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Green Glue - Miracle soundproofing?

Discussion in 'Home Cinema Building DIY' started by spamboy, Jan 19, 2005.

  1. spamboy

    spamboy
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    Thought I'd bring a product being discussed on avsforum to people's attention.

    http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=456614&highlight=green+glue (a couple of other threads too, search for them)

    Apparently more effective than resilient bar at soundproofing, especially good for controlling bass frequencies. Easy to apply, takes up less space than resiliant bar too.

    Now, this might be snake oil, but people over there seem to be rating it. Certainly it looks like a far easier \ cheaper solution than the alternatives. Just wish I found it before I put the floor I was soundproofing back down.

    I've emailed them to see if they'll ship to the UK.
     
  2. Piers

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    This stuff seems too good to be true, but as you say it has its followers on AVS. Will be interested to hear if they will ship to the UK.

    Piers
    www.homecinemaengineering
     
  3. spamboy

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    I was pretty sceptical, but the principle of it is that it doesn't primarily absorb the waves going through it, but damps the lateral motion of the two layers against each other, thus as the material flexes the energy is damped out.

    I'm still not sure it'll work, but the theory seems sound (just to clarify I have nothing to do with the company other than as a consumer but I'm a lapsed physicist so I vaguely like to think I know what I'm talking about). I'm keen to try it out.

    They are sorting out a UK distributor, but not for a while (unfortunatly not untill after I plan to do my hc). Shipping costs are going to be pretty extreme for direct shipping unfortunatly, unless I get a few people together to buy some...
     
  4. Piers

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    Maybe I also qualify as a lapsed physicist - albeit from about 25 years ago! Is it effectively bonding the two materials in such a way that the two react as one? If so I still don't understand how two relatively thin panels can absorb serious bass. All the training that I have had has suggested that mass is the bass killer.

    Piers
    www.homecinemaengineering.com
     
  5. spamboy

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    As far as I can work out the key to it's effectiveness is the fact it acts as a damper, internal friction turning the sound energy (kinetic) to heat. A massive object blocks sound as the energy required to vibrate it is high and the maximum amplitude of vibration of that object will be the maximum transferred to the object on the far side (resonance excepted).

    I'll use the car analogy for damping, I'm sure you don't need this but others might read it. If a car has no shock absorbers, it'll hit a bump and bounce up and down untill friction in the suspension slows it down. With dampers which turn that energy to heat, the suspension should compress and then extend once under control. One bounce only. (there are loads of reasons that this is a rubbish analogy and I'm missing loads of detail on how suspension systems work, but this probably isn't the place for this - you get the idea anyway.)

    Anyway, this works to a certain degree if the layer is in compression, however in this case how this is really effective is as a layer between two materals. As the materal flexes the two layers move different amounts (different radius of curvature and all that) and the shearing between them stretches the glue. This is damped in both extension and compression and works to dissipate the energy vibrating the material. Thus the vibration drops off more quickly = less sound. Remember also that sound is not a single event, but the product of continuous vibration of everything between the source and the listener.

    It seems like it's most effective at dissipating energy passing linearly along the treated surface. It looks like it would be particually effective at reducing the transmission of a wave along a plane, such as a floor that joins two rooms. So long as the exciting event it localised to one room, the damping effect would dissipate the wave as it passes along the surface. This also must have an effect on a wall, as the energy radiates away from the excited (flexible) areas this would serve to damp that energy.

    I'm sure I'm explaining it terribly - plus this is what I'm assuming having looked into this superficially. Have a look at their website www.audioalloy.com for some docs on this. I've been talking to Ted White there. Ted, if you're reading this correct me if I'm wrong.

    Regards,

    SB
     
  6. Ted White

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    Hi all,

    I am, in fact reading SB. Thanks for the descriptions. The best way to explain what Green Glue does is to visit our website as SB suggested. There are many graphs and diagrams that explain the concept well.

    We are in discussions with a few prominent distributors and should have product there soon. If a group could pool an order as SB suggests, then we could ship via ocean cargo. This would drop the freight cost substantially.

    I would be happy to answer questions regarding the Green Glue, its performance or its application.

    Thank you all for your interest.

    Ted White
     
  7. doink

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    The only thing that absorbs LF soundwaves is heavy mass. period.
     
  8. Ted White

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    Hi Doink,

    If you have a moment you might enjoy some of the information on our website. Trying to stop bass vibration with sheer mass is a different process than diffusing or damping bass vibration with a visco-elastic system.

    An effective damping compound, properly used, will remove bass vibration very well.

    Thanks!

    Ted White
     
  9. martian1

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    Any images of this stuff is it funny looking?
     
  10. Ted White

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    Funny looking? Well, it's green for one thing. After that it's in between two layers of panels like drywall or plywood, so you'll never see it again...

