Dampening echoes with slats
June 20, 2021 6:46 PM   Subscribe

The library at University of Portland has vertical wooden slats on the walls. I'm told they're to help keep it quiet and minimize echoes. I'd like to make a panel of similar slats for my parents, whose house is new and very echo-prone. Does spacing of the slats matter? Can they be horizontal instead of vertical? Are there other design considerations I should take into account?
posted by sibilatorix to Science & Nature (13 answers total) 6 users marked this as a favorite
If you Google "acoustic wall slats", you can find many vendors and installation photos. The good news is that the direction of the slats seems irrelevant, but the bad news is that the product seems like wood veneer slats mounted on panels of sound absorbing material. This means that putting solid wood slats on a wall seems unlikely to have similar sound absorbing properties.

Brand new houses often echo because they haven't been furnished yet. Bare walls and floors reflect sound while rugs and upholstered furniture absorb it. One reason that acoustic panels tend to be a commercial product is that large commercial spaces don't have as much soft furniture per square foot. Is there a chance that this problem will resolve itself with furnishings? If I were in your position, I would prefer to spend an equivalent amount of money on rugs and sofas compared to acoustic panels.
posted by goingonit at 7:12 PM on June 20, 2021 [4 favorites]

The geometry does matter, but unless you want to spend the next few years getting up to speed on acoustics math [IME, most of which is just a black box anyway] a general "rule of thumb" (because I have seen this exact geometry in a couple different acoustics products from different companies) would be wood slats being 0.5" deep, 1" wide, with a backing of 3/8" acoustic felt.

...however, note that I have not had to personally purchase and use these products, so I cannot speak to their effectiveness. I just got snail-mail spam on them, and noticed that they were the exact same geometry. These will not have much effect on transmitting sound to adjacent spaces, they're just about damping echo within a space.

Another geometry I've seen a lot is 1" deep by 1" wide with 1" slots (again, felt backing) and 45mm wide slats, 20-25mm deep, with 25mm gaps (also, felt backing. Makes me suspect the felt is the real worker here, and the wood is just for appearance).
posted by aramaic at 7:15 PM on June 20, 2021

Response by poster: Huh. Well, some of the slats at the UP library have no backing, but that photo led me to the manufacturer's product page, which says "The Cross Piece Grille can enhance acoustics via sound absorbing material placed over open reveals within the T-Bar grid. Insulation is typically provided locally." So I guess any acoustic benefit probably has nothing to do with the slats themselves. Drat! Back to the drawing board...
posted by sibilatorix at 8:23 PM on June 20, 2021 [1 favorite]

Another rule of thumb is that any acoustic panel weight at least 20Kg per square metre (with a open panel I'd tend to go heavier again as too light panels just make things worse).

There are (very compact) innovations using metamaterials but none I know of at room-scale yet (more at freeway scale).

I used to fit acoustic baffling inside boat engine compartments and the product was a sandwich of foam(to the outside)+leadsheet + polymer sheet.
posted by unearthed at 8:41 PM on June 20, 2021 [1 favorite]

Wooden slats don't do a whole lot to dampen sound. Breaking up a smooth reflective surface will have some effect but the wood may be more sound reflective than gypsum board. You need something that can actually absorb the sound in a way that wood can't.
posted by Candleman at 9:01 PM on June 20, 2021 [1 favorite]

posted by flimflam at 9:38 PM on June 20, 2021 [1 favorite]

Wood slats by itself doesn't help much. You really need acoustic foam. You can put a panel on TOP of it for decoration as long as they are acoustically transparent. There are a ton of different articles about making your own, as others linked.

I would also just walk into your local music equipment store and see if they have any ideas, and sometimes, DIY stores like Home Depot and Lowe's may have consultant services that may have some free info as well. Don't just "buy" stuff and expect it to work. You may have to measure the room first.
posted by kschang at 12:48 AM on June 21, 2021

I mean, the slats alone (without sound absorptive materials) are probably doing something, if just changing which frequencies echo & how badly. As Candleman notes, smooth reflective surfaces parallel to each other - bare wall facing bare wall - can produce really nasty echoes, and breaking up those echoes by getting rid of the hard flat surfaces even without sound absorption is one of the techniques used in recording studio construction, known as "diffusion." Of course this is done in combination with sound absorbing materials and proper placement of everything. Diffusion products from Sweetwater, just to give you an idea of what's out there.

Without downloading any of the manufacturer specs but looking at the pictures, it seems that all their installations use a lot of the panels, which is probably a factor in the system's effectiveness - if you've got whole walls and the ceiling covered in the slats it'll have a noticable effect, but, like, a couple of panels probably won't do much.

