Author Topic: Understanding the Triple Leaf Effect  (Read 3573 times)

frinknet

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Understanding the Triple Leaf Effect
« on: August 16, 2013, 05:51:03 PM »
I'm asking these questions as theory rather than practice in order to help teach a man how to fish. There is no Wikipedia page on the triple leaf effect. I've been scouring the Internet trying to find a full explanation of this effect, it's math and courses of mitigation. Sadly, I've found so much conflicting info that I'm just plain confused.

Here are some questions that I can't seem to find answers to:

  • Does the triple leaf effect crop-up even with a fully decoupled room floated inside another room, properly sealed?
  • Is this effect mitigated by doubling the mass of the drywall and/or adding dampening of some sort? If so which leaf should be doubled?
  • How much of a gap needs to be created to mitigate this effect?
  • Is the triple leaf problem caused by a closed space between the two layers of mass? Could extra cavities of air (like a closet or alcove) mitigate the effect by dissipating air pressure?
  • Does stud spacing play into this effect at all?

I guess the long and short is I don't quite understand the physics or the math associated with this effect. It's described mostly in non-concrete terms so there is no easy way to deal with it.

jhbrandt

  • Guest
Re: Understanding the Triple Leaf Effect
« Reply #1 on: August 23, 2013, 01:43:14 PM »
Triple Leaf:

It's all about RESONANCE and coincidental resonances. In other words; when a panel resonates at a certain frequency - due to it's mass & stiffness - the sound transmission loss of that panel moves from a negative number to a positive number. At resonance, a panel will pass sound waves as though the panel did not exist.

Two panels, designed for odd-order resonance (where there is no coincidence) will have a better low-frequency sound transmission loss without the sharp dip in STL at panel resonance. Even using two panels of identical resonant frequency the range of sound transmission loss is fairly even and calculable.

Stud-spacing affects the resonance of the wall. 24" on center will have a lower resonance, being more limp than 16" on center.

Triple leaf construction for sound isolation has been used for many years and is preferrable for voice-range isolation. The benefits of this type of construction is that sealing of one partition is less critical; where there may be outlets or other fixtures added or taken from one partition or another.

The triple leaf effect is often unavoidable in remodeling or adding a studio room to an existing house or building. It is best to design so that there are differing masses, air space, and associated resonant frequencies. This is often the least of one's worries when it comes to sound-proofing. ;)
More information is available on my publications page.

Cheers,
John

 

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