Confused about STCs

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Anlina
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Confused about STCs

#1 Post by Anlina »

With Milgard aluminum casements, when Glass 1 is 0.125 and Glass 2 is 0.25, the STC is 30.

But when Glass 1 is 0.1875 and Glass 2 is 0.125, the STC is 31. And it costs a lot less.
It seems to me that the second one is thinner, yet the STC is higher.
What am I missing? :)

And if lamination makes such a dramatic sound control difference, why does it only raise the STC one point?
1/4 over 1/8 is 35; and 7/32 lami over 1/8 is 36.

Thank you!

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Windows on Washington
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Re: Confused about STCs

#2 Post by Windows on Washington »

STC is often times thought of as an outdated metric now where OITC is all the rage. My general observations is that more is more here. More mass is more mass and more mass is better. In the case of airport windows, you will see a massive pane followed by smaller. The offset for the STC number is probably a result of the decrease in the air gap with the thicker lite of glass.

Air space is critical and especially when it comes to low frequencies (i.e. road noise) and that is probably the delta you are seeing there. I am sure the overall IGU thickness is a given, so when you have a thicker lite of glass, the air gap must go down by that same offset. Hence the decrease.

Anlina
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Re: Confused about STCs

#3 Post by Anlina »

Windows on Washington, thank you!

I'm not sure I understand completely...Are you saying the second one's STC is
probably higher because the air space is wider?

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Re: Confused about STCs

#4 Post by Windows on Washington »

Yes. Possibly.

WindowsDirectCinci
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Re: Confused about STCs

#5 Post by WindowsDirectCinci »

This is only my opinion and I'm not 100% if correct but wouldn't aluminum transmit more sound and vibration than say an insulated vinyl or wood window. Possibly that is why there isn't much a difference in STC when using laminated glass in an aluminum window vs what we would normally see in vinyl? More of the sound is actually transmitted through the frame than us vinyl guys would be used to?

Anlina
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Re: Confused about STCs

#6 Post by Anlina »

Thanks, Windows on Washington.

WindowsDirectCinci, that makes sense! It's too bad the price is still so high for lamination with aluminum. :(

ETA: I looked on Milgard's site and the STC of their vinyl casement 1/4 and 1/8 is 35.
For the next one up, 7/32 lami and 1/8, the STC is 36. So it only improved by one point as well! :o

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Windows on Washington
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Re: Confused about STCs

#7 Post by Windows on Washington »

Can't say I have seen a real delta between vinyl and aluminum, but the logic seems to work.

Laminated does, definitely, help. Its an expense, but if the issue is noise, you are going to want to spend the money and spend it once.

Anlina
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Re: Confused about STCs

#8 Post by Anlina »

Thank you, Windows on Washington.
Is lamination especially good at reducing reflected sound where the original source
is far away, but the sound is bouncing back off a nearby wall?

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Re: Confused about STCs

#9 Post by Windows on Washington »

Anecdotally, I find that Laminated is better with higher frequencies like voice and noise that we pick up as distinct. I find that deeper glazing is better with the low frequencies like the drone of traffic.

Anlina
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Re: Confused about STCs

#10 Post by Anlina »

Thanks! Which is better for the thud sound of a ball being hit?
And can you explain what deeper glazing is?

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Re: Confused about STCs

#11 Post by Windows on Washington »

Ball would be high frequency.

Deeper glazing IGU would be the depth of the air space. Those are the 3 things that contribute to STC: Mass, Air space, thickness (i.e. varying thickness).

Anlina
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Re: Confused about STCs

#12 Post by Anlina »

Thanks again, Windows on Washington!

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