Theoretical Theories Needed

SurferJoe46 · #1 12-28-2010, 09:51 PM

Sound-wise techno answer needed: what's the problem with putting cabs, side-by-side?

Say - 2, 410s alongside of each other.

What's the problem and is it coupling or comb filtering and if so what makes it different from stacked cabs?

JimmyM · #2 12-28-2010, 09:58 PM

before i knew of concepts like beaming and comb filtering, i just didn't care for the sound of sideways stacked rigs. i thought stacking vertically sounded way better. plus two cabs pointed to your ass vs two cabs with one pointed at your head and one at your ass? so much win!

SurferJoe46 · #3 12-28-2010, 10:01 PM

OK - my ass gets too much attention anyway.

I picked up a floor model of an Acoustic B-410 today (for a very good price I might add) and I was just wonderin'.

billfitzmaurice · #4 12-29-2010, 06:49 AM

Quote:

Originally Posted by SurferJoe46

Sound-wise techno answer needed: what's the problem with putting cabs, side-by-side?

The angle of dispersion is inversely proportional to the dimension of the source. Therefore wide sources have narrow dispersion on the horizontal plane. For that reason not only should cabs not be placed side by side, neither should drivers.

Arranger · #5 12-29-2010, 06:54 AM

So, I guess that tall sources have a narrow dispersion in the horizontal plane.

billfitzmaurice · #6 12-29-2010, 07:11 AM

Quote:

Originally Posted by Arranger

So, I guess that tall sources have a narrow dispersion in the horizontal plane.

The opposite.

blastjv · #7 12-29-2010, 07:55 AM

Bill,

I trust that this is true, because I accept that you know SO much more than me in this area, but I just can't wrap my head around why dispersion is different in the horizontal vs vertical plane, when the source (the speaker) is circular...

I'm sure you've explained this before, sorry if I missed it along the way...

-JV

SurferJoe46 · #8 12-29-2010, 10:26 AM

Do any of us remember the guy on here who had (AFAICR) two 410s under another 410 in pyramid formation? Thankfully I saved this pix:::

He said it sounded good - speculative, I know - but what's the problem with them in the triad-shape?

It seems to me that doing it that way would solve both the horizontal AND the vertical linear axis support - or lack thereof - and if comb filtering could be a problem it would be negated by this configuration.

billfitzmaurice · #9 12-29-2010, 12:05 PM

Quote:

Originally Posted by blastjv

I just can't wrap my head around why dispersion is different in the horizontal vs vertical plane, when the source (the speaker) is circular...

It isn't if you have just one driver. With two or more drivers the source is no longer circular.

Quote:

It seems to me that doing it that way would solve both the horizontal AND the vertical linear axis support - or lack thereof - and if comb filtering could be a problem it would be negated by this configuration.

That configuration makes everything about as bad as is possible.

blastjv · #10 12-29-2010, 12:53 PM

OK, that's obvious.....now...

What is the simple explanation (if such exists) as to why?

-JV

JimmyM · #11 12-29-2010, 12:57 PM

because sound waves do not act like light waves. they bounce off each other and cause interference with each other if not set up to where they don't. and the beaming principle states that the larger the driver, the more directional the higher frequencies become. that's why you can stand 2 feet away from your guitarist's amp and it sounds great, but stand in front of it and he drills a hole between your eyes with treble. two 10" drivers set side by side react like a 20" driver when it comes to beaming so using small drivers isn't the solution unless they're arrayed vertically.

honestly, i'm not so bothered by beaming, but it definitely exists and works in that fashion.

BurningSkies · #12 12-29-2010, 01:04 PM

Quote:

Originally Posted by blastjv

Bill,

I trust that this is true, because I accept that you know SO much more than me in this area, but I just can't wrap my head around why dispersion is different in the horizontal vs vertical plane, when the source (the speaker) is circular...

I'm sure you've explained this before, sorry if I missed it along the way...

-JV

I'm going to guess, and this is a non-scientific degree oriented guess...and how I've always understood it...

if you stack vertically, you're not necessarily changing the way the sound interacts in a vertical vs. horizontal plain as much as us humans move in a room in a horizontal dimension rather than in a vertical fashion (at least most humans I know do). Therefore, if you stack vertically the same bad interactions CAN happen, but since we happen to be listening in a very narrow vertical range (from about 3 feet off the ground from sitting to no more than 6 feet and change when standing) we don't run into half as much of the cancellation nodes.

abarson · #13 12-29-2010, 01:39 PM

Sometimes a picture is worth a thousand words. Does anyone have one that illustrates how sound propogates across the horizontal axis for these two configurations (side by side vs. stacked), possibly showing the beaming principle?

