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Rockwool RW5 Vs RW3

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Rockwool RW5 Vs RW3

Postby dbfs » Mon Sep 16, 2019 4:20 pm

Hi folks,

My understanding is that RW5 being 100Kg/m3 should absorb more bass than RW3 which is 60Kg/m3 in think. I have read that the RW5 will reflect more high frequencies and that is fine.

So if working in a room with some broadband absorption in place, would the RW5 be the best for building shallow traps i.e. 100mm depth than RW3 or lighter densities.

I have heard that for deeper traps you can even go lower that RW3 but I would like to build 100mm traps with a 100mm airgap and so was drawn to RW5.

Any advice appreciated.
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Re: Rockwool RW5 Vs RW3

Postby Wonks » Mon Sep 16, 2019 4:41 pm

Here's a post copied from another thread from SSG (who really knows what he's talking about, on the preference for 60 kg (RW3) vs 45kg rockwool.

Studio Support Gnome wrote:Just a note on density and absorption coeffiecents and which to use why.


the absorption curve of 60 and 45 is very similar, although slightly different.... , 60 on edge gives something closer to 45 flat fronted. Edge performance is higher as the gas entry impedance is lower.

I recommend 60 not necessarily because it is the best all round absorber, at the ultimate edge of theoretical performance , because it's not, but it's close enough to 45 to make bugger all practical difference in terms of real world performance, but I generally recommend it for DIY use as well as paid labour use, because it is by far the most practical , easiest material to actually build with.

As well as being easier to handle, easier to cut accurately, and least messy, generating far less fluff and dust , , and on top of that 60Kg is dense enough to be structurally self supporting when laid flat , with edge facing the room, up a 2.5-3 metre high stack.... no great problem, Higher if you're careful and precise with the edge bracing... so framing it is just a matter of a braced edge frame, and fabric finish over it... and building the thing only requires two uprights one at each face corner... placed so you :"just" have to tuck the corners of the slabs in to the upright. and you can use these uprights as the edge of the fabric mount as well

45 will "spring out in the middle when you try and stack it that high, so requires far more bracing and framing to make it stay still.... especially if you build a "super duper chunk" 4 feet across the front....

this then also makes getting a flat finish on the fabric harder , unless you also eat up more space by spacing it further away from the absorption material


When faced with building a number of these devices.... especially if paying for the labour, speed and ease of construction is a matter of some concern. The minimal trade off of absorption at some frequencies is more than made up for in the saving on costs. (labour being far more expensive than the materials of any density )

even bigger ones are built using a front section of 60, but the infill behind it is lower density... at that point using 30kg stuff is fine.... indeed layering different densities can give additional loss effects as the impedance change point between densities is a transmission medium interface .

and Studio tips did NOT invent the "large absorption mass " design. to give it a more PROPER name... ... this technique was around a LONG time before the internet even existed ...

thus I have always treated their appropriation of it as their territory with the contempt it deserved.

60Kg also has the benefit of maintaining a more consistent density once you start building properly large devices..... I've built traps 4 metres high with it with no discernible change in density , you try that with 45kg and you can SEE the lower section compress into denser material... just before the entire stack springs out of the corner , from the middle ,spraying itself all over the room. . (bitter experience in early days , before forums were a thing... )

45kg works equally well , and provides higher absorption performance at higher frequencies , but since we are primarily concerned with the lo end it's of little practical import, and it's a lot harder to build large devices with, but it works fine for smaller ones and flat framed panels.

similarly 30Kg is a viable absorption media , but an absolute twat to build with..... more so than 45 by a long stretch.

buit as infill behind a layer of denser material, it works well.

I have endless designs for such devices....

there's some I use more often than others, because they're practical to implement , and easy to adjust for odd specific elements of individual rooms .... and they can be delivered in a predictable time , at a fixed cost....

It is all to easy for the DIY evangelists to dismiss the time and ease of build concerns.... but before being swayed by these , you should ask yourself, quite seriously, what your time is worth to you, and your family.... and your clientele , if you're of the semi-pro persuasion....

is it better to spend a year building a studio that is 1% "better" than one you could have built and been ready to work in in 3-4 months ?

