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Soundproofing Forum Topics => Soundproofing your Condo, Townhouse or Bed & Breakfast => Topic started by: condo on November 09, 2011, 01:55:10 AM

Title: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on November 09, 2011, 01:55:10 AM
I have a two story condo that shares a common wall with a single story (vaulted ceiling) unit. I am going to be attempting some soundproofing on the common wall (more about that later) which is a staggered double stud wall. My question is regarding the floor joist cavity area that abuts the common wall.

My floor joist run perpendicular or 90 degrees to the common wall and the unit next to my two story is a one story with vaulted ceiling the area is at the very end of the floor joist inside the cavity on the common wall it self. I would like some ideas on what might be a good way to reduce the noise transmission in the area between the 12"-joists where the floor meets the wall


I can access that area buy cutting an opening in the drywall ceiling from below or from the floor above.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on November 09, 2011, 04:46:07 PM
If your trying to reduce impact and footfall from entering the ceiling next to you, than the only thing that will work is to float your floor above...reduce the impact at the source...once the impact is in the subfloor your not going to reduce it unless you float your neighbors ceiling.

You can insulate the cavity but that will only help on the airborne remittance of impact noise...it will not reduce the structural remittance of the drywall screwed into their ceiling.

You must break the connection and your not going to be able to do this in the framing.

feel free to contact me directly if you would like to discuss in more detail.

Randy S.
1-888-942-7723
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on November 09, 2011, 09:05:38 PM
Thanks not worried about footfall noise and the wall is staggered so I was considering drywall and Greenglue in the joist cavity on the common wall only and then some insulation. I realize the sound can travel through the structure but if it would reduce the noise overall I would do as described or maybe blow in some insulation in that area instead.

I have applied a 5/8" layer of drywall and GG in the Master bathroom and was told it could take up to 30 days for the GG to become totally effective so I am waiting to see the results and evaluate what to do in the Master Bedroom from that.

Space was limited in the bathroom so only one layer of drywall was possible due the toilet drain but I think I am going to need to address the flanking noise area also.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on November 10, 2011, 04:22:38 PM
Then in that case you are the right track, always fill cavities even if you can only do blown in...its better than having an empty cavity.
Green Glue will take a full 30 days to reach optimal performance, however look at green glue dampening compound like you putting your hand on a speaker while its playing....the speaker is still playing just not the same way....So if you want to "Beef up" the system you can add a layer of #1 Mass loaded vinyl w/psa directly to the existing drywall followed by new drywall with green glue sandwiched in between.
This will greatly improve the STC rating of your wall.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on November 10, 2011, 04:22:49 PM
Also there a couple of tips for applying green glue.
1) Do not leave a 2" border of drywall that is not covered with green glue... a 1/2" border is enough...if you need to clean it off your hands use Avon so soft.
2) A lot of methods of application are being thrown out there, like big squiggly lines or tic tac toe pattern etc etc..understand that when you make the sandwich you want the void sizes to be no bigger than a quarter so apply it like silly string all over the sheet 1/4" bead so that you get maximum coverage...you dont want 4" -8" void sizes on the wall.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on November 10, 2011, 05:10:37 PM
Great info only wish I had found this site before I hung the bathroom drywall. I didn't leave a 2" border rather I applied it to the existing drywall instead but I also didn't make as fine of a pattern you describe but no voids of 4" either.


Would 2 layers of green glue & 2 layers of 5/8" drywall be better or as affective than the MLV & one layer of drywall?

Just to clarify I can apply the green glue directly to the MLV?

And regarding the acoustic sealant 1/4" border gap around the drywall, is it ok to tape as normal over that area?

Thanks again ...




 

Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on November 10, 2011, 08:26:01 PM
good deal on your green glue, in the future it is easier to apply it to the back of the new sheet your installing.

a layer of MLV with green glue is better for airborne noise than the double GG w/ drywall

You attach MLV to existing wall then apply green glue to back of new drywall then screw into wall.

you do not need the gap around perimeter because you are not floating...so you can mud and tape corners.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on November 10, 2011, 10:25:00 PM
You the man Randy S ...

I applied the GG to the existing drywall due to the bathroom size I was unable to lay the drywall flat on the floor so it seemed better to do it that way and not have to deal with the mess if I had applied the glue all the way up to the edges. But in the Master bedroom I'll have more room to work it properly.

To keep my options open from good to best what are some types of insulation to use in the floor joist cavity?
The blown in would definitely be the easiest in this case and I may go that route if the wall is reducing the sound to a decent level.

