1) picture entered by Stuart:
http://www.johnlsayers.com/phpBB2/viewt ... 540#p94540
2) Document linked by Brien:
http://www.johnlsayers.com/phpBB2/viewt ... 553#p94553
Referring to Brien's link
2):
Ted White wrote:Page 36, figure 18. "A Comparison of the Transmission Loss Provided by Double and Triple Panel Constructions of Equal Total Mass and Overall Thickness." Also the panels referenced have no mechanical connections.
This is the heart of all of this confusion. I have not been describing equal mass and equal overall depth. I've mentioned adding a third leaf in front of an existing double leaf. That would mean more mass and more overall wall depth than was originally there. Your STC 30 wall compared to the STC 50 wall scenario for example.
Ted you like slogans don't you? There is no STC 30 wall nowhere + nobody knows the original measurements of that picture
1).
Here some calculations towards the MSM.
I stylized picture
1) as being gypsum board panels of 12.5 mm (ca 1/2"). The wool thickness 100 mm ( ca 4"), and that empty cavity 75 mm (ca 3"). That's just a rough visual scaling of picture
1)
For every next wall I increased that empty 75 mm (ca 3") cavity with the same amount (doubling, tripling, ....)
Hence I compared the principle of that wall 2 (STC 36) versus that wall 4 (STC 50) as suggested previously by Ted. That wall 1 is a sic wall which should be filled with absorption if meant for sound isolation properties (even blow-in if wall exists already).
The
fo of that picture 18 in link
2) relates to the MSM of a double leaf system. The
f+ to the fhigh (upper) MSM of the triple leaf system.
These real
fo and
f+ on that picture 18 are located somewhat lower in frequency and deeper on the y-axis scale. What is noted there is where these TL curves intersect with the mass law (but start deeper at the resonance frequency).
The basic problem at such resonance frequencies is just that you don't reach the mass-law TL level (serious dip in insulation), hence these curves dive below that mass-law curve.
In these calculations you find all kinds of combinations:
Triple & Double leaf calculations
What do you conclude from these calculations (within the uncertainties of possible unknown influences)?