Soundproofing a Bedroom window.

Hello. I need to be able to plug/close my bedroom window in order to avoid street noise when I need to make a recording but is necessary to be able to remove the plug when not working. I'm following the plug design you made in other topic but I have some doubts. 1. What kind of foam should I use in the perimeter? (neoprene, rubber, or just plain sintethic foam???). 2. You said that it's better to remove the outer 2 layers next to the glass and instead adding one layer to the inner mass. This means that the internal isulation should be exposed and towards the glass of the window?. Again I ask what kind of isulation should work best? (fiberglass, or thick foam???) Thanks a lot. Ed.

I really need this window plug to be done soon but I don't want to mess it buying the wrong components. Please Knightfly or John give me some advise about this simple questions. Thanks Ed.

For seals you want something closed cell, like weather-stripping foam - it should also be soft enough to conform to any irregular surfaces between the lip of the plug and your window frame. Here in the US there is a type of weather strip that comes with adhesive already applied, you just unroll what you need and peel off a paper backing and stick it onto whichever surface you want. The main thing is an airtight seal - so whatever you have available locally that will meet those criteria. If you don't care what the window looks like from the outside, you can just stuff the insulation into the perimeter frame of the plug and install the plug in the window. Otherwise you can cover the glass with aluminum foil (keeps things cooler) but you do NOT want a heavy mass near the window because it will form a 3-leaf partition and hurt your low frequency isolation. Because the glass is not a HEAVY mass, you need to compensate by using heavier thicker material for your INNER panel. Minimum 3/4" (19mm) MDF, and a second layer of gypsum inside (glued around the outer edge and flush AGAINST the MDF) will help. HTH... Steve

does the window need to remain openable? if you caulk the seams around the moving parts this should help. or as a more temporary fix i wonder if taping the track/window seams would help. or maybe you could tape, then caulk. i have dual pane windows above my bed and they leak so bad i always think they are open when they aren't.

First of all the window has to be openable so I can remove the plug when the room is not used as a recording space. As I understand there is not any layer of MDF near the glass, just in the inner mass "where the handles go". My window is 1.20x 1.25 m that's like 4' x 4' more or less with 8 cm deep to the glass that is 6mm. The layers will be one 20mm 1.40x1.40m MDF for the internal or fist layer leaving enough space for flanging the sides, then i'll glue/screw in the center 2 more layers of MDF with the exact size of the window cavity, that is 1.20x1.25 m that makes 3 layers glued together with no space between them. then I'll ad a 2x5cm lumber frame all around with foam in the perimeter for isolation, finally I'll stuff some more isolation foam into the cavity. This makes a kind of sandwich with the glass in the external layer, then the foam seal in the perimeter with isolation foam stuffed in the center, then 2 layers of 15mm MDF glued together to the last layer of 20mm that is flanged to the original concrete frame with foam all around the flanged sides. For making sure that once plugged it will be closed tight I'll put 6 long screws in the wall that can be inserted in 6 holes in the plug and adjusted firmly with rotating brackets. This way the window will be hermetic when closed. Here is a drawing for you to see and that way you can give me better asistance. Thanks again Ed.

Exactly right, except I would use either fiberglass or mineral wool insulation, NOT foam... Steve

It's easy for me to find fiberglass but I understand it can get itchy on the skin and because that part of the plug will be exposed I'll be better to cover it with some kind of fabric or clothing. Thanks a lot for your help, it points me in the right direction as always Ed.

I found this thread useful, thanks for the good drawings. It brings up an isolation theory question I have been wondering about. I get the the impression that high frequencies are relatively easy to block/absorb, and that low frequencies are the real challenge with isolation. Is that the case? If so, why bother with the fiberglass or mineral wool insulation shown in the drawing above? Won't the MDF easily block all the high frequencies (making the fiberglass unnecessary), and isn't the figerglass or mineral wool ineffective against low frequencies (making the fiberglass unhelpful)? Just trying to get my theory straight. Thanks to anyone who can enlighten me! Mark

Your theory is right, when considering both MDF and insulation seperately. BUT, when you add insulation to MDF, what happens is the insulation acts to dampen out some of the resonances in the MDF, turning that vibration (which would be re-transmitted as sound) into heat. This gives you improved low frequency performance due to the taming of resonant peaks. Cheers, Kris

Got it. Very interesting. Damping the vibration of the MDF makes total sense. So by forcing the MDF which is vibrating at low frequencies to push against the insulation, energy is converted to heat by the flexing of the insulation fibers? Similar to the way a shock absorber damps the motion of car suspension springs. Does the insulation have to be a little compressed for this to work. In other words, if the insulation was glued to the MDF but not touching the window glass would damping happen due to air resistance, or is the compression the key. Would more layers of MDF would be more effective than the insulation at damping the MDF vibration? Of course more MDF is heavier and less practical I realize. With the insulation alone the low frequency waves push and pull right through the insulation without flexing it much at all? Can you remind me why insulation absorbs higher frequencies better? I hope this is not too far off the thread topic. Thanks so much for your quick response and indulging my curiosity! Mark

Similar to the way a shock absorber damps the motion of car suspension springs.

