Glass window between control room / live room

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djgc

New member
I was wondering if the glass HAS to be tilted at an angle to treat the reflection of sound or can it just be straight where I can just put some absorbing material behind myself to absorb the reflections?
 
I was wondering if the glass HAS to be tilted at an angle to treat the reflection of sound or can it just be straight
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It depends on a few things. The thickness of the wall assembly(ie..single or double wall) the glass thickness and your skills. But usually, for home studios...straight is just fine. Lots of Pro studios have tilted glass. However, these panes are usually HUGE and can reflect a large wavefront. And in those cases, the whole wall is a massive diffuser... Like this...

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How deep are your pockets:D



On the other hand, many Pro studios have straight panes. I think its a discretionary decision by the designers depending on their point of view...of which there are MANY conflicts of opinion and "schools of thought".:rolleyes:

where I can just put some absorbing material behind myself to absorb the reflections?
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If you are between the glass and the absorber behind you...how would the absorber prevent the reflected sound from reaching your ears first?:D

Anyway, thats my .02 for what its worth.
fitZ:)
 
RICK FITZPATRICK said:
If you are between the glass and the absorber behind you...how would the absorber prevent the reflected sound from reaching your ears first?:D
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oh ya true that :P

well the gap between my control room and live room is about 10inch thick.
between is rock wool insulation and both sides have 2 layers of drywall.

So i will be installing 2 glasses in total. One on each end of the room. I forgot the thickness of the glasses but its fairly thick enough to soundproof.

I'm trying to make a semi pro studio =p well as pro as it can get hahaha. :D
 
The glass is slanted to to prevent (or try to) standing waves between the panes to keep the glass from vibrating.
Also, two different thickness panes can help with this.
 
So i will be installing 2 glasses in total. One on each end of the room.
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One on each end of the room? Or do you mean on each SIDE of the partition wall?

I forgot the thickness of the glasses but its fairly thick enough to soundproof
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"Fairly thick enough" means nothing. What tells you this is fact. This is why.

Personally, I'd be more concerned with the window becoming a "weak link" in the wall assembly. Rod Gervais(author of Home Recording Studio Build it Like the Pro's..and member here) told me recently that it takes ONE pane of THREE QUARTER INCH glass, and ONE pane of HALF INCH thick glass to equal the Transmission loss of a TWO LEAF wall assembly with 2 layers of 5/8" drywall on each leaf.
Furthermore, let me quote contridicting opinions from here:

http://www.acousticalsurfaces.com/acoustic_windows/acoustical_windows.htm?d=40

What you will also notice however is that the panes are all set at different angles, and none are vertical. Surely there has to be a good reason for this?

One possible reason is that somehow it improves the sound isolation capabilities of the window. The theory is that there could be standing waves between the glass caused by the direct reflection back and forth. However, BBC research has shown that there is virtually no advantage of angling the panes with respect to sound isolation.

The difference it does make however is in the control room and recording areas individually. Flat surfaces are always acoustically disastrous as they cause strong reflections that are not dispersed. And of course windows are always flat, and tend to be large. So it is in fact a good idea to consider where this reflection is going, and preferably the outer panes will be angled so that sound is reflected towards absorbent or diffusing acoustic treatment.

Also there is a purely visual aspect. Vertical panes create light reflections that travel directly back to whoever is looking through the window. And three thick panes mean there are six surfaces where reflections will occur. So the seeing through a window with three thick, vertical panes is not exactly clear. But if the panes are angled, then the light reflections are directed away from the observer. Consequently the view can be almost as clear as if the panes were not there.

So, angling the panes does not affect sound proofing, but for both acoustic and light reflections it is very worthwhile.
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And from here:
This article was published on February 6, 2006
From GreenGlue
Studio Control Room WindowThis is a hotly debated topic, with several points being debated by experts everywhere. These include questions of expensive laminated glass –vs.– lower cost conventional glass, angling of one side of the window to reduce standing waves between the panes, and general questions of what criteria should be targeted to maintain the performance of the walls. Let’s look at the factual side of each of these points one at a time.

Angled windows or straight? Many sources recommend angling one of the window panes to eliminate internal standing waves and/or to reduce direct reflections from the window.


We can’t help you with the question of acoustics and reflections, but we can offer this certainty: while the angled window may help somewhat with standing waves inside the air cavity, standing waves will still occur. And angling the window will always result in a smaller net air space, which will have a negative effect on low frequency performance. How much of a negative effect depends on how much of the net air volume between the panes of glass is lost. Depending upon how much low frequency content is present in the music, it is very likely that the isolation of a window will be maximized without angled glass.
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Like I said..take your pick.:D
 
To me the whole thing of having a control room with glass looking out on the talent is so old. Why are you doing this at all?
 
guido #2 said:
The glass is slanted to to prevent (or try to) standing waves between the panes to keep the glass from vibrating.
Also, two different thickness panes can help with this.
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This is a myth.

The angling of glass is only to prevent the endless mirror effect between the glass - for light reflection. It does not reduce comb filtering for micing close to the glass. It does not prevent any standing waves (VERY similar to slanting walls in a studio).

One thing slanting the glass does is effect the transmission loss. It makes it worse.

Two different thickness are excellent and recommended for best TL.