Thanks ...



Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on November 10, 2011, 10:55:14 PM
Our view points on insulation:

1) cotton fiber insulation (recycled blue jeans)
2) mineral wool

better than nothing in the cavity

3)fiberglass
4) blown in

And trust me, I have had clients see a value of noise reduction in all the types of insulation it really comes down to how much vs. cost.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on November 11, 2011, 01:22:52 AM
Good to know.


Thank you very much for all your help ...
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on December 16, 2011, 08:16:00 PM
It's been over 30 days and the intial improvement I saw is all I achieved with the greenglue. It is all I am going to do in the bathroom for now with the limited space,
 

The MLV and RC are more than Iam wanting to spend at this time.

So I am thinking about using a layer of styrofoam sheeting on top of the existing drywall (working on the Master Room now) then soundboard and finish with 5/8" layer of drywall. My thinking is the styrofoam would not transfer vibration readily to the soundboard which would then dampen the sound and also make for three differrent layers of different weight materials and properties.


Any thoughts?
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on December 16, 2011, 10:05:09 PM
I am not surprised, as I mentioned in an earlier post Green glue is a dampening compound not a mass value...

Here lies the problem, look at the screws like tuning forks and the structure like the amplifier finally the drywall as the speaker....there is the fastest path through the system...

if you want to see far better results in the bedroom I advise you to decouple at the very least...styrofoam will not help....well for building a cooler yes but not for soundproofing.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on December 16, 2011, 11:28:22 PM
Thanks Randy the common wall is a staggered double 2x4 so is it not already decoupled?


Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: Randy S on December 20, 2011, 08:42:04 PM
Well, some people view that as a decoupled system...however, when you look at the speed if vibration(sound) through wood it is 12x faster than airborne sound (around 13,000 fps) is it really decoupled...... I say no, it could be better.
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 06, 2012, 12:33:02 AM
I ended up working on the second upstairs bedroom since it is the quitest I felt it would have the best chance for success.

I used a layer of styrofoam sheeting on top of the existing drywall  then a layer of soundboard sheeting, another layer of styrofoam and finish layer of 5/8" drywall.

It has been several days now and I would estimate a noise reduction of 50% and I am fairly pleased with the results and cost.

I will evaluate more and post some observations later.
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: Randy S on January 06, 2012, 12:52:57 AM
well thats not to bad considering the materials and cost...Good job...
I would add up the cost of the styro foam and sound board and see if it came out more than MLV or a second layer of 5/8" sheetrock...just curious.
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 06, 2012, 02:28:21 AM
Way less than the MLV prices I've seen and for that matter also Greenglue and Resilient Channel but drywall's cheap and so was the styrofoam and soundboard. I can always add another layer of SB and DW for about $60 though. I may change up the configuration a bit in the master bedroom or just add a few more alternating layers of the soundboard and drywall also since it is the noisier of the two rooms.

I don't think the flanking noise is too much of a factor but that is part of what I am evaluating first before and if I proceed any further in second room.

I'll keep you posted.

Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: Randy S on January 06, 2012, 04:01:10 PM
Stick with double layer drywall, drywall is a better STC than sound board and if the cavity is filled with insulation you dont need double absorption layers...more mass=more blocking. ;)

Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 07, 2012, 12:10:25 AM
Prior to doing any work as a test I place a piece of drywall on the existing wall the put my ear to it and it basically sounded about the same as the original wall. Then a piece of styrofoam and then the drywall on top of that which produced a more noticable difference. It may only matter if you have your ear directly on the wall but seems like the vibrations are going to be more easily transmitted through the same type materials. My thinking is the styrofoam or soundboard are light and soft so that would help break the connection so to speak.

Also I drilled what I would call relief holes (about half dozen 3/8" size) in the ceiling drywall between the existing drywall and the new finish layer of drywall to insure that the wall wasn't completely airtight since both layers of drywall are sealed and not wanting it to act like a speaker box in a way.

All speculation on my part though ... ;D


Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: Randy S on January 07, 2012, 04:09:20 PM
hmm, you want air tight to achieve maximum reduction...I can see a value change with the sandwich (drywall/foam/drywall)..

well what I can say is, no matter what you do it will make changes in reduction. Some of the best cost effective systems have come from"out of the box" thinking....and using standard building materials have performed nicely when used in the right order.
It is very difficult to determine diminishing factors this way because the changes are not dramatic.
So, since your getting continuous reduction than you are doing it right.
Keep me posted on the noise reduction value as you proceed, it will be nice to know what total value you achieve.
 
