BEF from Norway,DIY Uncompromising Theater - Page 4

That is a serious system and some serious committment you have there sir. Congratulations!
The pictures of the finished room are simply astounding.

Great that forum members have provided expert diffuser critique but don't be discouraged.
Excluding Dennis Erskine's professional builds many people just line their walls with absorbption and call it a day...a dead, dull day.
Over the past two years I can probably count the number of AVS Forum theater builds which have taken a serious stab at diffusion on one hand (Roger Dressler's beautiful space and Landshark's 2.0 come to mind).
Kudo's to your effort.

yes, it is very common to see those blindly line walls with absorption - but even worse is the lining of the walls with "thin" porous absorption.

the same actually goes far too frequently with "diffusion" as well .. but the OP here has clearly understood the benefit a little extra material gives you, considering the bulk of the time spent on the PRDs has little to do with actual "length" of the wells. +1 again to good broadband design (a rarity it seems all too often) - but regardless, there are rules at play regarding reflection phase gratings (primarily, the 3x design frequency distance limitation to allow on to be in the "far-field" of the coherent spatially and temporally dispersed returns (vs the near-field of a RPG which is quite a chaotic superposed "mess"!)


far far too often we see the deployment of shallow reflection phase grating diffusers (eg, 3-5" max well depth). +1 to the OP for low design frequency.
Edited by localhost127 - 11/25/12 at 7:32am

+1 to both comments. Oh, and by the way....my theater's acoustics are being handled by Dennis Erskine to maximize the theater's performance after my investment in Procella loudspeakers which require more diffusion than most other speaker types.

What makes them different to any other controlled directivity speaker/anything with good off axis response?

Probably not huge differences, but when I said "other speaker types" I was referring to a traditional speaker without the benefit of the compression drivers and controlled directivity waveguides.

what's your definition of "diffusion"?

The special lens they used to shoot William Shatner in the last couple Star Trek movies.

No, no! He's just naturally unfocused...

How was it to work with this one, thinking about getting the same one for redoing my front wall? Any typical mistakes you can stop me from doing?

Did you remove the screws after it dried, or do one keep then there for good?

Thanks. I do keep getting feedback on the swedish forum that I way end up losing sound proofing in the low range by using it rather than just using multiple drywalls on their own, so currently I'm somewhat confused on how to proceed. I'll try to figure out the problem frequency range and then go over the different ways again to see what might work the best.

I'm certain it's a good product - my main speakers are laminated using it.

I will try this weekend to find out the frequency range I have problems with. Assumption is the very low end.

Primarily faktiskt.se, less so on minhembio.com

What an unassuming entrance to sonic terror that awaits inside ....

I could have financed my (future) build if I would have just invested in MDF stock before you started building speakers...

Heck of a place you have there. As others have said, your craftsmanship is excellent.

And a Gledelig Jul to you too sir.
Congratulations on being featured in an article. Well earned.

God Jul och God fortsättning!

Looking great so far!

This actually gets one wondering if that's not the way to go from the beginning, or at least to make sure I have masking available for the format.

The green glue that I have used, does not actually dry and is not actually an adhesive. It remains pliable. It is a sound/vibration deadening material. The second layer of drywall has the "glue" spread on it and should actually be held in place with special "drywall to drywall" screws sold by commercial DW suppliers. They are a fat , course thread, 1 1/2" long screw with the typical DW screw bugle head. The screws DO NOT hold into the wood, but rather the first layer of DW ONLY and are kept in place. This keeps the sound hitting the surface of the DW from transmitting through the screw into the wood/steel studs.

It should be noted that a 1/4" gap should be left around the perimeter of the wall or ceiling which gets filled with acoustic seal (comes in calking tubes) before the adjoining wall gets it's second layer of DW (especially at the floor). The second layer of DW should lap the joints of the first layer, as BEF has done, or run perpendicular to the direction of the first layer (this can help the 2nd layer sit flatter). There should be a bead of acoustic seal applied along the edge of the sheet, that the next sheet butts into. Basically, there should not be any unsealed cracks for sound to leak through. Acoustic seal can be messy to work with. It always seems to get onto your hands...and beyond. When applying the beads, apply only enough to seal the gap without bulging beyond the surface. These joints are then taped and finished in the usual manner.

The green glue also comes in large calking tubes and gets applied at the rate of two tubes/4 x 8 sheet.

Nice job BEF! I said, nice job BEF!

Thanks, I got that confirmed in my mailbox by the green glue company that one cannot remove the screws at at later point as the green glue does not have adhesive power to hold the drywall. I haven't yet asked swedac if their glue is the same, but I'd hazard a guess that the answer would be the same.

