The sound properties of living in a dome

One of the first things that intrigued me about thin shelled domes was that they could shut out the outside world. This property was attributed to their basic construction technique. Insulation sprayed on the outside and concrete as the inner shell, the design itself tends to reject outside noise pollution. The insulation reduces vibration sound waves against the concrete, and the density of the concrete and its hardness reflect other sounds away. Moving inside, special attention has to be paid to materials and placement of walls to avoid the natural parabolic created by the shell. The shell focuses sounds and accentuates them and the "reflectiveness" of the concrete floor and ceiling creates standing waves or echoes.

In our design we knew we had to address these problems and we had the added feature of a home theatre and its own sound problems.

1. Dealing with the parabolic: we split the parabolic with a floor to ceiling wall effectively halving the dome. After installing the second floor, it halved it again. This defocuses the sound energy on each axis.

2. The standing waves and echoes: we chose to use carpet and padding on the floors instead of our original choice of polished, stained concrete floors. This should reduce the parallel sounds bouncing against each other.

The bottom of the second floor is made from an ICF of styrofoam (Insul-Deck.org), which reduces transmission of sound by not transmitting vibrations of sound to the floor above (decoupling). This is also why ICFs were our first and only choice for our theatre walls (RewardWalls.com). Additional floor treatments will be added to the walls and to the ceiling of the theatre using drywall/gypsum board. The dome shell will be completely stuccoed on the interior.

On the interior drywall walls, we'll be adding insulation between the steel studs for privacy. Upholstered furniture has a nice acoustical property, due to our large spaces and ceiling height of 25 feet, we've chosen large overstuffed comfortable pieces for the living area. These pieces tend to dampen echoes. Potted plants and draperies help in diffusing sound waves. We are also designing a large faux skylight light fixture for the apex of the dome interior, it will look like a real skylight with daylight coming through it, using daylight balanced fluorescent lamps. This will also reduce standing sound waves.

You have to look at a dome as the whole picture and take in consideration how you want the living space to sound when you are complete. Many people come into our dome as it is, under construction, and hear the echoes and ask if it will be that way when it is done. They forget that any house that is empty without furnishings and carpet is filled with echoes. When considering a thin-shelled dome building, sound treatment should be factored into the design, not an afterthought fix like hanging material and carpets from the ceiling! Sound treatment is not expensive or difficult, just a little forethought and understanding of the materials will make a big difference in your dome.