Hello! New build, question about glass doors

[trillianjedi]

Hi everyone.

I'm in the middle of researching the conversion of my carport in Wiltshire, UK into a practice room for classic 4/5 piece rock and roll with a moderately loud drummer. From reading other members threads on here I'd say we're probably in the 110dB area, but have bought a sound meter which I'll use at next session to find out for sure.

The building is 3 sided with walls made of concrete blocks clad with Cotswold stone (so from the outside it's a nice looking building) and I believe it's good for what I want from a mass point of view. There is a single double glazed window on the rear wall about 3 foot square. Overall dimensions are 19'2 x 17'11 with a ceiling height of 8'. The floor is concrete slab.

Nearest neighbour is about 100 feet away and my objective is to not annoy them when playing with the full band during "normal" hours (we'll stop at, say, 10pm).

As mentioned I'm researching at the moment so haven't made final decisions or ruled anything out, but so far from reading other peoples posts in here about what they've done (incredibly useful) I think I can probably achieve what I need by adding a second leaf to walls and ceiling (probably 15mm gap then timber frame and double plasterboard leaf although I'm still researching this).

That leaves the problem of the fourth wall that doesn't exist yet.

Making this project somewhat complicated is that, for cosmetic/matching reasons, really this fourth wall needs to be made up of two tri-fold glass doors and really that is the core of the question I have behind this post.

The doors I'd be matching to are by a company called SolarLux and model is SL66. I decided to email the manufacturer to see what advice they could offer and they have stated that the standard double-glazed SL66 gives 36dB of sound attenuation in double-glazed form, and 45dB with the triple glazed.

This advice (admittedly I did not ask at which frequencies this is achieved) seems contrary to much of what I've read on here, which is that triple-glazed is usually worse than double-glazed for attenuation due to resonance.

So my key questions are:-

1. Is it possible to get reasonable attenuation with a double-glazed external glass door like this?

2. Am I correct in my understanding from here that triple-glazing is actually likely to make the attenuation worse?

Many thanks for any advice/insight you can give.

[xSpace]

"So my key questions are:-

1. Is it possible to get reasonable attenuation with a double-glazed external glass door like this?

2. Am I correct in my understanding from here that triple-glazing is actually likely to make the attenuation worse?"


1. Not at 110 dB, that would be a specific door with a specific sound isolation property.

2. It will make it worse in the frequency areas that musical range is considered, in the area of human speech it performs but is still over priced for even that.

[trillianjedi]

Many thanks Brien.

I've been doing some further reading through the sticky-d threads on this subject (really interesting) and one thing I'm not quite clear on yet is whether a third leaf at some air gap distance from the other two will make it better (albeit not the most efficient use of materials) or worse.

For example, in the below image, if I put an additional third leaf (of some reasonable mass) at a distance of X" from the double-glazed doors (new leaf in red), would I get some attenuation even if not the most efficient?

If that is the case, is there a way I can calculate what "x" should be ?

The reason for going down this path is, if I have to have the glass doors for planning reasons, I need to explore if I can put in a removable leaf on the inside to achieve a reasonable level of sound-proofing.

Thank you so much for you help.

[trillianjedi]

Sorry, one other thing. I've been reading Soundmans post in this thread here:-

http://www.johnlsayers.com/phpBB2/viewt ... ce#p133889

... about the natural attenuation from distance.

Given my nearest neighbour is about 100ft away (say, 30m), and if I assume an average 4.5dB drop per doubling of distance, my calculations give me about 22.5dB of attenuation over that distance. Does that sound about right?

If my 110dB figure turns out to be correct (I'll be measuring the band this Thursday) then that puts me at about 87.5 dB at the neighbours nearest window.

[Soundman2020]

Hi there "trillianjedi". Welcome!

really this fourth wall needs to be made up of two tri-fold glass doors and really that is the core of the question I have behind this post.

That's a pretty big problem! You aren't the first to want to try this (several other forum members have talked about it), but if you go ahead with it, you'd be the first to actually do that. The issues are rather daunting, and the manufacturer won't tell you about those...

gives 36dB of sound attenuation in double-glazed form, and 45dB with the triple glazed.