Yes, this is exactly the right analogy! The insulation does not have to be compressed in order to work. It will dampen the response of the cavity either way...via mechanical motion of vibration of the MDF/glass or just by the motion of the air in between the MDF and glass. Insulation attenuates sound by resistance...effectively the sound pressure wave hits the insulation and sets it (the insulation) in motion. The various fibers rub together to create heat. The reason why it doesn't work well at low frequencies is that the wavelengths are much longer, and you really need about 1/4 of a wavelength to effectively absorb sound. So, a 500 Hz tone has a wavelength of around 2 feet, meaning you need 6" of insulation for effective absorbtion. 100 Hz has a wavelength of 11 feet, so to get effective absorbtion with fiberglass alone you'd need close to 3 feet of thickness. By 20 Hz you'd need over 10 feet of insulation thickness!!!! Now you can see how a bass trap works too...you basically get a panel to resonate, and dampen it mechanically, thereby pulling energy out of that frequency.

Would more layers of MDF would be more effective than the insulation at damping the MDF vibration? Of course more MDF is heavier and less practical I realize.

More layers of MDF would not add any damping to the system. MDF adds mass, and stiffness, which alter the resonant frequency, but don't really offer any damping. Mass does improve sound isolation though... Hope this helps.... Cheers, Kris

That's very helpful, thank you. Once I get a suitable sound level meter I will take some reasonably scientific measurements of the noise in my room before and after building window plugs similar to the picture above. I'll post the results here just for fun. I suspect the windows are the main sound leak, we'll see. Thanks again! Mark

I haven't built the window plug yet but I want to tell that this window was closed before with bricks and concrete, I had behind the glass a board of MDF painted in blue color just for cosmetic reasons, then, behind the MDF were the bricks, that made an excelent isolation BUT the window was unopenable, later I decided I wanted that window to be openable so I had to made a little demolition of the brick wall, remove the MDF board and replaced the old glass with a new thicker one. I want to buy a good sound meter to make readings before and after and check the efectiveness of the plug.

I have the same desire to take before and after readings. I have been doing some research and shopping in that regard. As you know, sensitive sound meters are very expensive. Another option is to do isolations tests with very lound sounds to allow use of an inexpensive sound meter. (I am a little scared to share my noise with the neigbors.) Since I not only want to measure the before and after isolation but I want to actually measure and ensure that the noise level is my studio is pro-quality I am in the process of purchasing a used sound level meter that can measure down to 18-20db or so. PM or email me if you like, if/when I get the meter maybe we can work out some kind of a loan deal. Mark

I have now obtained a B & K 2204 sound level meter. It's old but very impressive engineering quality and capabilities. I realize that the calibration is probably less than precise at this point, but I think it is adequate for my before/after comparisons. I built three window plugs as described above for three 42-inch square windows. They came out very solid (and heavy!) and seem to have reduced the incoming truck noises by about 10 Db. I will take some more accurate measurements later when my assistant is available. (We used his vehicle at a set RPM as our reference sound for testing engine noise infiltration.) I suspect that the door to the outside is the biggest isolation weakness now, although it is very tight. With ambient noise running about 21 Db with peaks to 26Db or 27Db when there is noise outside I think I'll move on to other phases of the project and be content with that for now. I do have a question, however. Most of the noise that gets in now tends to be near the bottom of the human audible frequency range. Is there any disadvantage to applying an EQ cut below 100Hz to screen any remnants of those sounds out of my recordings of say, acoustic guitar? The noise tends to be mostly around 20-30Hz or even lower according to my sound leve meter. Thanks for all the help so far! Mark

Lowest note on standard tuned guitar is 82.4 hZ, so cutting below that should do minimal damage - as always in these cases, your ears should be the last authority... Steve

I do have a question, however. Most of the noise that gets in now tends to be near the bottom of the human audible frequency range. Is there any disadvantage to applying an EQ cut below 100Hz to screen any remnants of those sounds out of my recordings of say, acoustic guitar? The noise tends to be mostly around 20-30Hz or even lower according to my sound leve meter.

The problem is that filters have a phase shift that occurs above its passband. Figures 11 and 12 in Ranenote 122 Show this shift. So, as Steve wrote above me, with the lowest note on a guitar being 82 Hz, a filter would need a knee atound 42 Hz to avoid shifting the musical notes. If your frequency analysis is correct, no problem. I hope not to technical; Andre

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