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post #31 of 592 Old 01-07-2014, 04:01 PM
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Question: What are the best techniques to isolate a window when already installed windows exist in a wall that will be part of the "soundproof" room?

My main concern is for a window that must remain in use (basement egress). A plug is the most common recommendation here when the window will remain in use. How best to create this plug? Tolerance for the size of the plug compared to the size of the opening to be covered? Good build threads that present method for building the plug?

Alternative question could be for windows that can be covered - and probably an easier answer.

In my case, the wall around the window will be on clips, hat channel, DD + GG, or something very similar to this plan. Does this common method for room isolation of the wall around the window create any changes in recommendation?
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post #32 of 592 Old 01-07-2014, 05:05 PM - Thread Starter
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Quote:
Originally Posted by tmhouse View Post

Question: What are the best techniques to isolate a window when already installed windows exist in a wall that will be part of the "soundproof" room?

My main concern is for a window that must remain in use (basement egress). A plug is the most common recommendation here when the window will remain in use. How best to create this plug? Tolerance for the size of the plug compared to the size of the opening to be covered? Good build threads that present method for building the plug?

Alternative question could be for windows that can be covered - and probably an easier answer.

In my case, the wall around the window will be on clips, hat channel, DD + GG, or something very similar to this plan. Does this common method for room isolation of the wall around the window create any changes in recommendation?

Thank you for asking this question, because I'm going to have to do the exact same thing in my theater. In my case, it's not a basement, but it is still two very large windows that cannot be permanently covered.

The best build thread on a window plug that I've seen so far is in the Dark Knight Theater thread. Here's a link to the post with some details: The Dark Knight Theater - Window Plug Details Post

I'm still searching for even more details on pros/cons and possibly other options, if they exist.
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post #33 of 592 Old 01-07-2014, 09:14 PM - Thread Starter
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Quote:
Originally Posted by BasementBob View Post

SAE used to have some very nice summary pages on acoustical isolation techniques, again over a decade ago. One of the things they recommended for airlocks was hanging thin open-cell foam on the side of the doors on the inside of the airlock. Given the study of walls above it should be obvious why this helps.

Doors are remarkably sensitive to the seals they have, so a simple study of door types while indicative is not predictive of installed results. I seem to recall a bunch of multi frequency test results for single doors, where they glued the door into a test frame.

Well! This all led me down some very interesting paths. I got the Rod Gervais book and man, you are NOT kidding that that book is good! Very practical and very detailed in the parts that mattered. Reading his 'doors' chapter confirmed the importance of seals (not that I doubted you) and steered me towards this thread:

http://www.gearslutz.com/board/studio-building-acoustics/875142-jhbrant-door-design-diy.html

That site has a pretty terrible name, but it seems to be packed with acoustic experts. John H Brandt posted his PDF on making the Ultimate Studio Door and it even includes CAD drawings. It matches what Rod says in a lot of parts and deviates a little in some others. The thread contains the PDF as well as a discussion about building it.

I will start by saying that neither resource indicated any qualitative numbers on evaluating any particular door solution, but their practical advice may well override that. I'll summarize.

Rod prefers a single mass-loaded door to double "stock" solid core doors, although both are excellent. His door is a 1-3/4" solid core door (type doesn't matter) with a layer of 1/8" lead (8psf) and a "stepped" layer of plywood. The lead, alone, weighs some 160 lbs for a 36" door. It also costs somewhere in the $600-$800 range. The stepped layers allows for a "bank vault" style door seal. He strongly recommend a commercial door closer, since the very high weight of the door could absolutely cause injury for small children.

John also likes mass-loaded doors, but his design calls for two of them. He does not use a base solid core door but instead makes a door from scratch using plywood, 2x4s, and SAND. The design includes the bank vault door seals and commercial door closer.

Both also assert that the fact that the door frame couples the two walls has no noticeable effect on sound loss. That is, there is sound loss by the coupling, but not by enough that matters. More importantly, these doors are so heavy that it's imperative that they have a very solid frame (Rod's frame is made of 5/4 stock wood, rather than the typical 5/8" pine).