    Ted White
     
  11. doink

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    I've been working in recording studios since the age of 17, every single room is buillt in the same way, the only way to correct LF transference is with sealed heavy mass structures.
    These sort of solutions when used correctly are fine for controlling in-room resonance of course.
     
  12. spamboy

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    doink, what are similar products used in-room? I know the established solution is mass and I'd love to do the room in a room thing, however it's not always possible (space-wise) to build up the neccessary layers of materials. That's why I'm keen on finding an alternative if it exists.

    Ted, can you explain why this effective at absorbing LF sound when percieved wisdom goes that this isn't an likely solution? That's not obvious from the website.
     
  13. eviljohn2

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    I agree with spamboy, the website certainly doesn't cover any of the technical areas that I (as a physicist) and others are keen to hear. Just looking at results you've come up with yourself is hard to take seriously but I'm keen to learn about this stuff. :)
     
  14. shodan

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    OK, laymans (simple mans) thoughts... And please bear in mind that I didn't following half the stuff posted above except for the analogy to car suspension (which the author then said was a rubbish analagy!!!).

    Right so my question.. If this product (and lets just say it works to the level suggested) diffuses LFE sound waves (ohh, look at me getting all technical!!!) when they come into contact with it, where do they go to? Do the bounce off back into the room? This would just give you a sense of "muddled" bass would it not? Does the bass get absorbed by it? (ie it gets turned into another form of energy like heat or movememt or something?).

    What does happen to the bass when it meets this product?
    I know that in my HT the bass flies around being absorbed by the furnishings and furniture and my ears as well as reverberating around a little. Apparantly it also goes upstairs and has a look around their flat too sometimes... ;-)
     
  15. spamboy

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    The energy is converted to heat in the material. Due to friction?
     
  16. doink

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    impossible... if anything it would be transferred to the material thus making it into even more of a resonance soundboard!
     
  17. Ted White

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    Really guys, this isn't new science, and it's completely consistent with mass law. The actions of a constrained layer system using a visco-elastic compound have been well documented and understood for a long time. Long before Audio Alloy came along. Green Glue just happens to be a highly effective visco-elastic compound.

    In a Constrained Layer system, vibrational energy is converted to thermal. Different systems do this more effectively than others. Vibrational energy is thereby dissipated over time and distance. It's important to understand that it's not the VE compound alone that's creating damping. It's the actions of two rigid, dense layers in conjunction with the VE compound. The resultant system is what's converting the vibration and stopping its propagation.

    Ted
     
  18. spamboy

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    Erm, are you claiming that if you flex a material, it doesn't get hot. Try this - get a spoon, flex it repeatedly you will notice that it gets hot (and eventually breaks). The energy (kinetic, as in vibration) you are imparting to it is turned into heat.
     
  19. eviljohn2

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    So it works like this wall damp stuff?
    http://www.asc-soundproof.com/tech2.htm

    I think this could well work to a degree but remain sceptical as to how useful it could be at attenuating low frequency sounds. :)
     
  20. Brian Ravnaas

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    Hey everybody,

    Ted White above in this thread asked that i comment a bit about Green Glue as curiosity existed. I see this is a UK forum, i don't think it's available there yet, but i'd like to identify myself as affiliated with the product up front.

    GG is a constrained layer damping material, you can find a short discussion of those on the site that spamboy linked to above. You can also find a nice discussion of the general nature of viscoelastic damping here: www.earsc.com/pdfs/engineering/understandingdamping.pdf

    about viscoelastic materials Viscoelastic materials convert kinetic energy into heat, that is correct. And spamboy asked "Due to friction?". It's sometimes presented that way - as molecular friction. Viscoelastic materials dissipate energy because the energy that is put into them is not returned. Think about a rubber ball - drop it and it bounces back strongly. That bounce-back is energy being returned. A damping material like Green Glue doesn't return some, much, or most of that energy. The ANSI (probably something similar in use in the UK) definition of damping is the dissipation of energy over time or distance.

    how that can effect a common wall So, putting Green between two layers of drywall/plasterboard raises the internal damping (energy dissipation) of that material about 100x or so. This makes two nice things happen.

    energy decay over distance First, the structure cannot transmit vibration over distance very effectively at all. Think of a staggered stud or normal wood stud wall - sound can travel through the plasterboard/studs to the studs/baseplate and to the other side. This structural transmission is why products like resilient channel improve performance at some frequencies. When GG is in the board, the decay (conversion to heat) of energy over distance is immense. For example, at 1000hz the basic calculations would predict a decay rate of about 40-45dB/meter. Raw drywall as a comparison would decay at ~0.6 dB/meter. :thumbsup:

    resonance The second effect is it reduces or eliminates resonance problems in the various structure. For an excellent discussion of resonance in the common wood stud wall, please refer to Lin and Garrelick, JASA 1977, their paper "Sound Transmission Through Periodically Framed Parallel Plates" outlines the impact that damping can have on this wall type. A couple of very well known resonances are called coincidence and the mass-spring resonance. The former occurs at mid/high frequencies, and the latter occurs at low frequencies. The familiar term "mass-air-mass" resonance is a considerable over-simplification of a mass-spring resonance, the primary structural resonance shown by Lin and Garrelick is another. At resonance points, as is discussed in, for example, entry level college physics text, the transmission of a structure will be reduced greatly with an increase in damping.

