Construction Details

knightfly · Post by **knightfly** » Fri Jun 13, 2003 11:40 pm

Sen, you're right - I don't have exact figures for you, mainly because there isn't enough tested data available for all the possible permutations of wall construction. Generally, the first few inches of air space is lots more valuable than the next bit, dwindling down logarithmically (hope I spelled that right, it's 4:55 AM here) - anyway, going from 4 to 6" gets you probably 6-7 dB, 6 to 8" another maybe 4-5 dB, etc - the double wall, 63 dB example doesn't list a separation value but I would think that it's around the width of a framing member, or 3-4 inches, between frames. That would make the total wall thickness (not including wall board on either side of 10-11 inches (2x4's here are actually 3.5")

Note that from the SAE STC charts, you can get close to that same STC with 6" STEEL stud construction - part of that is the added "flex" of the lightweight steel studs, and part is the nearly complete fill of insulation.

As to the "is it worth it" - that depends on how dear each square foot of floor space is in your particular application, and how much isolation is needed (again, in your particular application.)

If you have a way of connecting the sound output of your computer into a SERIOUS sound system so you can approximate 100+ dB SPL, and you're at all curious, here is an eye-opener you can run to find out just what the various levels of attenuation REALLY mean -

http://www.auralexuniversity.com/NeighborsReal.html

BE VERY CAREFUL WITH THIS - if you don't set up on the LOUDEST test correctly, you can blow your speakers/ears/amps/neighbors' tolerance.

Also keep in mind that their SheetBlok product costs several TIMES what wallboard costs per square foot - Also note that they don't give any wall examples in the higher performance range that DON'T use sheet blok - personally, I'd tend to use a couple more layers of wallboard or a different sandwich layer except maybe in the case of a custom door where thickness is not as good as thin mass... Steve

Sen · Post by **Sen** » Sat Jun 14, 2003 2:29 am

knightfly wrote:going from 4 to 6" gets you probably 6-7 dB, 6 to 8" another maybe 4-5 dB, etc -

well...these figures look good. If you can achieve that much of an improvement it's probably worth leaving a bit bigger gap IMO....
I'll have a look at the link after....just got back from a party, and gotta play some stupid gig tomorrow...so I'd better go get some rest..(I'm blind

)... (..CAN'T EVEN DRINK ANYMORE)

THANKS

AndrewMc · Post by **AndrewMc** » Sat Jun 14, 2003 4:22 am

This BBC report is incredibly informative on different wall designs.

http://www.bbc.co.uk/rd/pubs/reports/1995-06.pdf

it never even mentions STC - and is much more valuable in that it shows the actual db transmission loss across the frequency range.

The double wall mass-air gap-mass (2 leaves) is markedly better at the low end around the freq of a kick drum or bass. But the 4 leaf wall is significantly better at the high end. Above 500Hz the 4 leaf wall wins hands down in terms of reduction. From 125Hz to 500Hz they are about the same, below 125 Hz the 2 leaf wall wins.

The whole 2 leaves is best mantra is true - but thats all things being equal - ie it's the best reduction for the cost - particularly in the troublesome low end. It's still certainly possible to get a better reduction with 4 leaves if you add enough mass. ie if you were having to work with something existing and didn't want to tear stuff out. In fact more mass on a 4 leaf wall is just going to be the best in the end.

If there is anything out there I trust info wise it is the BBC

Sen · Post by **Sen** » Sat Jun 14, 2003 3:05 pm

knightfly wrote:
If you have a way of connecting the sound output of your computer into a SERIOUS sound system so you can approximate 100+ dB SPL, and you're at all curious, here is an eye-opener you can run to find out just what the various levels of attenuation REALLY mean -

http://www.auralexuniversity.com/NeighborsReal.html

...wow...that is one hell of a good, straight to the point, comparison
And ..I did pump the system up quite good

...and with the last example all I could hear was just a bit of low end...very, very quietly....
That acoustic101.com is a great source too

thanks heaps

Sen · Post by **Sen** » Mon Jun 16, 2003 6:51 pm

It would be interesting to hear what would happen if they added another mass between the two walls in the last example....

knightfly · Post by **knightfly** » Tue Jun 17, 2003 10:50 am

Doing that (and ONLY that) would WORSEN the isolation - check out Andrew's BBC link if you haven't already...

BTW, Andrew - re your comments on 4 leaf, multi-wall, 3 foot thick wall construction - yes, if you do ENOUGH brute force things you can get better isolation. But for probably 99% of the people who post here, they are not willing to waste 3 feet of space for walls when 8-12 inches will get them within 1-2 dB of the same performance at 1/3 the cost and probably 1/10 the time/effort. I'm a firm believer in the KISS method as long as it works. The BBC info (I had grabbed that PDF last year, found out when I compared file sizes) doesn't really REFUTE the charts on Johns site, or the chart in the "air space" thread - it just expands on it by quite a bit. And, even according to BBC's own info, the 2-leaf method is still the absolute best bang-for-buck wall construction. (Not to mention the confusion of trying to figure out WHICH parts of WHICH wall you can allow to touch, and which need to be isolated, and which need to be caulked, yada yada yada...

Thanks for posting that link though, I agree that it's hard to find more detailed info that you can actually consider BELIEVING...

BTW, John, WTF is a "Camden" - (damn Redcoats:=)... Steve

AndrewMc · Post by **AndrewMc** » Tue Jun 17, 2003 2:40 pm

Agree completely. The BBC stuff is 100% agreement with the STC charts on different wall designs. The STC charts show scenarios using the same amount of drywall in each case - i.e 4 single layer leafs or 2 double layer leafs. The BBC stuff doesn't keep the quantity of drywall constant - but does clearly show the ability of the 2 leaf wall to handle lower end more effectively - which ultimately is the hardest part. The walls I'm building right now are 2 leaf using Johns inside out design - with lots of mass.

Post by **John Sayers** » Tue Jun 17, 2003 4:34 pm

WTF is a "Camden" - (damn Redcoats:=)...

pardon?? I have no idea - have I made a typo somewhere

:)

cheers
john

knightfly · Post by **knightfly** » Tue Jun 17, 2003 6:27 pm

Hehehehehehehehehehehehehe... :=) Sorry, John - I know the diff between an Aussie and a Brit - what I was referring to was the BBC paper Andrew linked to earlier in this thread - they keep mentioning "Camdens" which I think (from context and pix) must be a "standard" stud wall, or similar... I wasn't accusing YOU of using that term, just thought you might've run across it in your travels :=)