SAND??? does it really work for soundproofing?

I had my plan done and sorted basically, and after giving it to the builder, he came back with some different ideas! Main idea being sand filled slabs! So basically although I am yet to talk to him face to face about his new ideas, I think what he is planning is sand in the walls and ceiling, instead of rockwool...from what I can gather! I will put up his other ideas when I gt them, just to check if they are right, or his he doing it for his own good (although he is a family friend!) But I just said I'd through this up to get have a few suggestions for when I meet with him! By the way, The builder has quoted just under €30 thousand for all the construction, including labour material vat etc. Here are wthe plans I gave him; 20x15x10 2 rooms, 8x15x10 and 12x15x10 walls (from outer in) concrete block on flat (9" solid concrete) Then 4" gap to wooden frame, gap filled with rockwool, then a layer of drywall. Floor Sold concrete, with a thin carpet on top. Ceiling 6x2 wooden joists will be put on the outer concrete block walls. A layer of chipboard will then be nailed onto the joists for an extra layer of mass. Then a layer of felt to keep the moisture which might get through the tiles out, and 2x1 wooden battens will then be nailed onto the chipboard and into the 6x2 joists. Thick roofing tiles will be put onto the 2x1 battens. Then rockwool will be put between the 6x2 joists. Donnacona board will then be nailed onto the 6x2 wooden joists to keep the rockwool held up. Then an acoustical channel will be drilled onto the donnacona board to separate the layer of drywall to finish the ceiling. The drywall layer will then be drilled onto the acoustical channel. Thats an extremely basic version. Plus 2 double glazed windows inbetween live and control room. 2 back to back doors into studio 1 door between the 2 rooms. So is sand better than rockwool? And €29 thousand was the value... Sound about right?

I think what he is planning is sand in the walls and ceiling, instead of rockwool...from what I can gather! ... So is sand better than rockwool?

That's kind of like asking "Is a fish better than a bicycle?". :) They are entirely different things! But sand cannot be used to replace rock wool, as they serve two entirely different purposes in acoustics. Sand is mass, and assists with isolation. Rock wool is absorption, and assists with treatment. Mass resists the passage of sound by sheer brute force, so it is good at isolation, bad at treatment. Absorption does not stop sound: it merely converts some of it to low ground heat. So it is good at treatment, bad at isolation. Two entirely different, almost mutually exclusive, concepts. For example, if you have specified a proper 2-leaf MSM wall, built from two leaves of drywall with an air gap filled with rockwool, then you CANNOT substitute sand for rockwool! Doing so would destroy the MSM properties of the wall (and probably destroy the wall, too!), making into a single-leaf wall. That does not mean that the wall won't work to isolate sound. It does mean that you have changed the principle of physics on which the wall works from "resonant filter" to "mass law". Two entirely different principles. In this case, your wall would be governed by mass-law equations, not MSM equations. (Apart from that, the weight of the sand inside the walls will probably rip it apart, but that's another matter....). You'd be limited to 6 dB increase per mass doubling, so you'd need a very massive wall to get good isolation. That's not to say it wont work: just that you cannot simply substitute without taking into account that you are using entirely different principles of acoustics and physics. And construction, too. I'd think three times about using a contractor who tells you he can substitute sand for rockwool in an MSM wall..... Then I'd turn and run, real fast. I'd also be rather wary of a contractor who thinks that a single-leaf mass-law governed wall can do the same job as a 2-leaf MSM wall for the same price and with the same mass and thickness... - Stuart -

Thanks Stuart, haha...nice metaphor! Ya,I got that alright. So my idea was; concrete block (4"), sand, concrete block (4"), 4" gap filled with rockwool, drywall. Does concrete sand concrete make a 2 leaf wall, hense adding rockwool and drywall being 3 leaf? So keeping sand for mass and isolation, and rockwool for absorbtion. Which would reduce the amount of bass traps needed, if any.

mark.o.sul wrote:

Thanks Stuart, haha...nice metaphor! Ya,I got that alright. So my idea was; concrete block (4"), sand, concrete block (4"), 4" gap filled with rockwool, drywall. Does concrete sand concrete make a 2 leaf wall, hense adding rockwool and drywall being 3 leaf? So keeping sand for mass and isolation, and rockwool for absorbtion. Which would reduce the amount of bass traps needed, if any.

It is difficult to follow your description. For ideas of the fantastic isolation you can achieve with double block walls, look at ir586. Teh islaotion that you can acieve at low frequencies is amazing! Andre

Hi, Sand works in our walls. But it has to be dry and compacted. And if you're going to want anything heavy hung afterwards think about it before (drilling). We have 20cm hollow concrete blocks filled with sand. In some places we have 2 such walls, in others we have an outer 40cm stone wall. In all cases there's a 30cm air gap and we have rockwool stuck on the inner face of each cavity wall (not stuck with glue...shear...). And concrete floors are isolated as are walls to ceilings. Works a treat. http://montesaaudio.com

Why not simply pour concrete instead?