    why GG is sometimes associated with great LF sound stopping, why doink wasn't wrong about mass, and some more The damping of resonance is why so many folks associate Green Glue with good low frequency performance, and the combination of resonance and reduced transfer add up to lovely improvements at mid/high frequencies as well.

    Doink is correct above when he refers to mass as being the A-1 important factor for low frqeuency performance. Something called "mass law", which is generally presented as

    20*log(mass*frequency)-48 where mass is in kg/m^2 of surface mass

    does predict this. Also, things like mechanical decoupling (resilient channel or double-stud constructions) and absorbing material (rockwool in the cavities) fail at low frequencies, which leaves mass as your #1 and only ally in stopping low frequency sound.

    But resonance is your #1 and only enemy. Take a look at the transmission loss of many, many types of walls here: http://irc.nrc-cnrc.gc.ca/fulltext/ir761/ . You'll note a strong minima in performance in all wall typse in the "subwoofer" region.

    The good low frequency performance often associated with concrete and masonary relates to the high mass, but also relates to the lack of resonance. in MOST (but not all) assemblies featuring these materials, significant resonant activity is not present in the subwoofer range. In one lab test from Europe, however, a 10cm brick wall was shown to stop just 13dB at 50hz due to a resonance issue. Common plasterboard walls essentially all exhibit resonance in this region, however.

    so, doink isn't wrong, and nobody is claiming things at the AVS forum or herein or above that are outside of well established principles...

    i hope my comments weren't too lengthy, and i hope they helped.

    take care,

    Brian
     
  21. Brian Ravnaas

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    it's also worth mentioning that the general theory (as you might note if you read the document on damping that i linked to above) predicts an improvement in impact noise (footstep nise, floor noise, etc.) of

    10*log(newdamping/olddamping) when one raises the damping of the panel (floor in this case).

    it's also nice to note that this extends to the low frequency region of the floor, where carpets and underlayments become ineffective, making (i believe) damping the only substantially effective way of improving low frequency impact noise, or at least the most facile.

    it's a new product, and all of the relevant lab tests are in the works, but not available yet. They will be soon.

    take it easy everybody,

    Brian
     
  22. spamboy

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    Brian,

    A few questions. Your diagrams show the plasterboard directly attached to studs and a layer of GG between the sheets of plasterboard. Would using resilient bars improve the soundproofing further as the plasterboard is then decoupled or could it reduce the damping effect as the plasterboard is less rigid as it is less supported than if directly attached?

    Over here buildings are frequently brick or breezeblock construction. In this case should the two layers of plasterboard be attached directly to the wall with GG in between? Via battens? Using resilient channel?

    How strong an adhesive is GG? I know that your building regs require a certain density of screws (I'm going to find out what ours say - does anyone know?) However would it be capable of supporting the plasterboard without glue on the walls and \ or ceilings?

    Finally you mentioned that there are independent tests being done, when will these be available? You state that the low frequency performance is good, do you have figures for the sound reduction for a range of low frequencies of a typical GG construction vs standard stud?

    Sorry for all the questions, the product sounds very interesting and if it is effective would be a huge bonus in a project I'm working on, but I also go by the old maxim that when something seems too good to be true, it probably isn't.

    Thanks,

    Ralph.
     
  23. Brian Ravnaas

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    hey Ralph,

    the effect of resilient channels on this type of wall isn't one that we have spent a great deal of time exploring. The use of RC would change the nature of the low frequency behavior from a structural resonance to something more akin to the traditional mass-air-mass resonance. Nonetheless, people report good success with utilizing GG + resilient bars (same low frequency improvements). This is a combination that we hope to explore in the very near future in some quantitative way.

    You mentioned the use of Green in combination with masonary walls. Now, the performance of masonary walls has to be viewed a bit differently from that of plasterboard structures. They are very heavy, very stiff, and the "coincidence" phenomenon tends to occur at much higher frequencies. Low frequency performance (below 100-150hz) should already be quite good (unless it is a very lightweight type of masonary).

    This coincidence dip is damping controlled, and Green Glue could help, but you'd be best off to make the sandwich out of the painted masonary and something over the top of that. This is a very rare use here in the US, and not one that we've done alot of work on. It is used over concrete floors in this manner in theaters in the US at times to reduce sound conduction via the concrete into neighboring rooms. If you were to try this, i think it would be a good idea to let Audio Alloys labs do some legwork to see what effect is feasible.

