STC 30 is enough?
#1
05-25-05, 12:36 PM
STC 30 is enough?
Hi,
I am look for type of window to reduce road noise.
Is STC = 30 or so enough to block most of noise from road?
For example, now I am looking at Pella Double Hung and I get the STC data from the spec.
Thanks
Acton
I am look for type of window to reduce road noise.
Is STC = 30 or so enough to block most of noise from road?
For example, now I am looking at Pella Double Hung and I get the STC data from the spec.
Thanks
Acton
#2
05-25-05, 04:36 PM
Group Moderator
According to one source... (http://soundproofwindows.com/technical.html) it takes an STC in the 40's to provide any substantial sound reduction.
#4
05-29-05, 07:25 AM
Stc
An STC 30 is not really going to stop much noise, and as I mentioned in the past, STC is related to the overall spectrum and not to a specific frequency range. Traffic noise is low frequency and really is the hardest to attenuate or block.
Soundproof windows has a few different solutions listed on their site, but basically they are offering a laminated interior-fixed-storm window to block the noise. A pretty basic approach, but it will work.
From what I have heard, they do offer a pretty good product although I have also heard that they are very expensive. Also, if you like to occasionally open the window in question you might want to be sure that that is understood and that the "insert" is removable...which may potentially cut down on the overall effectiveness of the product.
Soundproof windows has a few different solutions listed on their site, but basically they are offering a laminated interior-fixed-storm window to block the noise. A pretty basic approach, but it will work.
From what I have heard, they do offer a pretty good product although I have also heard that they are very expensive. Also, if you like to occasionally open the window in question you might want to be sure that that is understood and that the "insert" is removable...which may potentially cut down on the overall effectiveness of the product.
Last edited by Oberon; 06-01-05 at 07:33 AM.
#5
05-29-05, 10:56 PM
I would think that in a general application to reduce the noise level, a set of tightly fitted rubberized drapes probably will do almost as well as an expensive alternatives.
By the way, since noise is in the audible spectrum of air compression waves....are the walls also acting as transmitters?
The beat goes on.
By the way, since noise is in the audible spectrum of air compression waves....are the walls also acting as transmitters?
The beat goes on.
#6
05-31-05, 02:50 PM
a bit of sound information
A quick (well maybe not so quick) overview of sound versus windows.
This is the long version and it is from a lecture that I gave a few years back. I am not sure that anyone really wants to read this whole thing, but what the heck!
A little “sound” background.
In order to have a sound you need three things:
A sound source, a medium to carry the sound, and a receiver to detect the sound.
In our world, we have lots of sound sources, some we like, some we would rather avoid.
The medium to convey the sound may be air, water, your window unit, or a combination of many elements.
And the receiver is…you.
If a tree falls in the woods and no one is there to hear it, does it make a noise?
Many people consider that to be a philosophical question, but it is also a valid question concerning the physics of sound. If one of the three elements is missing, then by definition there is no sound. The point being, we need to eliminate one of the three elements in order to make the unwanted sounds go away.
Obviously, we won’t eliminate the source(s), and most people would not care for the elimination of the receiver, so we need to do something to affect the middle element of sound transfer from source to receiver.
Since there isn’t much we can do to eliminate the air that carries the sound; in this case the medium that we want to affect is the window system because that is where the sound is coming thru to the inside of the house.
Now I will sneak in a few terms…db or decibel is a measurement of a sound pressure level or a measurement of the amplitude of the sound (I am avoiding saying how “loud” the sound is because it isn’t exactly accurate…imagine listening to music thru headphones. At half-volume you hear the music perfectly fine…at full volume the sound of the music might actually be uncomfortable. Now imagine the same scenario with enough background sound that you cannot hear the music at half-volume, but at full volume you can hear it fine and there may not be discomfort at that level…that is a difference in sound pressure level and “loudness”…that is not a perfect analogy, but this is going to be way too long as it is!)…
Hertz or Hz is the term used for sound frequency. One Hz = one cycle per second…kind of like one “revolution per second” of the particular sine wave…not to be confused with the “sound wave” which is what “carries” the sound. The sine-wave IS the sound and the wave length determines the frequency of the sound as measured in Hz (hope that made sense).
