Different cabs have different phase response and deviations in group delay at the low band which is caused by different cab design. Even different cabs but loaded with "matching" drivers can be (theoretically) very different, at the other hand different cabs loaded with different driver size can be very close in this regard, it depends. That's why I would never ever suggest to mix a ported cab with a sealed cab, for example mixing of a 410 ported with a 410 sealed was a good bet for phase and group delay anomalies at the lows.
Within a more "generic" cab family (like MI bass cabinets) the reasonably expecting phase difference at the lows is insufficiant to have "issues" like cancelation. The ball-park tuning of ported MI cabs 45-55Hz predicts constructice interference of two "different" sources rather than destructive interference.
In other words, you are saying that mixing cabs is a big no-no… and that mixing a Jensen BS 15N 350A with, um, a Jensen P6V will not result in
some phase cancellation -- out in the audience? Specifically, that this speaker combination will not result in more phase cancellation than using matched drivers - assume their sensitivity is equivalent, although it is not.
At the other hand summation of different voicings of different cabs at mids and treble of course is a crapshoot, thus more predictable with "matching" stuff.
Very typical for it's comb filter "issue" characteristic are all kinds of full range running compound/isobaric cab designs. The typical comb filter response is caused by the "effective" distance of the two cones which work together as one "new" driver. Although the issue is a no go in HiFi world I would not revile this design as an impractical design for MI application.
Obviously these cabs are most reviled for beeing very inefficient, two drivers which need twice the power for same SPL instead of a single driver, while the typical comb filter response seems widely unnoticed by players and "engineers" in forum discussions. That's paradox but, as the issue is probably widely unknown, why should it be noticed by ears, cause aren't these matching drivers? It seems like as long as all the stuff is matching then there can't be an noticeable "issue" present!
A 4x10 does not function as a single driver (=one "new" driver). Time, acoustics, and space still exist. That's why comb filtering and other phase cancellation occurs. The ear is very well adapted to phase cancellation because of acoustics. When somebody speaks in a hallway and their voice reflects of the wall, the brain (typically) discards that "interference". Bass and guitar speakers and cabs are not designed or produced for linearity. Well, they are to some extent but volume, sound/tone, cost and durability are higher considerations. Furthermore, the musicians want that familiar sound. Sure, not all musicians can explain phase cancellation. Many recording engineers understand the problem, and more generally acoustics and phase cancellation. I assume you'll find plenty of internet awareness of the issue if you look up recording guitarists' 4x12s. I would be surprised if a detailed writing on the subject of miking a 4x12 left out phase cancellation considerations. E.g. I am not talking about a blog post which reduces the process to "SM57. On axis. A few cm from the dust cap. Set trim. You may want a room mic for ambiance. Presto!".
Agreed. Precondition is to know the manner of cancellation if present.
The one half the distance of drivers centers wavelength is roughly the highest possible frequency for a plane wavefront. Line Arrays take essential benefit of this physics reality.
Instead of destructive interference (a wide valley) there is rather constructive interference up to this 1/2 distance wavelength. The worst "coupling" of full range running drivers was with multiple 15"s (wide distance of the sources centers) while the best "coupling" was with 10"s (narrow distance of the sources centers).
The mixing of different cabs results somewhere in between of the both.
Yes. Specifically, it's constructive from 270 around to 90 degrees. At 90 degrees (1/4 wavelength) it turns destructive. At exactly 180 degrees, you have total cancellation.
That's a chance
in theory that mixing drivers will work when you are standing on axis, but will result in a less consistent sound as you move off axis and as you throw that combination into a venue and acoustics are involved. Your audience cannot all be positioned in "The Sweet Spot". Note: Smaller drivers have wider dispersion.
Mixing drivers as you suggested introduces phase cancellation in hopes of achieving flatter frequency response by averaging (by having comb filtering using multiple fundamental wavelengths).
Would you say that the speakers used in a line array should be identical or would you encourage people to mix different speakers in a line array?
If you said "identical", then why do you believe this does not apply to an 8x10? If you answered "mixed" it would be very inefficient and the sound would be unpleasant from significant cancellation.
While there is this frequently adressed "phase issue" thing with mixing of different cabs, I think there are a couple of different parameters like cab system damping Qtc and impedance curve that can make a mixing of cabs delicate especially with tube amplifiers. But, unfortunatelly, the result of "indistinct" respectively bad sound is always adressed to phase anomalies. IMO that's a little bit of delusion. A very loosen indistinct muddy sound could also happen with matchin stuff but highish Qtc and highish impedance peak driven by tube amplifier with weak global feedback control.
Or an indistinct sound can be from a low quality cable, bad filter design, inadequate headroom, a low battery… I didn't blame everything on phase anomalies. I just suggested a way to minimize phase issues when I suggested a second 1x15
