Increasing STC

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Author Message Robin Treston (Unregistered Guest) Unregistered guest Posted on Thursday, January 29, 2004 - 02:08 pm:    I have a wall situation where we only have thickness for 3-1/2 inch acoustical batt insulation, but we need a higher STC. Is anyone aware of any gyp board type products that we can use to increase STC without adding thickness to the wall? Or, will "stuffing" more acoustical batt into the space work? Any thoughts? Richard L Matteo Senior Member Username: rlmat Post Number: 13 Registered: 10-2003 Posted on Thursday, January 29, 2004 - 02:23 pm:    Robin - Since you only have space for 3-1/2" insulation, I'm assuming your stud depth is 3-5/8", how many layers and what thickness of gyp. bd. do you have & what are your restrictions on overall thickness of partition? Also, what STC rating are you looking to achieve? I would suggest looking at Gypsum Association GA-600 or one of the gyp. bd. mfgrs. construction guides. Curt Norton, CSI, CCS Senior Member Username: curtn Post Number: 39 Registered: 06-2002 Posted on Thursday, January 29, 2004 - 02:30 pm:    Stuffing more insulation in the cavity will actually lower your STC rating. Try www.celbar.com they have a spray acoustical system that offers STC 53 for a 3-5/8 stud system. JK Brown (Unregistered Guest) Unregistered guest Posted on Thursday, January 29, 2004 - 02:45 pm:    Stuffing thicker insulation or more insulation will accomplish nothing. In fact if you use a thicker insulation in a 3-5/8 in. space you will decrease the R value of that insulation. I agree with Richard review Gypsum Association GA-600 it will be a useful tool. There sound board, but it is another layer to the wall assembly. C. R. Mudgeon Senior Member Username: c_r_mudgeon Post Number: 15 Registered: 08-2002 Posted on Thursday, January 29, 2004 - 03:50 pm:    Fill the wall with sand. Anonymous   Posted on Thursday, January 29, 2004 - 03:58 pm:    Depending on top-to-bottom span, you could consider looking at 1) "mini" chase wall with 1-5/8 inch studs, 2) offseting 2-1/2 inch studs, or 3) 2-1/2 inch studs with resilient channels. Depending on the wall details, you should also look at "flanking" paths both around and over the partition as contributing sources of sound "leakage". David E Lorenzini Senior Member Username: deloren Post Number: 29 Registered: 04-2000 Posted on Thursday, January 29, 2004 - 05:21 pm:    An STC rating is composed of fitting various frequencies under a standard curve. Your solution would depend on the frequencies you have to reduce. Low frequencies (such as mechanical equipment) need mass, such as concrete block (or sand as was mentioned), and higher frequencies are subject to the normal remedies. If your wall height allows you to reduce the wall thickness, as has been mentioned, you would have several options, although it doesn't appear you will be predict the actual STC result. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 187 Registered: 03-2002 Posted on Friday, January 30, 2004 - 08:41 am:    Robin, Can you let us know what type of noise you are trying to isolate from what type of space? I'm afraid that with the restrictions you have, you will have a hard time doing much to improve STC The three basic ways to reduce noise transmission through an assembly are mass (i.e. extra layers of drywall), damping (i.e. resilient channel, and some heavy plastic sheet acoustic-damping products), and de-coupling (i.e. double stud construction). Different approaches will have different noise level reduction curves when plotted against frequency. This is why it's useful to know what noise source you are blocking. It may also be possible to reduce noise levels at the source of the noise. A major source of noise transmission, however, is "flanking" noise. These are noise paths around the acoustic assembly you're building. This includes, for example, over the top of the partition, under the sole-plate of the wall, around edges of doors, through ductwork, and through back-to-back electrical boxes. You may get the best results focussing on those. It is true that insulation adds only a modest amount to the STC rating. Celbar is wet-sprayed cellulose insulation, and has a higher density than fiberglas which gives it more mass than fiberglass. There are other cellulose makers, too. (Over stuffing fiberglass may theoretically reduce R-value, but low thermal-transmittance does not sound like an objective here.) If you can replace the GWB with CMU, you will achieve a good rating. The idea of using shallower studs with more layers of drywall is good too, but deflection could become a problem. The suggestion of filling the wall with sand sounds like a possibilty too, since it adds mass.