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physical coupling

F

Fro 20

Feb 23, 2009
173
9
Buffalo, New York
#1
I tried searching. Totally really.

Is the X db (I keep hearing different numbers on here) increase of adding a second identical cabinet on top of another, lessened by the fact that the top cab is only touching the bottom one via the surface area of these 4 tiny rubber feet (as opposed to having no feet and laying across the whole top of the bottom cab)?
 
#6
Fro 20 said:
Ah.

When I seached "physical coupling" on TB, I got thread after thread and couldn't find the answer. So it's the proximity of being close to each other (1/4 wavelength?), and not the actual physical contact between the cabs, then.
Click to expand...
+1. There's no such thing as physical coupling, snake oil products that are intended to both increase and decrease its effect notwithstanding. Both mutual coupling of speakers and boundary coupling of speakers with walls, floors and ceilings are acoustical in nature, not mechanical.
 
#7
I hope this isn't too off-topic, but I have a "coupling" question. I use two GS112s and stack them on their sides (on top of each other) to get them closer to ear level. I would like to get the top speaker even higher and have wondered how to do this without adding a third cabinet. I would love to add another GS112, but would have to bring another amp.

I have added a pole-mount flange to the bottom of one of the GS112s, and I put it up on a speaker stand when I play upright. I considered adding a flange to the top of the other speaker and using a short, 2-foot pole to raise the top speaker to ear level when playing electric bass gigs. Would this effect the sound? I would be using two identical cabs in alignment, but they would be separated by 2 feet of air.
 
#9
Monkey said:
I would be using two identical cabs in alignment, but they would be separated by 2 feet of air.
Click to expand...
That's far enough apart to create a problem. Make a box to use as a stand, so that there's a solid face between the two cabs. Make it with no top and it can double as a gear tote or amp case.
 
#13
Bass_Pounder said:
No effect.

Doubling your speaker area (adding an identicle cab) adds +3db.

*IF* by adding the second cab, you are getting higher wattage output from your amp (solid state), then you are also going to pick up around another +3db from the increased power.
Click to expand...

True.
 
#14
billfitzmaurice said:
+1. There's no such thing as physical coupling, snake oil products that are intended to both increase and decrease its effect notwithstanding. Both mutual coupling of speakers and boundary coupling of speakers with walls, floors and ceilings are acoustical in nature, not mechanical.
Click to expand...

some info from the snake oil salesmen at Barefaced Bass.
Part 1 - Mechanical coupling
The key point to understand regarding coupling is that there are two forms of coupling - mechanical coupling and acoustic coupling.

With mechanical coupling the stage/floor is excited by the vibrations from the cabinet or by the acoustic output from the speakers/port and the floor itself becomes a resonating surface like a giant drum skin or speaker cone. The acoustic output from the resonating floor is very unpredictable, centred around the modes of resonance of the floor, which almost always results in a boomy onstage sound and unpredictable offstage sound (depending on how it reinforces and cancels the output from the speaker cabinet).

You should generally try to avoid mechanical coupling and this can be done by using a well-braced speaker cabinet which vibrates less, isolating the speaker cabinet by reducing the amount of physical contact with the floor (isolating foam/tilting cab/raising onto beer crate) and placing the cab at a more solid part of the stage (i.e. a corner). If you are on a small hollow stage see if it's possible to place the cab off the stage - also make sure that the PA subs are not on the stage, though any sound engineer with a clue will not have done this.
 
#17
Monkey said:
I hope this isn't too off-topic, but I have a "coupling" question. I use two GS112s and stack them on their sides (on top of each other) to get them closer to ear level. I would like to get the top speaker even higher and have wondered how to do this without adding a third cabinet. I would love to add another GS112, but would have to bring another amp.
Click to expand...
why not stack them vertically, instead of on their sides? you'll get a little more height that way.

alternately, maybe you could rig up a stable way to stack them that has the top cab tilted back a bit; they'd still be together, but the top cab would be aimed up more towards your ears.
 
#18
Obviously I need to spend some time rewriting the information on our site regarding coupling. The issue I'm trying to make clear by deeming there to be two kinds, mechanical and acoustic, is that pure acoustic coupling caused by boundary reflections or other woofers being in phase with the source woofer is a good thing.

The other sort of coupling which I've called 'mechanical coupling' is where the output of a cab (whether that be through acoustic output from the woofer or enclosure wall vibrations (if the cab has insufficient bracing) or anything else) causes other objects to resonate and in turn generate their own acoustic output. Most commonly this happens with hollow wooden stages and it's also the main feedback mechanism with acoustic instruments like double basses. This so-called mechanical coupling is almost universally a bad thing with loudspeakers as it causes additional distortion, uneven frequency response and poor transient response. You can call it acoustic coupling if you like but that doesn't half cause confusion when there's good acoustic coupling (boundary reinforcement and other in-phase woofers) and bad acoustic coupling (resonating stages etc).

Having spent more than my fair share of time knocking on the walls of various bass and PA cabs I can confirm that cabs which vibrate enough to set a stage shaking are sadly not non-existent!
 
#20
alexclaber said:
Obviously I need to spend some time rewriting the information on our site regarding coupling. The issue I'm trying to make clear by deeming there to be two kinds, mechanical and acoustic, is that pure acoustic coupling caused by boundary reflections or other woofers being in phase with the source woofer is a good thing.

The other sort of coupling which I've called 'mechanical coupling' is where the output of a cab (whether that be through acoustic output from the woofer or enclosure wall vibrations (if the cab has insufficient bracing) or anything else) causes other objects to resonate and in turn generate their own acoustic output. Most commonly this happens with hollow wooden stages and it's also the main feedback mechanism with acoustic instruments like double basses. This so-called mechanical coupling is almost universally a bad thing with loudspeakers as it causes additional distortion, uneven frequency response and poor transient response. You can call it acoustic coupling if you like but that doesn't half cause confusion when there's good acoustic coupling (boundary reinforcement and other in-phase woofers) and bad acoustic coupling (resonating stages etc).

Having spent more than my fair share of time knocking on the walls of various bass and PA cabs I can confirm that cabs which vibrate enough to set a stage shaking are sadly not non-existent!
Click to expand...

Thanks for elaborating! Still a little confused as you state that elevating or isolating a cab with foam can help but Bill says this is not real and stoops to the level of "snake oil". Please help us out.:)
 

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