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Diffusion with Wall Shelfs?

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I'm trying to add some diffusion to my room without resorting to putting more acoustic panels which probably aren't too effective at diffusing in the first place. (Something like the Skylines would be too far from being aethetically feasible)
I am wondering if putting up some Wall Shelfs... perhaps spacing them unevenly along the side walls (past first reflection points) with perhaps decorative pieces or picture frames on them would add something to the sound vs a complete bare wall. I understand it might actually add nothing but as long as it doesn't actually make things worse? Any thoughts on this?

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Re: Diffusion with Wall Shelfs? - Bruce B 11:12:27 11/23/04 (0)
are you trying to say "shelves"?
Regards,
Re: Diffusion with Wall Shelfs? - Rob G. 07:28:48 11/18/04 (1)
Go for it! Look at the side balconies of concert halls, which there do the same thing for the room's sonics: diffuse the sound by creating different reflective path lengths.
Four things to pay attention to:
1) Do not make these too deep. If you do, the space becomes a trap, one with very selective absorptive properties. This is one of the reason's why Philadelphia's Academy of Music is so dry and dead sounding -- the sound goes under the too-wide side balconies and never comes back out. In a typical domestic room of, say, 14' to 20' wide, I doubt you'd want to have these shelves more than about a foot deep.
2) Make sure you have enough vertical spacing between each shelf, and don't fill any shelf all the way to the bottom of the shelf above. Again, you need space for the sound to get in, do a bounce or two from the wall to the bottom of the shelf above, and then out again. My guess is that you want 5" or more between the stuff on the shelf ad the bottom of the shelf above.
3) As with diffusion panels like RPG's Skylines, you want to have stuff of substantially staggered depth on the shelves, not a solid line of books or records.
4) Your shelves do not need to be wall mounted to achieve the desired diffusive effect: free-standing shelving will do this as well (whether open- or closed-back).
In concert halls, you want all surfaces as massive and rigid as possible, to retain acoustical energy within the room. There are differing opinions as to rooms for reproduction, with some advocating absorption and others for rigid, reflective surfaces. Typical American "baloon frame" home construction is inherently absorptive, but most concert halls and custom recording studios start with a very massive, rigid structure (primarily for isolation from outside sound). For most of us, we're stuck with what we've got.
You say "past the first reflection point." Of course, it would be ideal to have a room wide enough that first side-wall reflections arrive at the listener's ears AFTER the (???) 5 millisecond (can't remember the correct timing) window where reflections would be perceived as part of the original sound (the Haas precedence effect, we perceive the sound to be coming from the first, loudest source). But whenever this first sidewall reflection arrives, I cannot imagine a situation where diffusing the arrival times of these reflections would not improve the clarity of the reproduced sound.
Rob Gold
- Re: Diffusion with Wall Shelfs? - Howie 12:48:39 11/25/04 (0)
  Thanks for the response. Although now I'm thinking of not doing it since having it on both sides to balance things out might a little bit ugly.

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