my current problem. We have one center speaker, a left, a right, and two subs. Right now, the L out from the board goes to the left speaker, the R to the right, and the mono out to the center speaker and the subs (Everything has it's own amp channel obviously). However, stereo separation is really not very good. The director and I would really like to be able to pan certain effects/actors for more spacial effect, and you can barely hear the pans right now because of the center speaker. What would be a better way to wire the center speaker? A good multi-channel pa mgmt unit would be great, but that's probably not in the budget at least until after the current show. I think the effect that I'm looking for is something along the lines of if the pan knob is halfway between center and left, the center speaker should be putting out half the output that it would be if the knob were in the center.

    Any ideas?

    Thanks,
    Wolfgang
     
  2. mbenonis

    mbenonis Wireless Guy Administrator

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    What I do is have the center speaker come out of a subgroup that is separate from the L/R feed. We also have the sub feed separate, on a postfade aux. This allows us to have playback cues with separate center and sub channels (as well as the surround and onstage channels), and it also lets me mix the mics to center only (I find this sounds better than L/R).
     
  3. waynehoskins

    waynehoskins Active Member

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    That's where a true LCR console sure would be nice.

    But in lieu of that, I would feed the center box one of:
    - from a matrix
    - from a group (not as flexible that way)
    - from the mono output, but delayed from the stereo rig
    - from an aux (a real PITA way, but really flexible)

    If the setup is more of an LCR, I'd go with a matrix feed first.
    If it's more of a stereo rig with a centerfill, I'd delay it.
     
  4. museav

    museav CBMod CB Mods Departed Member

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    I am a little concerned about your comment "finally wired in stereo". As Wayne noted, just having three speakers or arrays does not make it an L/C/R system and your comment makes me wonder if the system is actually intended to be a true L/C/R system or stereo plus center mono or perhaps it is actually an exploded mono cluster with each array covering a different area of the seating. This is a critical point as this is not your living room or a studio and unless the system was properly designed so that the left and right arrays each evenly cover all of the seating, you may not get the result you want. Between the distance from the listeners to the speakers and the speaker patterns, you can get dramatic differences in the perceived effect of any panning throughout the audience area unless the system was properly designed, installed and tuned. If not done properly, you may hear one thing at the mix position but portions of the audience may hear something quite different. The comment that you had to change the system to be stereo throws up a red flag that you may want to verify that the system actually supports usable stereo before planning on employing it.

    There are also probably some differences in how you want to use panning as once again, instead of an audience seated in a small defined area like a home listening environment, you have a larger audience spread out over a much larger area. Every listener has a different visual and aural perspective to the action on stage. If you pan based on an audience member dead center in the room that may vary from the visual and aural perspectives of people off to either side or at the front or rear of the seating. For mono sources, which includes any actors, panning for most rooms and systems typically has to be fairly subtle and may not be as much of a effect as you envision.

    Providing more information on the system and application would help people provide more directly relevant and useful responses. For example, what mixing console do you have? That could definitely impact how signals may be routed and what options are feasible.
     
  5. Wolfgang

    Wolfgang Member

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    As far as I know, it was designed to be a stereo system originally. From what I've been told, about five years ago a group came in to "fix" the PA system. Before them, it was a stereo system with the subs, pit monitors, and center speakers coming from aux sends while the L and R were just run left and right. They group in fact, as far as I can tell, really screwed the PA. They rewired it into mono with the L and R speakers run through a crossover and then the subs and center speakers fed directly from the board (not through a crossover), all with the same mono feed. They also installed XLR connectors on all of the speakers and cables. To me, that sounds like a pretty shoddy job. So yes, from what I know It was designed to be a stereo system. If it matters, our auditorium is about 1100 seats and quite a bit wider than it is deep.