    A common method of improving the performance of masonary walls is to build a stud wall in front of them with insulation and drywall. The addition of this plasterboard/air cavity changes the behavior of the structure considerably, and can cause low frequency problems. In general these rules should be applied

    1. utilize as deep of an air cavity in front of the masonary wall as possible
    2. utilize as much mass on the front of the stud wall as possible
    3. use insulation (fiberglass/rockwool) in the cavity

    This is an extremely common use for GG in the US - taming the low frequency resonance that arises from putting the plasterboard wall + cavity in front of the block.

    The independent lab tests are the data you seek, SB. We have tested the material in myriad walls, but in this market "3rd party" tests seem to be the only ones that are generally accepted, and as such we won't release our own until after the 3rd party data is available broadly (and it's not clear how much of our own test work will be released then, either).

    I think you are very wise to go by the old maxim of too-good-to-be-trues. But we sure don't think of GG as "miracle soundproofing", just one heck of a good damping material.

    I guess a place to go looking for comments about Green Glue until the lab data is in might be the avs forums if you are interested. You could find some threads, or post a new one, or whatever you wish.

    thanks for the good discussion, everybody, and take care,

    Brian
     
  24. doink

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    Snake oil in it's highest form
     
  25. Brian Ravnaas

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    hey doink, Ralph, all

    i forgot to answer one question, i'm afraid.

    Green is strong enough to hold drywall, yes. But not when wet. Here in the US building code (legal) mandates that screws or nails be utilized, and there is no value at all in accomodating the possibility of someone misusing the product.

    there is no advantage to not using screws with GG either, if anything the pressure from screwing will help form a continuous thin film between the layers. As such i would just recommend using them (Screws)

    if anyone would be curious, i would be happy to post some graphs showing a bit about how walls work (not green related, just general information)
     
  26. Brian Ravnaas

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    hey folks, just a follow-up, now that some 3rd party lab tests are in, and since the ol' green goop got snake-oiled above...

    this graph shows low frequency TL (that's what was under discussion) for a concrete block wall, a double-stud wood wall (two rows of studs), and that same stud wall with GG. Data from Riverbank Labs in the US (the oldest acoustical lab in the world, i think, and generally considered among the best). other data from NRC, Canada, and presented after contacting their copyright office.

    i don't know what else to add ;)

    [​IMG]

    FWIW, studies showing LF gains due to damping date back more than 20 years, originating (to the best of my knowledge) with USG in the early 80's

    I updated the pic to include the best LF wall tests i can find, they are from a different lab. At the same lab, a double stud wall with double 5/8" drywall and same 7" of insulation got STC=63, at other labs such walls have gotten STC 58-69. The variance stems from different labs having different limits before sound coming through the concrete, etc., outweighs sound coming through the wall, and when walls get really good, other differences from lab to lab may be amplified as well.The GG wall got STC=67, and STC=68 in two seperate tests.

    Brian
     
  27. eviljohn2

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  28. spamboy

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    Brian,

    So it looks like a 10dB difference at 50Hz on double stud - which is already more soundproof than standard stud wall. That's a decent improvement, however I notice that the lines intersect at 160hz, does the GG not have any effect on the upper frequencies?

    I'd be really interested to see the full report when it's published, is it going onto your website?

    Thanks,

    SB
     
  29. merseysider

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    Reading through this thread, I thought that I should jump in with a few comments.

    We (Rives Audio) are in the completion stages of a high-end Home Theater, in the Chicago area. We specified Green Glue for the first time on this project, having used soundboard (Celotex or an equivalent) before. In fact, I have been using 1/2" soundboard as a 'change of medium' between two layers of 5/8" sheetrock in my studio design work for 25 or more years.

    I have just returned from a site visit to the Chicago project and had a chance to evaluate the preliminary results. I have to say that the green Glue product is exceptional as a damping factor. It reduces the ability of the sheetrock to vibrate at its fundemental frequencies (relative to spacing and attachment) with great efficiency, so much so that we intend to specify it for all our future work.

    BTW, in an earlier posting to this thread, someone said that the only thing that stops sound is mass? That is not quite true? The two opposites - space and mass will stop sound. For instance, over a given distance, sound decays at a predictable rate. This is closely related to why we put soundboard or Green Glue and such products between two pieces of sheetrock - As a change of medium in lieu of an actual physical airspace. The space between two elements of mass, whether an actual airspace or a change of medium, can be just as important as the mass in effectively stopping or, at least, effectively lowering the transmission of low frequencies.
     
  30. Arkham Insane

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    seems the debate stopped 2 months ago, any progress on the gg front in the uk? anyone tried it, is it available?
     

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