So what can I conclude from this? Well, nothing qualitatively. However, expert advice says that two mass-added doors is better than one mass-added door but that one mass-added door is better than two unaltered doors. No matter what, have excellent door seals, preferably in a bank vault style double seal.
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post #34 of 592 Old 01-07-2014, 09:20 PM
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Hey fellow Gilbert resident check this window plug out.
Starting at this post.

http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/210#post_23740019

I think bigmouthindc did a window plug in one of his builds but I can't find the link on my phone

Pete
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post #35 of 592 Old 01-07-2014, 10:00 PM - Thread Starter
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Quote:
Originally Posted by xm15_owner View Post

Hey fellow Gilbert resident check this window plug out.
Starting at this post.

http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/210#post_23740019

I think bigmouthindc did a window plug in one of his builds but I can't find the link on my phone

That's a great one, thanks! That thread has a lot of other great detail, too, so it's a great subscription in any case.

The only plug that I remember Big doing was a permanent one (walled over it). I could definitely have missed one, though.
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post #36 of 592 Old 01-08-2014, 10:30 AM
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Quote:
Originally Posted by granroth View Post

He strongly recommend a commercial door closer.
The other advantage to a hydraulic door closer is you don't have to drill holes into the door for the door handle (little mass around mechanics) and latch (possibly where the seals are).
You put a vertical pull handle on one side with screws that don't go though the door, and nothing on the other side -- a combination that's obviously more air tight and even mass.

Heavy doors require, as you mentioned, heavy framing to hold them up. A warped wall or a warped door doesn't seal properly.
A 200 pound door that rips itself out of its frame and collapses is worse.
They also require hinges that can take the weight. Ball bearing hinges are popular.
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SAND.
Sand, in doors or walls, is good and bad, mostly bad.
It settles, which ends up causing the same kind of problem that NRC was worried about with insulation, a path around it.
It also is 'liquid', creating an outward force that'll be there forever, eventually breaking the door/wall at the bottom.
At resonance it liquefies, like Mexico City sand (soil) in an earthquake -- I've never seen STC measurements on this but I presume it's not a good thing.

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post #37 of 592 Old 01-08-2014, 07:18 PM - Thread Starter
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Quote:
Originally Posted by BasementBob View Post

Sand, in doors or walls, is good and bad, mostly bad.
It settles, which ends up causing the same kind of problem that NRC was worried about with insulation, a path around it.
It also is 'liquid', creating an outward force that'll be there forever, eventually breaking the door/wall at the bottom.
At resonance it liquefies, like Mexico City sand (soil) in an earthquake -- I've never seen STC measurements on this but I presume it's not a good thing.

That is very interesting! I am unable to find a reference of dry sand liquefying, though -- the only references I'm seeing all refer to the water content of soil (e.g., like in clay) causing liquefaction of the sand at resonance. Presumably any sand used in a door would have minimal water content.

JH Brandt's design separates the sand into eight compartments of 13-3/4" x 17-3/8" x 1-1/2". Assuming a stated weight of dry sand being 100 lbs/cu ft, then each square would weigh 20.73lbs. I interpret the design to mean that the 2x2 frame + plywood is intended to each old 20 lbs. That seems well within the design limitations of 2x2 material. The entire door, then, would have a sand weight of 166 lbs.

Notably, that is very similar (maybe 20lbs more) than the sheet of lead that Gervais recommends. In fact, the end result of the two door constructions appear to be similar widths and very similar weights. The Gervais design would run upwards of $800 while the JH Brandt design would be far far less -- the sand would be between $10-15.

Completely ignoring any liquefaction concerns for the moment, it appears that the Brandt design is a far more economical way of achieving the same mass.