    In addition, today we were trying to figure out why one of each of the L and R speakers weren't working (each side is a pair one hung above the other). Not only were the XLR connectors totally shot (IDK why they even used them on speakers in the past 30 years...), but upon taking the speakers down and opening them up, I find out that a) the woofers in the speakers are actually car subwoofers and that b) one of the internal crossovers is in fact an old crossover from a ~1975 JBL home theater speaker, like the kind with the little knob on the back that sets the high response. And that one of the cables running from the crossover in the speaker to the tweeter is an old piece of extension cable. Then I find out that when the group came in to work on the PA, they also made new boxes for the speakers and supposedly just put the old drivers and crossover, wiring etc, into the new box. But these subwoofers are clearly no more than 5 or 8 years old. As far as I can tell, the guy switched out the old woofers for his car's subs. Not gonna lie, I was pretty pissed off after that.

    So following that rant, I like the idea of running the mics out the center speaker and then using the L and R for other stuff. However, out center speaker sounds pretty crappy without the L and R. THe L and R are really tinny and the center is a bit muddy, but together they balance out alright. Not good, but approaching acceptable.

    Good point. It would more often be used to place sound effects I imagine. But any suggestions to how to better place people and effects would be appreciated.

    Good point, forgot about that last night. Our board is a Crest HP-8. Right now, the L, R, and M feed all run through separate EQ's to help with feedback and then into crossovers to filter. Obviously after that each is run to a separate amp channel.

    Sorry if some of this doesn't make sense, today was a tough first rehearsal day.

    Wolfgang Devine
     
  6. museav

    museav CBMod CB Mods Departed Member

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    Well, what you're doing makes sense but what you say was done previously certainly does not! It sounds like the "cluster" aspect of that project referred more to the work done than to a group of speakers.

    There should not be that significant a difference in the sound between the center and left/right arrays. The center array may not tie to the subs and would typically be tuned a bit more for vocal projection and intelligibility, but muddy is that last thing it should be. Nor should the left and right sound 'tinny', in fact they should be more full range. One has to suspect that the 'improvements' are responsible for your comments on the relative response of the arrays.

    It does sound like you have what was originally a rather nice system intended to be mono center plus stereo, the 2x2 left and right arrays are likely two wide to get more even coverage across the entire space with two high to create a sort of long throw/short throw coverage. It almost sounds like whoever did the last work tried to rewire the system as some form of center cluster and side fill.

    Given what you apparently have, I would typically approach it with the left and right arrays run full range with subs off the left and right outputs of your console. Since the mono bus on the HP-Eight is a totally separate bus assignment for both the channels and groups, I might actually run the center cluster off the mono output, then you can easily assign individual channels and groups to left/right or center. In almost all cases a source would either be run to the left and right arrays as stereo or run to the center array as mono but in those rare occasions where it might be useful you could route it to both. You could also use an aux send to feed the center array instead of the mono bus but that uses up a aux send and could possibly make operation less intuitive, unless you are often routing sources to both left/right and mono where you want to create a different mix for each then using an aux send for the center array instead of the mono output doesn't really seem that beneficial.

    Provided your crossovers and EQ support it, you could also run the subs off a dedicated aux send, allowing only the sources that really benefit from subs being routed to them.

    Hope that helps a bit.
     
  7. mixmaster

    mixmaster Active Member

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    If you have multiple cabs for left and right, and they sound thin, have you checked the polarity of the system yet? If the woofers in cabs are out of polarity with each other, that could account for the poor sound. For that matter, if you are currently sending signals to both the Center and Stereo channels and there is a polarity difference between them, that could really screw up the sound.

    BTW, you have mentioned that you had to "get the boxes down" to work on them, and they were built by a company that has demonstrated rather low standards for quality. Are these boxes fly-rated?

    Matt
     
  8. museav

    museav CBMod CB Mods Departed Member

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    Matt, great point about the flying rating, I missed that but if these are some homemade boxes that are not properly rated for flying then they should be taken down immediately, very few people can, or want to, accept the related liability.

    Given the other apparent issues, polarity should definitely be verified not just for each speaker but for each driver as well as through the wiring to the speakers. However, I would guess that some of the 'thin' sound of the left and right arrays is due to their being off crossovers but without the subs while the 'muddy' sound of the center cluster is likely at least partially due to both the subs and mains apparently being run full range with no crossover. I hesitate to even ask how the crossovers are set.

