Posted by tumara Baap (A) on September 13, 2006 at 21:37:25

The output of a loudspeaker can be affected by the distance it sits in front of a wall. Low frequencies are omnidirectional. They travel rearwards, bounce off the wall, meld with loudspeaker output, and obliterate certain frequencies. The usual way to handle this problem is to have the speakers way out into the room or have them soffit mounted. However I'm not sure whether placing broadband bass traps in the corners behind the loudspeakers would help SBIR distortion at all (I'm sure room mode issues are ameliorated regardless...) Anyone have experience with this?
I plan on having copious bass absorption in the ceiling. I was wondering whether there are unique benefits to having bass traps in the front corners of the room too.

Tumara Baap

• Re: Do bass traps affect SBIR? - Inmate51 16:24:16 09/14/06 (4)
  In Reply to: Do bass traps affect SBIR? posted by Tumara Baap on September 13, 2006 at 21:37:25:

  SBIR? I've racked my brain, looked in all the books. Can't find "SBIR". Is that an acronym for "sound bouncing in (the) room?

  No doubt, I'm the ONLY person who is confused. Please enlighten me.

  
  
  

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  • Re: Do bass traps affect SBIR? - Tumara Baap 23:17:27 09/14/06 (2)
    In Reply to: Re: Do bass traps affect SBIR? posted by Inmate51 on September 14, 2006 at 16:24:16:

    When I started browsing these groups many many years ago, I was often frustrated by a lot of the jargon. On visiting video sites, I still am. Browsing on the AVS forum revealed to me "audio" enthusiasts with a more severely depleted mojo than you, Inmate 51 ;-) (A post about speaker distance/optimal sub crossover relationship was overwhelmed by queries on the distortion phenomenon in question) For the sake of those just getting into the hobby, is an extra 20 seconds of typing time too steep a price for an iota of courtesy? As I absorb the musings of video enthusiasts, I very much hope not, even if it's disconcerting to the self worth of a handful few.
    Regards,
    Tumara Baap
    
    

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    • T.B., there you go again! - Inmate51 09:19:36 09/15/06 (1)
      In Reply to: Re: Do bass traps affect SBIR? posted by Tumara Baap on September 14, 2006 at 23:17:27:

      While hoping for a definition of SBIR, I now read "mojo".

      I'm going to assume that SBIR means Sound Bouncing In Rooms, or Sub Bass Impulse Response, or Some Beer Is Repulsive. I'd still like to read your definition.

      And, please don't tell anyone that you had to explain it to me, but, what the heck is "mojo"? And while I'm at it, what is a MILF?

      Thanks.
      
      
      

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      • Re: T.B., there you go again! - Ethan Winer 15:23:15 09/15/06 (0)
        In Reply to: T.B., there you go again! posted by Inmate51 on September 15, 2006 at 09:19:36:

        SBIR = Speaker Boundary Interference Response. LBIR is similar to SBIR, where L refers to the Listener. Either way, the root problem is comb filtering caused by reflections.

        --Ethan
        
        

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  • Re: Do bass traps affect SBIR? - Bayside Bomber 19:58:20 09/14/06 (0)
    In Reply to: Re: Do bass traps affect SBIR? posted by Inmate51 on September 14, 2006 at 16:24:16:

    I too am confused. For a moment I thought it meant Spouse BItching about Room treatments.
    
    

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• Re: Do bass traps affect SBIR? - Ethan Winer 12:08:47 09/14/06 (2)
  In Reply to: Do bass traps affect SBIR? posted by Tumara Baap on September 13, 2006 at 21:37:25:

  Tumara,

  > The usual way to handle this problem is to have the speakers way out into the room or have them soffit mounted. <

  Moving speakers out into the room does not avoid SBIR, it merely shifts the first frequency in the series of peaks and nulls to be lower. Moving them away from the front wall does reduce the bass shelving increase for being near a boundary though. Soffit mounting does avoid SBIR.

  > I'm not sure whether placing broadband bass traps in the corners behind the loudspeakers would help SBIR distortion at all (I'm sure room mode issues are ameliorated regardless...) <

  I believe corner trapping does help, though I admit I've never performed that exact experiment.

  > I was wondering whether there are unique benefits to having bass traps in the front corners of the room too. <

  Yes! All corners are valid for bass trapping.

  --Ethan
  
  

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  • Re: Do bass traps affect SBIR? - Tumara Baap 00:28:39 09/15/06 (1)
    In Reply to: Re: Do bass traps affect SBIR? posted by Ethan Winer on September 14, 2006 at 12:08:47:

    Agreed Ethan. The idea was that by pulling the loudspeakers out far enough, SBIR will manifest at frequencies low enough that they're only occasionally reached by most recorded material. Or that SBIR would be below the sub/satellite crossover point where it is the subwoofer that's mostly producing those frequencies. The distortion in practical terms would hence be ameliorated, if not altogether cured.

    Since I'll be very keen on getting all the space I can get in that small room, it's the ceiling that will get the heaviest treatment. I'll consider placing traps in the front corners if there are exclusive benefits from doing so.

    Tumara Baap
    
    

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    • Re: Do bass traps affect SBIR? - Ethan Winer 15:27:15 09/15/06 (0)
      In Reply to: Re: Do bass traps affect SBIR? posted by Tumara Baap on September 15, 2006 at 00:28:39:

      Tumara,

      > The idea was that by pulling the loudspeakers out far enough, SBIR will manifest at frequencies low enough that they're only occasionally reached by most recorded material. <

      Here's another idea: Put the loudspeakers as close to the front wall as possible, raising all the interference frequencies high enough to be cured with relatively thin absorption. As I explained previously, this will give a shelving increase at all low frequencies. But that is much less damaging than a series of numerous peaks and deep nulls. You could also counter that with a simple bass rolloff using a receiver's built-in tone controls.

      --Ethan
      
      

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