Then there is Transmission Loss, or TL, which is the actual measurement of db reduction during transmission (thus the name…clever isn’t it?).
STC – which stands for Sound Transmission Class is a number assigned by the building industry to “suggest” the amount of sound blocking ability (or sound passing ability) thru a particular building component, be it a wall or a window.
There are three primary factors affecting how sound passes thru the window system;
the glass, the window assembly, and the window installation.
Window glass has mass and any change in mass will affect how sound is transferred.
A sound wave will react to a change in transfer-medium density in three ways, it will reflect, it will refract, and/or it will pass straight thru while suffering a certain amount of TL depending on the mass of the “object” encountered (“object” isn’t the entirely correct term, but in this case it works because we are discussing a solid object – the window).
In all three cases the sound loss will be redirected as heat. Usually not enough to cause anyone to notice a difference in the heat coming from the object, but there will be a conversion of the energy.
TL for a very large sheet of glass should (theoretically) increase by 6db for each doubling of the sound frequency or doubling of the mass of the glass. However, the stiffness of glass will affect that formula to some degree as well as the nature of glass as a solid object.
Additionally, the prediction becomes much less precise when working with a typical window size lite (even a large window). The size of the lite in relation to the wavelength of the sound affects the TL of the sound wave (whew!).
Okay, here comes the math part. Wavelength and frequency are inversely proportional or the longer the wavelength, the lower the frequency…or the higher the frequency, the shorter the wavelength… f = 1/t and wl = c/f –> where f = frequency, t = time, c = speed of sound, and wl = wavelength.
And how does all that affect window performance?
Well, as I mentioned earlier, the soundwave when striking an object has three choices about how to react, the nature of glass allows a lower frequency (longer soundwave) more likelihood to be able to pass thru.
That is something of a generalization though. Everything has a resonant frequency, meaning everything reacts to a certain frequency range. This is why adding layers of glass, or adding an airspace, or adding laminated glass affects sound transmission loss.
A Mass Law Prediction can be used to estimate the actual TL from a sheet of glass. Unfortunately, as I suggested earlier, glass does not react as predicted. In fact, when tested, a sheet of 18mm glass will perform at about the predicted level of a 4mm lite above 500hz. Curiously, the 18mm glass will actually perform somewhat better than predicted below 500hz (go figure). In fact, near 500hz a 4mm (about 3/16”) lite will actually outperform an 18mm (about ¾”) lite in stopping sound…again, go figure.
If a manufacturer could build an IG with a vacuum between the two lites, then we would have a really energy efficient window and a very sound-resistant one as well.
Unfortunately, we cannot put a vacuum between two lites of glass for a variety of reasons, but primarily because the glass isn’t rigid enough to avoid being “sucked” into the vacuum and becoming distorted to the point that the two lites would actually touch in the middle of the window.
As I mentioned previously, single lites of glass perform very poorly in a sound deadening role.
When comparing STC values, note that there is very little increase in the STC number based on increasing the thickness of an individual lite. Basically, the thickness of the glass matters very little in a monolithic construction.
There are ways to improve single glazing performance, but I cannot imagine anyone worrying about improved sound performance and using single pane glazing.
When I noted that at 500hz, the 4mm glass actually had better performance than the 18mm glass, that was due to the fact that specific frequencies or sound waves will tend to bend or refract within the glass at a particular frequency range. This occurrence is referred to as a coincidental dip and it is seen in any material that sound can penetrate. Differing densities causes the sound energy refraction which in turn accentuates a particular modulation frequency based on the density of the obstacle.
In simpler terms, the object “likes” that frequency and allows it to pass almost unopposed.
Laminated glass has a much improved TL than solid glass at the same thickness and actually very nearly approaches mass law predictions above the coincidence frequency.
The plastic interlayer in the laminate absorbs much of the sound energy that has penetrated the glass. Again, we have a significant mass change which causes a soundwave bend or refraction at that point.
Insulating glass also offers a significant improvement over monolithic construction.
The important part of an IG unit, considering sound TL, is the airspace itself.
The larger the airspace, the better the product performs as a sound damper.
If the airspace is small, the STC might not be much better than an equal thickness of monolithic glass; or in some cases, if the airspace is really small, it might actually be worse than a monolithic or single lite. The vibration produced by the sound wave passing thru the small airspace might actually cause a resonance that would result in less TL than would be measured from the single lite.
