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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 => SR Forum Archives => LAB Lounge FUD Forum Archive => Topic started by: David Hoover on October 18, 2010, 10:52:40 PM

Title: Splaying Speakers...
Post by: David Hoover on October 18, 2010, 10:52:40 PM

When you are splaying speakers, is there ever a time when it is better to point them in toward each other than away from each other.  For example, with certain BFM full range cabinets he recommends cross firing them for the best coverage.  A guy I work with though says you never do that because the comb filtering would be horrible.  Yet, I've read on the internet that sound from two speakers crossing doesn't effect one another.  So, which is true?  And, do the horns/woofers couple better if faced toward one another?

Title: Re: Splaying Speakers...
Post by: Brad Weber on October 19, 2010, 08:19:11 AM

Combfiltering is a localized phenomena that relates to relative phase differences at a point and only applies to that point.  What happens in terms of combfiltering in one location does not affect any other location.  So combfiltering is not really any more of an issue with them crossfired.

However, the close proximity of the drivers and enclosures can affect one another in other ways.  Even though not in a common constrained space, one speaker may somewhat 'load' the other.  And one has to consider how the physical enclosures may impact one another.

You might want to look at http://srforums.prosoundweb.com/index.php/m/481089/50089/0// /13457/#msg_481089.

Title: Re: Splaying Speakers...
Post by: Silas Pradetto on October 19, 2010, 08:24:01 AM

You either need all your sources to be within 1/4 wavelength for coherent summation (very hard with HF drivers unless the horn is the full width of the box, and sometimes it still doesn't sound good), or you need them splayed enough so that the patterns meet at about the -6dB point so they sum to 0dB down.

Title: Re: Splaying Speakers...
Post by: Jeff Wheeler on October 19, 2010, 10:52:18 AM

Silas Pradetto { wrote on Tue, 19 October 2010 07:24

You either need all your sources to be within 1/4 wavelength for coherent summation (very hard with HF drivers unless the horn is the full width of the box

What does the width of the horn have to do with it?

Title: Re: Splaying Speakers...
Post by: Bennett Prescott on October 19, 2010, 12:21:32 PM

I'm sure Silas meant to say the apparent acoustic epicenter of the loudspeaker, AKA the driver, which is why cross firing cabs makes comb filtering worse at HF (but often better at LF!).

Title: Re: Splaying Speakers...
Post by: Brad Weber on October 19, 2010, 12:40:59 PM

Bennett Prescott wrote on Tue, 19 October 2010 12:21

I'm sure Silas meant to say the apparent acoustic epicenter of the loudspeaker, AKA the driver, which is why cross firing cabs makes comb filtering worse at HF (but often better at LF!).

However, it is the locations of the acoustic centers, not the crossfiring, that is the issue.  'Stack and splay' with one speaker stacked on top of the other and splayed relative to each other is a form of crossfiring that can actually align the acoustic centers in the horizontal plane and minimize combfiltering.

Getting picky but the acoustic center is not necessarily the driver, for example in a compression driver and horn combination it may be somewhere in the horn and may shift with frequency.  The HF horns used in some line array boxes actually try to create multiple acoustic centers closely spaced to one another driven by a single driver.