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SOUND WALL Solutions Kyle Cavaness, LC/DBM Figure 1: Studies of T-profile sound walls show that adding absorptive material to the top horizontal section (Fig. 1) increases the efficiency of the barrier by up to 2���3 decibels, an effect comparable to raising the barrier by three feet, without negative secondary impacts or taxing the wall���s foundation. Above: Other important factors in sound wall installations include foundation requirements, structural issues, debris collection and durability. Precast concrete walls, such as those manufactured by Superior Concrete Products (pictured), provide sound barriers that have the decorative look of stone, brick and wood, require no maintenance and use a modular construction for future expansion or adjustment. 34 LC DBM tially increasing the barrier height, and at a much lower cost than replacing the barrier with a taller structure. Recommendations in the FHA report for sound wall materials included transparent panels, acoustical treatments and specially designed wall top treatments. Much of the available research points to treatments for the top edge of the barrier, such as curved or angled tops, irregular top edges, or ���T-top��� treatments. These designs are meant to alter the hard linear edge that ���bounces��� sound over a wall. Contractors adding a wall to a residence or commercial project can improve noise-reducing properties by selecting uneven or natural-faced stone, which will deflect more sound, or add a T-top cap to the top edge. Studies showed that a T-top edge at the top of a sound wall reduced noise levels in a residential area by 1.0 to 1.5 decibels, compared with a conventional vertical barrier of the same height. LC DBM Top: Sound walls are barriers that reduce noise pollution from roads, industrial areas and other sources. While useful in some circumstances, installers should be aware of potential negative impacts, including blocked scenery, cost of installation, and maintenance and drainage concerns. Sound walls, or noise barriers, are landscape elements typically constructed of cast-in-place concrete or masonry block to absorb or deflect noise from roads, railways and industrial areas. These barriers can effectively reduce noise levels, but often cause undesirable secondary impacts, such as blocked views of mountains and other scenic features, decreased visibility, or large shadows cast across a resident���s backyard for extended periods of the day. Sound walls are most efficient when they are 30 percent taller than the line-of-sight between the noise source and the receiver, but raising the barriers to achieve further noise reduction can exacerbate the secondary impacts. According to a Federal Highway Administration research project, innovations in sound wall designs and treatments can retrofit an existing noise barrier to achieve a higher level of noise reduction without substan-