[LP1]

I desperately need to replace the Home Depot temporary shades in my listening room with something more appropriate. How important to a room's acoustics are window treatments? Should they absorb, diffuse or both? Is there a preferred material? Thanks.

[Big Red Machine]

Depends on where they are in the room.  They pretty much will reflect no matter where they are, but if at first reflection points then you'll want either some absorption or diffusion at that spot because they will be the ultimate reflector (in a bad way).  I prefer diffusion at the first reflection points and many prefer absorption.  Window treatments will be poor at both when it comes to curtains or blinds.  You might be able to hang a panel over that spot only during listening.

[LP1]

Thanks for the response. You said:

"Window treatments will be poor at both when it comes to curtains or blinds."

Does this mean that I should just choose a window treatment for aesthetic reasons as they won't make a meaningful acoustic impact?

[rbbert]

There are special drapes and/or drape liners sold by acoustics companies, such as msr-inc.com.  They are likely expensive, though.

[JLM]

Diffusion requires varying depths of non-absorbent materials of several inches to be effective down to roughly 1,000 Hz and would be quite heavy. To be effective absorption requires 2 - 4 inches of high density 703 fiberglass or equivalent. Either solution would be constructed as sliding panels. Floyd E Toole recommends not going overboard on treatments (like either of these solutions) as we're used to living/hearing in "normal" rooms.

[jk@home]

I used double layers of fabric cellular shades on the windows (one smaller inner size plus one larger outer size, for some absorption. Not broadband, but better than nothin. Doesn't let in much sunlight, which is OK for this home office/ listening room.

Since both windows also fall into the area needing absorption panels, placed 2 x 4 x 4" 703 panels in front of the windows, where needed.

One of the windows on the back wall butts right into a corner, so I did an inverted bass trap with a 6" panel on the right, 4"er on the left. The 6" panel is secured to the wall, the 4"er is hung onto the 6 with door hinges. It can be unlatched and swiveled over if the window needs to be opened.

[Housteau]

One thing for certain is that each room and set up will be different.  It is hard to say in a generic way which is the best solution.  I suppose a good first step is to find out if in fact you actually have a problem that you can hear and need to deal with.  Just because it may be written somewhere that it is a bad idea to do, or have certain things does not automatically make it so.  I have sometimes  gone in the face of what is thought to be common acoustical wisdom and ended up with very good results.

So, I suggest experimenting with common household materials first for absorption, diffusion and diffraction in the areas you are concerned about.  Take your time and then judge if any of those offer you a better window into your music.  If one does, then you can look more seriously down that path for proper ways to achieve that.

[Hipper]

I agree with Housteau that despite what any of us say only you can tell by experimentation if your windows affect your sound. What to do if they do?

The window in my listening room is on the speaker wall and certainly affected the sound in the traffic noise that came in from outside, and to a lesser extent, reflections. Glass can also resonate at certain frequencies but mine doesn't seem to.

The windows are double glazed but I put in a third set of panes specifically for noise reduction. It has reduced some but not all the really low frequency energy - 50Hz and lower (based on measurements and my ears) - and has also prevented a lot of higher frequency stuff and I think that has added to the detail I can hear in the music.

For reflections I have GIK panels on my back wall that will prevent a lot of energy getting to my ears, and I placed additional moveable panels (with feet) in front of the windows that stop more.