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Author Topic: Wall boundary vs separate source distance cancellations  (Read 1035 times)

David Allred

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Wall boundary vs separate source distance cancellations
« on: January 02, 2017, 05:20:23 pm »

Often quoted here is the "less than 2' or greater than 8'"recommendation for subs from a wall.  How does that mantra relate to a second sub, or in other words, if 2 subs are in a room and not near a wall boundary, Is there zone of distance between that is not acceptable?  Is it the same, or a multiple?


I have an upcoming set-up where the wall will be at least 18' from speaker A (also 18' from mirror speaker).  A & B will be 30-35' apart.
I can center cluster the subs (2 x USC1) in front of a small stage.  If I do this the sub will pull dual duty at monitor risers, as the stage and UCS1's (on their sides) are the same height.  If placed together, the monitors (x2) will be difficult to get the best coverage, but maybe OK coverage for the gig.  I can spread the subs to 9' of box gap so the monitors get good cross fire coverage, and are flush to the stage edges.  The box gap can be 9' between the near edges of the horn mouths (bottoms in), or approx. 13' between the nearest edges if they are laid horns out.

How does the "at least....or greater than...." apply to 'sub to sub' separation?  FYI, I cross at 100hz.

Thanks,
David






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Ivan Beaver

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Re: Wall boundary vs separate source distance cancellations
« Reply #1 on: January 02, 2017, 06:26:20 pm »

It is not just the distance-but also the HIGHEST freq of interest of the sub (or other speaker).

As a general rule, any spacing more than 1/4 of the highest freq of interest is going to cause cancellation problems.

How much?  That is up to you and what you are willing to "accept" or deal with.

So if 100Hz is 11.3' then 1/4 that is 2.8'.

Of course that is NOT the distance between the sources, but rather the distance between the sources (or reflections) and the listening position.

As the listening position moves, this distance from the different sources will also be different.

The idea to placing the subs apart is that the levels from the different sources will be great enough that there will not be much cancellation.

HOWEVER-at some listening position, that distance will be short-and therefore the levels will be very close to equal.

So at some seats the idea of spacing them apart works well, but at OTHER seats, you will still have the short distance-equal level issue and cancellations.

The "best idea" is to use a single source that is loud enough.

As soon as you start to add cabinets (from any manufacturer) you will start to introduce cancellation/interference issues.

So you need to think about ALL of the seating positions, not just one.  Unless that one is the only one you are concerned about.
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Ivan Beaver
Danley Sound Labs

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David Allred

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Re: Wall boundary vs separate source distance cancellations
« Reply #2 on: January 03, 2017, 12:21:03 pm »

It is not just the distance-but also the HIGHEST freq of interest of the sub (or other speaker).

As a general rule, any spacing more than 1/4 of the highest freq of interest is going to cause cancellation problems.

How much?  That is up to you and what you are willing to "accept" or deal with.

So if 100Hz is 11.3' then 1/4 that is 2.8'.

The "best idea" is to use a single source that is loud enough.

With the design of the UCS1 (bottom exit horn), if they (2) are placed on their sides, bottoms touching... is that essentially a single source?
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ProSoundWeb Community

Re: Wall boundary vs separate source distance cancellations
« Reply #2 on: January 03, 2017, 12:21:03 pm »


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