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Speaker placement

Postby Drewid » Fri Sep 20, 2019 1:25 pm

Hi all. I know this has been covered in at least one SOS article, but I need to check my setup with your collective wisdom, since my combo of speakers might present me with issues.

I have 4 x QSC K12 tops
2 x QSC 212c (cardioid) subs
2 x QSC Ksubs

I'm doing sound for a rock band in a large room and I know for using the 212cs alone in the past that I will need as much low end as I can get for this gig. My thinking is to get the 212cs side by side under the stage (if it's open fronted and can accommodate them) with the Ksubs either side and the two pairs of tops between the sides of the stage and each Ksub.

If there isn't space to do that I'll be going with the configuration in figure 8 here: That is, 212cs 16 feet apart, with tops on tripods, then the Ksubs on the outside, 24 feet apart. I'm using a QSC TM16, so delays etc are no problem as I'll run the Ksubs on their own aux and the 212cs out of the back of the K12s.

Sorry for the rambly post, but I'm not sure how my mix sub models will affect the different configurations mentioned in the article.

Thanks in advance!
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Re: Speaker placement

Postby blinddrew » Fri Sep 20, 2019 5:33 pm

What shape / size is the room?
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Re: Speaker placement

Postby Wonks » Fri Sep 20, 2019 6:55 pm

Can't remember seeing that article before. What it doesn't consider are the room modes, which despite the author's statement, do have an effect on the bass in the room. However that's room specific, so I can understand the room effect being ignored for the article and just the ideal interactions shown. But reflections from walls, floors and ceilings are also going to mess with the distribution patterns, so you won't get exactly those patterns unless it's a very large room indeed.

It doesn't help that the polar plots have no scaling on the amplitude rings. Are they 5dB, 10dB, or maybe even only 1dB apart? There's no clue in the text. If a 'deep null' is only -10dB deep, then maybe the more practical way of positioning the subs within the venue, and without the need for delays, is a better choice than one which produces a -5dB null. But if it's say -30dB vs -10dB, then it makes more sense to go for the more complicated solution.
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Re: Speaker placement

Postby James Perrett » Fri Sep 20, 2019 8:57 pm

Probably the best people to answer this are QSC themselves as they would know how their subs are best configured when used in multiples.
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Re: Speaker placement

Postby Mike Monte » Sat Sep 21, 2019 12:40 pm

IMO: K12's are not rock boxes...depending on the size of the room (if it's a bar, let's say), they may be a large room no way IMO.

For what it's worth I feel that you'd be best to post this question on Prosoundweb as that board has more traffic than this one.

You can contact QSC for answers but in all honesty, you should seek answers from those that work similar gigs "in the trenches".

What I have found, in general, is tech support as far as speakers, etc. is dodgey at best. Most of the time you'll be speaking to someone that has never gigged the equipment and all they do is refer to the specs/owner's manual for their generic answers.

I suggest that you talk with people that do this type of gig and see what they use. You may find that what you have to use will work.....but don't hold your breath.

For the record, I have had very little luck putting subs under a stage for a "one-off". I have found that it creates more problems (feedback, etc.) as the subs react with the stage.
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Re: Speaker placement

Postby Drewid » Sat Sep 21, 2019 12:44 pm

Thanks everyone for your considered answers. Stage design and height allowed me to put the 212c side by side under the front of the stage, and, because they are cardioid, left the stage itself pretty rumble-free. The only feedback in soundcheck came from the ksubs to the extreme left and right of the stage. Had low end to spare, so was very happy.
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