But let's not ignore liquefaction. In saying that I can't find references to it, I'm not in any way saying that I think you are wrong! I am now officially fascinated by the topic and would love to find out more.
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post #38 of 592 Old 01-08-2014, 07:34 PM
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Take concrete or steel.
(or Gervais's sheet lead)
Shape it into a column 8' tall and 1' diameter.
What happens?
It's so solid and unchanging that people make supports out of this stuff, even buildings thousands of feet tall.

Take play sand, or water.
Shape it into a column 8' tall and 1' diameter.
What happens?
The weight at the top pushes out the bottom. That downward force at the top, becomes a horizontal force near the bottom.
It's that horizontal force that has to be held in check.
That horizontal force is proportional to the height of the sand above it.
That horizontal force is there every moment of every day, forever.
With a hollow wooden door, that shrinks and contracts with every change of heat and humidity, is being reacted upon by this sand force, but unlike a floor which contracts back to the same place, the door is being held apart by the sand force, until the next expansion contraction phase, until eventually it splits and the sand pours out.
With a concrete block wall, with sand (not grout or poured concrete in the block holes), the same sort of thing happens. Its less force than freezing water, but its still there.

Seismic shaking can transform water-saturated sand into a liquid mass that will not support heavy loads such as buildings. This phenomenon, called liquefaction, causes much of the destruction associated with some earthquakes. Mexico City, for example, rests on the ancient lakebed of Lake Texcoco, which is a large basin filled with liquefiable sand and ground water. In the Mexico City earthquake of 1985, the wet sand beneath tall buildings liquefied and most of the 10,000 people who died were in buildings that collapsed as their foundations sank into liquefied sand.

hydrokinectic fusion (example by humor)
http://www.oocities.org/timessquare/dungeon/3459/watertrick.html

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post #39 of 592 Old 01-08-2014, 09:11 PM - Thread Starter
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Those are very good points. I've now done more research on the topic and have, indeed, come across quite a few cases of people who build sand-filled doors and ran into the same issues as you describe are inevitable.

I did see at least one reference to building such a door but sealing everything with poly, first. The idea is that even when the wood expands, the poly will keep the sand from leaking. I don't see how that would solve the issue you bring up about the sand settling each time the wood expands, though. But let's look at how much the wood could expand. If we assume that we are using dimensional lumber made from Douglas Fir, then the expansion coefficient is 0.00267. If we assume a maximum moisture change of 10% throughout the year, then a 1-1/2" piece would expand a maximum of 0.04" or 1/25" -- roughly halfway between 1/16" and 1/32". In other words, not a lot. Not a lot is not nothing, though. If the sand was able to settle enough 1/25" every year, then it would take only about 6 years to expand by 1/4"; likely enough to cause structural problems. Hmm...

Okay, so you mention concrete and there are definitely concrete filled doors. Concrete is even denser than sand is similarly inexpensive (relatively speaking). It absolutely does not have the same issues with settling that sand will, since it's incredibly rigid. So if you made the same wood frame and then lined the cavities with poly (concrete is very wet and essentially stays wet forever), the wood would definitely be strong enough to hold it up and the poly would keep it from rotting from inside.

Now to brainstorm some potential problems. Concrete is rigid, but it does expand and contract. It does so mostly based on temperature, though, and the temperature in a house tends to be relatively stable. I wouldn't expect that the concrete would "move" all that much. The wood will still expand and contract, based largely on humidity. The concrete won't settle so it's just an issue of "gaps" -- which aren't big enough to cause any issues.

What are your thoughts on that? I haven't seen any examples (yet) of using concrete to fill cavities in a wood frame door (the doors are invariably steel). What else am I missing?
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post #40 of 592 Old 01-10-2014, 08:17 AM
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Great thread here, I would like to hear more regarding the concrete door. What was the out come?
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post #41 of 592 Old 01-10-2014, 10:10 AM
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One would have to do something about the door handle,
but here's one way to do a concrete door.
http://www.sportsmansteelsafes.com/nbc_vault_doors.htm
http://www.americanbombshelter.com/blast-door-single-leaf.html
The steel door, with openings at the top, is shipped empty
and concrete poured in after its installed with a crane.
1400lbs Empty. 2500 Filled with local Concrete.


