Air Cavity??

[James]

I'm building a double wall with an air gap in between. Does the size of the air gap matter? What's minimum?

Do I have to put insulation in the gap or will putting it in the studs and leaving the air gap be fine?

What would be an approximate STC rating for a wall like this?

It's double 75mm stud walls with the air gap. 75mm insulation and one layer of 16mm plasterboard on either side.

What's an ideal or realistic STC rating to keep most sound out and bearable for those in the rest of the house?

Thanks
James

[John Sayers]

Check this chart out James

http://www.saecollege.de/reference_mate ... 0Chart.htm

cheers
John

[Guest]

Is the staggered stud wall as good as a double wall?

What would the STC of a double wall be?

Do I need to fill the air cavity with insulation even though i've got it in the studs?

Thanks
James

[John Sayers]

check this.

cheers
john

[John Sayers]

Here's another chart for you relative to your question

[James]

Ok thanks. That's really helpful.

One last question,

If I put two layers of plasterboard, is it better to put different thicknesses or two of the same? I say this because I remember reading that sound doesn't like going through different thicknesses or densities.

Thanks again
James

[John Sayers]

yes that's sorrta correct james, it really prefers a different medium more than a different thickness. i.e drywall - mdf - drywall.
whaqt thickness of drywall were you intending?

cheers
john

[jazzman]

To continue with your idea of using a different medium, e.g. drywall - MDF, how well does particle board work in place of MDF? I can get 4' x 8' sheets of 3/4" particle board easily here for something like $18 a sheet. Does particle board work well inside a wall? Is it anything like that "canite" product you show in your insulation hanger design?

[John Sayers]

particle board is more like mdf than soft fibreboard (canite) and yes you can use particle board as a wall treatment- make sure you seal the joins though.

cheers
john

[knightfly]

Here are a couple more extremely informative links, both from US Gypsum - they don't talk about materials other than Gyp-rock, alias Sheet-rock, alias gypsum wallboard, etc, but they cover nearly every type of framing method known to man, with several versions STC rated and some even (gasp) MTC rated...

http://www.usg.com/Design_Solutions/2_3 ... ontent.asp

(Be prepared for this - as a Word document, it was about 125 pages -

For this next link, you can either view online or download the pdf file - I had problems downloading, but if you start reading online, then click the "save" icon, it will download it to your drive for offline use. (At least it worked that way for me)

http://www.usg.com/Expert_Advice/const_ ... .asp?menu=

The first link had some insight on stairwell building, (such as how NOT to attach) for those of you who have upstairs studios - all in all, some serious reading... Steve

[knightfly]

James, your original question about the width of air gap should be answered here - Think of the air between wall surfaces as a spring, having a fixed rate per length - the longer the length, the softer the spring, hence the more de-coupling between surfaces. The more decoupling, the less transmission...

Just an observation, open to comments -

Did anybody else notice that in the chart of wall construction vs. STC ratings, posted by John above, that the chart seems to support Eric DeSart's statement that multiple leaf walls (beyond two) actually WORSEN the STC rating?

Note that the transition from one normal wall to two normal walls ONLY increases the STC from 36 to only 40. (Seems like a small gain for TWICE the materials) -

Then, removing one inner layer (which changes the wall from quad-leaf to triple) increases STC to 50.

Next, removing the other inner layer (changing the wall to a double leaf with only ONE air space) increases the STC by 7, to STC 57. Finally, replacing the mass that was removed in the earlier steps, but as a part of the only two leaves remaining, further increases the STC to 63.

In my limited understanding of "Air as a spring" theory, this would make sense (decoupling-wise) when you look at one long spring, vs. 3 shorter springs of the same diameter, etc - the three short springs (in series) would have a higher spring rate since each is stiffer.

Anyway, somebody wanna blow the smoke away here? Or is it all "Clear as Muddd"... Steve

[AWS]

Hi..

I´m buiding my recording studio... so I want to "see" this configuration with all of you... to accept agrees or comments (good or bad).