My rather pragmatic view is that it is not.... not even if you're trying to build a mini abbey road... 10 or 20% , then you'd have a valid argument, but 1% ?? I think not.

The difference in monitor speaker quality and set up in the room will make more odds than the 1% on that corner trap .

Where i DO like to go bananas on detail is in isolation design.... room geometry , ergonomics, and wiring .

Making the place a nice environment to be in , as well as and accurate monitoring environment, is key to productivity in actual use.

Without detailing why, I know SSG doesn't think 100kg rockwool is any good at all for corner bass traps.

GIK Acoustics recommend 100kg/m3 for 50mm thick bass traps, but for 100-150mm thick traps then 60kg/m is best. 100kg/m3 can be too dense when used in depth and the sound waves can't penetrate far. For soundproofing, RW5 is good stuff, but for sound absorption, RW3 is generally better, especially when used in depth.
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Re: Rockwool RW5 Vs RW3

Postby Martin Walker » Mon Sep 16, 2019 6:51 pm

Wonks wrote:Here's a post copied from another thread from SSG (who really knows what he's talking about, on the preference for 60 kg (RW3) vs 45kg rockwool.

Without detailing why, I know SSG doesn't think 100kg rockwool is any good at all for corner bass traps.

I suspect that the main reason for this is that you are buying material by weight, and since 100kg/m3 weighs more per slab than 60kg/m3, yet offers little or no additional acoustic benefit, it's not a cost effective choice.

Wonks wrote:GIK Acoustics recommend 100kg/m3 for 50mm thick bass traps

Once again, when the slabs are only 2-inches thick, it makes sense to have them a little 'stiffer' for mounting purposes, and you won't be paying much more per slab over 60kg/m3 at this thickness.


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Re: Rockwool RW5 Vs RW3

Postby dbfs » Tue Sep 17, 2019 8:04 pm

Many thanks for the replies guys. You are the best.
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Re: Rockwool RW5 Vs RW3

Postby Studio Support Gnome » Tue Oct 08, 2019 11:32 pm

geek moment.

expanding on the comments I wrote that Wonks copied....

Fundamentally, the absorption performance depends largely on the gas entry impedance .

for a material to work effectively as an absorber, it must not reflect by means of a significant molecule movement impedance barrier as a surface... the gas pressure wave needs to enter easily, and then molecular impulse must be slowed and converted to heat by friction... within small interstices internal to the material... ideally in a material that is not inclined to resonate structurally...

this makes certain densities of rock wool very good for this application...

the point at which absorption coefficients start to tail down rapidly at both LF and HF is at around 80kg/m3 , and that process is just starting at the 60kG point, thus the slight differences between 45 and 60... but at this point they are slight, and you should note that I make a point of noting that the gas entry impedance of 60kg WHEN ON EDGE , rather than front facing... is still more than acceptable and provides superior performance that front surface ....

The primary reason is how the material is made, combined with it's density on average.

at densities higher than this, the material becomes more of a solid than a porous absorber.

the outer surface layers on the large faces of all densities, are especially unhelpful, the outer skin region is denser than the centre.... and once you head up to 70/80 kg/m3 the gas entry impedance is very high compared to 45kg/m3 or edge facing 60kg/m3

you get reflection more than absorption at that point.... and as the density increases, this gets worse.....


at these densities, it's suited to use as a resilient material for floating structural floors with high static and moderate dynamic loading... (see the product "rock-floor" as an example. )

it is not suited for use as an absorber in a large absorption mass application. ....

a 50mm panel works more as a damped structure, than a straight porous absorber.

and even then I personally would not bother....
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Re: Rockwool RW5 Vs RW3

Postby CS70 » Wed Oct 09, 2019 10:29 am

Love these geek moments! :clap:
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Re: Rockwool RW5 Vs RW3

Postby Hugh Robjohns » Wed Oct 09, 2019 10:39 am

CS70 wrote:Love these informed engineering moments! :clap:

FTFY! :ugeek:
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Re: Rockwool RW5 Vs RW3

Postby CS70 » Wed Oct 09, 2019 11:24 am

:bouncy:
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