Steel fire doors are a lot lighter (up to around a mere 300 pounds), often filled with honeycomb or insulation. I thought there were some that were filled with a gypsum or grout or concrete like substance, but I can't find any today except from China.

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post #42 of 592 Old 01-10-2014, 01:03 PM - Thread Starter
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Quote:
Originally Posted by BasementBob View Post

One would have to do something about the door handle,
but here's one way to do a concrete door.
http://www.sportsmansteelsafes.com/nbc_vault_doors.htm
http://www.americanbombshelter.com/blast-door-single-leaf.html
The steel door, with openings at the top, is shipped empty
and concrete poured in after its installed with a crane.
1400lbs Empty. 2500 Filled with local Concrete.

Steel fire doors are a lot lighter (up to around a mere 300 pounds), often filled with honeycomb or insulation. I thought there were some that were filled with a gypsum or grout or concrete like substance, but I can't find any today except from China.

Yeah, the option of buying a steel door and filling it with concrete is definitely a thing. As your links show, most seem to be concerned with security. I did find a few references to "normal" sized steel doors that can be concrete filled.

I think the outstanding question, though, is if it's possible to make a wood-frame concrete-filled door. It would be very similar in theory to the sand-filled door, but since the concrete does not move (practically), it shouldn't have the same drawbacks. I went into a little more detail a couple posts above.
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post #43 of 592 Old 01-10-2014, 06:22 PM
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Density
MDF (medium density fiberboard) : 830 kg/m3
Concrete : 2,242 kg/m3
Lead : 11,350 kg/m3

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post #44 of 592 Old 01-10-2014, 09:43 PM - Thread Starter
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Okay, so here's my thoughts on how you might construct a pretty massive wood-frame concrete-filled door. This is assuming a 32" x 80" door.

First, start with a layer of 1/4" ply then Green Glue then a layer of 3/4" MDF. On the bottom of this is an automatic door seal (I spec'ed a Zero International partial mortise).

Massive Door - Layer 1

Then, create a wood frame using 2x4s and 2x4s ripped in half (1-1/2" x 1-5/8", accounting for the width of the saw blade). This creates 8 cavities. Line the cavities with poly film and fill them with concrete. Let the concrete cure for at least a week.

Massive Door - Layer 2

Add another layer of poly and then a layer of 1/4" ply capped with a slightly smaller layer of 3/4" MDF.

Massive Door - Layer 3

Before getting to the specs, I wanted to cover a couple points. The slightly smaller layer of MDF is intended to create a "bank vault" effect, with staggered door seals. This double seal should do a fantastic job of blocking any air leakage. The Green Glue is important because mass without damping only covers half the battle. A quote from Ted White from another thread:
Quote:
Originally Posted by Ted White View Post

The issue is more than just the mass, as a damping of that mass would improve things as well. So the combo of mass + damping would yield great results.


This assumes things are sealed up very well. The seals are always the weak link.

The 1/4" ply is there simply because this door is already quite thick. As I write that, I realize that it would make more sense to use two layers of 1/2" MDF than 1/4" Ply + 3/4" MDF. It would be more dense and damping works best with layers that have the same mass and density, anyway.

So what are we looking at?

This door is 3-1/2" thick (roughly twice the width of a standard door) and is massive. How massive?

Assume that MDF is 49 lbs cu ft; Plywood is 32 lbs cu ft; concrete is 133 lbs ct ft; and Douglas fir studs are 31 lbs cu ft. There are 0.731 cu ft of plywood, 2.122 cu ft of MDF, 0.662 cu ft of wood, and 1.56 cu ft of concrete. Do the calculations and you have a door that weighs 355 lbs!

(Actually, it would be slightly more than that if you replace the plywood with MDF)

Is that enough?