It only leaves some question about how those premanufactured drywalls with green glue in them from the start are made, of course.

We have such a board called Quietrock. I believe it stays together because it is 1) rapped as a unit with paper, 2) has a complete thin coat with no voids, 3) held up as a unit with screws penetrating both layers and 4) the surfaces bonded are not perfectly smooth. If you cut a small square, you can get it apart, but a thin "film" of gypsum seems to coat the green glue layer, so there may also be some penetration into the surface of the gypsum by the glue.

Did you have any luck finding the drywall to drywall screws? My regular building supply companies have never heard of them, but the drywall specialty outlets, who handle Quietrock type DW would have them.

Of course to avoid the expense of Quietrock, resilient tracks could be used to help keep the sound vibrations from going up through the ceiling structure if a separate frame for the ceiling is not used as done by BEF. The second layer of DW with green glue could be used with regular DW screws also into the same resilient tracks. Using 5/8" DW also helps. This is not as good as two layers of Quietrock however.

Any holes cut through the ceiling for such things as pot lights, junction boxes, vents, etc., that do not have sound traps will of course negate all of the time and expense of the double DW. Pot lights create their own problem since the heat they create must dissipate to at least 6' of joist space, unless a Insulated Thermal Unit is used to safely contain the heat and minimize the risk of fire. Ceiling speakers should have sound traps. This holds true for any openings in the walls as well. Sound will travel/reflect through any open space to rooms beyond. And vibrations will travel through solid materials to other rooms if no dampening or isolation is incorporated.

This is absolutely not correct. The second layer of drywall needs to be secured to the structure holding the wall board whether it be channel or studs.
Edited by BllDo - 12/30/12 at 2:58pm

Can you speak a little bit to your thought process regarding the change? I'm currently debating a new screen size and leaning towards either 16:9 or CIA.

I'm afraid we disagree on this point. This is the installation technique I got from Quietrock and the people selling the products. And my own experience.

The logic is that sound waves hitting the surface of the board can transmit through the screw to the stud (this is limited to frequencies with wavelengths equal to or shorter than the length of the screw), thus allowing higher frequencies to transmit. By screwing to the first layer of DW only you are breaking this link.

The green glue people would also like to see you use a bead of green glue on the studs before installing the board which would further dampen this connection. It didn't look like BEF had used this bead on the stud, so I was limiting my comments to installing a second layer of board to an existing drywalled room which is, I believe, where Nightlord is proceeding from.

FYI...The issue with attaching DW to a new wood stud without green glue, is that the stud will probably shrink slightly as the wood acclimatizes to the room humidity. The screw holds fast in the wood and when the wood shrinks a gap can develop between it and the DW, allowing movement. If you have ever seen a "popped" DW screw, if you push on the DW, you will probably see movement at the screw. This is why. This can also be a major problem with old, very dry studs, if you drywall in the summer in an un-air conditioned room. The studs actually swell in the humidity and shrink once the building is sealed and the heat/ A/C drys the air. Now, if you have a layer of DW that can move, it acts as drum skin and makes the air in the stud space vibrate like a drum and those nasty lower frequencies have escaped.

Now, this is all pretty picky in the grand scheme of things, and as I have previously said, all for not, if you then start cutting holes through the DW for lights, wiring and ventilation without sound traps!

There will always be different opinions about how things should go together. What works in one case won't necessarily work in another. You literally have to look at all the details around a particular situation. I'm just trying to share my experience in trying to "minimize" sound transmission that I've learned through watching and listening to others in the construction industry and my own trial and error R & D as a contractor over the past 30 years.

...But, as always, I'm willing to listen to your argument.

You can disagree all you want, I don't really care. I'm not going to clog BEF-NO's great thread with your troll fodder. If you'd care to start a new thread to discuss the merits of your "expertly" advised drywall installation methodologies, I'm sure the many experienced members around here (including Ted White one of the co-founders of Green Glue) would love to rip me to shreds. In the meantime, I'd challenge you to provide even one piece of documentation from a reputable manufacture or municipal building code that would recommend the use of laminating screws as the sole method of securing multiple drywall layers with damping compound.

BEF,

Great theatre! Seems like you Norwegians really got the knack of it. There's also Atledreier who posts on HTShack, he uses the same LCR. And there's Akto, who posted pics of his stunning HT here:
http://www.blu-ray.com/community/gallery.php?member=akto

Good for you to go to a 2,35/1 screen. I have one waiting in a box until our HT is ready. Same size: 130"...

I am especially interested in those inConcert Miles. But it seems the designer is no longer in business. Are there variations available such as your surrounds or did you come up with those yourself?