Left to right (materials)

Plasterboard (9.5mm) + Glasswool (50mm) + Concrete Block (200mm) + Air Space (100mm) + Glasswool (50mm - bTW concrete walls) + Concrete Block (200mm) + Glasswool (50mm) + Plasterboard (9.5mm)...

How much STC can I get with this configuration... I think thay maybe It´ll be better to replace a Plasterboard for another with more thickness (15mm).

Thanks a lot!Fernando Musarra
AWS

[knightfly]

Fernando, there are several problems I see with your proposed construction -

First, unless concrete block construction is much cheaper in Argentina than it is here in the US, there are much less expensive ways to achieve the same or better sound isolation.

Second, please re-read John's post of Mar. 2, and mine of Mar. 17, in this thread - the comment I referred to by Eric De Sart, addresses the physics of "getting the most for your money", so to speak - Mr. DeSart is one of the moderators of studiotips.com, and a degreed acoustician, which is only one of the reasons I have a hard time understanding some of his comments, but here goes -

When building a wall for sound control, it (apparently) works best if you concentrate all the mass in only two leaves (layers) with only one air space between them. This can be seen in the diagram John posted about STC values of different wall construction, posted on Mar.2 (or Mar.3, depending on your time zone) - read my post of Mar.17 for clarification.

Your proposed wall construction, if I understand correctly, would have a layer of thin wallboard, then an airspace filled with insulation (but still, an air space) then a concrete block wall (filled or hollow?) then another air space, then another concrete block wall, then another air space filled with insulation, then another thin sheet of wallboard.

If concrete block construction is ridiculously cheap in Argentina, you could improve the STC of your wall by probably 15-20 points just by placing the wallboard directly on the outer sides of both concrete block walls and placing the insulation BETWEEN the block walls - The result would be even better if you filled the blocks with well-rodded concrete.

Perhaps a better way, if you intend on having an exterior wall that is concrete block, would be to put up only one block wall, fill the holes with concrete (or at least, sand), maybe stucco the outside, then attach either wood or metal studs to the inside of the concrete vertically, 24" apart, then Resilient Channel horizontally per the USGypsum links I posted, and then two layers of 5/8 (15mm) wallboard on the RC, using real Acoustic sealant for caulk.

Again, I don't have a clue what materials are going for in Argentina, but at the very least you should use a construction that has only ONE air space between TWO layers of mass.

Another thing you didn't mention, is what is the ambient noise level where you're planning your studio? If you're not planning on using the studio for hire, and there are quiet times available for sensitive recordings, you could be wasting a lot of money that could go for equipment.

Any professional studios I've been aware of, have always had a study done at the proposed location that covers at least a week, usually more like a month - the actual sound levels at the site are recorded by the person doing the study, then analyzed to see what kind of construction is necessary in order to achieve the desired Noise Criteria curves.

I've talked to people who live out in the country far enough that they actually do some recordings using only a tent to keep the gear from getting wet - granted, this is rare - I only mention it to help make the previous point -

On the other hand, if you have close neighbors and they are picky and you intend to record acoustic drumkits at two AM, you will need all the isolation you can get. Under those conditions, I'd shoot for an STC of at least 75, hoping it would be adequate. Keep in mind, that STC (Sound Transmission Class) only covers frequencies down to 125 hZ - what this means is that two walls, both rated for STC 60, may have quite different amounts of attenuation down at 30 hZ with a vigorously applied kick drum. For a better idea of what kind of isolation a recording studio needs, we refer to MTC, or Music(Machinery) Transmission Class - these numbers are universally less optimistic than STC, since it's harder to stop low frequencies.

For exterior walls, if you want serious isolation, you need to follow the "two layers, one airspace" idea no matter what materials you use. And, if one of those layers can flex a little, it will make a big improvement in performance. Also, doors are the weak link in any partition, so plan for a double-door airlock.

Finally, the rule of thumb I follow in any sound proofing plan is this - If it won't float, it won't stop sound. (Exceptions would be well-designed, baffled and absorbed air passages)

If I mis-understood your proposed construction, feel free to start over - preferably with some kind of drawing to clarify... Steve

[AWS]

hello!

