Just to be clear for those still paying attention, the bolded part of Soundman2020's post statement above needs to be clarified- here's why: the overall assembly of the wall as a Structural System is made stiffer (which equals stronger, but more so for forces exerted along certain planes) by the addition of the third leaf, even if the individual plates (drywall sheets, for example) for each leaf are not made substantially stiffer. Just as in the MSM case and all its variants (MSMSM, MSMSMSM, etc.) a Structural System is created by a third-leaf addition which need to be judged as a new or different system as soon as there is any modification of the original form. The example I will provide that most will understand easily is that of a corrugated cardboard Structural System. All real mathematics have been spared, as the rigorously examined Structural System calculations are absolutely non-trivial; indeed more than a few doctoral dissertations have been written on the exact science of corrugated cardboard configuration strengths. Simple text character illustration follows, with "fake" numbers employed for demonstration purposes (too many real variables exist for them to be in any way accurate): I (single sheet of card stock- "bending strength" or stiffness equals 1X) II (two sheets of card stock sheets glued together- "bending strength" or stiffness equals 2X) III (three sheets of card stock glued together- "bending strength" or stiffness equals 3X) I~ (most simple single-faced corrugation- "bending strength" or stiffness equals 3X) I~I (simple double-faced corrugation, a.k.a. Single Wall- "bending strength" or stiffness equals 6X) I~I~I (heavy-duty triple sheet corrugation, a.k.a. Double Wall- "bending strength" or stiffness equals 12X) Now, in the case of our triple-leaf construction, the overall assembly may have gained substantial improvement of stiffness as load-bearing members in the direction of gravity (resistance to compressive forces, as well as torsional stiffness (resistance to twisting forces), lateral stiffness (resistance to sideways forces), etc. What it would not improve subtantially is the Plate Stiffness, which is the kind of stiffness that takes over for Mass Law in the lowest frequency ranges for our typical wall assemblies. To accomplish an improvement in Plate Stiffness, something similar to the corrugation example above would have to be employed, triangular interconnections ("webs" in Structural Theory) in-between the plates, which in effect would negate the fully decoupled isolation advantages of independent leafs. To be complete in this assessment, the air gap between each leaf in our wall assemblies does provide some very small increase in stiffness, but because air is a compressible medium, it is negligible compared to what the solid materials provide. In the heat of discussion it can be difficult to be as carefully provisional as possible to avoid misunderstandings without getting too wordy. In the case of Internet Discourse, where future generations may be hinging their understandings on the use of every word by an individual who is being vital to the discussion, some care must be taken both by the reader and the statement writer as to the implications. As a "newbie" student in the field of acoustics, I've often made incorrect assumptions based on examples which weren't fully qualified by others in the immediacy of the moment. Hence the reluctance by Avare, and others to be completely exhaustive in their answers or statements- this world of Acoustics (like many real sciences) is incredibly complex, and often counter-intuitive!Also, it isn't just MSM vs MSMSM that we are talking about: below the MSM region, stiffness rules, and adding a third leaf does not change the stiffness of the wall. So, if the resonant frequency is higher, stiffness now governs a larger chunk of the spectrum... And drywall isn't know for its rigidity...
double leaf effect cost more than triple in most situations.
Originally posted at johnlsayers.com, topic 13629.
Hello i'm new here.
I dont know if it's the right place to post my question.
Im building a drum room in my garden.
Neighborhood at 10 meters. Calm country.
The wall are in "cinder block".(Cinder block 20 cm +15cm air (filled with rockwool)+2 layers of drywall)
For the external wall (cinder block) i will make a "coating finish".
My question is : do i have to do a coating on the interior wall ?
If I do this, will it reduce the sound outside of the room ?
Thanx in advance from France to the community.
Welcome. Better if you repost starting a new thread. A layer of cement plaster 12mm thick should increase the Transmission Loss ( Soundproofing) of a wall by about 3dB. More important is to make sure the cement between the bricks has no air holes or gaps.
Thanx for your answer. I will create a new post ;)Welcome. Better if you repost starting a new thread. A layer of cement plaster 12mm thick should increase the Transmission Loss ( Soundproofing) of a wall by about 3dB. More important is to make sure the cement between the bricks has no air holes or gaps.