I'd take those numbers with a pinch of salt! First, ask what they mean by "45 dB of sound attenuation". Are they talking about an STC-45 rating? Or are they really claiming to get 45 dB of transmission loss across the entire spectrum? Those are two very, very different things. For example, ask them if they will guarantee that when a drummer is playing an acoustical drum kit on one side of the glass, at a measured level of 115 dBC, that the measured level on the other side of the glass will be no higher than 70 dBC. Ask them to put that in writing: I'm guessing that they wont! Because getting 45 dB of transmission loss across the spectrum, from a triple-glazed window that is also moveable... well, lets just say that I'm not a big believer in magic spells nor magical products that appear to defy the laws of physics...

This advice (admittedly I did not ask at which frequencies this is achieved) seems contrary to much of what I've read on here, which is that triple-glazed is usually worse than double-glazed for attenuation due to resonance.

Yup. But do ask the manufacturer in any case, just in case they make their glass from exotically strange materials, and use equally exotic gasses and inter-layers... In fact, just ask them for the actual report from the independent acoustic testing lab where they had their doors tested. If they won't give you that report, or tell you that they tested it in their own labs... well... draw your own conclusions....

1. Is it possible to get reasonable attenuation with a double-glazed external glass door like this?

Possible? Yes. Very hard, very complex, and very expensive to do? Yes.

2. Am I correct in my understanding from here that triple-glazing is actually likely to make the attenuation worse?

For low frequencies, yes. For high frequencies triple can indeed be better, but that really doesn't matter: for studios, all of the big problems are in the low end, below about 500 Hz. That's the hardest part to isolate, and is exactly the area where a 3-leaf system will have lower isolation than a two leaf system, all other factors being equal.

Here's why:

2-leaf-vs-3-leaf.jpg

I'm not quite clear on yet is whether a third leaf at some air gap distance from the other two will make it better (albeit not the most efficient use of materials) or worse.

Well, yes! You can compensate for a triple leaf by increasing the mass on all of the leaves, and increasing the air gaps between them. For optimal isolation with a 3-leaf system, most of the mass must go on the middle leaf (it must have the same mass as the other two leaves combined), and the two air gaps must be the same size. Going from 2-leaf to 3-leaf moves the resonant frequency up by about half an octave, so you have to add enough mass and air space to bring it down again. That implies four times the mass, or four times the total air gap, or some combination of the two.

If that is the case, is there a way I can calculate what "x" should be ?

Here are the equations for calculating the MSM resonant frequencies in both cases:

double-triple-equations-GOOD!!!! f0.jpg

The NRC has a paper on triple glazing that is quite interesting: it is NRCC-22651.

Given my nearest neighbour is about 100ft away (say, 30m), and if I assume an average 4.5dB drop per doubling of distance, my calculations give me about 22.5dB of attenuation over that distance. Does that sound about right?

Well, yeah, but once again "pinch of salt" applies. That's just a rule of thumb, and in the outdoors strange things can happen... such as wind blowing from your place towards their place, or refraction through layers of air with different temperatures, or buildings, trees, and other things that reflect or guide sound in a specific direction.... So the actual level at their place could end up being significantly higher or lower than what is predicted from simple air attenuation. I wouldn't reply on that...

If my 110dB figure turns out to be correct (I'll be measuring the band this Thursday) then that puts me at about 87.5 dB at the neighbours nearest window.

In theory, and "Caveat Emptor", etc... And even so, 88 dBC is pretty darn loud! Assuming you can get 40 dB isolation from your glass A big assumption in itself!), you'd still be at nearly 50 dBC at your neighbors place, with still air on a calm day, and all the stars shining favorably on you... That's still loud, and annoying, for drums...

I'd suggest that you need over 50 dB isolation, aiming for 60. That's hard to do even with well designed walls, but pretty much impossible with commercial triple glazing, no matter how good it is on paper. Thin lass, thin air gaps, and the ability to move those very large panels, make it unlikely in the extreme... You stand a better chance of Santa and the Easter bunny both knocking on your door tonight, to tell you that you won the jackpot in the lottery for every major city in your country, all on the same day....




- Stuart -