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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Tony Mamoh on September 20, 2018, 06:51:32 AM
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I admit I am a novice when it comes to application of acoustics to live sound in the real world. I am seeking basic technical information on the pros and cons of placing a pair of 1-18 subwoofers vertically (stacked on top of each other) or horizontally (stacked side by side).
Sometimes, to give the illusion I have a dual 18 subs like the real pros, I place the 1-18 subwoofer pair side by side/horizontally. However, I had a scenario recently where I did an outdoor event. We needed to place the FOH mains speaker on a pedestal as high as possible.....in order to throw as far back as possible to the audience. We 'experimented ' with stacking the subwoofers on top of each other (vertically); and placed the dual 15/horns full range mains speaker on top. I must confess that we achieved the primary aim of getting a good throw as far as possible to the audience from the mains speakers.
But I really don't know if that is a good practice, and what the (sometimes theoretical and academic) low frequency response might be from the subwoofer placement position.
I also confess that I am yet to read the famous book on acoustics and psycho acoustics of live sound. Those of you that have either read the book, or have many years of experience with the acoustics coupling from subwoofers may be kind enough to share one or two things with me.
Thanks!
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With the subs placed directly against each other, they will acoustically couple, meaning they will act as one speaker. You won't hear any discernable difference between horizontal and vertical orientation. It's when you start spacing cabinets out that you start changing the coverage.
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^^^ Yep, won't matter either way...vertical or horizontal they will couple together and actually provide a little more output. When possible, I always put my subs side by side (or on top of each other) to get that benefit. If you have the floor space, horizontal may be safer than stacking them if you don't have straps.
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generally speaking with only a pair of subs, they will couple almost entirely and do what they do. It changes depending on how long the array is though. If you were to take 4 subs and line them up horizontally across the stage you would have strong sub energy directly in front of the subs, but as you started to get off to the sides of the line you would have heavy cancellation.
If you had 4 subs and stood them up side by side vertically, you would have the same coupling and energy, but you would have less cancellations off the sides. This is because it would only be as long as two subs laid down side by side. Or in other words, not long enough to have major cancellations off axis. Now if you were to double up again with the subs in their vertical orientation, you would again have lots of cancellations off axis, but you would gain another 3-6db in subs output!
It works the same way if you stack the subs vertically. Because the floor acts as a boundary the top of the sub-stack would start to cancel, but you get a cardioid type response off the top of the array. This is a good trick to help keep low-end energy from bouncing off the ceiling if you have a room where that can be an issue.
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Many times I have stacked my 2 SRX818sp on one side of the stage and placed my SRX828sp on its end on the other side to match. Looks good and sounds great. Each side sounds about the same in level- as it should (although difficult to hear with subs sometimes)
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Every surface that is larger than the longest wavelength of interest ( say 40 hz for low E on a bass guitar at the low end ) will act as a mirror for the subs adjacent to it. Keeping the subs on the ground ensures thats true for all frequencies the sub is likely to deliver. Even at 80 hz ( a common frequency to low pass out of the subs ) the wavelength is over 12 ft so the coupling holds true. Where it gets complicated is when you separate the subs by distances large enough for the sound to start to cancel as it arrives increasingly out of phase. Like on opposite sides of the stage. A big reason why large sub arrays are usually a continuous line across the front of the stage.
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I have 4 kw-181’s. I always stack when deploying all 4. The port configuration is why. Ported on the side. Feet on the bottom.
Vertically, the ports and drivers align.
Horizontally, unless you flip one on it’s head, thereby burying the pole mount and performing unnecessary roughness on the coating... you got speaker, port, speaker port. Not as good...
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The port is only really doing anything at around 40Hz. Does port placement really make much difference? We're talking about wavelengths of the order of 30'.
Chris
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The port is only really doing anything at around 40Hz. Does port placement really make much difference? We're talking about wavelengths of the order of 30'.
Chris
It is not as much about the port placement, as the woofer placement.
You want the woofers to be closer so that at the upper end of the range they will couple better.
This of course depends on the freq and size of cabinet/distance away from each other.