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Confusing phase and timing when we say that different size speakers together is bad?

Discussion in 'Amps [BG]' started by sbpark, Feb 9, 2013.


  1. sbpark

    sbpark

    Joined:
    May 26, 2010
    To start, I'm sure this topic has been discussed ad nauseum, and this is in no way an attempt to troll. I'm pretty new to this forum, and have to say in the short time I have been here I have learned and gained a PLETHORA of knowledge that I cannot thank everyone here enough for. This post is merely an attempt to continue that trend and to educate myself even further.

    The general consensus here is that it is bad juju to combine different cabinets that have different size speakers. I'm sure there is evidence that can both prove and disprove this, but the problem I have is when people say that it's due to PHASING issues. I am not an engineer nor do I have any kind of formal technical background, so I am just trying to understand this from a layman's standpoint. But I always thought phase had nothing to do with timing, and is something completely different. Phase would have to do with the way the cabinets were wired, and if one was wired opposite of the other you were using, THAT would cause phasing issues. Basically the same thing would happen if you hooked up one of your stereo speakers opposite of the other, then they are said to be out of phase. This I understand, but am sure there is an industry standard as to how the leads are connected to what terminals on the speaker in order to prevent cabinets from being out of phase with each other.

    The other issue I have is when others mention TIMING issues or differences when using cabs with different size speakers, because of the differences in speaker size, they will move at different speeds, thus resulting in an identical frequency from say a 10" speaker will reach a certain distance at a different time that that same frequency coming from a 15" speaker. This to me in theory sounds like it makes sense, but I am still having a hard time believing that it would make any discernable difference in the real world. And although there may be a SLIGHT difference in the timing or delivery of an identical frequency produced by two different size speakers, the wavelength of that frequency is going to be the same size, regardless of what size speaker produces that frequency. I mean, sure, EVENTUALLY if the signal was strong enough, and had the amplitude and power behind it to travel far enough, there MAY be a point eventually where those two identical frequencies produced by two different size speakers in the same rig MIGHT end up out of phase, but I really doubt that that could ever manifest itself in a real world situation, and cannot imagine it happening in a small venue, bar, club, etc.

    The reason I think this is hard to believe is because we are surrounded with devices that use different size speakers together in the real world and have never heard it being an issue, be it in a television, desktop speakers, pro-audio/powered monitors, etc.

    I'm not saying its all a bunch of b.s., because I 'get it' from an analytical perspective, but in real world application I really think it's reaching here, especially if your using cabs from the same company, the same design, that just have different size drivers in them.

    Am I way off here and missing something?

    And thanks to everyone who read this long winded post, and encourage your feedback and thoughts!
     
  2. Downunderwonder

    Downunderwonder

    Joined:
    Aug 26, 2009
    Location:
    New Zealand
    You're missing a key point. Each speaker has a characteristic phase response across its frequency operating range. The music is always misphased with itself but it doesn't bother our hearing of it, we hear the sum of harmonics as if in phase.

    But combining misphased outputs of incompatible cabs gives bumps and hollows in the sum.
     
  3. sbpark

    sbpark

    Joined:
    May 26, 2010
    So what is defined as an incompatible cab? Or should I ask it this way...are there cabs that are compatible that have different size drivers? For example, using two Portaflex heads, one with 115 and the other with 210. They are different size speakers, but one would think they are 'designed' to work together...
     
  4. Downunderwonder

    Downunderwonder

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    Aug 26, 2009
    Location:
    New Zealand
    One would think but one wouldn't always be correct.
     
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  6. Vince Klortho

    Vince Klortho

    Joined:
    Jan 8, 2013
    Location:
    Squierville, California
    Incompatible means they do not sound good together. Some combinations of cabinets do sound good together and some do not. Only your ears can tell you how if they do.

    I should add - as with all sound-related things, what sounds good is a very subjective thing and people's opinions vary.
     
  7. T-Bird

    T-Bird

    Joined:
    Apr 29, 2007
    Location:
    Finland (Northern Europe)
    Hi.

    First of all, randomly mixing different size drivers/cabs is generally worse than using multiple ones that are the same.
    Things get very, very different when cross-overs of any kind are added to the equation.


    Phase:

    What You describe as phase, sounds more like a polarity, ie. 180 degrees apart.
    Because of the behaviour differences of the motor + impedance matching cone in different drivers, the phase difference between two dissimilar drivers at a given frequency, regardless of their size, can be anything from 0 to 180.
    That is the reason for active cross-overs and/or very complicated passive Hi-Fi cross-overs.
    For optimal results, the phase of the two different drivers to be bundled together has to be the same about an octave on both sides of the cross-over frequency. Adjusting that phase isn't easy with a passive system.

    Timing:

    You have me stumped there, but I'm no expert, just a hobbyist.
    I think I have never seen anyone pull that card out when speaking about MI drivers/cabs.

    When two motors are at a different vertical plane, that obviously creates an arrival time difference between 'em, but in relation to the wave-lenght of the normal frequency range in MI use, and on the other hand the distance to the listener in a real world situation, I for one fail to understand its significance.

