Hi everybody,

I am new here and relatively new to room acoustics so I apologize in advance if this question is too dumb or if it has already been answered. I have been searching for a while without finding a specific answer. The answer at least should be probably simple.

I have been treating my home studio for a while with 2" panels, 4 and 6" bass traps etc, using mostly OC703 and Safe and Sound. I recently got a hold of some 1" panels of 3lbs Knauf insulation boards and I have some leftover Safe and Sound stuff from previous projects. I need to build 4 more bass traps at least and I was wondering if it would be ok to use 2 layers of Safe and Sound with a final top layer of 1"Knauf. The goal is to have a more rigid face on the bass traps, since my previous panels made with Safe and Sound are kind of bulging. My question: Is it ok to mix different insulations like that? Will they perform the same? I understand 6" thick Safe and Sound panels do well as broadband absorbers. I just wonder if by adding one last layer of 1" 3lbs Knauf I will not be affecting negatively the performance of either product. I am assuming this 7" bass traps should actually be even better but I want to be sure of that before I proceed.

Thanks

Is it ok, yes
Does it behave the same, no

You'll have to look up gfr or air flow resistivity for the resp products, ref Common Gas Flow Resistivity numbers., at the end there are some files gathering most of the information

Then use the calculator on http://www.acousticmodelling.com/8layers/multi.php to model the different layers and see which theoretical effect they have on absorption

From the head, SnS is 10k rayl, oc703 is between 15k and 25k, depending who you ask. 'Knauf' is not specific enough, it is a manufacturer, not a model or type of insulation.

Thanks so much for the input and sharing your expertise. I am just trying to decide how I could use the materials I have in the most effective way. I could just use the Knauf panels (I got them from GIK and I was told they are more or less equivalent to OC703 panels) and make a couple of bass traps with those panels and use the SnS for different panels. But since I also care for the aesthetics of my studio, I thought it would be great if I could use the more rigid Knauf as a face for the SnS stuff and make more better looking panels that way.

Have you ever tried a AMG Soundflow for calculations? There you can also add density and not only rayls. Density seems to make quite big difference even as two materials have same rayls. Spoiler: Higher density stonewool gets a lot better results in Soundflow than in Multilayer calculator.

And yes, Just Knauf tells nothing. I bought 5k Knauf Ecobatts only to find out it was actually 8.3k (19kgm2) :D

Hi Thanks,

No, I have not tried really any calculations. I am too ignorant on the nitty gritty of this subject so I am trying to find some basic established knowledge to build the panels I need using the products available. What I have done so far falls within that established knowledge for basic bass traps I believe: put together 4inch think of OC703 or 6inches of SnS to build basic bass traps that work. I also understand the Knauf acoustic insulation boards with Ecose (the ones I have) also work similarly to OC703, being just greener.
But since the last batch of Knauf acoustic boards with Ecose (3lbs) I got are one inch thick and I have a significant amount of SnS I thought: what if I cover the SnS bass traps with one inch panels of Knauf acoustic panels. Provided I still get similar results to what I already get with just 6 inches of SnS (based on published data
3” 6”
125 Hz 0.52 1.11
250 Hz 0.96 1.28
500 Hz 1.18 1.15
1000 Hz 1.07 1.06
2000Hz 1.05 1.03
4000 Hz 1.01 1.15
NRC 1.05 1.05

I will be happy to just keep those numbers. Since i haven't read or heard anything about mixing different insulation products in the same panel I just thought it would be better and reasonable to ask first in case there could be something in more rigid insulation (like Oc703 or Knauf acoustic boards) that will negate the benefits of SnS type of insulation if installed in front as the first point of contact for the sound waves. I am assuming bass waves will have just more material to go through and therefore I will get somewhat more absorption, so that is what I am trying to confirm or see corrected if there is some knowledge about how insulation works that I am ignoring.

I think i have the same 1" 3lbs 19.5kg/m2 Knauf. It's not like 703 as it is a lot less dense. If it is the same, then it's also quite "fluffy" and might also bulge. Not as fluffy as 5kPa material, but still not very ridgid.

That Knauff (if the same) is ok in front of SnS. But one way to prevent the bulge: Add three stripes of wood to the front of the trap: One top and bottom and one in the center. Then wrap around the fabric. The middle wood stripe will prevent the bulge.

Thanks for the input and recommendations. My plan b with the SnS was actually to use it for panels with a perforated reflective membrane made of 1/8 or 1/4 mdf or plywood in the front. That way I add a little bit of diffusion and deal better with the fluff. But this Knauf panels are as rigid as OC703. At least that's how they look and feel. https://www.knaufnorthamerica.com/en...sulation-board Great stuff to work with since it does not itch or release fiberglass when cutting it. My room is not the smallest studio you will find in the US (22X11X9ft). But small enough that I am still wary of adding any diffusion. That is why I am considering a more rigid panel as a face instead of plywood. I can also try what you recommend. Thanks.