Secondary glazing + double glazing: sound insulation?

[SteamyTea]

When I lived in France (1970's) a 14 year old on a Vespa was the main problem.  Cheese wire string across the street at neck height was suggested at one stage by our French neighbour.

[Gone West]

8 minutes ago, SteamyTea said:

Cheese wire string across the street at neck height was suggested

When I was a teenager cycling over to my mates at Barming, the gypsies used to string barbed wire across the lane at North Pole Woods. Fortunately I had been warned.

[SteamyTea]

2 minutes ago, Gone West said:

When I was a teenager cycling over to my mates at Barming, the gypsies used to string barbed wire across the lane at North Pole Woods. Fortunately I had been warned.

There was a case of wire across the cycle path in Milton Keynes about a decade ago.

Think there was a Sherlock Holmes story about it as well "The Ordinary Bicycle".

[Garald]

Seriously, the thing that irritates me most is the motorbikes going loudly by in the evening. No doubt delivery men earning an honest living delivering Uber eats to the tired and/or lazy, but still. A cavity between windows tuned at 60Hz sounds like a wonderful way to turn that into a silent movie.

[SteamyTea]

1 hour ago, Garald said:

A cavity between windows tuned at 60Hz sounds like a wonderful way to turn that into a silent movie.

A single cylinder 4 stoke engine has 1 power stroke per 2 revolutions of the crankshaft.

Never known anyone to stay below 7200 RPM.

 

Still, come 2035 there will not be any new ICE machines on our roads, just the old noisy ones left.

 

 

[joe90]

Thinking outside the box…….https://www.moondreamwebstore.co.uk/sound-insulation-curtain-86?gclid=EAIaIQobChMImOKru46KggMVgevtCh39hwN4EAAYAiAAEgJo9PD_BwE

[Garald]

2 hours ago, SteamyTea said:

A single cylinder 4 stoke engine has 1 power stroke per 2 revolutions of the crankshaft.

Never known anyone to stay below 7200 RPM.

 

Wait, that means >= 60Hz. So, a big nice thick space with a resonance frequency under 60Hz would be great, no?

 

2 hours ago, joe90 said:

Thinking outside the box…….https://www.moondreamwebstore.co.uk/sound-insulation-curtain-86?gclid=EAIaIQobChMImOKru46KggMVgevtCh39hwN4EAAYAiAAEgJo9PD_BwE

I have one of that exact same brand, to put over the door. People who have them for sound insulation purposes seem to be often a bit disappointed - and of course they work for sound only when they are drawn!

 

Still, they could add a finishing touch - but I have a William Morris habit.

 

 

[Garald]

Incidentally, how do you determine whether condensation could form between two windows? I know there's the U-Wert website, but I want to know the principle.

[RobLe]

8 minutes ago, Garald said:

Incidentally, how do you determine whether condensation could form between two windows? I know there's the U-Wert website, but I want to know the principle.

Double glazing should have a dry inert atmosphere in the gap.  

Secondary glazing is best I think with an air gap which ideally comprises of outside air.  It's not generally done this way - 2ndary is normally aftermarket added onto the inside, so likely to dominantly have high absolute humidity indoor air in the gap that may condense on the outer pane in winter.  So it will suffer less from condensation if the original windows are a bit leaky, and the new added 2ndary stuff is well fitting.

 

 

[Garald]

1 hour ago, RobLe said:

Double glazing should have a dry inert atmosphere in the gap.  

Secondary glazing is best I think with an air gap which ideally comprises of outside air.  It's not generally done this way - 2ndary is normally aftermarket added onto the inside, so likely to dominantly have high absolute humidity indoor air in the gap that may condense on the outer pane in winter.  So it will suffer less from condensation if the original windows are a bit leaky, and the new added 2ndary stuff is well fitting.

 

 

My windows are new and pretty high-grade. This is actually an argument in favor of letting the secondary window be double-glazed: if both windows have about the same R, then the air in the middle will be at the average of the temperatures of inside and outside air (so it will stabilize at 5 C when it's -10 C outside and 20 C inside).

[SteamyTea]

2 hours ago, Garald said:

so it will stabilize at 5 C when it's -10 C outside and 20 C inside

Well apart from the edge losses, and radiation losses. Though they are generally quite small.

 

You can calculate the dew point from the temperature, relative humidity and air pressure quite well.

But for these purposes then this will do.

https://www.calculator.net/dew-point-calculator.html

 

I think it uses:

Td = T - ((100 - RH)/5.)

where Td is dew point temperature (in degrees Celsius), T is observed temperature (in degrees Celsius), and RH is relative humidity (in percent).

[Garald]

Returning to the main issue - 

 

- determining the resonance frequencies is an extremely nice bit of 19th century mathematics. Bottom line - yes, the main resonance frequency is about 85 Hz ( = speed of sound/(2*2m)).

