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Mixing Cabs and Phase Cancellation

Discussion in 'Amps and Cabs [BG]' started by JN8642, Oct 8, 2017.

  1. JN8642


    Aug 19, 2015
    So I've searched for an answer to this more specific question but couldn't find all that much. I know mixing a 1x15 and a 4x10 or 4x8 is bad in most situations and that matching speaker sizes will produce in a better result.

    Is part of that a wattage issue? Say if you have a 300w 1x15 and a 400w 4x8 or 500w 4x10 and you have a 200w head that has multiple 4ohm and 8ohm outs, would that still cause phase cancellation and it not generally sounding as good as matched speaker sizes?

    Part of the reason I'm asking is cause I was offered a 300w 1x15 from a friend for cheap and was looking at a 4x8 or 4x10 as well, but am also generally interested.
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    You might look here for a start. We have discussed in great detail many times, and I have provided information about why mixing driver sizes is not automatically bad, but by the same token may not be good depending on the specific combination and how they were designed.

    Mixed cabs, double dog dare me
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Comb filtering is cause by phase cancellation (and summation) of 2 or more sources with different arrival times. Different arrival times can be caused by several things and does happen with identical driver cabinet combinations as well. (otherwise, line arrays wouldn't work the way they do)
    GregC, Grumry, Stumbo and 2 others like this.
  4. DigitalMan

    DigitalMan Bring Back Edit/Delete Supporting Member

    Nov 30, 2011
    Bay Area, CA
    Matching speaker sizes makes no difference in the context of phase response and mixing cabs. Cabs are either identical or they are not, irrespective of speaker size.
    Al Kraft likes this.
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Speaker systems can have identical acoustic response, even though the drivers may not be identical.

    Just like you can get the identical answer of 12 by adding either 6+6 or 8+4.
  6. Watts don't come into phase until too many watts cause distortion.
  7. crguti


    Feb 14, 2011
    if you're a bad player you get phase cancellations even with 1 speaker. :rolleyes:
  8. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    This Bloke called Dunlavy experimented with many different diameter loudspeaker chassis, all time aligned, all carefully chosen from different manufacturers with absolute minimum in the way of passive crossover components at very low slope rates, and therefore wide overlaps between the coned drivers.
    I know a couple of well known mastering engineers that would cheerfully pay $10,000 for a pair in good order, delivered.
    In case you were thinking of replacing your Fearfulls they unfortunately weigh in at circa 500lbs per speaker.:)X
    PS Theories are just theories after all. You still need to experiment in practice.

    Attached Files:

  9. DigitalMan

    DigitalMan Bring Back Edit/Delete Supporting Member

    Nov 30, 2011
    Bay Area, CA
    Completely agreed. Just pointing out a common fallacy regarding size. As you state, it’s all about spec.
    agedhorse likes this.
  10. micguy


    May 17, 2011
    I played a gig once where I accidentally wired my 2 cabinets out of polarity - they were out of phase at low frequencies pretty much wherever I stood. Even with the amp full out, I couldn't hear myself on stage, until later in the set when I figured out what was up, and disconnected one speaker.

    Playing with mixed cabinets may (or may not) result in phase cancellation where what I encountered happens for a range of frequencies (though not all). Given typical phase responses of bass speakers, that range of frequencies is likely to be at the low end of that bass guitar's frequency range. Think of the notes below A on your E string all being pretty weak as a symptom that might occur - the logical response might be to crank the bass control on your amp. If you do that, you'll probably get too much low end on your A string, and you'l be pushing your amp and speakers really hard for the lowest notes.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    A polarity reversal (or broad band 180 degree phase shift between sources) is a special case as it causes energy cancellation across most of the audio range (below say 500Hz) whereas the phase deviations from different speakers typically affect only a smaller range of the spectrum and the cancellations are nowhere near as deep or broad band. The equations governing these scenarios are quite different (with the polarity reversal being the simplest by far).
  12. Ewo

    Ewo a/k/a Steve Cooper Supporting Member

    Apr 2, 2008
    Huntington WV
    Listen to @agedhorse! This is an important distinction.

    It's easy enough to fix a polarity reversal: just switch the leads to the speaker that's opposite the others in your array. The gist of it is that you want all the speaker cones in your cab array to move out at the same time and in at the same time if you feed them a simple sine wave.

    That's not the booger that may come up when you mix cabs and/or drivers. Comb filtering is a different problem, without a simple fix; hence the caution about mixing. A given assortment of cabs and drivers might sound good, or might not.

    So if you want to add another cab to what you've got, the course of action least risky to your wallet is to get another of the same cab.
  13. NKBassman

    NKBassman Lvl 10 Nerd

    Jun 16, 2009
    Winnipeg, MB, Canada
    The problem with watts is different from the problem with phase.

    Say you have your 300W 1x15 and a 500W 4x10, and a head that will put out, say, 500W into 4 ohms (each cab is likely going to be 8 ohms, so when combined the total load on the amp is 4 ohms). Each cab will get half the power from the head, so in our example that is 250W per cab. The 4x10 further divides this between each speaker, so ~63W per speaker, while the 1x15 is pumping 250W into just one speaker. So the 4x10 is barely breaking a sweat while the 1x15 is being pushed pretty hard. Now also consider that the 4x10 will (probably) be louder than the 1x15 as well, so if you turn up your amp too high you may not even notice that the 1x15 speaker is sounding stressed to the max before it blows.
    packhowitzer likes this.
  14. Coolhandjjl


    Oct 13, 2010
    When you have more than one driver covering the same frequency range, acoustic interference happens. How much of it is noticeable or bothersome is a function of the design of the system.
  15. Huh?
    Could you expand further? I'm not following what you mean.
    agedhorse likes this.
  16. JN8642


    Aug 19, 2015
    Thanks for all the replies so far everyone, very stoked to be learning new things!
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Right, even identical drivers will have acoustical interference between them because the acoustic centers are not identical. This introduces some time offset that varies with listening position.

    Here's an example of how dissimilar sized drivers COULD have better phase response performance. Say we have a 15" and a 12" driver covering the same range, and we are able to design the drivers so the acoustic properties were very close. The phase response will also be very close (in a properly designed enclosure) but when comparing the 15"+15" to the 15"+12", the acoustic centers are closer in the mixed driver cabinet, the time offsets will be smaller, so in theory the SYSTEM phase response will be "better". Now in practice, it's unlikely for a 3" difference in acoustic centers to be a big deal for bass guitar, but for pro audio, especially HF arrays, it's a huge deal because of the much shorter wavelength that HF signal is.
    NKBassman likes this.
  18. TonyP-

    TonyP- Excuse me but you have your I-IV-V in my II-V-I Gold Supporting Member

    Aug 21, 2003
    Boston Mass
    A-Designs Mike Lull GK Tsunami Cables GHS Strings RMI Basswitch Nordstrand Pickups Darkglass
    All those fearful designs remind me of
    agedhorse likes this.
  19. Send an xlr to foh and play whatever cabs you like. Just keep your stage levels reasonable so you're not overworking the weaker cab or causing phase issues between your rig and the PA which is the phasing problem people who play outside of their bedroom are concerned with.
  20. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    You always have to complicate things with complex math.
    smogg likes this.

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