Well, JH Brandt suggests that the door must have at least as much (and preferably) mass as your walls. If you assume that you have double walls with two layers of 5/8" drywall on each side and further assume that the insulation has negligible mass; the studs add only a little; and drywall is 2.2 lbs sq ft, then we have a mass of 8.8 lbs sq ft for the walls. Round up to 9 lbs, factoring in the studs.

Our door is 32" x 80", which is 17.8 sq ft. If we want our door to have at least as much mass as our walls, then it would need to be 17.8 x 9 = 160 lbs.

Our actual door is more than TWICE that massive. When you consider that it is also damped and fully sealed, then it's hard to imagine that this door wouldn't do a fantastic job of sound proofing.

Maybe too good, actually. Overkill is sometimes good, but exceeding the mass by that much might not be justified. That's a pretty extreme door.

I also have NO idea if it would actually work, since I haven't seen it done.
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post #45 of 592 Old 01-10-2014, 10:10 PM - Thread Starter
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Quote:
Originally Posted by BasementBob View Post

Density
MDF (medium density fiberboard) : 830 kg/m3
Concrete : 2,242 kg/m3
Lead : 11,350 kg/m3

Heh, every single place that I've seen density numbers of materials have different numbers for everything. I'm honestly not even sure what people are measuring, if all measurements are different.

Anyway, lead is clearly far more massive than concrete, which is quite a bit more massive than MDF. Price definitely comes into play.

Let's see... a 32x80 door (like my concrete door example, above) is 17.8 sq ft. If I by that much 1/8" lead at $26 sq ft and 8 lbs sq ft, then I paid $463 for 142 lbs. But only 1/8" thick.

Assuming concrete is 133 lbs cu ft, then we'd need 1.068 cu ft to hit the same weight. Lead is 710 lbs cu ft, so the layer would have to be just over 5 times thicker or around 3/4" thick. That would cost around $10.

Assuming MDF is 47 lbs cu ft, then we'd need 3.021 cu ft. We'd need a layer 15 times thicker than lead, so 1-7/8" rounded to 2" thick. That'd be roughly two layers of 3/4" plus one 1/2". With the going price of MDF around here, the cost for 142 lbs would be (math math math) $55.

To sum up:

Concrete - 3/4" thick; $10
Lead - 1/8" thick; $463 (46x concrete)
MDF - 2" thick; $55 (5x concrete; 1/8x lead)
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post #46 of 592 Old 01-11-2014, 05:12 AM
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Massive Door - Layer 2

Lead and MDF are also naturally flat, and handle flex problems forever without thought.


How do you guarantee:
a) no air gaps (triple leaf effect)
b) no flex problems (rattling piece of broken rock).

Possible remedies:

a) an excessive amount of PL Premium glue, all over the concrete and final wood layer. You can't use anything compressible like soft foam because that'll be a triple leaf effect. But anything rigid that fills the gap due to any inconsistency in the 'concrete' pour flush/level will be fine. If the gap were larger (1+ inches) I'd recommend expanding foam to couple the leaves, but I presume we're talking about errors and dips and possibly even stones, on the magnitude of 4mm.

b) Doors flex a lot. They flex by opening/twisting. They flex by impact. They warp/expand/contract by humidity and gravity. Even carrying it to install it it'll flex.
Concrete isn't good at flex. Concrete is often filled with rebar in three directions or jacketed by steel to avoid flex.
Perhaps if you drove screws through your wood, bed-of-nails style, every square inch, within 5mm of the depth of the cavity, so that the concrete would have something to hang on to.
2 1/4 inch screws, fully threaded (no shank). Perhaps drywall screws due to their wide thread. Although normally with concrete you'd want galvanized or the blue ones for concrete, here I don't think there are moisture or electrical problems (both of which contribute to rust), although there's still the intrinsic concrete alkalinity.
Just to be paranoid, you might throw in a bag of those glass fiber things (rebar replacement).


When you're talking about concrete, I presume you're talking about non-shrinking grout (e.g. Quikrete).
Or a self leveling and non-shrinking like Loctite® Fixmaster® Fast Set Grout.
In both cases it may take several applications to build it up, allowing time for each layer to fully set.


