Sound Absorption

I'm wondering about the sound properties are of a straw bale constructed building? I have an interest in building a small outbuilding that would be my office and possibly a small studio space for a band to practice -- drums, electric guitar, keyboard, etc. It won't be a recording studio space, per se, but space for a 3 or 4 people to get together and jam. Still, that creates quite a few db SPLs, so I'm looking for construction methods that will keep costs low, properly insulate the space and keep heating costs down, along with reducing sound levels that escape the space.

I live in the city so, reducing sound leakage to the neighbors would help me sell the idea to them, and maybe help them get involved with the project.

Hi Ricky, and welcome to Permies.

I did a google search for 'sound damping qualities of straw" and came up with these results, which don't surprise me:

Straw Bales as Soundproofing

So the answer to the question is yes. Yes, straw bale buildings are incredible insulators from sound. If you live on a very loud street or perhaps you back to an interstate, these walls will eliminate almost all of the noise that you currently live with. You can build a straw bale house or consider building a straw bale landscape wall. Although not as good as an entire house of straw, they still work really well to eliminate sound.

Acoustical Characterization of Straw Bales as Structural Elements

Straw bale walls, in addition to being highly insulating, inexpensive, and providing minimal impact on the environment, have the ability both to impede and transmission of sound energy and absorb noise over a wide range of frequencies. As architects begin to take advantage of straw's acoustical strengths, straw bales could be used more extensively in building construction and in other applications. For example, this study suggests that straw bale walls would be excellent candidates for use an inexpensive outdoor barriers to reduce environmental noises such as highway noise.

Straw-bale Sound Isolation and Acoustics

The 53dBA test result might seem low but in fact is very good. Most conventional wall systems including a brick cavity wall with much higher mass have a lower performance. Specifically interesting to note is the 2-3dB better performance at very low frequencies of the straw-bale test sample when compared to brick-wall systems. Nearly all wall systems, including stick frame, are able to sufficiently subdue high-and mid-frequency sound, but low-frequency sound is problematic. In practice, better performance at low frequencies is worthwhile because it means that the ever-present background noise in suburban areas is perceptibly reduced.

What did surprise me is that Google wanted to correct my search to 'sound dampening qualities of straw', which would be the ability of straw to get sound wet, I guess.

The sound absorbing qualities of plastered straw bale walls are largely unstudied and anecdotal.  That doesn't mean that they are not quite impressive!  And it makes sense.  Just looking at the materials you see a densely packed (but not solid) block of irregularly shaped stems and edges encased by plasters.  Sound waves strike one wall's surface, which itself may have a rough plaster coating that further absorbs and deflects sound energy.  The waves proceed through this tangle of irregular edges and air spaces until they strike the opposite wall and bounce back through the bale.  

I live in a straw bale house and work in a straw bale shop.  We never hear the UPS or FED EX trucks pull into our driveway, a mere twenty or so feet from either building, and only know someone is there when they knock on the door.

CASBA is making a list of much needed research that needs to be done so straw can be used more fully in construction.  One of the barriers to using strawbales in a shared wall in multi-family housing (among the lowest cost, energy efficient ways to build!) is that we don't have the test data to tell us what we already strongly suspect--that a plastered straw bale wall assembly is an outstanding sound barrier.

This is the kind of research that proceeds from sales of the book "Straw Bale Building Details: An Illustrated Guide for Design and Construction" will support.

Thanks for responding Tim and Jim.

I suspect, too that it would have all of the properties that one would want in a sound absorbing wall -- dense, trapped air, and irregular shapes to contort sound waves and dissipate sound energy into multiple diretcions.

I haven't studied what roofing materials are compatible with straw bale construction, but that may indeed be the single biggest sound leakage point. Soundproofing a space is a mixture of material selection and filling up air gaps.

I saw a few articles about recording studios being made with straw bale construction, so I'd think I'm on solid footing.