Cheers,
John

ps. I use a very slight angle in my designs to prevent annoying light reflections which does not affect the TL.
 
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My studio window has in fact been in 3 different studios over 15 years, we moved it each time frame and all. When I first built it all I could afford was one sheet of 5 mm and one sheet of 6 mm. While the thicker the better this is all I could afford. The frame is set up with one pane sloping as I also was told that it broke up standing waves. The frames are completely independent, one in each wall frame, with sound absorber between the fames (inside) to soak up and sound that gets between the fames.

How good does it work? If there is a full on rock band on one side (recording room) and we close the doors to the corridor, you can only hear a very slight bottom end from the bass, and I believe this is more through the floor than the glass, and I mean they are playing loud (coz we can't get our sound unless we are loud man! sigh) If someone shouts as loud as they can in the recording room you cannot hear them in the control room and vice versa.

This is just a guide line, if you can get thicker then do so, but it's also in the frame design and wall design.

Cheers
Alan
 
Alan,
That's a pretty good window - especially with the separate frames.. well done.

Glass thickness should not be determined arbitrarily -- a tempered or laminated (safety) glass of 8mm thickness will have the same mass as a frame wall with two layers of 15mm gypsum board. If your walls are constructed using a total mass of 30mm gypsum board per side, you should use at least 8mm thick glass per side. -- Also, to minimize resonance dips in the TL, glass thickness should be different in each piece. Ie; 8mm on side & 10mm the other.
These are minimum thicknesses for matching the mass of the wall mentioned above, otherwise the window will lower the effective TL of the isolation wall, being the weak link.

Air gap then comes into play with the 'system'. By tilting the glass the air gap is reduced, reducing the effective isolation.

Cheers,
John
 
Thanks John,

I should also have pointed out that the internal distance between the glass is about 8" at the narrowest point, as I have seen some with a gap of only an inch or 2 and I don't believe this is as effective.

Cheers

Alan.
 
witzendoz said:
Thanks John,

I should also have pointed out that the internal distance between the glass is about 8" at the narrowest point, as I have seen some with a gap of only an inch or 2 and I don't believe this is as effective.

Cheers

Alan.
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8" is brilliant... at that point you can 'tilt away' without worry. :D
comparing the exact same window with 8" airspace vs 2" airspace... there would probably be as much as 12db difference in TL and possibly more. :)

Cheers,
John
 
guido #2 said:
The glass is slanted to to prevent (or try to) standing waves between the panes to keep the glass from vibrating.
Also, two different thickness panes can help with this.
Click to expand...

This is not correct - there is NO acoustic advantage to slanting the glass....... in fact there is a distinct disadvantage - that of a slight reduction in TL value due to a smaller "air spring" between the panes of glass.

Let's see - an 8" air space would (at half the wavelength) support a wave of about 830.61Hz, that's a G#5th....... hardly a low enough frequency to set up a "standing wave" capable of resonating the glazing........

If that could make the glass resonate then you have hell to pay with that glass when it comes to true modal activity from low frequencies in the tracking room (assuming that you deal with all the issues in the control room).........

The fact of the matter is that this is primarily an issue with architectural preference.... it may offer some reduction in mid and high frequency reflections off that wall towards the desk - if the angle is enough to reflect into the back of the desk, and it definitely offers some benefit from the fact that it will not reflect light directly back into your eyes..... but that is it........

Maximum isolation exists with parallel frames -

differing glass thickness is a totally separate thing - the thinnest piece of glazing should be at minimum (for standard annealed glass) the same mass as the mass in your wall - and then increase glass thickness by 1/4" to introduce an assembly that has different resonant characters as well as different ranges of coincidence - which will help to maxamize your isolation.

Then - strictly because of the added mass in the window (over and above the mass of the adjoining wall surfaces) - the loss in isolation due to tilting the glass becomes a moot point........

Rod
 
Regardless of wether the angle helps with the sound isolation, I also thought that angling the glass helps with the actual room acoustic as you don't have a large reflective surface parallel to the wall. The angle of the glass will act as a defuser.

Cheers
Alan.
 
RICK FITZPATRICK said:
Furthermore, let me quote contridicting opinions from here:
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Rick -

With all due respect,

I am not seeing a conflict between the 2 - they both note no acoustical advantage to tilting the glass......

The BBC paper (which I could not find at the link you provided) states that there is no advantage - they did not state that there is no disadvantage........

They both tear apart the crap about this stopping standing waves - the BBC makes a judgment call (most probably based on the same outlook I have - which is that (in studio construction) by the time you are done dealing with the amount of mass in these windows the tilt becomes meaningless at the end of the day......

The Green Glue engineer (you know who he is) takes the stand of an engineer - a MSM system has maximum isolation with maximum spring.

Physically the moment you begin to reduce the spring you begin to reduce the TL value of the assembly..... this is not open for debate - it is a scientific fact - it is physically measurable -

He did not make a statement as to the degree of isolation lost - nor to the effectiveness of the assembly due to the loss in TL value - he simply noted a fact......

It doesn't matter if the loss only equaled .0000009 dB in one particular frequency...... that is a loss in TL........ it would be (however) meaningless for all practical purposes.......

I see the 2 as being in agreement with one another...

Rod
 
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