Page 37 - January 2007

THE ACOUSTICS OF FLOORS IN CONDOMINIUMS
Marshall Long1
Marshall Long/Acoustics Sherman Oaks, California 91423
Joe Stewart2 and his wife Ellen
recently purchased a condominium
in an upscale neighborhood in Playa
del Mar, CA. The location was excel-
lent, less than a mile from the beach,
south of Marina del Rey. The condo-
minium was comfortable, about 1600
square feet, and the builder had a repu-
tation for quality. Unfortunately, even
with a $700,000 price tag, the noise
problems were considerable. Movements
of people upstairs, both footfall on the
hard surface floors and walking on car-
peted floors, were loud enough to wake
them in the morning. When toilets
were flushed upstairs, it sounded like a waterfall running through their walls. The closing of doors, cabinets, and drawers could all be clearly heard. Walking in the upstairs hallway was plainly audible.
Situations such as these are increasingly common in Los Angeles, where the city building department and elected offi- cials refuse to enforce the State’s building codes on noise. Even if they were enforced, they are so anemic that minimum code compliance does not yield a quiet living environment. In fact when Stewart complained to the builder, subsequent acoustical tests showed the building to be in compliance (barely) with California minimum code standards.
As a growing population is extruded into highly urban- ized areas, multifamily dwellings have become the most com- mon way of packing more people into less space. Pressures of population and cost force people together, and noise and noise transmission between occupied spaces are significant con- cerns. People want their apartment and condominium homes to be quiet and free from intrusions, just like a single-family residence, but the reality is quite different.
Floor ceiling noise transmission
The most common noise and vibration problem in con- dominiums is transmission through floor–ceilings and it falls into four categories: 1) airborne, 2) footfall, 3) structural deflection, and 4) floor squeak. Plumbing noise is also a fac- tor particularly when plastic piping is used in waste stacks or when pipes are undersized and not vibrationally isolated from the structure.
Airborne noise can be generated by neighbors’ frank exchange of views (diplospeak for a spat), or by a Kiss concert played on their child’s stereo. Footfall noise is generated by heel impacts, like having a flamenco dancer upstairs. Structural deflection is slightly different—like having a sumo wrestler upstairs, who even though he may be barefoot, still
“People want their apartments and condominium homes to be quiet and free from intrusions, just like a single- family residence, but the reality is quite different.”
causes the floor to deflect like a trampo- line as he pads along. Floor squeak sounds like a birdcall, which produces noise by metal rubbing on wood.
Most floor-ceiling noise problems fall into one or more of these categories although occasionally there are struc- turally transmitted sounds due to equip- ment, doors or drawers closing, or fur- niture sliding along the floor.
Airborne noise
Airborne noise is created in one space and is transmitted through the air and through an intervening partition
into the adjacent space. Sources might include TV, stereo sys- tems, or simple conversation. The isolation of airborne noise such as speech is well characterized by the Sound Transmission Class (STC) rating. The STC rating is the result of a test performed in accordance with ASTM E 90 or ISO 140 laboratory test standards. To do the test a partition is built into a heavy wall separating two concrete test chambers in a laboratory. A standard sound is created in one room, called the source room, and transmitted through the parti- tion and into the receiver room. The difference between the levels in the source and receiver rooms, adjusted for the area of the partition and the absorption in the receiver room is the transmission loss in decibels. The measured transmission loss values in 16 third-octave frequency bands are compared to a standard curve (ASTM E413) to determine the STC rat- ing. The higher the STC rating, the better the partition is at stopping airborne noise. Under field (F) conditions the meas- ured FSTC rating is about five points lower than the labora- tory rating, and this difference is acknowledged in the build- ing codes. Thus if an STC 50 is the required laboratory rat- ing, a field test of 45 is equivalent. In California the test pro- cedure has been diluted by eliminating the inclusion of the correction for the absorption in the receiving room.
Reasonable expectation of the buyer
In selecting the appropriate design criterion for a given level of quality, the designer should consider the type of building and the level of quality expected by the buyer. As the perceived quality of a residence increases, so too do the expectations for a quiet environment. This expectation of quality may be based on cost, location, sales information pro- vided to the buyer, or because a person is purchasing a per- manent home rather than renting an apartment. Unfortunately, too often builders put money into the appear- ance of a residential building but little into noise isolation.
Acoustics of Floors in Condominiums 35