    I really recommend trying to either get a consultant to come in and do a thorough survey of your system or getting a qualified contractor in to help straighten out what you have and to document the system for the future. Having an outside party document some of the issues and give their professional input may help push being able to get a real solution rather than your having to 'make' what you have work. Just confirm the qualifications of this party before they start the work!
     
  9. cjthedj

    cjthedj Member

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    I can feel your pain ;). I too work with a poorly installed P.A. system 3 times a week. I am having one of the same problems you are.

    Here is what I have done to cope with the problem, I don't know if it will work for you but you can certainly try it.

    > Turn up the Left and Right channels a bit.

    > Run your subs thru a Post-Fade AUX.

    > Turn the center array down a bit so that it fills in the gaps in the house but it does not overpower your L/R arrays and thereby reduce the stereo effect.

    Hope this helps.
     
  10. museav

    museav CBMod CB Mods Departed Member

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    If the system is designed for L/C/R or left/right plus mono then typically no signal should be in all three arrays. Increasing the level of the left and right arrays and reducing the level of the center array may increase the stereo effect but almost certainly also reduces intelligibility. In my experience, that is usually not a desired compromise, but it all depends upon the situation.

    If the center array is required to fill in gaps in the coverage of the left and right arrays then that is likely either a separate problem with the system design or the system may actually be an exploded mono system and not meant to be run stereo. If the output is normally routed to both the 'stereo' and center arrays and each array covers only part of the entire seating, then it may well be an exploded mono system.

    This simply shows how important the relationship between the design intent of the system and the system operation as the two are strongly interdependent.
     
  11. Anonymous067

    Anonymous067 BANNED USER

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    If I were you, I'd stop right at the finding of car electronics in your system, and call in a consultant or professional.

    Unless you're one yourself, you'll need an expert to evaluate the system and get you pointed in the correct direction.

    It doesn't sound like the system is operating in the way it was designed to.
     
  12. TimmyP1955

    TimmyP1955 Active Member

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    This may have been stated before, but:

    The Left, Center, and Right clusters must each cover the entire seating area in order for a system to work properly as an L/C/R system.

    The Left and Right clusters must each cover the entire seating area in order for a system to work properly as a Stereo system.
     
  13. mixmaster

    mixmaster Active Member

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    Experts in the field can give very valuable advice, I'm not disagreeing with you, but there are things that the OP (or anyone for that matter) can check before spending money on an expert. Basic troubleshooting and repair like checking wire connections to make sure things are clean tight and bright, making sure that polarity didn't get swapped in a splice, checking to make sure equipment is hooked up in polarity, replacing sub par wiring and install methods, and generally making sure that the system is correctly patched may go a long way towards cleaning up the rig, and the OP will know his system that much better. He will also be in a better position to help the "expert" if things escalate that far.
     
  14. jkowtko

    jkowtko Active Member

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    Following some of the ideas already voiced and based on what I've done at my theater, here's my suggestion:

    * I will assume that you are driving the L, C and R and Sub channels separately from the board, so you have full control from the board as to what goes to each channel.

    * Set up L and R to your main outs on the board, subs on one Aux, and center on another Aux. This gives you individual control of any of the four output channels from any source of input.

    * Stereo program material: send left input channel to L and Sub, and partially to C. send right input channel to R and Sub, and partially to C.

    * Mono program material: send equally to L, C and R. If vocals, no Sub. If FX, then maybe add Sub.

    * Tune the Center output channel: Walk the house when playing the stereo and mono material (separately), to figure out how loud to adjust the center speaker for each. That's where putting Center out on the aux helps -- you can make it louder for mono channels to create a "wall" of even volume sound from the stage, and softer for stereo channels to hear that stereo separation.

    * Tune the Subs in the same manner.

    Unfortunately using auxes directly from the input channels makes you lose your groups -- so as already mentioned, if you have a board with matrix outs then you can use the combination of LR and Matrix outs (or solely matrix outs) to take feeds off the groups instead of directly off the input channels, thereby preserving the ability to use groups.

