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A Heartbreaking Thread of Staggering Conjecture.

Discussion in 'Live Sound [BG]' started by eyeballkid, Dec 5, 2013.


  1. eyeballkid

    eyeballkid

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    So...
    We all by now have probably become aware of the debate, science, opinion, and 'gospel truths' around the issue of speaker placement and comb filtering, as well as that applying to mixed speaker sizes.

    (in case you dont a quick primer is that it the accepted 'wisdom' is that it is best to NOT seperate bass cabinet to different parts of the stage due to sound waves interfering with each other and spiking some frequencies while squashing others, and even better is to vertically align speakers whenever possible.

    also it is best to stick with matching cabinets, speaker types, and sizes whenever possible for the most predictable and pleasing sound experience.....

    thats the condensed view...)


    ANYWAY... question is, does this theory/rule apply ONLY to a single sound source such as the bass, or does it apply as well to multiple signal sources?

    in other words, I know if I put one bass cab on one side of the stage and one on the other there are potential and real sound problems that can arise determined in some ways by the shape and size of the room, BUT... Do those same issues arise by having one bass cabinet on one side of the stage and one guitar cab on the other? for example, lets say the comb filtering model shows that two bass cabs X distance apart would spike the frequency of 30hz and kill 500hz at 50ft out, would those same frequencies be affected the same way if the guitar and bass played matching notes at the same time and the guitar cab is in place of the 2nd bass cab?


    ( and im just pulling random number here for an example that are probably not accurate... but run with it please )

    now lets have a good clean fight.
     
  2. Joe Louvar

    Joe Louvar

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    [​IMG]
     
  3. eyeballkid

    eyeballkid

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    I guess the impetus behind the question is "for best sound, should the bass and guitar cabs be placed together?". I ask because there are shows we've played where there seems to have been this effect and was it the room, or cab placement?
     
  4. Joe Louvar

    Joe Louvar

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    Look at an orchestra.
     
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  6. HolmeBass

    HolmeBass Supporting Member

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    I'd say to much lesser extent, it is possible, but the timbre differences between guitar and bass, even when playing the same note, are proof that the harmonic series of those instruments are not identical. Add in the slight difference in timing between the two players, and difference in EQ of the amplifiers, then I don't think it would be nearly the same issue as it is when projecting the exact same source between speaker cabinets located in different parts of the room.
     
  7. gkbass13

    gkbass13 Supporting Member

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    Great Dave Eggers shout out in the thread title.
     
  8. eyeballkid

    eyeballkid

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    I figured the feats of intellectual acrobatics destined to appear in this thread would rival his, AND it seemed an accurate title for what asking the question would bring...
    mea culpa.


    My first conjecture to break a heart would be that an orchestra isnt a good example as they tend to ONLY play in rooms optimally designed for sound dispersion. The vast range of tonal differences is about as great as it gets, but guitar and bass are VERY similar and just separated by an octave usually (effects aside). Orchestras also do tend to group the families of instruments as close as possible, if i recall correctly... sooooo let the conjecturing begin!
     
  9. Downunderwonder

    Downunderwonder

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    Guitar and bass are discrete signals. Being similar sounding means they are always smearing each other to a degree, no matter where the cabs are placed. This is why we "slot" eqs to produce a mix.
     
  10. eyeballkid

    eyeballkid

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    Which is why I ask how it affects live sound.
     
  11. Downunderwonder

    Downunderwonder

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  12. Cycho

    Cycho

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    Two bass cabinets slaved together are "coherent" -- like laser light. Two speakers with two different sources are incoherent, hence no problem with interference patterns. And yes, if you want to tell your guitar player they said on TB that his playing is incoherent that would be OK with me.
     
  13. Joe Louvar

    Joe Louvar

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    Actually, an orchestra is a perfect example of proper stage placement of musical instruments. And they perform indoors as well as outdoors, and with different as well as similar tones - so there's no need to try and reinvent the wheel - just saying.

    :rolleyes::rollno::rolleyes::rollno:
     
  14. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    There's likely some cancellation and reinforcement in the overall spectrum, but because the separate signals are different frequencies and are not in phase to start with, as would be the case with two cabs connected to the same amp, I wouldn't expect there to be any orderly or predictable pattern to the interference.
     
  15. walterw

    walterw Supportive Fender Gold Supporting Member

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    as i understand it, with two different sources it's no big deal. they may occasionally happen to both produce a certain frequency at the same time and cause cancellation or whatever, but the ear hears all that as the normal spatial placement in the stereo field (besides, different instruments are supposed to mostly stay out of each other's sonic way anyway).

    then there's the idea of "dual PA"; with PA top boxes, you don't want them side by side, because they'll comb filter and do weird stuff when the identical signal reaches your ear at slightly different times. (the problems that bass cabs and subs have when they're 15' apart, top cab horns have when they're 2' apart.)*

    with a dual PA, you have pairs of top boxes side by side on each side of the stage, but carrying different instruments; the inner set might be doing nothing but vocals and snare drum, while the outer set handles the rest of the instruments.

    even though they'll happen to produce the same frequencies here and there, the overall effect is to keep the sound distinct from each box.


    *the idea of line arrays, with a row of identical speakers hanging down, is that each speaker has a very narrow dispersion, so in effect you only really get hit by one speaker at a time from any given spot in the audience.
     
  16. Rocksolid

    Rocksolid

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    The only time I have experienced cancellation was at an outdoor gig. I had my 1100w Eden rig turning itself inside out and couldn't hear it for love nor money. Turn the FOH off and it near killed us all, but with the 4 18" subs under the truck we were playing on it was like standing in the eye of the storm.

    Subs were under the flat bed we were playing on, different size drivers, Truck bed between us etc. To this day I shake my head about that gig.

    To answer your question - I haven't the slightest idea.
     
  17. will33

    will33

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    Guitar and bass has totally different timbre/harmonic content even if they are playing the same note, so it's not the same as mixing different speakers together that are playing the same signal.

    The separating speakers thing is due mostly to less/non directional frequencies as they'go everywhere and collide even if the speakers are pointed away from each other. Hence the advice to cluster subwoofers to prevent cancellation yet spread the PA tops for wider audience coverage, as they are playing more directional frequencies.

    That's all in a perfect world. In real life, you do the best you can with the situation you're given, which was likely not designed with acoustics as a top priority and probably no priority at all. Helps to know how stuff works in the hopes of improving your sound rather than making it worse, but sometimes you have to break the "rules".
     
  18. will33

    will33

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    That is the "don't separate low frequency sources" thing. Your rig and the subs were both making LF some distance apart. That caused a cancellation where you were standing that made your rig sound virtually disappear. At some other listening spot, they would've summed together and the lows would be overwhelming.

    They probably didn't have the subs time-delayed to the backline.
     

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