Rational Acoustics



Dr. J
January 25th, 2014, 01:19 AM
Hi guys - I have been experimenting with Meyer's MAP Online prediction program. You can only load up their speakers which mostly consists of dual 18 boxes for subwoofers. I ran thru several ground stacked sub configurations and it seems that 3 subs clustered together in the middle with the middle box polarity reversed has excellent coverage. At least for the places that I go which is small venues.

I currently have single 18 boxes. I couldn't find any single 18's from the Meyer selection. Do you think the sub predictive behavior will be similar for single 18's? Or does it really change things for a dual 18 versus a single 18?

I also applied delay to the center polarity reversed sub with NO success. It looked better with no delay. This went against some articles I have read.

Any ideas?

irwan
January 27th, 2014, 02:32 AM
To make cardioid subs configuration, you need to reverse direction & reverse polarity one of them.After that, you need to delay reversed sub by 1/4 wavelength from the highest freq of subs.
With this technique we can cancelled back lobes of subs.
But because you only use 3 subs, you need to attenuate -3dB for unreversed subs to make polar response more consistent over entire freq range.
Hope this help, and sorry if my english is bad.

irwan
January 27th, 2014, 02:54 AM
From my experience, the behaviour is still close.Even you use double 18' to simulating single 18'.Because mostly subwoofer have omni directional polar response
For more fix, better you measure when its in real situation.Smaart is one of the good measurement software to do that.

Dr. J
January 27th, 2014, 07:00 PM
To make cardioid subs configuration, you need to reverse direction & reverse polarity one of them.After that, you need to delay reversed sub by 1/4 wavelength from the highest freq of subs.
With this technique we can cancelled back lobes of subs.
But because you only use 3 subs, you need to attenuate -3dB for unreversed subs to make polar response more consistent over entire freq range.
Hope this help, and sorry if my english is bad.

Thanks Irwan! What box did you choose for that configuration? I have another sub box. I can do 4 across but not sure on how that behaves. Guess I can try it with Mapp and see. I run into a lot of boundary issues because of poor stage placement... In the center seems like a better route. Trying to figure out how to do that the best way.

Dr. J
January 29th, 2014, 01:16 AM
I can't seem to select the center box, spin it 180 degrees, invert the polarity and apply delay without it affecting the other two boxes. It changes the other boxes to what the center is doing even though I did not select them. I have made sure that the center box is on a different channel but no luck.
Any ideas to those who have used this software?

irwan
January 29th, 2014, 04:08 AM
I choosed hp700 for the simulation i've attached, 2 subs facing right with front rig reference point & 1 sub facing left with rear rig reference point.
You should insert them one by one into mapp online, use delete row to do that.
And apply different processor channel so you can reverse polarity & insert delay to a specific sub you've inserted.

In case you want to make polar response more consistent, you need to attenuate -3dB for both of subs that facing right.Just try this & compare in mapp online with or without attenuation.
In real situation,off course it's better use 2 subs rather than 3 subs with attenuating -3dB if we want to make polar more consistent.

You can do subwoofer steering with many approach, one of them is cardioid/gradient.This is one of good article from Chalie Hughes about how to steering subwoofer.
http://www.excelsior-audio.com/Publications/AES131_LS7_Subwoofer_Arrays.pdf

hope this help, thanks...

Dr. J
January 30th, 2014, 12:32 PM
Thanks Irwan - I figured it out. It is clear to me that left and right sub configurations cause major comb filtering. Spacing my subs out across the front really smooths that comb filter out but then loads the stage. That may be a better trade off. I know I can do the reverse sub, polarity and delay once I figure out how to program my DSP to give me another separate delay line.
I have used Smaart on a sub stack next a boundary to see where the cancellations were. For fun - I tried to EQ that cancellation out and of course it is impossible. The trace never budged. I then pushed the sub stack away from the boundary in 1 foot increments so I could see the cancellation travel to a different spot. Really slick! I settled on a cancellation area where I knew the kick wasn't. I then brought down the buildup peaks until it sounded balanced with the rest. Loads of fun!
Now how about the comb filtering in left and right top boxes? I was a bit shocked to come across that finding but I cannot really hang two boxes in the center on my portable system.
Thanks for the screen shots and links!

irwan
January 31st, 2014, 01:02 PM
You're welcome Dr.J

Anyway, this discussion will lead us into sound system design.Which is a huge topics.There is so many things that we must take into account and i can't simplified.
There is some good resources to learn about sound system design, like Sound System Engineering ,written by Don Davis & Eugene Patronis and Sound System Design & Optimization, written by Bob McCharty.Try this link also :

1.http://www.acorn-designs.com/articles/pssdm_1.pdf
2.http://www.acorn-designs.com/articles/pssdm_2.pdf