So yeah, as others have noted, getting a similar effect in residences is usually accomplished with, y'know, residential stuff - chairs, couches, rugs, bookshelves, etc etc etc.
posted by soundguy99 at 4:14 AM on June 21, 2021 [1 favorite]

Curtains made out of a thick, heavy material would do it, especially if it’s a curtain wall. Shirred fabric walls. Hang attractive rugs on walls like a tapestry. Hang quilts on walls.
posted by TWinbrook8 at 4:47 AM on June 21, 2021 [2 favorites]

Looks like you're not doing wood but I was going to say that anything horizontal is going to require more dusting.
posted by bonobothegreat at 5:00 AM on June 21, 2021

I haven’t tried them, but IKEA have an ODDLAUG “sound absorbing panel” that might be worth a try if you like its appearance as it’s not super expensive. £25 in the UK store. IKEA.com is very resistant to allowing me to look for it in other countries’ stores.
posted by fabius at 5:09 AM on June 21, 2021

Here's the ODDLAUG on Ikea's US page. $29.99 for a pack of fifteen, seems to require a curtain rod or similar, some reviewers report using multiple sets of them.
posted by box at 6:20 AM on June 21, 2021


Those hard wooden slats are acoustical diffusors. They don't eliminate echos, they modify their character. To minimize echoes and quiet a room, you want absorbers. This is my go-to for absorptive panels. ATS Acousics they sell pre-made panels plus the materials if you want to make your own or have them built into your house. If you are on a budget foam or thin felt will do some good, but for a real sense of quiet a thicker material with more mass is needed. However, there's a trade-off solution that I'll explain in a bit.

The sound waves are made by molecules of air that are moving around a lot - they will continue to move until they can transfer their movement energy to something else. The waves of movement energy "bounce" off of hard surfaces and then they transfer their energy to your parent's eardrums - making the eardrums move.

Absorptive materials suck up the movement energy by giving the air molecules something to transfer their energy to. The materials have to be soft so they can wiggle (microscopically) and massive so that wiggling them takes some energy, and permeable. If they are thick, they will absorb longer-wavelength wiggles, and if they are permeable, the longer wavelength wiggles will be able to penetrate to the fullest depth of the absorptive material.

The most effective materials are mineral-fiber insulation, 2" or more in thickness. the mineral fibers are heavy so they take up a lot of energy, and they are soft enough and porous enough that the sound can go all the way through. I treated a very-echoey playroom space with hard floor, hard walls, and cathedral ceilings by adding 4' x 6' panel of this material behind a thin cotton wall hanging. That plus a thin rug in the middle fo the floor killed the echoes completely, though it is not recording-studio quiet.

If you go thinner with the material, or lighter in weight, it will still reduce the echo, but only for higher frequencies. That may be enough as 1" or less will deaden most echo in the human vocal range - but lower sounds like traffic or bass rumble from music or electric motors will not be decreased.

Also, you can trade off square footage for effectiveness. So if you can cover most of several walls and the whole floor with 1/2 thick materials (curtains, rug, etc) that will do better than investing a lot of money in two 2' x 4' acoustical panels that are 4"thick of the best absorptive material. Lower pitched sounds will still be louder. Unless you are in a concert-hall size space, you can get great results covering half the surfaces treat only one of each set of two parallel surfaces. So don't treat the floor and ceiling but leave all walls bare - the echos will ping pong from wall to wall. Treat the floor (rug), one wall (curtains) and the other wall 90 degrees from the first (more curtains, panels, soft couch with panels above). A sound wave will then bounce at most off of one hard wall before hitting absorbers on the next and dying out. That one initial echo will be so close in time to the original sound you will not hear it as an echo.

Lastly, about diffusion and those wooden slats - sometimes too much sound absorption is a bad thing. If you absorb all the sound reflection in a space it sounds oddly quiet - it can be discomforting as all the spatial cues of echo are eliminated. The space will sound like a tiny cave with soft walls, but look like a large room. Spaces like libraries and concert halls are designed to reflect a measured amount of the sound energy to create a feeling of space without the hard echoes. Diffusion materials take the sound energy and reflect back scattered both in the time and space domains, this has a blurring effect on the sound. For library, where people want quiet but also enjoy the low-level sonic ambiance of the space, it can allow sounds like foot traffic and quiet conversations to be heard but muffled or diffuse, but without the distracting echo of hearing every word that someone is saying two tables over. Also hard surfaces are much easier to clean. If you combine diffusion with absorption you get the best of both worlds.
posted by sol at 7:19 AM on June 21, 2021 [16 favorites]

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