The resonance frequency for a typical residential IG construction is around 200 to 400hz, or about where traffic noise is at its worst!
If a homeowner needs to improve performance at the 200 to 400hz frequency range, there are a couple of options available.
Increasing the thickness of the one of the lites in the IG will help. Using two different thicknesses of glass in the IG will increase attenuation because each lite will have a different resonant frequency and each lite will attenuate frequencies that the other lite will pass. Additionally, increasing the width of the airspace to the maximum possible will help considerably.
For example, two lites of 3mm glass with a ¼” airspace will have an STC of around 30, while a single pane of 3mm glass will also have an STC of about 30. In fact, at about 300hz to 800hz, the single pane will actually outperform this particular IG (narrow airspace) at attenuating unwanted noise.
But, by doubling the airspace you will realize gains of about -3db for every time the width of the airspace is doubled. There is a down side unfortunately.
An airspace starts losing its effectiveness as an “insulator” as it gets wider. Given that this is a very gradual process and not anything dramatic, still at about 7/8” or so you will start to lose energy efficiency as the airspace between the lites grows. This is caused primarily by convection currents in the airspace itself. Argon and krypton are both more viscous than air and will help retain energy efficiency as the airspace width increases, but eventually you will lose the energy efficiency advantage of the IG by widening the airspace.
Every time you double the width of the airspace you gain about “3” on the STC scale.
Sounds great, but figure a ¼” airspace is a 30, so a ½” is 33, and a 1” is 36, and a 2” is 39, and a 4” airspace gives an STC of 42.
A 4” airspace isn’t really very practical.
A monolithic laminated construction consisting of a ¼” glass / .060” PVB / ¼” glass has an STC of 39…this is in a ½” thick construction.
An IG consisting of 1/8” glass / .060” PVB / 1/8” glass / 13mm airspace / ¼” glass has an overall thickness of 1” and an STC of 42. So it is ¼” the thickness of the IG alone with an equal STC.
What about triple glazing? At lower frequencies, there is a slight gain due to the increased density of the overall construction due to having three lites, but overall there is no advantage over double glazing unless the airspace is correspondingly wider as well.
A triple pane IG with an overall thickness of one inch will perform almost exactly the same as a double pane with an overall width of one inch assuming the thickness of glass and other components are the same.
And the recommendation that using different thickness of glass in the IG will improve performance?
That is true. In fact, an IG with a 1/8” lite and a ¼” lite will perform as well as, and maybe a little better than an IG with two ¼” lites…again assuming an equal airspace….the lites will have different resonant frequencies and as such will not reinforce one another.
Okay, what does all this stuff mean?
Basically, it is easier to limit or dampen higher frequency sound transmission than to deaden lower frequencies. No big surprise. I suspect that everyone reading this has had the opportunity of listening to someone else’s bass (music or occasionally a facsimile of’) in your home as a car drives down the street or in your car while stopped for a light. You may not have heard anything else, but the bass comes thru loud and clear.
Bass equals low frequency sound source; low frequency sound source equals the ability to travel long distances with comparatively little TL compared with higher frequencies.
The trick to making a “sound-resistant” window (or door or wall) is the ability to stop or at least attenuate the bass, the low frequencies.
We were all born with the ability to hear sounds in the 20 to 20,000hz range. By the time we are teenagers, we have pretty much lost the ability to hear anything above about 13,000hz. People sometimes comment that children can hear things adults can’t? It’s true, children can hear at both higher and occasionally lower frequencies than can adults.
Just a bit more trivia: The earth resonates at about 18hz. Although very few people can hear “low enough” to actually hear this resonance, there are people who can hear it. From what I have read, they hear it as a persistent “hum or buzzing sound” that can be quite annoying at times. The amplitude of the earth’s resonance does, apparently, vary at different locations, and can occasionally vary in the same location as well, otherwise I would suspect it might drive people nutty.
Our low frequency world.
During the cold war, the US Navy used underwater listening devices (hydrophones) to track Soviet ships and submarines by listening for low frequency sounds.