    Not the most perfect of analogies when speaking about mixing different drivers and their arrival time differences I know, but the time-delay-towers in huge outdoor concerts could be something we all have experienced. When moving around, there will be spots where the sound is percieved as "normal" (especially between the towers), no matter how far away from the stage you are, and when going outside of the designed range, the delay or phasing effect may become unbearable. That's the scale the arrival differences have a meaningful effect, in a stack not so much. IME anyway.
    OTOH, the same problem occurs if the bass rig of a formidable power blasts several meters behind the FOH and the two signals overlap and fight without any arrival time difference compensation.

    Regards
    Sam
     
  8. sbpark

    sbpark

    Joined:
    May 26, 2010
    Thanks for this.
     
  9. gearhead1972

    gearhead1972

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    Feb 21, 2012
    Location:
    Kent NY
    Actually, the phase issues have everything to do with timing. one simple way to look at it is, say you have a 15 and a 10 running off the same amp. The 15 may have more mass and take a little longer to replicate the same note as the 10, this in turn would put the wave these are producing of the same frequency out of phase.
     
  10. sbpark

    sbpark

    Joined:
    May 26, 2010
    it would only be out of phase to where they cancelled each other out if it had the time and distance for them to line up that way. I am thinking sort of like what we used to do with two tape decks in the studio to get that effect.

    T-bird pretty much covered this in his reply using the examples of a big FOH set up in an outdoor setting, and also touched on the timing differences with the stage cabs being set back a ways from the FOH speakers.
     
  11. Vince Klortho

    Vince Klortho

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    Squierville, California
    As to your original post, phase and timing refer to essentially the same thing. Timing refers to when sound waves arrive at your ear in time. If the speakers that produce them are at different distances from your ears then the sounds will arrive at different times. The sizes of the speakers are irrelevant to this. The effect of this time misalignment is the sound waves will be slightly out of phase from each other. When speakers are wired "out of phase" the result is signals that are 180 degrees out of phase from each other or one half of a wavelength for all frequencies. When speakers are misaligned in time the result is a phase difference that depends on the frequency (and wavelength) of the sound. Nearly any time there are multiple speakers, regardless of size, there is a time misalignment and the amount will depend on the difference in distance between the centers of their cones and your ears. For speakers in the same stack the time difference is small and constant with frequency. The difference in phase will be less significant with lower frequencies because it is a smaller percentage of the waveform. Also - human ears are less sensitive to phase differences in low frequencies than they are at higher frequencies.

    I wrote, "Nearly any time ..." because some speakers are mounted so they are time-aligned. There are also active crossovers that can do time alignment for the different frequency bands in PAs. I have heard this in action and it can make a huge difference.
     
  12. sbpark

    sbpark

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    May 26, 2010
    So in your opinion its more about speaker placement and alignment than using two of the same cabs from the same manufacturer that are loaded with different size speakers?
     
  13. Vince Klortho

    Vince Klortho

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    This is not true. They are both reproducing the same waves and will take the same amount of time to do it. They just move different distances and at different velocities.
     
  14. sbpark

    sbpark

    Joined:
    May 26, 2010
    And as T-bird pointed out, speaker alignment (if on of the speakers is in front of/behind the other will have more affect on this.
     
  15. Vince Klortho

    Vince Klortho

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    Jan 8, 2013
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    Squierville, California
    No, in my opinion the phase differences do not matter very much for bass frequencies as long as the speakers are close together. I think the composite frequency response of the cabinets matters more.

    Occasionally you will see bands with stacks of speakers on both sides of the stage. Usually that can cause problems but not so much when the stage volume is blasting loud. In that case you can't hardly hear one stack on the other side of the stage.
     
  16. Vince Klortho

    Vince Klortho

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    Jan 8, 2013
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    Yes, I see that now. When I started writing he had not posted and I was interrupted in the middle of my writing so I did not see his post when I wrote mine.

    However, my point is that different speakers will take the same amount of time to reproduce the same frequency.
     
  17. sbpark

    sbpark

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    May 26, 2010
    I'm just wondering, and the reason I started this thread was to see if it really mattered in a real world situation, where someone was playing in a small bar with a 1x15 and a 2x10 cab from the same manufacturer. I personally think it's insignificant, but then again I have no real world experience to go off of yet. I've only ever played through 2x10, 4x10 or 810 cabs.
     
  18. sbpark

    sbpark

    Joined:
    May 26, 2010
    I agree with you on that. Others claim that some speakers are faster than others, but seriously, aren't we talking milliseconds here, and will that really make a difference? I doubt it!
     
  19. JimmyM

    JimmyM Supporting Member

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    Apopka, FL
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    Endorsing: Ampeg Amps
    All speakers respond at the same speed regardless of size.

    I would also argue that rather than being unimportant, phasing issues are the bane of my existence as a bass player. Nothing I hate worse than hearing some notes and not others.
     
  20. sbpark

    sbpark

    Joined:
    May 26, 2010
    I'm sure most bass players would agree with that statement!
     
  21. David Jayne

    David Jayne

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    Jan 16, 2006
    Location:
    Brookfield, CT

    +1. They do. Otherwise they wouldn't play the same note.
     

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