Garald

My guess is that "3626391/24" codes some valuable information in a compact way. Unfortunately the code seems country-specific: Saint-Gobain glass made in France uses one code, Saint-Gobain glass made in Poland uses another code. I thought perhaps someone here could play Sherlock better than I can. It turns out that "JAR" stands for "Jaroszowiec" - more specifically, "Saint-Gobain Glassolutions Jaroszowiec". I've written to them - I'll call on Monday.

I'm getting conflicting information about what kind of double glazing was really installed at my place, and wish to get to the bottom of the matter. There's a code stamped in between the window panes. It reads "SAINT-GOBAIN GL JAR 28/11/22 SGG Climaplus 295x1782 3626391/24 PLASTBUD SP. Z 0. 0" for the fixed panes and "SAINT-GOBAIN GL JAR 28/11/22 SGG Climaplus 387x1782 3626391/25 PLASTBUD SP. Z 0. 0" for the panes in the middle (which do open). Here 28/11/22 is obviously the date of manufacturing, whereas 295x1782 and 387x1782 are the dimensions. But what can one deduce from the rest of the string? In particular, what do I learn there about the thickness of the different panes of glass, the width of the space between them, the dB rating, etc.? (It may also be the case that one can deduce from the above that the glass was manufactured for Saint-Gobain somewhere in Poland; if so, that's completely unsurprising - the contractor is Polish. Now I know, for instance, that one can get Polish paint in specific colors from the Farrow Ball catalogue, such as "Winsome Persimmon" and what have you. But that's another story.)

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.

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.

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?

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).

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.

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

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.

Everything is closing properly; these are new windows and new window-frames. (Well, at one point one window wasn't closing properly because we had not closed it right after opening it fully, and we could really notice the difference.) Don't get me wrong - these are good windows. All the same, it's a first story right in front of a busy two-lane street.

Right, that's one of the possibilities I was mentioning. I'm a bit alarmed at how skeptical people at https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing seem to be - are they right, or are they just not getting that we are talking about two separate window frames?

There's also the question of how to design the secondary glazing so that I can still open my existing windows (which open towards the inside, both "à la française" (like a book) and by tilting; let's call this combined operation "the German way"). I was just asking in a French site, and someone was saying that sliding windows wouldn't do - the rail would get on the way. (Perhaps window rails are thick in France?) Is the only option to have windows that open in the same way as my existing windows - be it in exactly the same way (four panels, side panels fixed, middle panels opening in the German way) or else having two large panels, both opening in the French way?

The conversation in https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing is getting interested; people seem skeptical.

Applied people care an enormous lot about algorithms. Admittedly they care about practice performance rather than just about asymptotic complexity. And believe me, applied math can get complicated. If anything, it's pure mathematicians who find unnecessary complications (and decimal points) unaesthetic. There's also a lot of crossover - said applied friend keeps telling me about applications of my field to his.

Hey. On the other hand, this mathematician does not have a sheet of clear plastic at hand - he'll have to get one. And that opinion came from an *engineering* stack exchange! The applied-maths friend I talked to liked the idea of secondary glazing.

Someone here https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing seems to be implying that the additional sound reduction would be of only 2dB, which is very little indeed. Is that correct? Or are there effects that they are neglecting? I suppose much of it depends on whether the secondary glazing is airtight?

That does look very nice (and inexpensive). I don't have manual DIY skills I know of, so I guess I'll have to order a kit and install it together with the contractor and his guys. What CAD do you use, by the way? I've been using OpenSCAD, since, at the same time that it's free, it is much programmer-friendly than the supposedly "user-friendly" free software I've been able to find.

We are talking about a 160mm-200mm gap - this should be OK for sound, no? I don't know whether an air layer that deep is 3/4 as good or 1/10 as good as a 30mm-deep layer (I'm getting contradictory information), but that's a secondary consideration - my energy rating is very good, it's the noise from the street that still bothers me (particularly when I sit close to the window, and particularly in the higher frequencies: I simply dislike the sound of motorbikes).

That sounds very encouraging. I can look into that; I got a reasonable-looking quote from a place called Clearview. I am based in the Paris area, though, so I'd much rather find a EU-based manufacturer. Brexit shafts us again.

Thanks, though that does not seem to be made for Linux-based folk...

Where can I find information on the dB reduction (on top of that provided by double glazing) I am likely to get in the following scenario? Existing acoustic double glazing + thick layer of air (windowsill created by insulation!), between 16cm and 20cm + secondary glazing (single) This was a solution proposed in another thread: Calculating the effect on heat insulation is probably simpler: just add the R of the secondary glazing itself (poor, like any single glazing) and the R of the air laye (skimming https://www.wufi-wiki.com/mediawiki/index.php/Details:AirLayers suggests it's only a bit worse than a 3-5cm thick layer (R<0.16); is this right?).

I'm really looking forward to seeing it.

Right - the switch on the side (which controls the awnings) is further out than the handle anyhow. Asked my applied friend - the fact that we'd have a space of at least 16cm between the two frames (because of the switch) should not be a problem; it just means that the entire thing will be "tuned" lower than usual (its resonance frequency will be lower) - it's hard to see how that is a bad thing.

There's 3.3cm - just measured it. The current windows open just fine.

They are an option, in that we are not talking about sun protection during the summer (the awnings take care of that). But would they have better sound-insulation properties than outside shutters? I suppose secondary glazing amounts to internal shutters with the extra property of transparence.