Detections of low frequency sounds at ranges of 3000nm, or more, were not unheard of and these long range detections were from ships and submarines that were designed to be quiet. Many of these submarines were quieter than a modern car and certainly quieter than the bass from the neighborhood kid’s sound system. Low frequency sounds are persistent.
Ever notice that most ceiling fans have an odd number of paddles? One might think that designing a fan with an even number of blades would be much simpler than designing a fan with an odd number; balancing 4 blades seems like it would be much simpler than computing the balance for 5,.
Also, and curiously (there’s that word again!), the vast majority of warships have an odd number of propellers and it doesn’t seem to matter who built them.
What do Naval architects and fan designers have in common?
They both want a quieter product. An odd number of blades, be it a propeller, a ceiling fan, or wherever else “blades” are used, is quieter than a device with an even number of blades.
This phenomenon has to do with harmonic reinforcement or “adding” the sound of one blade to the sound of the next blade (not even going to put the formulas in here! This is already too much!).
So what does that have to do with window construction? Remember that different thicknesses of glass in an IG affect the transmission sound loss thru that IG…using two lites of different thicknesses is superior to using two lites of the same thickness…you have a different resonant frequency for each lite, and like the propeller analogy that does affect the resonant frequency (both different) and the harmonic reinforcement of the sound. Remember the “narrow” airspace I discussed earlier?
The narrow space can act almost in a “megaphone” and actually increase the sound pressure level – the sound can theoretically be louder after passing thru the window than it was previously.
You can improve the performance of any IG by changing one of the lites to laminated glass. If there is a relatively wide airspace between the two lites, even better; so long as the airspace still maintains the energy efficiency that was intended.
This is also where having an argon or krypton fill really makes a difference. Since argon and krypton are denser (the better term might be more viscous) than air there is an advantage in sound propagation in that the fill will help prevent the sort of air currents within the airspace that affect the energy efficiency of the unit and will allow you to make a wider airspace and still maintain a greater energy efficiency as well as greater sound propagation barrier (again, whew!). And the additional viscosity of the gas fill will also affect sound propagation by affecting the soundwave itself as it penetrates the airspace.
Now, after all that, I am finally done…for awhile!
Like the bunny, I can keep going and going and going…
This is the long version and it is from a lecture that I gave a few years back. I am not sure that anyone really wants to read this whole thing, but what the heck!
A little “sound” background.
In order to have a sound you need three things:
A sound source, a medium to carry the sound, and a receiver to detect the sound.
In our world, we have lots of sound sources, some we like, some we would rather avoid.
The medium to convey the sound may be air, water, your window unit, or a combination of many elements.
And the receiver is…you.
If a tree falls in the woods and no one is there to hear it, does it make a noise?
Many people consider that to be a philosophical question, but it is also a valid question concerning the physics of sound. If one of the three elements is missing, then by definition there is no sound. The point being, we need to eliminate one of the three elements in order to make the unwanted sounds go away.
Obviously, we won’t eliminate the source(s), and most people would not care for the elimination of the receiver, so we need to do something to affect the middle element of sound transfer from source to receiver.
Since there isn’t much we can do to eliminate the air that carries the sound; in this case the medium that we want to affect is the window system because that is where the sound is coming thru to the inside of the house.
Now I will sneak in a few terms…db or decibel is a measurement of a sound pressure level or a measurement of the amplitude of the sound (I am avoiding saying how “loud” the sound is because it isn’t exactly accurate…imagine listening to music thru headphones. At half-volume you hear the music perfectly fine…at full volume the sound of the music might actually be uncomfortable. Now imagine the same scenario with enough background sound that you cannot hear the music at half-volume, but at full volume you can hear it fine and there may not be discomfort at that level…that is a difference in sound pressure level and “loudness”…that is not a perfect analogy, but this is going to be way too long as it is!)…
Hertz or Hz is the term used for sound frequency. One Hz = one cycle per second…kind of like one “revolution per second” of the particular sine wave…not to be confused with the “sound wave” which is what “carries” the sound. The sine-wave IS the sound and the wave length determines the frequency of the sound as measured in Hz (hope that made sense).
Then there is Transmission Loss, or TL, which is the actual measurement of db reduction during transmission (thus the name…clever isn’t it?).
