Harmony Central Forums
Announcement
Collapse
No announcement yet.

Subwoofer Standing wave cancellation .... and summation

Collapse



X
  • Time
  • Show
Clear All
new posts

  • Subwoofer Standing wave cancellation .... and summation

    This is the venue I did last weekend for my niece's wedding reception. The room holds ~320 people with a minimum booking of 270. I couldn't fit the entire room in the picture on my iPhone, but it was wide and deep. The room was shaped like a large square with the top of an octagon on top of it and as you can see from the photo, it had pretty high ceilings.

    I had my X32 Rack under my DJ table, and my DSR112's over my PRX618S-XLF's out front. The speakers were positioned about 5 feet in front of the rear wall about 25 ft apart (the top of the speakers are at ~7 ft in the picture.

    Sitting behind the speakers in the center there was a bass node of such huge intensity that with the system up at clip flicker, it was physically uncomfortable.

    Out front of the speakers within the first 10 ft of the plane, there was a null where little bass was present, then it got right down thumpy in the middle of that long dance floor. By 3/4 of the way through the dance floor ... another null, then as you got off the dance floor and into the seating area, the bass got louder again.

    Most of the night there were between 50-100 people on the floor (packed). We even got quite a bit of people from other weddings since our dance floor was so successful.

    There were a few things I found walking around with my iPad:

    First, at low volumes, I had to enhance the HF so that people could hear the music better. During cocktails and dinner, the music was low and people were talking, and that many people make a bit of noise.

    Second, when I got to the dance music, I cranked the system up and the dance floor was packed. The HF was way too loud and I had to turn the tops down to tame it. When running flat out on EDM (which was predominantly what the bride and groom wanted for their young crowd), I had the XLF's tickling the red lights, but the DSR's were breathing quite easily.

    Third, the Shure ULX / Beta 87a wireless rig I rented was first rate. I was able to get crystal clear speeches even though the maid of honor held her mic near her waist. The room was so deep that it created an apparent echo to the person speaking (I noticed this when I setup my notch filters earlier in the day). The best man had no issues with it, but the maid of honor took a few seconds to get used to it.

    Fourth, I popped a breaker 2 times before I had the banquet engineering people come down and show me where the next circuit was located. I had run my lights and system on a single 15amp breaker several times before without issue, but this time I added a PC to the mix which apparently pushed me over the edge ..... good to know.

    If I had it to do again, I would likely center cluster those subs and put the DSR's up on higher stands. I think that would project the highs from the tops better at low volumes, and even out the sub frequencies so that the coverage was more uniform.

    It really was a very successful night. My niece did pick out a very strong dance mix for her age group (25-30).

    I get the feeling that the DSR112's could have handled 2 XLF's per side for this kind of music. I generally have the XLF's closer to limit than the DSR's even in my band, but it was even more disproportionate with EDM.

    How would you guys handle a room like this?
    Attached Files
    Last edited by OneEng; 07-28-2014, 08:01 PM.
    With Greater Knowledge Comes Greater Understanding

  • #2
    Cardioid subs (LS801P's)
    Veni, Vidi, Velcro;

    (I came, I saw, I stuck around)

    Comment


    • #3
      yea, center clustered. 25 feet apart does create some wicked alleys. Mains above heads. I don't see how a PC pushed you over the edge, probably more like pushing the system, EDM, music tracks with no dynamic range and bumping the LF. are those LED lights? How much power you need is something to estimate and plan ahead for during setup.

      Comment


      • #4
        Don't count on center clustering your subs to fix your problem. It will just change your problem. True you will eliminate your power alley in the center but your room mode cancellations will likely be much more severe. Sorry, no free lunch
        Don Boomer

        Comment


        • #5
          A site visit to find out what circuits are what, where the breaker panel is and if it's accessible during evening hours, is a good idea - I've found this out the hard way!

          I agree with Witesol, PC's don't take much juice, it's probably the extra thump and possibly the fact that the circuits might have been rated under what you've previously used. There might even have been something else on the circuit that you weren't aware of. That's happened to me.

          Kudos for paying attention to what was going on and making adjustments to help mitigate the situation.

