Help with deciding acoustic panel design.

[privilege15]

While scrolling through this topic I didn't notice anyone mentioning the density of the filling. It's very important! If the Rockwool is too dense, the panels will start reflecting higher frequencies back into the room. At the same time if the Rockwool is too fluffy, it may not provide enough resistance and dampening. The rule of thumb is if you can make thicker panels (and by thicker I mean much much thicker than 4") then it's better to use lighter density Rockwool. Thicker but fluffier panels better catch bass frequencies and better work as overall broadband absorbers. However if thicker is not an option, then you can get away with denser Rockwool but thinner panels before they start reflecting back. It's all related to gas flow resistivity of Rockwool.

 

[HŪS]

I have a triangular prism under concrete stairs that is 5feet deep 5feet tall and 6feet long, with a wall on one side. Thinking about leaving 1feet space from that wall and stuffing all the rest with lower density rockwool. Do you think that will work well for low frequencies? Upper freq RT60 is pretty good as there is a lot of 4" panels on walls but bass decay is still really long.

 

[nathan]

I have a triangular prism under concrete stairs that is 5feet deep 5feet tall and 6feet long, with a wall on one side. Thinking about leaving 1feet space from that wall and stuffing all the rest with lower density rockwool. Do you think that will work well for low frequencies? Upper freq RT60 is pretty good as there is a lot of 4" panels on walls but bass decay is still really long.

Show us the RT60 graph but from what you describe I’d suggest multiple subwoofers to tame the low end. That said yes some very thick material will help a little little bit.

 

[kemmler3D]

I have a triangular prism under concrete stairs that is 5feet deep 5feet tall and 6feet long, with a wall on one side. Thinking about leaving 1feet space from that wall and stuffing all the rest with lower density rockwool. Do you think that will work well for low frequencies? Upper freq RT60 is pretty good as there is a lot of 4" panels on walls but bass decay is still really long.

Denser material might work better. But the major thickness should be good for bass.

 

[HŪS]

Denser material might work better. But the major thickness should be good for bass.

By lower I meant like 50kg/m3. I have myself thought the denser the better but some people suggest it might not be so, with this thick (4feet) absorber. Meaning a one too dense will reflect the soundwave at some point.

 

[HŪS]

Show us the RT60 graph but from what you describe I’d suggest multiple subwoofers to tame the low end. That said yes some very thick material will help a little little bit.

Don't have it right now, but basically from low mids up it's more or less at 0,5sec, but when going to bass it shoots up to like 1,5-2sec decay time.

 

[kemmler3D]

a one too dense will reflect the soundwave at some point.

Very dense material will reflect high frequencies, but that's OK, in this case you would want that. Corning 703 rockwool, which is used for "bass traps" pretty often, is around 105 kg/m3.

Given that you have a fairly large volume of space that you can devote to bass traps, have you considered helmholtz resonators?

 

[HŪS]

Very dense material will reflect high frequencies, but that's OK, in this case you would want that. Corning 703 rockwool, which is used for "bass traps" pretty often, is around 105 kg/m3.

Given that you have a fairly large volume of space that you can devote to bass traps, have you considered helmholtz resonators?

I have but as far as I know they need to be in a specific place to work well not just where it is easy to put them and only work on specified frequency like bass reflex?

 

[kemmler3D]

I have but as far as I know they need to be in a specific place to work well not just where it is easy to put them and only work on specified frequency like bass reflex?

Correct, one frequency at a time, but if you know what your room modes are, you could possibly start to knock them out that way.

A big absorber might well be more useful.

 

[Audio Science Pal]

... stuffing all the rest with lower density rockwool. Do you think that will work well for low frequencies?

Buy several bundles of rockwool. Leave the plastic wrap intact, as the plastic barrier has no effect on lower frequencies. Stack the bundles under the stairs and hide them with a fabric curtain. It should improve your sound quality, but if for some reason it doesn't, you can return the "unused" bundles for a refund.

Likewise, for anyone needing an economical big bass trap, just wrap a blanket or sheet of fabric around a full plastic wrapped bundle (24"x16"x48") and stand it in the corner.