John Sayers' Recording Studio Design Forum Archive

I was wondering about windows and how they affect the sound in a studio.

I know they absorb some sound but how much of the sound passes through?

At what frequency do the waves get reflected, which ones pass through? I suspect the highs mostly get reflected and then at some point around 500hz perhaps they start to just bypass the window all together.

How do curtains effect this? Do you simply add their absorption coefficient to that of the windows to see what is absorbed and the rest either passes through or is reflected.

Has there been any studies of this?

Depends greatly on the window you're talking about. higher frequencies are going to bounce off back in to the room, some specific frequencies are going to excite the glass into moving a little, which basically absorbs some of the sound energy (and transmits some out the back end), and some are going to mow right through fairly efficiently.

The thickness, size, and bracing of the glass, the number of panes, and the amount of air in between panes will be a huge determining factor as to what frequencies do which. Not to mention what the wall and window frame transfer, and the effectiveness of the seals if the windows are openable.

The curtains will be another matter, and will absorb some as well- what *they* absorb will be determined by the density/weave and thickness of the material, how densely it's draped/hung, and how far off the window it is. In general, I think that the lower cut off point for the curtains' effectiveness will still be higher than the lowest frequency that the window can reflect back efficiently, so you're really talking about two unrelated effects in different frequency ranges.

lex wrote:I was wondering about windows and how they affect the sound in a studio.

I know they absorb some sound but how much of the sound passes through?

At what frequency do the waves get reflected, which ones pass through? I suspect the highs mostly get reflected and then at some point around 500hz perhaps they start to just bypass the window all together.

How do curtains effect this? Do you simply add their absorption coefficient to that of the windows to see what is absorbed and the rest either passes through or is reflected.

Has there been any studies of this?

Thanks Jon.

These windows are very thin (about 2mm I would guess) with a large air gap of about 2 cm in between. I was thinking the air gap would be beneficial. I'm not exactly sure if the sound get's reflected more or absorbed more as a consequence. If it was thick non reflective material I would say absorbed, but what about windows? Each window is about 2'x5'.

These would be medium density curtains I figure. Medium density with wavy folds. With curtains in front you are absorbing the highs and eliminating the frequencies the windows would reflect back in to the room. At what point does this not work? That's what I'm getting at. What gets reflected back in, what goes out?

The windows face out into the street so they're not internal.

From a practical standpoint, what type of window complements studio work?

With the right type of window and curtain could you potentially reach full absorption (counting those that bypass as absorbed)? On the other hand, are there drawbacks like sound coming in from the outside easier?

Well, the 'right type of window' for full absorption would be easy- a hole in the wall with no glass! Everything would just leave and not come back.

Little problem of sound transmission, though.

Here's my oversimplified understanding. In the very high end, sound hits glass with not enough energy to excite the glass itself much, and bounces back into the room. As you move more into the mids, the glass starts moving a bit, transmitting sound to the other side. This gets more and more pronounced as you get lower and lower (ignoring resonant frequency of the glass for now), and at some point, the glass is basically ineffective at keeping any sound in or out.

The thicker the glass, the lower frequencies it can effectively block.

Some of the energy gets absorbed just by moving the glass back and forth, which is why panel traps work.

If you've got an air gap and two panes of glass in there, the air acts as a spring, compressing and contracting, and basically making the transmission of energy from one pane of glass to the other fairly inefficient, further attenuating the sound. The wider the air gap, the more effective the spring (intuitively, there must be a point where this either gets worse or stops getting better, but I don't think it's a practical distance anyway).

The thicker the glass, though, the lower the frequencies it will just bounce back, as it takes more energy to move the glass. So, the more effective you want your windows to be in the low end, the bigger the absorption you're going to have to put in front of them to absorb what's bouncing off.

With fairly thin glass, and decently thick curtains, you're probably ok, as the glass is just going to let most of what the curtains can't absorb straight outside anyway. You're just going to hear outside noises as well.

That was a good explanation, thank you.