Mixing rockwool densities?

[Mark Alexander Leonard]

Hey there,

So I'm in the middle of building some ceiling acoustic panels for above my listening position.

My general understanding was that I would be best with a rockwool density between 40-75Kg/m3 for this position so that it's focussed on general broadband frequencies.

I have found Rockwool Termarock 50 which has 50Kg/m3 but I can only get it in 6cm thickness. My panels have space for 10cm thick rockwool.

I then found Rockwool Termarock 100, which has 100Kg/m3 density, but is 4cm thick.

I was wondering - would it be effective to layer the two different densities in my overhead panels? So I'd have Termarock 50 on the bottom 6cm, and Termarock 100 on the top 4cm.

I guess I could just put two Termarock 50 panels on top of each other and trim the excess 2cm, but that feels like a very messy option

Any thoughts appreciated!

[Drew Stephenson]

I was wondering - would it be effective to layer the two different densities in my overhead panels? So I'd have Termarock 50 on the bottom 6cm, and Termarock 100 on the top 4cm.

Short answer: yes.

Longer answer: the problem, as I understand it, with denser materials is that they can become reflective to higher frequencies. However if your higher frequencies have already had to wade through 6cm of 50 then they should already be significantly attenuated anyway.

Smarter people may be along in due course to disagree with me, in which case listen to them.

[Hugh Robjohns]

Yes ^ wott Drew zed...

[Martin Walker]

I agree with Drew (and of course Hugh, who slipped his reply in while I was writing mine ), except that in my experience with 45Kg/m3 material, it really doesn't maintain its shape very well, whereas that 100Kg/m3 of yours will stay put beautifully.

So, unless you intend to have a tight acoustically-transparent covering on your ceiling clouds, I'd be inclined to place the saggier 50Kg/m3 above, and the solid 100Kg/m3 below for beautific reasons

[Mark Alexander Leonard]

Thanks for the speedy answers everyone!

That puts my mind at ease and will save me lots of time hunting far and wide for thicker panels.

Luckily I plan to have very firmly stapled Camara Lucia fabric coverings, so I'm hopeful that they'll hold shape very well

[Sam Spoons]

You do need the RW to be sufficiently rigid not to sag when using it for ceiling panels, I have found that 50mm thick batts of RW3 (60kg/m3) are pretty much self supporting so your 50kg/m3 batts may be ok but can you support them with something behind the fabric just to be sure? The best option would be to source some RW3 which is available in 50mm, 75mm (I think?) and 100mm thicknesses. Alternatively spacing the RW off the ceiling leaving a void behind is an effective way of improving performance so there may be little or nothing to be gained by filling that void with the lower density RW.

[Drew Stephenson]

So, unless you intend to have a tight acoustically-transparent covering on your ceiling clouds, I'd be inclined to place the saggier 50Kg/m3 above, and the solid 100Kg/m3 below for beautific reasons

The problem there Martin is that you'd be increasing the chances of HF reflection off the denser material.

[Matt Houghton]

I've used three 10cm thick 100kg/m3 Rockwool panels for the mirror point ceiling cloud above the listening position. Largely because that's what I happened to have available, but also because it holds its shape very well. It's suspended lower at the front (speaker end) than the rear, so as to ensure any HF reflections from the speakers are directed away from the listening position. Seems to work OK!

[Drew Stephenson]

Ah yes, good thinking that man!

[Wonks]

He's not just an ugly face!