I don't think you need to worry about poly from a moisture point of view. Concrete in the ground wicks moisture and wood needs to be protected from that, but this door is suspended in the air -- it'll dry to the room's moisture within a few days. While its wet some types of wood would swell.
On the other hand, this guy did something similar, and used poly
http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=12664&start=105

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post #47 of 592 Old 01-11-2014, 05:14 AM
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Quote:
Originally Posted by granroth View Post

JH Brandt suggests that the door must have at least as much (and preferably) mass as your walls.
Door same mass per square foot as walls. Sounds good to me.

By 'same' I mean: not larger, not much less.

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post #48 of 592 Old 01-11-2014, 05:47 AM
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Some comments on sand. Note 'avare' is a good fella.
http://www.gearslutz.com/board/studio-building-acoustics/291823-filling-hollow-door.html


Two big acoustic doors
- 850,000 lb., 40’ x 60’ x 2’ concrete filled acoustical door
- 166,000 lb swing door with pneumatic seals, tested to 165 db at 35 and 50 Hz
http://www.appliedhandling.com/doors/specialty/

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post #49 of 592 Old 01-11-2014, 05:54 AM
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Here's a fella that poured concrete into the recess of a door
http://www.avsforum.com/t/1189103/the-take2-theater-design-build-thread/30

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post #50 of 592 Old 01-11-2014, 12:12 PM - Thread Starter
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Quote:
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Here's a fella that poured concrete into the recess of a door
http://www.avsforum.com/t/1189103/the-take2-theater-design-build-thread/30

I did see that earlier and even added it to the summary posts at the top of this thread. Curiously, though, I never correlated the "leveling compound" with "concrete". They are essentially the same, though, so I'm not sure what I was thinking.

So, cool, we do have a couple examples of concrete filled doors in the real world. At least in the Take2 case, it was a much thinner layer than the above plan, but the concept is the same. Neither builder appears to be active now, which is unfortunate, since I'd be very curious to see how they have held up over the past 3-4 years.
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post #51 of 592 Old 01-20-2014, 06:09 PM - Thread Starter
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Where, exactly, does "sealing" fit in with regards to sound proofing? I'm talking about sealing the electrical outlets with putty; cracks with caulk; doors with auto-closers; etc. These are all very clearly recommended steps... but what are they specifically doing?

I ask from the perspective of the "four elements of soundproofing", as laid out by @Ted White and summarized in the first post of this thread. To wit, they are:
  1. Decoupling
  2. Adding Mass
  3. Damping
  4. Absorbing

Is there a fifth element called "Sealing" and, if so, where does it lie relative importance? If it's part of one of the existing elements, then which one and why?
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post #52 of 592 Old 01-20-2014, 08:15 PM
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post #53 of 592 Old 01-21-2014, 05:40 AM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post

A crack has no mass. Filler up.

That makes sense. If you assume that air -- as a reference level -- has no mass, then adding caulk or putty or similar would increase it infinitely.

But that's just relatively speaking; the actual amount of mass added by sealing products is pretty minimal compared to what we are typically referring to by "adding mass". If we think about caulking the seam between the bottom plate of a wall and the floor and weighed the new bottom plate, I think we'd find that the additional weight from the caulk would be completely dwarfed by even the possible differences in the type of bottom plate used (pressure treated, douglas fir, whitewood, etc). Further, I don't recall ever reading about differences in mass, when it comes to sealing products.

So like I said, it does make sense that sealing is also adding mass, but considering the outsize impact that sealing has for such a little amount of product, I have a hard time reconciling that that's all that's going on.
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post #54 of 592 Old 01-21-2014, 07:17 AM
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Granroth:


BIGmouthinDC is correct when he answered your question about which of the four types of soundproofing would apply to holes, in that the answer is mass.

But your analysis is going the wrong way. The important part is not: adding mass to the wall relative to the walls mass.

