Office Isolation Ortho Biotech

Spirit Acoustics has installed the Speech Guard System to improve the office-to-office isolation in the Ortho Biotech facility. The drop-tile acoustical ceiling was identified as the flanking path, providing for poor speech isolation. Spirit Acoustics installed Shield Guard Tile Backers on the top of the ceiling tiles to provide increased transmission loss. In addition, Speech Guard light hoods were installed above the light fixtures to reduce this flanking path. Finally, in some spaces wall treatment in the form of fabric-covered glass fiberboard had been applied. Our measurements indicate that these various applications have provided a significant improvement in the isolation between spaces.

Project Background

Airborne sound describes sound that travels from office to office in either direction and includes conversational speech and noise from equipment such as computers. The transmission path is not structure-borne (vibration) although by necessity, part of the path is via the structure. Airborne Isolation is described in terms of the STC (Sound Transmission Class), or NIC (Noise Isolation Class). The measurement of these parameters is made by producing broadband noise in one room and measuring the one-third octave spectrum in the source and receiving rooms. The difference in the measured sound levels is then adjusted for the receiving room acoustical characteristics for STC measurements (unadjusted for NIC measurements) and curve fitted to provide a one number rating of isolation performance. The basic differences between the two measures is that the STC value is a rating of the demising structure performance (wall between offices), while the NIC value describes the obtained isolation in the specific installation. NIC is therefore the best metric to assess the speech isolation provided by the entire construction, walls, ceiling, interior materials, etc.

Data Acquisition

We visited the facility on the evening of 14 December 2004 to carry out isolation measurements. The measurements were made using a Bruel & Kjaer Type 2250 Precision Sound Level Meter/Real Time Analyzer. A powered loudspeaker with a signal from a pink noise generator was placed in one office, and the system was adjusted to provide a sound pressure level of 95 to 100 decibels. Measurements were made at eight locations in the office in which the loudspeaker was placed (source room). The source was left running and the measurements were repeated in the receiving office at similar locations. Measurements of background noise in the receiving space were made with the sound source off to ensure that the receiving sound levels were the result of the sound source and not other unrelated noise sources. Measurements were made in a total of 5 office pairs described in Table 1.

Results

The measurement results are provided in Figure 1 and summarized in Table 1. The NIC values are calculated by curve fitting the third octave data to a standardized curve using an ASTM specified procedure. It is clear from the measurements that the treatment is effective in increasing the noise reduction (average sound pressure level in source room – average sound pressure level in receiving room) and therefore increasing privacy between the spaces. The NIC values for the treated rooms were 15 points higher than the untreated rooms. Furthermore, the light hoods are an integral part of the system, with half the increase in noise reduction resulting from the addition of this component of the system. Where the fixture hoods were not yet installed (3359 and3 358), the noise reduction was noticeably lower than the fully treated rooms. The wall treatment also increases (mainly high frequency) noise reduction and provides some increase in performance.

Table 1

Office Pair	Conditions	NIC
3402 and 3404	Speech Guard Light Hood & Shield Guard Tile Backer	42
3101 and 3103	Untreated	27
2234 and 2235	Speech Guard Light Hood, Shield Guard Tile Backer, & Interior Wall Treatment	41
2104 and 2105	Untreated	26
3359 and 3358	Shield Guard Tile Backer	36

It is clear from the measurements that the noise isolation between private offices is clearly insufficient (less than NIC 30) under baseline conditions. With the treatment installed, the NIC values above 40 fall in line with typical recommendations.

Office Isolation Ortho Biotech

Project Background

Data Acquisition

Results

Table 1

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