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 07, 2012, 09:49:52 PM
I knew that it was suppose to be airtight but I got it in my head in this configuration that the small amount of air could be more of a factor than a larger air cavity. The best improvements were with the tv, microwave oven, cupboards and the ac unit (which is literally less than 15' and level with that room). TV and microwave are for the most part inaudible now. The cupboard noise is not as intrusive and is exceptable as is the ac unit also now. Voices are in the good range but could be better, dog barking could use improvement for sure but is ok but still not to the level I would prefer.

What I am trying to determine is if the added layers would be of benefit or if it is flanking noise. I may have to install another layer to find out and I can always take it down and use it in the master bedroom if it has no affect.

I will keep you posted.

 
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: ArminRU on January 08, 2012, 12:10:42 AM
Our view points on insulation:

1) cotton fiber insulation (recycled blue jeans)
2) mineral wool

better than nothing in the cavity

3)fiberglass
4) blown in

And tst me, I have had clients see a value of noise reduction in all the types of insulation it really comes down to how much vs. cost.

Randy, do you have any stats to back up your ranking?  I've always heard that R19 pink fiberglass insulation is just as good as mineral wool and anything else.  Do you have first hand experience comparing the same wall setups and just different insulation?
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: Randy S on January 09, 2012, 11:03:12 PM
you can always review the NRC data provided by the manufacturers,
just remember that field results and lab testing is  different end results.
Ex: cotton fiber has a NRC of 1.15 and an astm e90 test result of 57 for R19.
However, in the field you should only use the value of .95 max and true STC rating would be determined by assembly being decoupled or coupled.
The statement I made in my post is purely off of a field evaluation in noise reduction.
Feel free to contact me directly if you would like to discuss real world reductions based on materials vs. assembly.
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 22, 2012, 06:43:11 AM
Have been looking at the test result charts at the Greenglue site, I was interested in the soundboard and drywall results which are not being compared with each other on the same chart but was easy enough to print and combine the two into one. Interestingly enough the soundboard and drywall have very similar results except in the 800-2500 Hz the soundboard actually out performs the drywall up to about 5 dBs as far as sound isolation. Anyway I think my original configuration of existing drywall /styrofoam/soundboard/styrofoam/drywall is probably a good way to go in the Masterbedroom also when I get to it.

Nothing much more to add other than I feel for the same money as I spent in the small bathroom using the Greenglue I was able to do the bedroom for and the results were much more impressive in the bedroom.

Probably be awhile before I do anything else but will post then.
Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: Randy S on January 23, 2012, 01:45:38 AM
so based on what you have learned would you say the value of vibration absorption in a material with in contact to the studs, including the amount of hard connections are what actually delivered your sound reduction value?
In the end, what you are seeing as the primary value is decoupling....break or reduce the amount of hard surface or direct connection to the surface that is vibrating...
also as a side note..the frequency you mention happens to be human speech frequency which is the best data across most test specimens..
wave length  1/4" to 1/2" max...(frequency / 1129 fps.)= wave length.
..

it is a pleasure having your input and feed back!
Thank You Condo...Keep it coming my friend.

Title: Re: Floor Joist Cavity Sound Dampening Seggestions
Post by: condo on January 23, 2012, 04:57:04 AM
That is a good question and it's hard for me to say which one is most responsible for the sound reduction. The materials all conduct sound by themselves when I use a small sample on the wall to test but I would say the styrofoam is the poorest sound conducter then the soundboard with the drywall seemingly to produce the clearest sound of the bunch. As far as using different combinations of the materials the best test results are ones that include the styrofoam so I do feel some decoupling affect is being achieved by it's use though hard connections have to play some role in the final results, also if I stack drywall on soundboard as a test the improvement is only a little better than each by itself. Pretty primitive method so take it with a grain of salt. The master bedroom will be a better indication of the materials effectiveness though so we will see.

Thanks for the side note I'll probably double the soundboard in the Master Bedroom for that reason.
Title: Re: Floor Joist Cavity Sound Dampening Suggestions
Post by: condo on March 09, 2012, 11:09:23 PM
Haven't got to the Master Bedroom yet because I wanted to be sure I had done all that I could in the other room before proceeding and after some time I feel the flankinging noise is louder that the wall I worked on so it wouldn't make sense to do more in that particular room. Textured today will paint and finish up this weekend probably ...

2-1/4" was all I lost in that room but I most likely will double that in the master since it is much louder in that room still not bad for the cost comparitively ...