The mass is what's used to resist the transfer of sound. If there's a path without resistance, then that's a significant transmission path.

If you have a source room (with a stereo), and a quiet room (with a bed),
and a wall of 100ft^2 between them that's 3' of solid concrete,
and there are no other flanking paths (ceiling/floor -- fiction but I'm simplifying),
and the stereo is played at 80dB at frequency F,
and the wall stops 90dB at frequency F,
then the sound heard in the quiet room is -10dB at frequency F, and -10dB you probably can not hear.

Now open up a six inch square hole in that wall connecting the two rooms.
So 99.5 ft ^2 is transmitting -10dB,
and that 0.25 ft^2 hole is transmitting 80dB.

Now let's convert that to energy, and back to dB.
-10dB * 99.5 = 0.1 * 99.5 = 9.95
80dB * 0.25 = 100000000 * 0.25 = 25,000,000
Add them together, 9.95 + 25,000,000 = 25,000,009.95
and divide by the total wall area 25,000,000 / 100 = 250,000
Which gives us 54dB at frequency F in the quiet room.
Which you will definitely hear.
(my math/physics are probably a little bit off in a couple of ways, but the idea is to add the energy)

Now, instead of a single 6"x6" hole, let's have that solid concrete wall, hovering in the air the way drywall attached to studs might, with a gap all the way around it that's the same area. The sort of gap around the edge of drywall that one might fill with acoustical caulking (because the building moves over time).
The 4 edges of the wall are 40' in length (10' x 10' wall). So a 0.1 inch gap all the way around would total over a 6" x 6" hole's area.
Same rules apply as the previous paragraph -- lots of noise goes through.
Technically it's a little lower than this, because the air in that tiny gap has more resistance/impedance than the single 6" x 6" hole.

Now fill that edge gap with acoustical caulking. That caulking is not a lot of mass relative to the 3' thick concrete wall, but its coupled with the massive wall, providing resistance/impedance to the sound wave. The actual relationship here is complex, but it's a lot more than air.

NRC had some statements about having electrical boxes back to back.
Brian has some interesting measurements about the effects of having electrical boxes back to back, and offset by a stud, and with and without putty packs -- as I recall back-to-back electrical boxes weren't as bad as he was expecting, but separating them and putty packs did help.

Of course you knew all that instinctively from experience -- I just gave you a little dB energy math, and asked you to think of a big hole as a long crack. When it's noisy outside, you close the window.
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post #55 of 592 Old 01-21-2014, 09:31 PM - Thread Starter
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That was a very helpful post, Bob! I'll admit that I'm very familiar with the "long crack == big hole" scenario, as it's a very prevalent concept in heat transfer (insulation, etc). However, with regards to heat transfer, the hole needs to be plugged specifically because of the convective qualities of the air. Caulking will help a tiny bit with conductive heat transfer, but it's so little that it's not worth mentioning compared to the convective heat transfer savings.

The example may be the same but the reasons, it seems, are completely different. Sound doesn't travel convectively at all (that I know of) so there's no savings there. It's always about conductivity with sound.

Now if we look at the suggestion that a long gap is strictly equivalent to a square hole, then I'd have a hard time swallowing that at face value. One could then imagine that the 6x6 hole was covered over with a 1/4" layer of caulk to be truly equivalent, and then a comparison of energy through that wall and that hole would show a drop in energy transfer compared to an empty hole, but since caulk has relatively low mass/density, I'd assume the drop would not be very significant.

Therefore, we'll treat the gap to hole analogy as a logical comparison to indicate the scope of the problem. But in reality, the caulk is extending the already massive wall (or door or whatever) and so it's impact is outsized.

