ground cancellation?

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himhimself
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ground cancellation?

#1 Post by himhimself » Tue Jul 03, 2018 12:25 pm

To use the v-plate I am making with my T30s, they obviously have to be nice and flat on the ground - which isn't always the case outside. I was thinking to build a light frame, perhaps out of 1x4s, with leveling feet, so I can have a nice flat landing zone for the cabs. So the closest to the ground they would be is about 4 inches, maybe up to 7 inches with an adjuster turned all the way up. Is there going to be any negative effect with the cabs being off the ground a bit? I think it's 8" or more from a wall that can cause cancellations, right?. So as long as the mouths don't get farther up from the ground than that, will I be okay? I don't want to unwittingly sacrifice any boom!
thanks
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Bill Fitzmaurice
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Re: ground cancellation?

#2 Post by Bill Fitzmaurice » Tue Jul 03, 2018 12:56 pm

Yes, you'll get a ground reflection cancellation, in the vicinity of 500Hz. I don't see that as a problem. :)

himhimself
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Re: ground cancellation?

#3 Post by himhimself » Tue Jul 03, 2018 2:08 pm

Well, that's good to know. Thanks Bill. Will build my "tuba sled" tomorrow 8)
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heavybdrums
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Re: ground cancellation?

#4 Post by heavybdrums » Wed Aug 22, 2018 10:41 am

I have had quite a few outside venues where the ground is not flat. I use two pairs of "V" plated T39's. All I do is carry around a box of chock blocks, pieces of wood (1/2", 3/4",5/4", 1&1/2") blocks cut 5&1/2" square. I use them to level up the array after attaching the "V" plates.
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Bill Fitzmaurice
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Re: ground cancellation?

#5 Post by Bill Fitzmaurice » Wed Aug 22, 2018 10:48 am

This does bring up a valid point. Ground reflection cancellations are a problem with single cab PA systems. If the cab's on the ground you can get cancellation in the mids, if it's on a pole you can get cancellation in the lows. With a dual cab system the subs are too close to the ground for there to be cancellation in the lows, the mains are too high for there to be cancellation in the mids.

T_Gowan
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Re: ground cancellation?

#6 Post by T_Gowan » Wed Aug 22, 2018 12:33 pm

Something I was trying to get across to the people in the band. Just because you don't need subs for a gig are you still causing power alley because the low end reinforcement from the pa on the sticks is separated rather than clustered in proper sub placement?
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Bill Fitzmaurice
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Re: ground cancellation?

#7 Post by Bill Fitzmaurice » Wed Aug 22, 2018 12:39 pm

PA on sticks doesn't go low enough for power alley to be a consideration.

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