STC – which stands for Sound Transmission Class is a number assigned by the building industry to “suggest” the amount of sound blocking ability (or sound passing ability) thru a particular building component, be it a wall or a window.
There are three primary factors affecting how sound passes thru the window system;
the glass, the window assembly, and the window installation.
Window glass has mass and any change in mass will affect how sound is transferred.
A sound wave will react to a change in transfer-medium density in three ways, it will reflect, it will refract, and/or it will pass straight thru while suffering a certain amount of TL depending on the mass of the “object” encountered (“object” isn’t the entirely correct term, but in this case it works because we are discussing a solid object – the window).
In all three cases the sound loss will be redirected as heat. Usually not enough to cause anyone to notice a difference in the heat coming from the object, but there will be a conversion of the energy.
TL for a very large sheet of glass should (theoretically) increase by 6db for each doubling of the sound frequency or doubling of the mass of the glass. However, the stiffness of glass will affect that formula to some degree as well as the nature of glass as a solid object.
Additionally, the prediction becomes much less precise when working with a typical window size lite (even a large window). The size of the lite in relation to the wavelength of the sound affects the TL of the sound wave (whew!).
Okay, here comes the math part. Wavelength and frequency are inversely proportional or the longer the wavelength, the lower the frequency…or the higher the frequency, the shorter the wavelength… f = 1/t and wl = c/f –> where f = frequency, t = time, c = speed of sound, and wl = wavelength.
And how does all that affect window performance?
Well, as I mentioned earlier, the soundwave when striking an object has three choices about how to react, the nature of glass allows a lower frequency (longer soundwave) more likelihood to be able to pass thru.
That is something of a generalization though. Everything has a resonant frequency, meaning everything reacts to a certain frequency range. This is why adding layers of glass, or adding an airspace, or adding laminated glass affects sound transmission loss.
A Mass Law Prediction can be used to estimate the actual TL from a sheet of glass. Unfortunately, as I suggested earlier, glass does not react as predicted. In fact, when tested, a sheet of 18mm glass will perform at about the predicted level of a 4mm lite above 500hz. Curiously, the 18mm glass will actually perform somewhat better than predicted below 500hz (go figure). In fact, near 500hz a 4mm (about 3/16”) lite will actually outperform an 18mm (about ¾”) lite in stopping sound…again, go figure.
If a manufacturer could build an IG with a vacuum between the two lites, then we would have a really energy efficient window and a very sound-resistant one as well.
Unfortunately, we cannot put a vacuum between two lites of glass for a variety of reasons, but primarily because the glass isn’t rigid enough to avoid being “sucked” into the vacuum and becoming distorted to the point that the two lites would actually touch in the middle of the window.
As I mentioned previously, single lites of glass perform very poorly in a sound deadening role.
When comparing STC values, note that there is very little increase in the STC number based on increasing the thickness of an individual lite. Basically, the thickness of the glass matters very little in a monolithic construction.
There are ways to improve single glazing performance, but I cannot imagine anyone worrying about improved sound performance and using single pane glazing.
When I noted that at 500hz, the 4mm glass actually had better performance than the 18mm glass, that was due to the fact that specific frequencies or sound waves will tend to bend or refract within the glass at a particular frequency range. This occurrence is referred to as a coincidental dip and it is seen in any material that sound can penetrate. Differing densities causes the sound energy refraction which in turn accentuates a particular modulation frequency based on the density of the obstacle.
In simpler terms, the object “likes” that frequency and allows it to pass almost unopposed.
Laminated glass has a much improved TL than solid glass at the same thickness and actually very nearly approaches mass law predictions above the coincidence frequency.
The plastic interlayer in the laminate absorbs much of the sound energy that has penetrated the glass. Again, we have a significant mass change which causes a soundwave bend or refraction at that point.
Insulating glass also offers a significant improvement over monolithic construction.
The important part of an IG unit, considering sound TL, is the airspace itself.
The larger the airspace, the better the product performs as a sound damper.
If the airspace is small, the STC might not be much better than an equal thickness of monolithic glass; or in some cases, if the airspace is really small, it might actually be worse than a monolithic or single lite. The vibration produced by the sound wave passing thru the small airspace might actually cause a resonance that would result in less TL than would be measured from the single lite.
The resonance frequency for a typical residential IG construction is around 200 to 400hz, or about where traffic noise is at its worst!
