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Glasswool or Rockwool?

Discussion in 'Studio Construction & Acoustics Forum' started by sign, Sep 20, 2003.

  1. sign

    sign Guest

    Hi Ethan, Rod, Eric and all.

    A friend of mine gave me a copy of a book about studio construction and making rooms soundproof.

    The author states that rockwool is more expensive than glasswool, but it works better (between walls) he says.

    I have the feeling he is wrong. Am I right or what?
     
  2. Rod Gervais

    Rod Gervais Moderator

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    Nope - he is not wrong.........

    "Glasswool" is what you would call fiberglass... "rockwool" is thermafiber....

    It's more dense than standard fiberglass insulation and thus is better for sound isolation.

    Rod
     
  3. sign

    sign Guest

    Ahah!!, but I thought glasswool was better for absorbing low freqs.

    So rockwool absorbs more?

    Thanks!!
     
  4. Rod Gervais

    Rod Gervais Moderator

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    light and fluffy - high
    heavy and thick - low.......

    like i always say - when you deal with low frequencies - you want mass mass and more mass...

    Tis me mantra.......... :D :D :D

    Rod
     
  5. sign

    sign Guest

    That was quick Rod!

    But why don't basstraps have rockwool instead of glass?

    Let's make it clear, in Europe glasswool is sold by Isover. It's much less heavy as rockwool.

    Glasswool is yellow, rockwool is grey. Are we talking about the same products? You call that yellow stuff fiberglass?

    Peace.
     
  6. Rod Gervais

    Rod Gervais Moderator

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    Glasswool is yellow and very light fluffy.....right?

    Rockwool (here) is browner and much thicker heavier........ Right?

    Fiberglass (Glasswool - the material used in basstraps) when manufactured as a panel - tends to stay together much better than rockwool does.. rockwool tends to break up........

    Glasswool is manufactured from spun glass......

    Rockwool is manufactured from Loose Wool obtained from melting and then fiberizing of minerals through centrifugal processing reaching diameters of 6 +/- 2 microns with a length of 60 +/- 10 millimeters.

    OK - now you tell me - are we talking about the same things?

    Happy Hunting

    Rod
     
  7. sign

    sign Guest

    Absolutely! :D

    The fiberglass comes in plates that are indeed 'stronger' than the rockwool. But it also comes on 'rolls', just like rockwool does as well.

    Now the next question is: is the difference significant, or not so very?
     
  8. Rod Gervais

    Rod Gervais Moderator

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    Han,

    you're talking apples and oranges here....

    The intent of a sound isolation wall (they really aren't "soundproof") is to keep sound inside of the room....... to not let it escape. Although some of the process is absorbtion - the majority winds up being reflection.

    For low frequencies this means mass.......

    The intent of a trap is absorbtion..... - trap it and keep it there. And according to Eric Dessart - some of that energy is transfered through the back of the trap and decreases the isolation value of the wall behind it.

    Picture, if you would - a concrete wall 12" thick.... it is an excellent source of isolation due to it's mass........ and would make a lousy bass trap because of it's reflective qualities.

    What works for isolation is not what you want for a trap.

    It's just that simple.

    As far as the value of Rockwool for a bass trap goes....... if what was installed was the same density as the fiberglass (which i believe would require an adjustment of thickness) then i would imagine it would work as well........ however i do not know this to be a fact.

    I always try to stick with that which has been tested...... but then again - tis those with imaginations greater than mine who develope and test these products in the 1st place......

    Happy Hunting

    Rod
     
  9. sign

    sign Guest

    Apples and oranges?

    IMO the mass is there to stop as much energy as possible and keep it in the room (or out). But what goes through must be absorbed and converted into warmth by a soft material like fiberglass, rockwool or something like that.

    Although a bass trap has a very different task, the fiberglass is also there to absorb, like you say.

    I know if I screw 12 plates of gypsum board to the wall, I won't need much fiberglass/rockwool behind it.

    ? :D

    I'll be back tomorrow, it's 2.30 am here. :w:

    Thanks!
     
  10. Rod Gervais

    Rod Gervais Moderator

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    Han,

    Get a good nights sleep my friend....... ;)

    Rod
     
  11. knightfly

    knightfly

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    And when you wake up, check out this -

    http://www.usg.com/Design_Solutions/2_3_7_insulationperf.asp

    My interpretation of the different sources is that the TYPE of insulation inside a wall isn't as important as the DENSITY. The main function of insulation in a wall is to help break up air currents, therefore transmission. USG found that 2.5 pounds per cubic foot (40 kg/cu meter) is optimum - stray either way very far, and you unbalance the Transmission Loss of the wall. Unbalanced TL makes the frequencies that DO get thru, more noticeable because of "un-natural" frequency response.

