I just discovered your very helpful site. I have a question. We recently purchased a ten year old home that has good quality, double glazed vinyl windows (the operable kind, single hung, vertically opening). We hear traffic noise in our master bedroom, which faces the street and I am looking for a method to reduce it as much as possible. I had thought of buying some heavy fabric roman shades that would fit inside the frames, but doubt that this approach would do much. I am not sure if the sound is simply being transmitted from the outer pane, through the air space and onto the inside pane or if it is getting through the area where the window slides in it’s frame. Do you have any thoughts on this? I am am a Mechanical Engineer but have no real knowledge in acoustics.
Thanks very much for your thoughts. I hope you can shed some light on this.
Windows can be a little bit tricky, but there are two pretty basic and simple things to keep in mind when you are trying to block sound. I’ll throw you a little curve ball at the end, but want to go through a couple things first.
The two most important things to keep in mind when you are dealing with a sound transmission issue are eliminating ANY common air spaces and increasing the amount of mass/density in between your noise source and a potential “listener”. A 1% air gap in any kind of a noise barrier will leak 30% of the sound from one side to the other, and a 5% gap will allow for a 90% leak. If you consider that sound travels through air, you can quickly see how even a tiny gap will allow for a significant amount of sound transmission. Additionally, the more mass and density that you introduce as a sound barrier, the weaker the pressure wave will be after it passes through the mass.
I have one product for each topic above:
The Climate Seal™ Acoustic Series Window Insert is going to perform the best, be the least visually intrusive as well as the easiest to install. Furthermore, because of the increase in thermal performance of the window, it will also pay itself off in a few years. It is, however, more expensive than the other option. Basically, this system is a “snap into place” window that is held in place by a magnetic bellows system similar to the seal around your refrigerator door. You (or a local installer) will cut and screw a thin metal ‘L’ bracket around the window frame to create a metal surface for the magnets. Inside of the magnetic bellows perimeter will be a ¼” thick piece of clear plastic called Lexan. This plastic is scratch resistant, fairly light weight and will never yellow. The only consideration will be the cleaner used to clean the window when needed, but we can talk about that if needed.
This window was designed to be a re-usable heating and cooling thermal product but because it does such a good job at eliminating any kind of draft or common air space between the inside and outside of the house, we found that it does a very good job at blocking sound as well. The price for each window will depend on the size of the window, but I usually suggest people use a $23-25.00 per square foot ballpark price Shipping is harder to estimate, and usually the best way to get them to a job site is by putting them onto a plywood pallet and sending them on a truck. Estimating performance is also a bit of a hard subject because of the variables involved. The performance of the window will depend on the sound transmission rating of the casement window as well as the decibel level and frequency of the noise source. It will also depend on the ambient level of the room in which the windows are being installed.
The other product that has been used in similar situations is the Quilted Curtain product. This is not a curtain in the traditional sense of the word as it can not be pleated up like a hospital curtain or a min-blind. This is more of a fairly rigid acoustical panel. It originated as an industrial grade product which could be used to enclose a noisy machine in a manufacturing plant or be used as a movable sound wall. It is usually fairly challenging to get it into a residence not only because of the look of the product but also because of the weight. The “active ingredient” in the curtain is an 1/8″ thick, 1lb. per square foot Mass Loaded Vinyl noise barrier. On either side of the vinyl, we place a nominally 1″ thick piece of fiberglass, and then quilt the whole product in a heavy duty vinyl. We pound grommets through the top of the panels to use as a mounting point. Because these curtains weigh about 1.5lbs per square foot, they are cumbersome and not easy to move. Usually when they are installed, they are left in place all of the time. These are also made on a per job basis, and I usually tell people to ballpark for a $12-14.00 per square foot price.