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Two Cabs - positioning

#63
Coolhandjjl said:
Excellent question, I wish more people asked it.
When two drivers playing the same frequency ranges are placed next to each other, the sound waves they produce will overlap in certain places. Where they overlap, or collide, the waves created a null or drop out in certain frequencies as you walk along the stage from left to right. The higher the frequency, the worse it gets. Combing really messes up the goal of even dispersion. 410 guitar cabs suffer from it dearly. And a stack two cabs wide with 410's or 412's is the worst thing ever to happen to the guitar backline. It happens to bass cabs as well, any 410, 610, 810, etc, comb filters. And the guy who sets up two stacks of 410s, 610s, or 810s has no idea how badly he is messing up his output. Some people think it adds to a cabs unique sound, some hate it. In either case, it is a defect. Why do people use 410, 610, 810, or set cabs together side x side? Because they saw the other guy do it, and it is stuck in the zeitgeist now.

The general principle of driver placement to mask destructive interference with the other driver (combing), and maximize dispersion, is to stack vertically for horizontal dispersion. That is the purpose of backline gear. You want even horizontal dispersion for you when you walk about the stage, for your bandmates, and for the audience on the floor right in front. The combing will still be there in the vertical plane, but only noticeable if you run up and down a ladder. Now you know why there is so much science involved in PA rigs. The audience is both horizontal and vertically arranged in a theater.

Try this: drop a pebble in a pond and look at the waves radiate evenly. Now drop two pebbles about 6" apart at the same time. You will notice weird wave front interference where the wave from one pebble collides with the wave from another. There's lots of diagrams to Google for that illustrate it better than me.
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This is a real good explanation for comb filtering. I ran across the term on BFM website, and Bill's explanation was great, but I wasn't planning on getting college credit for reading it. I sometimes run a 2x10 cab with a 1x15. It's a lot better if I put the 2x10 on its side on top of the 1x15, so that all the drivers are lined up in the same vertical plane....like CoolHand said.
 
#64
WildBill987 said:
This is a real good explanation for comb filtering. I ran across the term on BFM website, and Bill's explanation was great, but I wasn't planning on getting college credit for reading it. I sometimes run a 2x10 cab with a 1x15. It's a lot better if I put the 2x10 on its side on top of the 1x15, so that all the drivers are lined up in the same vertical plane....like CoolHand said.
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Actually it's an extremely poor description of why noticable comb filtering is more likely with a lateral 2 x something
Versus a vertical 2 x something.
It's not about ripples in a pond other than at a boundary, like an out of phase reflexion from a wall.
It fails to explain that this is an off axis effect caused by the length of time it takes the sound to travel to the listener being different for a lateral cab and the same moving from side to side for a verticle one.
Dropping two rocks six inches apart in an incompressible medium 800 times denser than air has 0 similarity to the wave front of a close coupled pair of speakers in a light compressible medium.
And can't explain the reasons for the answer to the original posters question at all, as there would be no difference between these colliding pressure ridges in either orientation.
Basically as science it's just over simplified bollocks.:-)
 
#67
I'm not on GK's, mine are aguilar GS212's. With one, my bass was too weak in our (very loud) setting. It just lacked the oomph and when i turned up the amp to be audible, the higher frequencies came through all right, but the fundament was weak. Just like the OP. Another cab did the job just as expected. More volume, more oomph, more everything. I tried several settings and settled for Fig. I.
best sound plus i put wheels on the lower cab so i can move the stack around with one hand if needed.
 
#68
BassmanPaul said:
This thread go t full fast!! :)

Number one for me every time. I've done #2 swell but once I tried the "skinny" stack with my 2x10s I never went back! :D
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I can arrange my cabs vertically OR horizontally and still have everything aligned as the deity of your choice demands! :bassist:

Rig-1200_0085a.jpg


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#71
The comb filtering & narrowing dispersion thing is going to happen anytime you have more than a single point source (more than one speaker playing the sound), as the sound from one will arrive at the ear some split second earlier or later than the sound from the other(s) any time you are any place other than equidistant from all the sources.

The different positioning allows you to move the effect to where it is most beneficial/least destructive for the listener position in relation to the sources (speakers).

The only way to eliminate it is to only play through a single speaker, and even then that doesn't take into consideration the time arrival differences between the direct sound (straight off the speaker), vs. the reflected/reverberant sound (the sound that leaves the speaker and bounces off walls/ceiling/floor, etc., then arrives at the ear).
 
#72
will33 said:
The comb filtering & narrowing dispersion thing is going to happen anytime you have more than a single point source (more than one speaker playing the sound), as the sound from one will arrive at the ear some split second earlier or later than the sound from the other(s) any time you are any place other than equidistant from all the sources.

The different positioning allows you to move the effect to where it is most beneficial/least destructive for the listener position in relation to the sources (speakers).

The only way to eliminate it is to only play through a single speaker, and even then that doesn't take into consideration the time arrival differences between the direct sound (straight off the speaker), vs. the reflected/reverberant sound (the sound that leaves the speaker and bounces off walls/ceiling/floor, etc., then arrives at the ear).
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We can't win, can we? :smug:

Headphones!!! :)
 
#74
Mr_Martin said:
What is the most efficient positioning concerning driver coupling, bass frequencies, loudness etc.
And what are the advantages/disadvantages of these three different positions in the rehearsal room?

View attachment 551796
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If "uniform coverage" had been one of your criteria, I'd have suggested a slight modification to Number 1: Angle the top cab about 20-30 degrees toward the side you stand on, and angle the bottom cab about 20-30 degrees away from the side you stand on. This would broaden the horizontal coverage considerably and make it more uniform (no on-axis "hot spot"). Admittedly this might be more useful for gigging than for practice.

If "drummer being able to clearly hear the notes" had been one of your criteria, I'd have suggested another Number 1 variant: top cab straight ahead, and bottom cab aimed at your drummer.
 
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