The sound waves involved in double-glazed windows
sandra <|¬ºŞ;'`'
characteristics of those windows is that
a) using two glass sheets of different thicknesses will let through less
sound than using glass sheets of the same thickness
b) NOT mounting the glass sheets completely parallell to each other will
also reduce the amount of sound let through (this fact is used in recording
studios).
c) having the two sheets of glass mounted very close to each other will make
a sound insulation system which may even work worse than a single-glazed
system.
I have performed experiments to check those hypothesises and they appear to
be valid. However, my teacher (no, I am not a professional scientist. In
fact, I am very unprofessional) believed the amount of sound let through
depended wholly on the air gap and the air between the sheets of glass
vibrating. That is probably only part of the truth, because the physical
vibrations of the actual glass sheets (chladni figures may be applicable)
seem to be just as important in eg. hypothesis a).
The problem: Neither me, nor my dear physics supervisor now know how exactly
the results of the experiment should be analyzed, or even if it is the
physical vibrations of the glass sheets or not that is the variable which
affects the results. There are also other factors we are unsure of,
concerning the frequencies of the sounds let through, and I would love to
give more details if there is anyone in this newsgroup who knows anything
about the way sound travels through glass, especially the way sound changes
direction or spreads when changing medium. Or someone that knows anything at
all about anything at all (eg. chladni figure) which they believe could be
helpful for this project.
I apologise for just jumping into the newsgroup without getting to know you
and without finding out whether this is the right newsgroup for this topic
at all (after all, not all physics newsgroups seem to be concerned with
sound), but time is running out for me and I am not getting much wiser... so
helping hands are welcomed.
--
sandra Barcella
<|¬ºŞ;'`'
P.S. I would be very pleased if anyone who knows something about this topic
and writes to me about it would also include information such as his or her
name and also accept that I can use the information he or she gives me for
my projects, so that I will not have unknown sources in my project. Thank
you in advance.
Jeremy Watts
are two types of wave - transverse (the vibration does not occur in the same
direction as the direction the wave is travelling in), and longitudinal (the
vibration occurs in the same direction as the direction of the wave).
Now in some media, I think I'm right in saying most, sound travels as a
longitudinal wave, but others it travels as a transverse wave. This may
have some bearing on your project, as you need to know how sound travels in
glass and air.
What else I remember about sound is that lower frequencies travel further -
this is why the first thing you hear when approaching music is the drums and
bass. This will have relevance as far as transmittance of sound goes.
You need to read up on it.
"sandra <|¬ºÞ;'`'" <sand...@telia.com> wrote in message
news:OGtb9.4903$e5.7...@newsb.telia.net...
> <|¬ºÞ;'`'
Rune Allnor
> The problem: Neither me, nor my dear physics supervisor now know how exactly
> the results of the experiment should be analyzed, or even if it is the
> physical vibrations of the glass sheets or not that is the variable which
> affects the results. There are also other factors we are unsure of,
> concerning the frequencies of the sounds let through,
The analysis of sound propagating in layered media is standard material
in seismics and physical acoustics. While there are many textbooks available
that treat this kind of analysis, I think the most to-the-point introduction
is a paper that was published a few years back:
Hovem: Acoustic waves in finely layered media
Geophysics, July-August 1995, Volume 60, Issue 4, pp. 1217-1221
Here you will find an analysis of how material parameters and layer thiknesses
influence the transmission of sound through media like your window, as
function of frequency.
Rune
Higini Arau Puchades
> I am currently doing a project about double-glazed windows. Some of the
> characteristics of those windows is that
> a) using two glass sheets of different thicknesses will let through less
> sound than using glass sheets of the same thickness
> b) NOT mounting the glass sheets completely parallell to each other will
> also reduce the amount of sound let through (this fact is used in recording
> studios).
> c) having the two sheets of glass mounted very close to each other will make
> a sound insulation system which may even work worse than a single-glazed
> system.
