Questions about the sound reduction index

[bham]

History of talking about noise pollution, I appeal to the big heads of the forum, possibly acoustician because I row a little.
Okay, I would like to know if the value of the sound reduction index increases as the noise increases or vice versa?
I see for example on this site http://www.wicona.fr/fileadmin/Files/pv ... 0E-2-1.pdf
That the Rw index increases with the frequency of the noise.
But the more the frequency increases the more we are in the treble right?
If it's true, what does that mean? that treble sounds are louder than bass sounds or vice versa?
This is if there is a good soul to enlighten me ...

[Woodcutter]

Apparently, this means that the material tested (Saint Gobain glazing) has optimal performance in terms of weakening around 2000 Hz.

Considering that the audible spectrum must go from qq hundreds of Hz to approximately 15-20 kHz, I think that it is not amazing (or even studied for! )

It does not predict the "strength" of the sounds depending on the frequency ...

On the other hand, the glazing lets more serious sounds through (a size problem?) And to a lesser extent the treble

[bham]

Thank you Lumberjack for this unearthing of subject and for your answer (I see that you make up for your absence ).
In fact I am thinking about buying a roof window and as usual when it comes to finding and / or comparing technical data, the resellers are absent subscribers.
I therefore compare two Velux windows, one with "comfortable" double glazing and one with triple glazing.
Comparison in terms of winter and summer insulation, in terms of brightness and in terms of sound insulation.

[Leo Maximus]

I used to work in an acoustic design office to develop special measurement equipment, especially for performance halls.

Basically the index R is proportional to the product of the mass by the frequency so it is normal that this index increases with the frequency and that it decreases with the latter for a given material per unit area. (See mass law and frequency law)

A double or triple glazing will (acoustically) insulate little if the glazing is thin, it is its mass which especially counts therefore the thickness of the glazing. The space between the panes also plays a role.

Acoustics is a very little known science that makes anyone say anything. It is quite normal for a seller to know that slab. Insulation sellers do not differentiate between thermal insulation and acoustic insulation when it has nothing to do with it.

[Woodcutter]

[...] The sellers of insulation do not make the difference between thermal insulation and acoustic insulation whereas that has nothing to do.

I don't necessarily agree with that ...

[Leo Maximus]

[...] The sellers of insulation do not make the difference between thermal insulation and acoustic insulation whereas that has nothing to do.

I don't necessarily agree with that ...

Disagree with what? Maybe I misspoke. By "salespeople" I meant those from Casto or elsewhere who generally have no training in acoustics.

[Phonotone]

Hello
I read your message and I see that you look all confused.

the curve shown in the acoustic test report corresponds to the acoustic attenuation by frequency band of the product.
as with any material, the acoustic loss increases with frequency. that's normal, physics is like that.
that means that the more you are in the treble, the better the sound insulation.

the easiest way to assess the performance of the window is to look at the RA index, tr. it is the overall sound reduction index compared to a traffic noise. it is on this criterion that you will be able to compare the different windows.
there you have 38 dB it's already very good. it all depends on the ambient noise around you. if you are in the open countryside, it is oversized, unless you do not like to hear outside noises. in an urban environment, it is well suited, unless you give directly onto large infrastructures.

in terms of glazing, you have very good glazing: double acoustic laminate with 20 mm air (or gas) layer.
be aware that the thickness of the air space affects the thermal but not the acoustics.
it is the thickness of the glazing, and the fact that it is laminated or not, which plays on the acoustic performance.

voilà
at your service !

[Phonotone]

Apparently, this means that the material tested (Saint Gobain glazing) has optimal performance in terms of weakening around 2000 Hz.

Considering that the audible spectrum must go from qq hundreds of Hz to approximately 15-20 kHz, I think that it is not amazing (or even studied for! )

It does not predict the "strength" of the sounds depending on the frequency ...

On the other hand, the glazing lets more serious sounds through (a size problem?) And to a lesser extent the treble

be careful, what is tested is a Wicona window door fitted with SGG glazing, and not the glazing itself.
the curve presents a "hole" in low frequencies (125 Hz) and a "bump" in high frequencies: this is completely normal. it is the same for all glazing and all windows.

the French window lets the bass pass more than the treble, but it's physics that wants that. it can not be helped. there is no particular "problem".
but you're right when talking about the size, because the larger the glazing the less efficient it is in sound insulation at low frequencies.

a+

[Leo Maximus]

know that the thickness of the air gap affects thermal but not on acoustics.

It is a fact that we will hardly hear a difference between a 20 mm air space and a 30 mm air space and that the thickness of the glazing will play a more important role. Absolutely. But to say that "the thickness of the air space does not affect the acoustics" is totally wrong, my apologies.

Rather than a long speech, I copied an extract from René Lehmann's “Que-sais-je”: “The acoustics of buildings”. It is the most widely used book on acoustics and is easily found. We can read there: "the average sound insulation index of two identical glass panes, each 2,5 mm thick, is approximately 30 dB when they are very close to each other; it goes to 40 dB if they are separated by an air space of 10 cm and it reaches 50 dB for an air space of 35 cm ..."

[Phonotone]

to say that "the thickness of the air gap does not affect the acoustics" is totally wrong, my apologies.

yes it is sure if you put 10 cm between 2 panes, you will have an acoustic improvement. as much for me.

what was said about common glass frames (or at least those that I know of) and where the spacing goes from 4 or 6 mm to 20 or 24 mm.
in short, a basic 4/6/4 window has the same acoustic performance as a 4/12/4, 4/16/4 or 4/20/4 window.

a+