Will painting an acoustic panel lower absorbency?

I would venture to say that painting the panels would lower and alter their absorbency.

I would HIGHLY suggest reading Jon Risch's website regarding the sound dampening panels that he designed. To briefly summarize his suggestions, you should take and cover those panels in Dacron i.e. polyester batting used for pillows and comforters and then cover that in Burlap. Burlap can be dyed to any color that you like and will not lower the efficiency. One could even weave, sew or dye patterns into the burlap so long as only cloth or stain was used ( no paint ). Sean
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http://www.geocities.com/jonrisch/index.htm

Hi J:
Hi Sean
Nice question.

Have to agree with Sean on this one. Make no claims of any expertise but will pass on a couple things. F. Alton Everest makes the following statement about mid/high frequency absorption.

“ The absorption efficiency of materials depending on the trapping and dissipating of sound energy in tiny pores can be seriously impaired if the surface pores are filled so that penetration is limited. Course concrete block, for example, has many such pores and is a fair absorber of sound. Painting that block fills the surface pores and greatly reduces sound penetration, and thus absorption. However, if spray painted with a non-bridging paint, the absorption may be reduced very modestly. Acoustical tile painted at the factory minimizes the problem of reduced absorption. Under certain conditions a painted surface can reduce porosity but act as a diaphragm that might actually become a fair absorber on a different principle, that of a damped vibrating diaphragm.” (Everest, Master Handbook of Acoustics, p 189)

He makes no mention of paint in his short section on fiberglass panels. He does however say, “semi rigid boards of glass fiber do not excel cosmetically, hence they are usually covered with fabric.” (p190) He does not say to paint them.

From this I conclude that he has no problem with paint as such. If he did wouldn’t we all be in trouble. However, it becomes a problem if your rigid panels depend “on the trapping and dissipating of sound energy in tiny pores.”

A short piece from an acoustics supply site I used before reads:

“7: Painting over sound absorbers. Many high-frequency sound absorbers work as a function of their surface porosity. It is intuitively apparent that compressed fiberglass panels and cellulose fiber coatings work in this way and few people would question the fact that these surfaces should not be painted. Not so obvious (judging by the number of people that paint them) is the fact that suspended lay-in acoustic tile, acoustic plaster and concrete block should likewise not be painted. The miniscule pores in each of these materials allows sound to be absorbed into the material, changing sound energy to heat. Painting tends to close up these pores so that absorption cannot proceed. Actually, these surfaces can be painted but only with thinned, water-based paint and by those with enough experience to predict the result.”
http://www.wconline.com/CDA/ArticleInformation/features/BNP__Features__Item/0,3299,16422,00.html

Both tend to say the same thing. Possible, but a touchy proposition. If you do it thin the paint and use a sprayer.

Rives posts here lately. He is an acoustics professional and maybe he can add something.

I remain,

Thanks Sean and Clueless for your responses. I will read with great interest the links you provided, but the information you have already provided in your answers has convinced me to go in the direction I originally planned, which is to remove each panel, cover it with fabric, and reinstall.

I really appreciate your help.