- I'm trying to learn whether there's a simplified model that can roughly predict how much an improvement I can get.

- I'm starting to suspect that I'll end up having to use double glazing for the secondary window, simply because there isn't any simple glazing in the market, at least not here in France (where secondary windows seem to be near unknown). It would seem that an ordinary double-glazing window of the kind I'd need (four panes, 2mx2m) is a bit under 1000eur, which is not really different from the one quote for secondary glazing of that size I saw from a UK source. A stiff price but not the end of the world. Whether double glazing is better than single glazing (of the same total thickness or the same total mass) - no idea. Probably not, in this context? Or does the fact that there's argon (say) rather than air between the two panes still help a bit?

- Should I put *something* between the primary and secondary glazing - should I cover the borders in some way, say? Is there anything that would fit in 16cm-20cm that could help with that 85Hz dip, or with anything else for that matter?

 

Edited October 23, 2023 by Garald

[SteamyTea]

47 minutes ago, Garald said:

I'm trying to learn whether there's a simplified model that can roughly predict how much an improvement I can get.

Isn't it simple harmonic motion.

Punch in the material parameters i.e. mass, density, flex modulus, and the answer should come out,

I actually missed the lecture about sound waves when at university (had to see the eye surgeon about my cataracts), so when I read the notes I seem to remember that because the ends are attached to a non moving part, they are modelled like a piano string i.e. only full or half waves allowed.

[Garald]

19 minutes ago, SteamyTea said:

Isn't it simple harmonic motion.

Punch in the material parameters i.e. mass, density, flex modulus, and the answer should come out,

I actually missed the lecture about sound waves when at university (had to see the eye surgeon about my cataracts), so when I read the notes I seem to remember that because the ends are attached to a non moving part, they are modelled like a piano string i.e. only full or half waves allowed.

Really? I think it's a bit more complicated. Took a course on waves back in the day, based on Vol. 3 of the Berkeley Physics Course, but we didn't cover all of it; time to review. A glance makes me think I'll find it less readable than if it assumed *more* mathematics. Maybe there's something in Feynman.

What you do get from the model you say is the resonance frequencies. It's not just like a piano string because the window cavity is three-dimensional, rather than one-dimensional - but yes, the "main" resonance frequency in a 2mx2mx16cm window cavity is the same as for a 2m-long piano string. But then you also have a resonance frequency (probably much muddier and hence less important in practice) that would correspond to a 2/sqrt(2) = 1.412... m-long piano string. The reason is basically that

 

sin(x) sin(y) = (cos(x+y) - cos(x-y))/2

 

and cos(x+y) = 0 both when (x,y)=(pi/4,pi/4) and when (x,y)=(-pi/4,-pi/4), and those points are at distance pi/sqrt(2) from each other. In comparison, the resonance frequency from the 2m-long piano string is due to sin(pi)=sin(0)=0, but pi and 0 are of course at distance pi from each other. So, a distance pi/sqrt(2) corresponds to a (2 m)/sqrt(2)-long piano string.

[SteamyTea]

7 hours ago, Garald said:

sin(x) sin(y) = (cos(x+y) - cos(x-y))/2

Shall have a look here when I have time.

https://math.libretexts.org/Courses/Rio_Hondo/Math_175%3A_Plane_Trigonometry/02%3A_Graphing_Trigonometric_Functions/2.04%3A_Transformations_Sine_and_Cosine_Functions

7 hours ago, Garald said:

Maybe there's something in Feynman

Surely your Joking!

[Garald]

36 minutes ago, SteamyTea said:

Shall have a look here when I have time.

https://math.libretexts.org/Courses/Rio_Hondo/Math_175%3A_Plane_Trigonometry/02%3A_Graphing_Trigonometric_Functions/2.04%3A_Transformations_Sine_and_Cosine_Functions

 

Or you can just remember that cos(x) = (exp(i x) + exp(-ix))/2 and sin(x) = (exp(i x) - exp(-i x))/(2i), and derive everything from that.

[SteamyTea]

33 minutes ago, Garald said:

 

Or you can just remember that cos(x) = (exp(i x) + exp(-ix))/2 and sin(x) = (exp(i x) - exp(-i x))/(2i), and derive everything from that.

Gets a bit slippery down the natural log

[Temp]

Some interesting info at this page. Particularly the notes about using different thicknesses of glass. Sadly no figures for the combination of double and secondary. Perhaps ask them?

 

https://www.kjmgroup.co.uk/products/windows/soundproofing#:~:text=The best sound reducing gap,or external) is not important.

 

Quote

There is a fourth option, is a combination of the above....Replacing both the outer window with good quality, tight fitting double or triple glazing and then add secondary glazing as well. This is the ultimate soundproofing for windows but the most costly of course!