If I interpreted all that right, then we're right on the same page.
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post #56 of 592 Old 01-22-2014, 05:27 AM
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Just to add an almost trivial part to this discussion, 5/8 firecode Drywall is about .027 lbs per cubic inch. USG brand acoustical caulk is .0519 in the tube. So relatively speaking caulk holds it own in the mass faceoff.
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post #57 of 592 Old 01-22-2014, 05:49 PM
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Question: This soundproofing neophyte could use some sage advice from the Grand Masters. Here's the skinny: we bought a home with a mostly finished basement apartment with 7 foot ceilings in said apt. Due to some incredibly poor workmanship in framing, we needed to open up half of the basement ceiling to reinforce floor joists.

1) To improve soundproofing, I am planning on adding R13 to the 2x8 floor joists then hanging 5/8 Quiet Rock. With no room for hat channel, does this make sense?

2) The primary basement bedroom is directly below a bathroom with tile flooring. With this bedroom ceiling currently open, does the installation of mass loaded vinyl prior to Quiet Rock add value?

3) The remaining basement ceiling with sheetrock intact is below a living area with hardwood laminate flooring. It will cut into the 7 ft ceiling height, but I was considering adding Quiet Rock here with green glue as a decoupler?

Any help is greatly appreciated~
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post #58 of 592 Old 01-22-2014, 09:23 PM
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If using first layer OSB and second layer drywall, does one still need to worry about hitting the studs and channel with screws when hanging that second layer?
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post #59 of 592 Old 01-23-2014, 10:16 AM
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Quote:
Originally Posted by 30peppered View Post

7 foot ceilings in said apt. Due to some incredibly poor workmanship in framing, we needed to open up half of the basement ceiling to reinforce floor joists.

1) To improve soundproofing, I am planning on adding R13 to the 2x8 floor joists then hanging 5/8 Quiet Rock. With no room for hat channel, does this make sense?
Sounds like the best you can do.
Given that you have 2x8 floor joists (probably can't take more weight -- ask an engineer), as suggested by
the joists were probably damaged and presumably somewhat sistered as much as you're willing/able, and
a 7 foot ceiling (which eliminates lots of options) with building code limitations on required minimum height.

You might want to flip through these for ideas:
http://archive.nrc-cnrc.gc.ca/obj/irc/doc/pubs/rr/rr219/rr219.pdf
http://www.nrc-cnrc.gc.ca/ctu-sc/files/doc/ctu-sc/ctu-n35_eng.pdf
http://archive.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir811/ir811.pdf
Quote:
Originally Posted by 30peppered View Post

2) The primary basement bedroom is directly below a bathroom with tile flooring. With this bedroom ceiling currently open, does the installation of mass loaded vinyl prior to Quiet Rock add value?
Generally speaking, mass loaded vinyl is a waste of money. Just buy more drywall.
Quote:
Originally Posted by 30peppered View Post

3) The remaining basement ceiling with sheetrock intact is below a living area with hardwood laminate flooring. It will cut into the 7 ft ceiling height, but I was considering adding Quiet Rock here with green glue as a decoupler?
Green Glue is CLD (constrained layer damping -- absorbs sound by stretching and converting it to heat), not a decoupler.
Quiet Rock and Green Glue are mutually exclusive. If you're using Green Glue just use drywall. If you're using Quiet Rock then green glue is a waste of money. Quiet Rock has metal and CLD in it.

hmm. I haven't been to the Quiet Rock website in a couple of years. I see they now sell 1-3/8” thick Quiet Rock.

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post #60 of 592 Old 01-23-2014, 05:55 PM - Thread Starter
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Quote:
Originally Posted by joshp14 View Post

If using first layer OSB and second layer drywall, does one still need to worry about hitting the studs and channel with screws when hanging that second layer?

I'd be about 90% certain that the answer is that you can screw the second layer of drywall in anywhere, since you are using OSB. Curiously, though, I haven't tracked down anybody saying that explicitly. There's a lot of suggestions to that effect, though.

See some of the later posts in this thread: Does OSB seem all that less dense?. The strong implication is that they are installing the drywall without having to worry about screw placement.

But yeah, I'd like to get direct confirmation of that as well. The only non-ambiguous examples I've heard all center around attaching internal components and structures, not the drywall itself.
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