>
Hello Sandra,
I realized my doctoral thesis, ( "Contribucion al estudio de la
atenuacion sonora de dobles y triples paredes simétricas, asimétricas,
isotrópicas, homogeneas y viscoelasticas". (1984. Barcelona
University)), in this aspect, extended to any material, for single,
double and triple walls. Many part of this subject was published in
ABC de la Acustica Arquitectònica. (1999) CEAC. The problem for you is
in spanish, however the formulae are expressed in the language common
and universal for all persons.
Many questions by you asked have been developed in:
Quirt, J.D. Sound Transmission trough windows: 1. Single and Double
Glazing.
J.Acoust.Soc.Am 74(2). August 1983
Quirt, J.D. Sound Transmission trough windows: 1. Double and Triple
Glazing.
J.Acoust.Soc.Am 74(2). August 1983.
More information very detailed is supplied Saflex, search in google.
Cremer, L: Theorie der schall dämmung wände bei schrägem einfall.
Akustike Zitschrift VII, 1942.
A.London Transmission of reverberant sound trogh double walls,
J.National Bureau Standards Vol 42, paper RP1998. (1949)
A.London Transmission of reverberant sound trogh double walls,
J.Acoust.Soc.Am 22(2). 1950
H.Arau: A new contribution to the study of sound transmission los of
single walls, Fortschritte de Akustik FASE/DAGA '82 (Vol.1, pages
267-270), 1982.
I can to supply you many much information.
Answering to the questions indicated by, we have:
Point a) Yes it is true, but the critical frequencies of glasses must
be well different among them trying that that the lowest critical
frequency be very high in frequency, because that if we have a great
chamber among glazing panes then is powered the transmission loss TL
very much in the frequencies below to the critical frquencies. If you
put in this case absorption in the perimeter frame of the chamber then
you will improve more the TL.
Point b) J.D. Quirt, before indicated, showed by experimental analysis
that this question is not important. The inclination, or not
parallelism among glasses is not important for improve the TL.
Point c) Yes, it is true. Because in this case is very important the
air cavity resonance among glasses. This resonance frequency is placed
in the mean audible spectrum. Normally we have very much problems with
the critical frequencies, that ever are producing a troubelsman, that
now in addition we have the resonance frequency that does a great dip
of TL. The glases with very few cavity are called thermical glasses.
I hope that my information be useful for you
Higini
Noral D. Stewart
>
> > Point c) Yes, it is true. Because in this case is very important the
> air cavity resonance among glasses. This resonance frequency is placed
> in the mean audible spectrum. Normally we have very much problems with
> the critical frequencies, that ever are producing a troubelsman, that
> now in addition we have the resonance frequency that does a great dip
> of TL. The glases with very few cavity are called thermical glasses.
> I hope that my information be useful for you
>
> Higini
I am not sure the original poster Sandra understood that the most
important resonance is the one you discuss, the mass-air-mass resonance,
and not resonances due to the dimensions of the glass itself as would
occur with a single pane of glass. Sandra, while those resonances may
be factors in some cases, they are usually secondary factors. The
mass-air-mass resonance effect is well understood. The frequency at
which it occurs is easily predicted.
Also, to reinforce what Higini said, there is no strong evidence that
angling one of the panes really helps and most evidence indicates it
does not help. Glass is often angled in studios to prevent light
reflections and to even reflect sound in a different direction.
Higini Arau Puchades
> I am not sure the original poster Sandra understood that the most
> important resonance is the one you discuss, the mass-air-mass resonance,
> and not resonances due to the dimensions of the glass itself as would
> occur with a single pane of glass. Sandra, while those resonances may
> be factors in some cases, they are usually secondary factors. The
> mass-air-mass resonance effect is well understood. The frequency at
> which it occurs is easily predicted.
>
> Also, to reinforce what Higini said, there is no strong evidence that
> angling one of the panes really helps and most evidence indicates it
> does not help. Glass is often angled in studios to prevent light
> reflections and to even reflect sound in a different direction.
Hi Noral,
Yes, you have reason, the resonance that I wished to speak is due to
the coupling mass-air-mass.
With reference to the inclination among panes many people think that
it improve TL, however I think with you that it may be more useful to
avoid a something bad reflection produced in the room, or as you say
to avoid light reflections.
Very thanks for this correction.
Higini