Broadband absorber - difference between cloth and wallpaper?

[Sky]

Hi guys!

I did a search on this but couldn't seem to find anything.

I was just wondering what the differences in acoustic properties would be between cloth (thin cotton)
and wallpaper (thick paper) as the outer layer in a broadband absorber?

Specifically, I plan to cover the ceiling above my mixing position (3x4 meters) with 20-30 cm thick
insulation and cover it with something that is more or less acoustically transparent; I was thinking
either cloth or wallpaper.

The primary goal is to absorb low-mid and bass frequencies, but to some degree I'd like broadband
absorption as well because parts of the area are 1st reflection points.

The reason I'm considering wallpaper is because it would likely be a little easer to mount given its
relative sturdiness, and also I expect the wallpaper to reflect a bit more high frequencies than cloth,
which I think would be a good thing (as long as it doesn't reflect too much).

The question is, how big a difference will it be? I'm quite familiar with the effect of cloth over insulation
but I have never tried wallpaper. Anyone done this?

Thanks!

[Soundman2020]

Good question!

The cloth is pretty transparent to sound at all frequencies, and won't affect the acoustics of your devices much at all, provided that it is "breathable" cloth. Wallpaper, on the other hand, will reflect back some of the high frequencies into the room, so they never reach the underlying absorber. This can be good, since small rooms need a lot of bass trapping, which also sucks out too much of the highs as well, so having a thin membrane of some sort in front of your bass traps can help keep the highs in the room. There's an equation somewhere that tells you where the cutoff point is for the membrane, based on thickness, so you know which frequencies it will reflect and which will get through it.

Specifically, I plan to cover the ceiling above my mixing position (3x4 meters) with 20-30 cm thick
insulation and cover it with something that is more or less acoustically transparent; I was thinking
either cloth or wallpaper.

For your ceiling, you definitely do need to cover it with something for another reason: most types of insulation shed fibers slowly as time goes by, and those fibers are highly abrasive (to equipment) and highly itchy (to people). You don't want them filtering down all over you and your gear over time... better keep them up there, where they belong!

That said, it is better to use a very thin plastic for the ceiling absorption at your first reflection points, so as to NOT reflect too much of the highs back down at your ears! I use that very thin plastic that they sell in hardware stores for use as painter's drop cloth, meant to protect furniture while you are painting. That's all you need to keep the fibers in place, an it does practically nothing at all to highs.

You can use thicker stuff in areas that are not first reflection points. I have never used wallpaper, but I don't see any reason why it wouldn't work.

- Stuart -

[Sky]

That's a great answer, Stuart. Thank you!

About plastic:

I have treated big parts of my walls with insulation covered by a cotton cloth. No plastic.
Would you say that insulation fibers will be able to penetrate the cotton and get into the
room? Should I rip the cloth off and put plastic behind it? Or will the cloth stop most of it?

[Soundman2020]

For walls, you are probably OK with just cloth, but do take a careful look at your floor to see if the insualtion is shedding fibers through the cloth: Vacuum it thoroughly, then check several days later to see if there are any fibers laying on that weren't there before.

However, for ceilings or clouds, I would definitely put plastic on them. Anything overhead definitely needs attention.

- Stuart -

[Sky]

Cool, thanks a lot!