Well... you really undertand me.. that was what I tried to explain...

First, the Concret Block 20x20x40cm is about $1 (argentine pesos = u$s 0.35)... It´s very cheap compare with a gypsum board $10m2 (u$s 3.22)!

So... in resume... It´s convening that my material aplication would be gypsum (9mm) + Concrete (200m) + Air filled with insulation + Concrete (200) + gypsum (9mm).. is this ok?

In argentine the prefer materials for construction are concrete blocks, gypsum board (9/15/18mm), vynil rubber, wood, plasterboard, glass wool, glass fiber... etc.

We already think about what kind of costumers and aplications will going to do, it´s a comercial studio... So, figure out... drum kit at 125/130 db... (heavy metal or new metal mostly), loud guitars, etc.

I want to achive something like 29/30 NC (if it´s possible)... but that have to be tested once the studio is done.

For the neighbors there´s no problem... all the walls are separated from the original wall and roof... I wanna try to get rid of the mechanical transmission... (if it´s posible too!).

When you refer to "flex" a little a material... you mean that make it curve with a few degrees ?


My wall is going to have 210mm of thickness... this is enought space to put a door frame for two doors? I imagine that this doors are going to be very thin... but with a lot of density/m3... or not?

Well Steve... I really preciate your help in this project, for me it´s a honor to take your knowleadges and put in practice!

Best Wishes!
Fernando Musarra
AWS

[knightfly]

Fernando, If I'm following your prices right you can build a 4 foot by 8 foot section of block wall for about $12.60 US - where a single layer of sheet rock would be $3.22 US, since it is a 4 foot by 8 foot sheet, correct? This would mean that two layers of sheet rock would cost $6.44 US, unless that price was for the 9mm stuff - I'd not use any less than 15 mm personally though.

In your case, if you're into headbanger volumes, you would be better off with a single concrete block wall, adding Resilient channel and two layers of 15 mm gyp-board - I'd make sure to fill the blocks with either sand or well-compacted (rodded) concrete, it will make several dB difference.

Also, here are some other factors: bare, non-filled concrete block in 8", or 20 cm, typically has an STC rating of 45. Putting two coats of paint on each side raises it to STC 48. Plastering both sides raises the STC to 56, and although I don't have figures to back it up I would estimate that putting two layers of 15 mm gyp-board on just one side, over RC, would raise it to around STC 62 or thereabouts.

Keep in mind that 32 square feet of block wall will cost about $12.60 US, where 32 square feet of double-layer 15mm gyp-board would cost the price of two sheets, or around $11 US. Add the cost of the RC-1, which here runs about $1.80 US per 12 foot length, and you're looking at about $27 US per 32 square feet of wall, with an STC of around 60+... Those costs do NOT include fasteners, tape and texture, caulking or labor obviously. Don't try to save costs with cheap caulk - even if you have to import it, get true Acoustic-rated, non-hardening caulk. Remember, a 1/16" crack 10 feet long in this particular wall will lower your STC by at least 15 points, maybe more.

As to doors, I read recently of a test where a 60 dB wall (tested) was cut and two standard, solid-core, exterior doors were installed, and CAULKED SHUT so that they weren't doors at all - it still lowered the test results to STC 44 ! Reading that just finished convincing me that sound-lock doors are the only way to go. Don't try to put two doors that close together, you're better off with a vestibule with two doors, preferable NOT parallel to each other, and with some kind of absorption/trapping in the vestibule.

My comment about flexing did NOT refer to INSTALLING a panel with a built-in flex, but to mount one half (say, the gyp-board side) of a wall on Resilient Channel, so that the wall will be allowed to flex when a sound wave hits it. This creates a natural bass-trap effect, and improves the STC of the wall by about 4-6 dB compared to solid mounting.

The downside of making two RIGID walls, is that you will need lots more bass trapping inside the rooms to compensate for the lack of "natural" bass trapping afforded by flexible walls. This would probably make the "one block, one gyp-board" approach much less costly in the overall picture.

I hope this helps... Steve