Quick insulation question

I just read this over at the green glue website and it conflicted with what I thought to be true. I'm hoping someone here could clear this up for me. Speaking about in wall insulation.... "Often it is thought that using denser insulation is the cure-all to sound problems. But this simply isn’t the case. In general, it is preferable to use standard building type insulations (i.e., normal fiberglass) and it is never desirable to utilize expensive, very dense insulations, as in addition to the expense, they tend to make low frequency performance worse by raising resonance frequencies." If this is true does that mean that mineral wool and 703 don't perform any better inside the wall than the standard R-13 you can buy for much less? I thought that was one of the reasons for using the dense fiberglass, to more effectively absorb lower frequencies.

It's all over this board "use the common flufffy pink stuff". That stuff's about 48kg/m3 in density. The 703 has great NRC which means great overall absorption. has nothing to do with density.

yup, it sure is true - I keep telling people this, as do a ton of other posters on the board...... as was just mentioned by Ro...... No sense to throwing your money away......... BTW - you cannot compare a material tested inside of a reverb chamber (to determine it's absorption) to the insulating of a sealed wall cavity and expect t to work anywhere near te same. Rod

OK thanks guys. I've seen many people here use 703 or mineral wool in their walls I just assumed, perhaps I shouldn't have, that it was the right way to go about it if money wasn't an issue. Does the low resonant frequency go up because dense insulation inside of a wall works more like a mass and therefore makes the chamber between the the leafs smaller? Please let me know if I have this correct now... 703, 705 and mineral wool should only be used as acoustic treatment in the actual environment where the source sound is occurring? Any other time you want to use standard pink stuff as a rule of thumb? Is the reason because the insulation in the wall is only for dampening or because 703 and the like have no added STC value over the pink fluffy stuff? Sorry for all the questions. I just want to make sure I'm on the right track. I've read so much in the last couple weeks that I'm probably starting to get things crossed. I much rather understand how and why something works than to just take it at face value.

if you specify dacron insulation your builder will love you :)