    Good luck!

    And .. yes ... I'd replace those car speakers next.
     
    Last edited: Dec 3, 2008
  15. museav

    museav CBMod CB Mods Departed Member

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    I have to disagree here. in a stereo plus mono system stereo sources are normally sent to either the left/right stereo arrays and mostly panned hard left or hard right while mono sources are sent only to the center array. In an L/C/R system sources pan from left to center to right. In neither of these approaches is a signal ever routed to all three speakers simultaneously. When you start assigning signals to left and right as well as center via an aux then by having the same signal in multiple speakers covering the same area you create all sorts of combfiltering and interaction.

    Also, if you have a signal routed to the center channel as well as the left and right arrays then both the panning and the center channel level affect the apparent source location, changing the center channel level will change both the apparent location and the overall level. So you have to keep track of not only panning but also the related aux send and unlike panning which fades the signal to maintain a consistent overall level, to really have a center source and maintain a consistent overall level you'd have to raise the aux level and lower the mains level at the same time as you pan towards center, then inverse that to pan hard left or right. Doing that seems to require a third hand.

    In a practical sense, how you route signals is going to depend on the speaker system and the room, without knowing that then anything is guessing.
     
  16. mixmaster

    mixmaster Active Member

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    Not sure I agree with this. In a stereo-mono system a mono source (like vocals) should land in the mono center cluster. Sending it to the stereo clusters eliminates the whole reason for going with a mono center to begin with. and an Aux send is the worst place to develop a center channel. If you have to do this, it should be a post fade send so that it follows the mix you build with the sliders.
     
  17. Gretsch

    Gretsch Member

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    What do you use your system for primarily? I think you are fine to keep you L/R+ Mono setup on your board since its easily assignable on the hp-8, but I would deffinatly suggest running your L/R through a good programable rack eq and crossover and use it to split and control your subs. But most of all I would suggest getting new speakers, you will not get the quality or control while you are using ghetto rigged mains that aren't rated for overhead use. Try to find a midrange set of JBL's from a reputable used audio dealer if you don't have the bugget to buy new....also get rid of those xlr connectors for your speakers, replace them with speakon connectors making sure to retain your polarity so you can avoid any phasing. Also, as has been mentioned before, for plays, lectures and musicals you should send your speaking vocals through your center/mono channel and make sure to avoid excess lows and low-mids they tend to muddy up and make words unintelligible. Hope this helps and makes sense.
     
  18. jkowtko

    jkowtko Active Member

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    Brad and Mixmaster,

    According to Wolfgang's description of this theater and equipment, (a) the theater is very wide and (b) the center speaker "doesn't cut it" by itself ... therefore coverage across the entire audience left-to-right would appear to be an issue. Unless he replaces his speaker system, using L, C and R all together for mono sources, and likewise stereo sources, is the only way to get the sound uniformly out to the audience. And when I say "together", I don't mean all at the same volume.

    An Aux send is not the worst place to send ... conversely it's one of the most versatile channel outputs you have. Using a Group locks in ALL input channels with the same volume level (i.e. Unity) sending to that Group. Using the Aux allows you to tailor the volume level of each individual input channel to the output bus as needed. And of course you do this post-fade, otherwise you lose the control of your input fader. Maybe you are still thinking in terms of using groups as "groups" ... see in my post the mention of either losing the "groups" capability, or using matrix outs to retain it.
     
  19. museav

    museav CBMod CB Mods Departed Member

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    As was mentioned earlier, for L/C/R or stereo plus mono, each array has to cover the entire listener area. If they don't, then you can't really run the system like you would for one of those approaches. If you have to use the center array as 'fill', then you probably have an exploded mono array and it should be run as mono.

    I interpreted the comment about the center array differently and believed it related simply to the center array not sounding good, not surprising with all the apparent miswiring and likely poor system tuning that seems to have been introduced. In a way this all plays together and in this case it seems to make sense to get the system operating properly before addressing anything else.
     

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