BassIan · #14 12-29-2010, 01:41 PM

Quote:

Originally Posted by BurningSkies

I'm going to guess, and this is a non-scientific degree oriented guess...and how I've always understood it...

if you stack vertically, you're not necessarily changing the way the sound interacts in a vertical vs. horizontal plain as much as us humans move in a room in a horizontal dimension rather than in a vertical fashion (at least most humans I know do). Therefore, if you stack vertically the same bad interactions CAN happen, but since we happen to be listening in a very narrow vertical range (from about 3 feet off the ground from sitting to no more than 6 feet and change when standing) we don't run into half as much of the cancellation nodes.

This is pretty much bang on.

BassIan · #15 12-29-2010, 01:51 PM

Quote:

Originally Posted by abarson

Sometimes a picture is worth a thousand words. Does anyone have one that illustrates how sound propogates across the horizontal axis for these two configurations (side by side vs. stacked), possibly showing the beaming principle?

Check out the applets at this website to play with the concept a bit. You can play with 2-D, 3-D interference plots between two sources (speakers). A good one to try is the Ripple Tank simulation, since it actually animates and can show 3D plots of wave propagation. Seriously, play with these. I could come up with a million examples to post here, but it's way more instructive to do it yourself.

http://www.falstad.com/mathphysics.html

This one is cool for visualizing waves in a plane.

http://www.falstad.com/ripple/

This one is cool for 3-D visualization.

http://www.falstad.com/wavebox/

In the included picture, the sources are 30cm apart, which roughly approximate the spacing of a pair of 10 or 12" drivers. The plot shown is what the interference pattern looks like for a 2khz sine wave. Bright areas are loudest, dark areas quietest.

EDIT: Added second picture for better visualization.

For side by side speakers, this is the pattern you'll get if you're looking down from the ceiling at the floor (top view). So, as you walk left to right across the room you'll walk through light and dark areas, perceiving the volume changes as you go.

For vertically stacked speakers, this pattern would be the same, but it's now oriented in a vertical plane. You'd experience the same volume changes as before if you climbed a ladder and changed your altitude in the room. As it is though, audiences in the venue will be walking around roughly in the center loud node all the time.

This issue gets more complicated when more than two identical sources are used (4x10 or 8x10), and even more when the sources aren't identical (mixed drivers!). Then, phase and amplitude response differ between the mixed drivers. But, the macro-level result is the same. Multiple sources result in interference patterns. Vertical stacking is better in nearly all venues to avoid the most easily noticed effects of interference patterns.

Obviously the effects and associated design are much more complicated in a large stadium-seated venue, which is why advanced simulations are used to design the flown arrays in such venues. Meyer Sound is known for their simulation packages that aid in the design of such large arrays.

JimmyM · #16 12-29-2010, 02:00 PM

www.jblpro.com has some excellent papers on how sound operates, too.

**Matthew_84** · #17 12-29-2010, 02:12 PM

Wow... Sure glad i read this post

Arranger · #18 12-29-2010, 02:27 PM

Wouldn't comb filtering be conical in it's shape, since the speakers are round?

billfitzmaurice · #19 12-29-2010, 02:32 PM

Quote:

Originally Posted by abarson

Sometimes a picture is worth a thousand words. Does anyone have one that illustrates how sound propogates across the horizontal axis for these two configurations (side by side vs. stacked), possibly showing the beaming principle?

http://www.falstad.com/wavebox/
Use the source separation slider to see not only what happens with two versus one driver but also the effect of how far they're separated. Use the phase slider to see what happens with mixed drivers.

Quote:

Wouldn't comb filtering be conical in it's shape, since the speakers are round?

No. Comb filtering is when the response varies across the bandwidth with a series of peaks and valleys, resembling the teeth of a comb. Worse, as you move across the sound field those peaks and valleys shift, so the sound is different at every listening position.

BassIan · #20 12-29-2010, 02:33 PM

Quote:

Originally Posted by Arranger

Wouldn't comb filtering be conical in it's shape, since the speakers are round?

Yes, a single circular source will produce a conical pattern, with the width (angle) of the cone depending on frequency and source diameter. However, for easier visualization, the two sample plots I included are 2-D sections of 3-D space.