Help with STC rating of improved walls (or perhaps NOT)

I'm having trouble finding an STC rating for my existing and improved conditions. These are demising walls in residential units. I used 6" 20-guage steel studs with 3.5" fiberglass batting and 1/2" type-c then 1/2" GWB on each side. I created two experimental improved conditions, but I'm having trouble converting my dB readings to STC rating ranges. Here is an illustration of these conditions: The base condition seems to reduce noise by 41 dB. Improved Condition 1 Seems to reduce noise by around the SAME. Improved Condition 2, with RC, seems to reduce noise by 46 dB. My problem is how to convert these into STC ratings. Noise was generated by playing "pink noise" through a basic boombox creating roughly 90 db on one side, then taking reading on the other side of each condition (back and forth). Sound was measured using an Extech 407738 Sound Level Meter. Clearly, I'm not a sound professional. Just a builder trying to figure out sound issues. Please help however you can. Thank you.

Study for hundreds of wall construction tests. Tell us more about your situation. Be sure to follow all the points in the "Before You Post" announcement. You'll get good feedback if you follow the guidelines. --Keith :mrgreen:

Travis, No one can answer your quiestion - because it isn't done like that. A partition is given an STC rating by measuring its Transmission Loss over a range of 16 different frequencies between 125-4000 Hz. Not only that - it has to be done in a lab setting where the flanking limits are known. Seeing as there are no individual measurements to average - nor is there any way to determine (for either us or you) what contribution flanking has to do with your results (even if you measured individual frequencies) no one can answer the question. The layman's answer would be that the original wall would seem to be around an STC 41 and the best fix was an STC 46. But I don't understand why you aren't just using tested designs - why experiment with anything new? Sincerely, Rod

Thanks Keith and Rod, I've downloaded and will review the Construction Tests - that's really great. I'll re-read the "before you post" and update any missing information too (tomorrow). I'm trying to address an existing condition that isn't giving me the results I desire. The Base Condition just isn't reducing as much noise as I'd like. I'm trying to fix this without tearing down finished walls in finished spaces - unless I absolutely have to. I have learned that dB reduction amounts do not directly correlate with STC ratings, for example (from another posting on this forum): “...The approximate difference between what you have now, and what you'd get by ripping out the inner ply/bad insulation and using the right insulation with double frame, 8" air gap and 3 layers of 5/8 wallboard - 20 dB vs 35 dB @ 50 hZ, and STC 73 vs. STC 40 for overall wall performance. Pretty large difference –“ Note that the dB does NOT correlate to STC ratings – that a difference of 15 dB results in an STC difference of 33 (in this case). I'm not sure how these numbers are arrived upon, but I guess I'd have to find my exact condition in some STC lab test results somewhere - maybe in the construction tests... Thanks again, Travis