    That said, this link

    http://www.domesticsoundproofing.co.uk/tloss.htm

    explains why I think that putting 2.5 pcf insulation in a wall with the "fluffy stuff" on either side of it, TOUCHING the wall panels, (damping) should make a better wall at low AND high frequencies. Using different thicknesses of wallboard combined in each leaf helps too, by shifting the Coincidence dips of successive layers to different frequencies. This only works if you DO NOT glue successive layers - otherwise, you've just made ONE panel with ONE coincidence dip, and that frequency will get through easier.

    You might wanna have your coffee BEFORE reading this - oops, too late... Steve
     
  12. eric_desart

    eric_desart

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    [ December 31, 2003, 07:16 PM: Message edited by: Eric Desart ]
     
  13. knightfly

    knightfly

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    Hi, Eric - long time no hear :=)

    Your comment "When I compared 32 kg/m³ glassfiber with 60 kg/m³ rockwool, the glassfiber came out slightly BETTER than the rockwool (mainly at the low frequencies)" - goes along with conclusions regarding density and wall performance (think it was in the Stan Roller study, don't remember for sure)

    My layman's assumption on this is that, for INSIDE a wall, the density is more important than the type of insulation - that's why my comment about using 40 kg/M3 in a wall, with fluffy stuff on both sides contacting the wallboard for damping.

    Do you agree that this approach, combined with the other accepted, correct ways of gypsum wall building such as multi-layers of dissimilar panels, separate frames, proper caulking, only one air space, proper application of RC on one side, offset joints, no gluing of successive layers, etc, should give a well-isolated wall even into lower octaves below the STC cutoff of 125 hZ?

    If not, what did I miss?

    I remember you downplayed my interest in varying Coincidence Dips, and that's part of why I think damping of wall layers is important - I don't remember you giving reasons at the time - if you have the time now, I'd really like to hear more about that particular facet of wall performance. If not, I can wait.

    As usual, looking forward to your comments... Steve
     
  14. sign

    sign Guest

    Rod

    Thank you buddy, I've slept very well! :)


    Steve

    Thanks for responding and for the links. :D


    Eric

    Now that's exactly what I wanted to know. Thank you so very much! It's great to have you and your expertise here.

    This forum rocks!

    Peace, Han
     
  15. eric_desart

    eric_desart

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    [ December 31, 2003, 07:16 PM: Message edited by: Eric Desart ]
     
  16. knightfly

    knightfly

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    "I've slept very well!" - Now, I suppose it's my turn - it's 02:50 am here, and lots of stuff to do when its daylight -

    BTW, I remember Alton Everest commenting on this same topic, to the effect that inside a wall it didn't make much difference WHAT kind of insulation, so it appears we're about to have a quorum on at least that point... Steve
     
  17. knightfly

    knightfly

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    Thanks, Eric, it appears that we're "passing in the night" - I'm off to bed, will check in later. I'm assuming that in your comments, you're referring to the TL graph I posted??

    Thanks... Steve
     
  18. eric_desart

    eric_desart

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    [ December 31, 2003, 07:17 PM: Message edited by: Eric Desart ]
     
  19. Rod Gervais

    Rod Gervais Moderator

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    Eric,

    Welcome - and thanks for jumping into this one - I am finding this very interesting....... and look forward to learning some more now - it seems i have bought into some "myths"..... and am looking forward to "re-learning" some of what i thought i knew......... :c:

    Rod
     
  20. knightfly

    knightfly

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    Eric, don't apologise for being busy, we all have that problem to varying degree - I doubt that I'm the only one here to appreciate the time and information you ARE able to contribute.

    On that "sticky" - other than the link, here is the entire paragraph I quoted from - "Wood fiber sound deadening board, when used as a base layer under gypsum panels, offers some advantages by virtue of its decoupling and damping characteristics. A wood-stud partition with 1/2-in. USG Sound Deadening Board base layer and 5/8-in. SHEETROCK Gypsum Panel face layer laminated to each side will provide STC 49. The same construction with SHEETROCK Nail-applied will test only STC 36 -- the nails providing a direct sound transmission path through the studs. One obstacle to the use of wood fiber sound deadening board is the installed cost index of 151. By comparison, the cost index of an STC-52 wood stud-resilient channel-wool blanket partition with single-layer gypsum panels is only 136."

    I couldn't find anything more on their "sound board" either, it sounds to me like the stuff that sells by the name "sound board" around here, which is kind of crumbly, lightweight wood fiber board - celotex is another name I've heard, also Homosote ?!?

    My main point there was more about the fasteners flanking the panels when used to attach a second layer onto wood studs, or to Structural grade metal studs for that matter.

    I haven't yet played with your Sound Selector file, gotta get back to the Yahoo site more often. Interesting, also, about Coincidence vs. leakage - I know acoustics and Logic almost never seem to agree, but I'm still struggling with why different layers with different frequency dips wouldn't be better, if only slightly...

    The good news (from a selfish standpoint) is that my own new studio probably won't see a shovel full of dirt moved for at least two years yet, so by then I should know absolutely EVERYTHING, right? Right? Eric, how are you gonna answer me when you're laughing so hard? :=) Steve
     
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