          Comment


          • #6
            Originally posted by dboomer View Post
            Don't count on center clustering your subs to fix your problem. It will just change your problem. True you will eliminate your power alley in the center but your room mode cancellations will likely be much more severe. Sorry, no free lunch
            Agreed, folks seem to think of all kinds of "solutions" without considering the tradeoffs.
            -------------------------------------------------------------------------------------------------------------------------------------------------------------------
            Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

            Currently product development engineer: Mesa Boogie

            Comment


            • #7
              Originally posted by Bobby1Note View Post
              Cardioid subs (LS801P's)
              How many do you propose to achieve meaningful steering?
              -------------------------------------------------------------------------------------------------------------------------------------------------------------------
              Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

              Currently product development engineer: Mesa Boogie

              Comment


              • #8
                seeing as to the size of that room, if the dance area was near the PA system, IMO the center cluster still the better choice rather than try to hit everyone with subs 25 feet apart. ..or trying to focus them onto the dance floor, guessing at wall modes. I'd let the tops float sound over the area for dinner and speeches and center the subs, letting the inverse square law try to help you out! A quick check/walkabout after setup to listen where things focused in the room may not have been an option?

                I guess you really have to be in the space with the gear to decide, other than that, it's theorizing
                Last edited by witesol; 07-29-2014, 05:05 PM.

                Comment


                • #9
                  The empty room test I did earlier in the day could not be turned up like I did later in the evening. Wouldn't a room full of people change the dynamics of the room as well?

                  Walking around that room there were some very interesting bass coverage patterns. On the far left (off the screen) it was pretty heavy. Someone kept turning my left sub inward when I wasn't looking thinking that it was going to lower the bass on that side of the room Must have been an older person since all the young people pretty much stayed glued to the dance floor all night until I turned off the music.

                  Yea, I should have checked out the circuits before hand and made sure that I had 2 dedicated to my rig. The lights are incandescent PAR56's rated at full on 300W. I have the levels turned down to around 200W, and it is rare when all 8 are on at once. When they are all on at once, they are only in that state for about 1 second. Normally there are only 2-4 on at any given time.

                  The load could have been the draw from having the subs up all the way. I am guessing that my computer draws about 2 - 4 amps from the wall socket. Certainly the entire rig got me over the top of whatever size breaker I was on (I am guessing 15 amps). It is also possible that there were other loads on the circuit.

                  How would one know if you were on the same physical circuit with two different sockets? Do you guys have a meter of some kind for this purpose (seems like it should be possible using the hot line which would be common)?

                  Not sure what could have been done about the uneven bass response. I am sure I was the only one that noticed it since I was actively listening for it. Everyone else on the dance floor were to busy dancing and too intoxicated to notice

                  How might the center cluster make things worse?
                  With Greater Knowledge Comes Greater Understanding

                  Comment


                  • #10
                    Center cluster makes things ...well, different. worse would be up to you to decide! I always find it solves more issues than it creates. Don is wrong, you do get some free lunch...it's just that somebody is taking some bites out of it elsewhere. You get some free performance clustering but that increased performance will bounce and have modes too. sometimes the bodies will make the bass seem stronger since other frequencies get absorbed leaving the hearty big waves!

                    You could have drawn as much as 3a each sub, 5a for the tops. Slightly less than an amp per each 100 watts lighting. All on one circuit. a small laptop draws less than an amp.. Macbook PS 85 watts

                    Sometimes i will use a lamp and extension cord to try some circuits on the panel.

                    Probably a 15a circuit unless you saw the sideways lug.

                    except for the power going out, you were a success.

                    don't you love people who mess with your stuff. The thing about weddings is knowing where people have been seated; grandparents where, older people/families where?
                    Last edited by witesol; 07-29-2014, 05:56 PM.

                    Comment


                    • #11
                      Figuring out circuits... When I am scoping out a venue I take my "kill-a-watt" meter because it is convenient to plug it in and see the voltage. But any voltage meter would work. I bring a compact space heater that draws about 12 amps and use that to see what kind of sag I get on the proposed outlet(s). You can also tell if two outlets are on the same circuit if the voltage at the second outlet sags when the heater is plugged into the first outlet and turned on. Not very "pro" but simple and effective.
                      --Mike"If your not confused, you don't know what is going on!"Live Sound for the Mt. Shasta areaShastaLiveSound.com

                      Comment


                      • #12
                        Originally posted by agedhorse View Post
                        Agreed, folks seem to think of all kinds of "solutions" without considering the tradeoffs.
                        Andy,

                        Are you suggesting there's a "perfect" solution that's been missed here, or are you saying that the lesser of many evils is the way to go,,,and how do you establish that in this particular case?

