Sec. 58.382. - Sound Level Reduction (SLR) Design Requirements.
General Requirements. The SLR requirements found in Section 58.381 may be achieved by any suitable combination of building design, choice of building materials and execution of construction details in accordance with established architectural and acoustical principles. The SLR requirements shall apply to all occupied rooms having one or more exterior walls or ceilings, when furnished in accordance with the intended final usage of the room.
No new building or structure for which an SLR of 25, 30, or 35 is required by Section 58.381 may be constructed unless and until a building permit therefore has been issued by the City. No such permit shall be issued unless and until conformance with the requirements contained in Section 58.381 is indicated by plans and specifications for the building or structure.
The City may require, prior to granting final approval of the finished building construction, at the expense of the owner, a field test by a Qualified Acoustical Consultant to verify the sound level reduction (SLR) of the building. In lieu of field testing, the City may accept, at the owner's expense, a certification of design criteria by a Qualified Acoustical Consultant, verifying the sound level reduction (SLR) of the building.
Verification Testing Procedures/SLR Design Information. Sound level reductions shall be determined for at least four aircraft fly-over events by a typical air carrier-sized jet aircraft for each room tested. The resulting value assigned to the room shall be the average value of the individual fly-over events. Using the noise signal generated by an individual aircraft fly-over event, outside and inside noise levels may be measured simultaneously. The noise levels measured outside and inside the room being tested may be observed directly by simultaneously reading the maximum noise levels on two sound level meters; or the outside and inside fly-over event may be recorded on magnetic tape, and the required noise level reduction determined by analysis of the recorded signals. In either case, the two measuring systems used for outside and inside noise measurement must satisfy the requirements for a Type II Sound Level Meter according to ANSI S1.4-197. The two systems shall be calibrated prior to and following the fly-over events so that they indicate the same level within one decibel for the same noise, using suitable calibration procedures as specified by the manufacturer. For calculations undertaken for purposes of meeting the requirements of this Part, the City, owner, or qualified acoustical consultant may use the assumed outside spectrum shown in Figure 7C.
FIGURE 7C. OCTAVE BAND NOISE SPECTRUM
[image omitted; see the official code]
This spectrum may be used to make calculations for determining how the standards of this Part are to be met. Such calculations shall take into account the area and sound transmission loss characteristics of exposed room surfaces, and the amount of sound absorption in the room.
In residential structures, the assumed ratio of sound absorption to floor area for each room is as follows (making an allowance of at least two decibels for sound leaks and flanking sound transmission paths):
Octave Frequency Band (H2) | Sound Absorption Floor Area
63 | 0.30
125 | 0.50
250 | 0.75
500+ | 1.00
Inside Noise Levels. In residential structures, inside noise levels shall be measured with a single microphone, four feet above the floor, near the center of the room. For other structures, inside noise levels shall be measured with a single microphone, five feet above the floor, either near the center of the room, or inside the room eight feet from the exterior wall most directly exposed to the aircraft noise, whichever distance from the most directly exposed wall is less.
For residential structures, it shall generally be sufficient to conduct tests in two rooms. One of the rooms to be tested shall be the bedroom most directly exposed to aircraft noise. The other room to be tested shall be either the living room, dining room, or family room, whichever is most directly exposed to the aircraft noise. The Building Official shall have sole authority in determining the number of rooms and the particular rooms to be tested.
For structures where a number of rooms receive nearly equal exposure to aircraft noise, tests need only be conducted in two of the near identical rooms. For structures in which several rooms are to be evaluated, tests need only be conducted for those rooms whose exterior walls are most directly exposed to the noise source. If noise level reduction requirements are met for these rooms, the tests need not be repeated for rooms of similar construction which are not directly exposed to fly-over events.
Adjustments for Unfurnished Rooms. When the sound level reduction is measured in an unfurnished or partially furnished room an adjusted sound level reduction shall be computed by adding ten times the logarithm and the base ten of the ratio of the floor area of the room to the sound absorption in the unfurnished or partially furnished room but in any event, such correction shall not exceed two decibels. The adjusted noise level reduction value shall be used in determining compliance with the SLR requirements. If the noise level reduction is measured in a furnished room no adjustment in the noise level reduction may be made.
Outside Noise Levels. The outside noise level shall be measured in an unobstructed location near the center of the wall most directly exposed to the aircraft noise source, approximately five feet above the level of the floor of the room being tested and eight feet from the wall.
(Ord. of 9-16-1991, Doc. #25094; Ord. of 8-23-1999, § 15, Doc. #32283; Ord. No. 2010-47, § 6, 10-18-2010, Doc. #1010181112)
