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Author Topic: Acrylic sheet thickness  (Read 6138 times)

sticklebricks

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Acrylic sheet thickness
« on: September 17, 2013, 12:38:42 PM »

I have a problem with traffic noise coming through a bedroom window. I got a secondary window installed - a 6.4mm stadip silence window, and this mostly does a good job, but low frequency noise still sometimes vibrates the  secondary window (usually buses accelerating or trucks). I stuck a 10mm acrylic sheet on top with magnetic strips, but this has only slightly improved it.

I was thinking of getting either a 20mm or a 15mm piece of acrylic to replace the 10mm piece. Would either of these be effective? I'm worried that as 20mm plastic is roughly equivalent to the 6.4mm glass that is would not really work as it would vibrate at the same frequency.

Many thanks

Randy S

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Re: Acrylic sheet thickness
« Reply #1 on: September 17, 2013, 04:46:47 PM »

Yes, like thickness's will most likely have the same resonance frequency. the only way your going to increase the performance of the system is to increase the dead air space.
What size air gap do you have now?
Randy Sieg

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888-942-7723
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sticklebricks

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Re: Acrylic sheet thickness
« Reply #2 on: September 17, 2013, 05:25:25 PM »

There is the outside double glazed window, then a 15cm gap and the 6.4mm glass, then the 10mm acrylic is stuck on top with a tiny gap of about 0.8mm.
I can't see a way to increase the gap by any significant amount.

What are my other options do you think?

Randy S

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Re: Acrylic sheet thickness
« Reply #3 on: September 17, 2013, 05:39:13 PM »

you have quite a decent air gap...Im not sure how much more improvement your going to get...you are most likely at or near diminishing point of return. If you go thicker on the acrylic you might see another 5% reduction...now it up to you to decide if the reduction is worth the extra cost.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

sticklebricks

  • Guest
Re: Acrylic sheet thickness
« Reply #4 on: September 17, 2013, 06:45:39 PM »

Thanks for your advice. So, for example if I was to replace the 6.4mm window with an 8.5mm window you don't think it would have too much effect? The gap is key?

sticklebricks

  • Guest
Re: Acrylic sheet thickness
« Reply #5 on: September 18, 2013, 12:26:45 PM »

Is there another material I could use instead of the acrylic to stick on top of the secondary window? It doesn't have to be clear. I could lose the window to get some sleep. There is a ledge of 12mm that the material can sit on, which helps me fit it to the secondary window.

jhbrandt

  • Guest
Re: Acrylic sheet thickness
« Reply #6 on: October 16, 2013, 06:11:43 AM »

Stickle,

GLASS.

Glass is denser (heavier) than acrylic and in the competition of "thickness vs cost vs performance"; - GLASS wins every time. You don't see acrylic windows in professional recording studios or police station interview rooms....

Laminated glass is by far the best way to go. Sound-proofing from TRUCKS (vibration range from 5Hz ~400Hz) will require as much mass as you can afford to throw at it. :)

If you have a double mass system with an air space, the GAP will affect the STL, however I doubt that increasing the gap between a standard thin window glass and any substantial mass, like 5/8" laminated glass will have much effect, if any.

But my best 'guess' for 5/8" laminated glass installed as a 'plug', tightly sealed in your window is ~ STC 37.
Mass Law for diffuse field calculations show almost 13 dB @ 25 Hz. - Not too shabby.

You should build a frame for the laminated glass from 3/4" trim, possibly quarter-round. Use glazing tape and some neoprene spacers at the bottom so that the glass has something to sit on other than the window frame. Cut the glass 1/4" smaller than the opening (height AND width) so that is has room to 'grow'. - Expansion/contraction.
Then seal the glass around the perimeter with something like 'Big Stretch' caulk in the gap between the glass and the frame. THEN install the quarter-round finish trim.

Good luck!
- That should solve your problem. If not, you likely have sound ingress from wall gaps and/or the STRUCTURE is flanking sound directly from the ground vibrations. Flanking noise from the road is very, very expensive to remedy. - Let's hope that is not the issue.

Cheers,
John