If a homeowner needs to improve performance at the 200 to 400hz frequency range, there are a couple of options available.
Increasing the thickness of the one of the lites in the IG will help. Using two different thicknesses of glass in the IG will increase attenuation because each lite will have a different resonant frequency and each lite will attenuate frequencies that the other lite will pass. Additionally, increasing the width of the airspace to the maximum possible will help considerably.
For example, two lites of 3mm glass with a ¼” airspace will have an STC of around 30, while a single pane of 3mm glass will also have an STC of about 30. In fact, at about 300hz to 800hz, the single pane will actually outperform this particular IG (narrow airspace) at attenuating unwanted noise.
But, by doubling the airspace you will realize gains of about -3db for every time the width of the airspace is doubled. There is a down side unfortunately.
An airspace starts losing its effectiveness as an “insulator” as it gets wider. Given that this is a very gradual process and not anything dramatic, still at about 7/8” or so you will start to lose energy efficiency as the airspace between the lites grows. This is caused primarily by convection currents in the airspace itself. Argon and krypton are both more viscous than air and will help retain energy efficiency as the airspace width increases, but eventually you will lose the energy efficiency advantage of the IG by widening the airspace.
Every time you double the width of the airspace you gain about “3” on the STC scale.
Sounds great, but figure a ¼” airspace is a 30, so a ½” is 33, and a 1” is 36, and a 2” is 39, and a 4” airspace gives an STC of 42.
A 4” airspace isn’t really very practical.
A monolithic laminated construction consisting of a ¼” glass / .060” PVB / ¼” glass has an STC of 39…this is in a ½” thick construction.
An IG consisting of 1/8” glass / .060” PVB / 1/8” glass / 13mm airspace / ¼” glass has an overall thickness of 1” and an STC of 42. So it is ¼” the thickness of the IG alone with an equal STC.
What about triple glazing? At lower frequencies, there is a slight gain due to the increased density of the overall construction due to having three lites, but overall there is no advantage over double glazing unless the airspace is correspondingly wider as well.
A triple pane IG with an overall thickness of one inch will perform almost exactly the same as a double pane with an overall width of one inch assuming the thickness of glass and other components are the same.
And the recommendation that using different thickness of glass in the IG will improve performance?
That is true. In fact, an IG with a 1/8” lite and a ¼” lite will perform as well as, and maybe a little better than an IG with two ¼” lites…again assuming an equal airspace….the lites will have different resonant frequencies and as such will not reinforce one another.
Okay, what does all this stuff mean?
Basically, it is easier to limit or dampen higher frequency sound transmission than to deaden lower frequencies. No big surprise. I suspect that everyone reading this has had the opportunity of listening to someone else’s bass (music or occasionally a facsimile of’) in your home as a car drives down the street or in your car while stopped for a light. You may not have heard anything else, but the bass comes thru loud and clear.
Bass equals low frequency sound source; low frequency sound source equals the ability to travel long distances with comparatively little TL compared with higher frequencies.
The trick to making a “sound-resistant” window (or door or wall) is the ability to stop or at least attenuate the bass, the low frequencies.
We were all born with the ability to hear sounds in the 20 to 20,000hz range. By the time we are teenagers, we have pretty much lost the ability to hear anything above about 13,000hz. People sometimes comment that children can hear things adults can’t? It’s true, children can hear at both higher and occasionally lower frequencies than can adults.
Just a bit more trivia: The earth resonates at about 18hz. Although very few people can hear “low enough” to actually hear this resonance, there are people who can hear it. From what I have read, they hear it as a persistent “hum or buzzing sound” that can be quite annoying at times. The amplitude of the earth’s resonance does, apparently, vary at different locations, and can occasionally vary in the same location as well, otherwise I would suspect it might drive people nutty.
Our low frequency world.
During the cold war, the US Navy used underwater listening devices (hydrophones) to track Soviet ships and submarines by listening for low frequency sounds.
Detections of low frequency sounds at ranges of 3000nm, or more, were not unheard of and these long range detections were from ships and submarines that were designed to be quiet. Many of these submarines were quieter than a modern car and certainly quieter than the bass from the neighborhood kid’s sound system. Low frequency sounds are persistent.