                        What I'm asking here is, what exactly would you have done in this scenario?

                        I offered the suggestion of "cardioid subs" as one option (one possible alternative to "doing things differently"), but from my perspective, and given what we know from the limited room description, and given the equipment "on-hand", I think in general that OneEng did the right thing by concentrating the power-alley on the dance-floor. As for reducing standing waves, or boominess in certain corners/locations, I can't really comment since I wasn't there to EQ the room. I probably would have chosen to reduce the offending frequencies in the room edges/corners(via EQ), and live with the results in the power-alley.
                        Last edited by Bobby1Note; 07-30-2014, 10:28 AM.
                        Veni, Vidi, Velcro;

                        (I came, I saw, I stuck around)

                        Comment


                        • #13
                          Biggest issue was the 5 feet from the back wall thing - that introduces a partial cancellation at ~50Hz directly in front of each sub as you experienced.
                          Last edited by RoadRanger; 07-30-2014, 10:27 AM.

                          Comment


                          • #14
                            Originally posted by Bobby1Note View Post

                            Andy,

                            Are you suggesting there's a "perfect" solution that's been missed here, or are you saying that the lesser of many evils is the way to go,,,and how do you establish that in this particular case?

                            What I'm asking here is, what exactly would you have done in this scenario?

                            I offered the suggestion of "cardioid subs" as one option (one possible alternative to "doing things differently"), but from my perspective, and given what we know from the limited room description, and given the equipment "on-hand", I think in general that OneEng did the right thing by concentrating the power-alley on the dance-floor. As for reducing standing waves, or boominess in certain corners/locations, I can't really comment since I wasn't there to EQ the room. I probably would have chosen to reduce the offending frequencies in the room edges/corners(via EQ), and live with the results in the power-alley.
                            Short of the impossible prospect of acoustic treatment of the room, there's no perfect solution, and OneEng did the best he could to balance the variables and make the system sound good where it counted most...in this case, the dance floor. I think Don and Andy were noting that changing subs will merely change the problems, and even if they somehow worked perfectly in that venue (which is highly doubtful, as a bad room is bad no matter what gear is used in it), they'll be "wrong" for another room. Mostly I think this story illustrates the worth of using what's on hand to best advantage rather than assuming more or different gear will fix a bad room.
                            "If you don't know where you are going, you might wind up someplace else" - Yogi Berra, 1925-2015

                            Comment


                            • #15
                              Originally posted by Craig Vecchione View Post

                              Short of the impossible prospect of acoustic treatment of the room, there's no perfect solution, and OneEng did the best he could to balance the variables and make the system sound good where it counted most...in this case, the dance floor. I think Don and Andy were noting that changing subs will merely change the problems, and even if they somehow worked perfectly in that venue (which is highly doubtful, as a bad room is bad no matter what gear is used in it), they'll be "wrong" for another room. Mostly I think this story illustrates the worth of using what's on hand to best advantage rather than assuming more or different gear will fix a bad room.
                              Agreed. In SR there are rarely perfect solutions but rather tradeoffs. I work in a room where at the mix position, the middle notes of the bass guitar are just flat out missing (with a couple of exaggerated notes distributed throughout). If I boost these frequencies, it just cancels more so no change (but wasted power). Unfortunately the subs are in a fixed position. Fortunately when you walk the room, most of the bass notes are there. If I could change the sub positioning, it would just change WHERE the comb filtering occurs, not fix the problem. A bad room is a bad room.
                              J.R. Previously jrble

                              See my Dog Of The Hair studio at: http://www.dogoth.com/studio/

                              Quote from someone: Flat response? Get out the jack and change the tire.
                              If you think "power is knowledge", you have it backwards.

                              Comment









                              Working...
                              X