Ever notice that most ceiling fans have an odd number of paddles? One might think that designing a fan with an even number of blades would be much simpler than designing a fan with an odd number; balancing 4 blades seems like it would be much simpler than computing the balance for 5,.
Also, and curiously (there’s that word again!), the vast majority of warships have an odd number of propellers and it doesn’t seem to matter who built them.
What do Naval architects and fan designers have in common?
They both want a quieter product. An odd number of blades, be it a propeller, a ceiling fan, or wherever else “blades” are used, is quieter than a device with an even number of blades.
This phenomenon has to do with harmonic reinforcement or “adding” the sound of one blade to the sound of the next blade (not even going to put the formulas in here! This is already too much!).
So what does that have to do with window construction? Remember that different thicknesses of glass in an IG affect the transmission sound loss thru that IG…using two lites of different thicknesses is superior to using two lites of the same thickness…you have a different resonant frequency for each lite, and like the propeller analogy that does affect the resonant frequency (both different) and the harmonic reinforcement of the sound. Remember the “narrow” airspace I discussed earlier?
The narrow space can act almost in a “megaphone” and actually increase the sound pressure level – the sound can theoretically be louder after passing thru the window than it was previously.
You can improve the performance of any IG by changing one of the lites to laminated glass. If there is a relatively wide airspace between the two lites, even better; so long as the airspace still maintains the energy efficiency that was intended.
This is also where having an argon or krypton fill really makes a difference. Since argon and krypton are denser (the better term might be more viscous) than air there is an advantage in sound propagation in that the fill will help prevent the sort of air currents within the airspace that affect the energy efficiency of the unit and will allow you to make a wider airspace and still maintain a greater energy efficiency as well as greater sound propagation barrier (again, whew!). And the additional viscosity of the gas fill will also affect sound propagation by affecting the soundwave itself as it penetrates the airspace.
Now, after all that, I am finally done…for awhile!
Like the bunny, I can keep going and going and going…
#7
05-31-05, 03:36 PM
Group Moderator
Oberon,
I read the whole thing. Do I get some sort of prize? LOL... Actually, I found it interesting in a twisted, curious sort of way.
I read the whole thing. Do I get some sort of prize? LOL... Actually, I found it interesting in a twisted, curious sort of way.
#10
06-14-05, 06:28 PM
Stc
Sorry Acton, not something you can do yourself. STC measurement is performed in a special laboratory setting under some really stringent conditions and using some serious (and very expensive) equipment.
#11
06-14-05, 08:11 PM
Operated by bespectacled, wispy haired individuals who will unceremoniously ask you to LEAVE if you don't shut up.
Several years ago, the CO. I worked for assembled the Ron Howard screening room in the Robert Zimmecus (SP) building at USC.
Interesting, we had it insulated and isolated so well, they had to install a noise generator to achieve acoustic balance.
Several years ago, the CO. I worked for assembled the Ron Howard screening room in the Robert Zimmecus (SP) building at USC.
Interesting, we had it insulated and isolated so well, they had to install a noise generator to achieve acoustic balance.
#13
06-15-05, 09:37 PM
We didn't acheive no noise, just close to dead air.
Isolating the room is critical to success. So the speakers and their support structure are within the Isolation and the cameras, projection and sound source equipment is outside the isolation.
The Isolation is created in part, by saw cutting a 1" separation in the slab, all the way through, just inside the existing walls. which creates a floating slab, isolated from exterior or adjacent noise producing influences.
The ceiling was 3-5/8"DW hung off of 16ga. "I" beams suspended from the floor structure above through spring loaded Isolation brackets. This cavity was filled with loose fill, unfaced batt insulation. There is a rehearsal hall above.
Isolating the room is critical to success. So the speakers and their support structure are within the Isolation and the cameras, projection and sound source equipment is outside the isolation.
The Isolation is created in part, by saw cutting a 1" separation in the slab, all the way through, just inside the existing walls. which creates a floating slab, isolated from exterior or adjacent noise producing influences.
The ceiling was 3-5/8"DW hung off of 16ga. "I" beams suspended from the floor structure above through spring loaded Isolation brackets. This cavity was filled with loose fill, unfaced batt insulation. There is a rehearsal hall above.
