Reverberation Time Design for IM Building Addition

Transcription

1 INTRAMURAL BUILDING Reverberation Time Design for IM Building Addition Project 1 Andrew Brouwers Kelly Cerri Melissa Consiglio Michael Devaney Kenna Markel March 20, 2014

2 Table of Contents Introduction Background Results Discussion Summary Appendices Appendix A: Tables Appendix B: Graphs Appendix C: Plots Appendix D: Manufacturing Data Information Appendix E: Hand Calculations

3 Introduction: The IM building at the Pennsylvania State University is currently under construction for an addition and renovation. As a result of the addition, the new IM building will contain several different room types, such as classrooms, offices, and fitness rooms. Therefore, each room type will have a different purpose and acoustical performance requirement. In this case, three specific spaces within the addition were investigated- Classroom 008, Conference Room 101L, and Multipurpose Rooms 124 and 125. For this evaluation, Multipurpose Rooms 124 and 125 are not divided by the moveable partition. The goal of this evaluation was to see how close the reverberation times of these spaces are to the target reverberation times, and what changes could be made to improve this accuracy. Conference Room 101L, with the smallest total surface area of the three spaces, contains carpet tile, acoustic ceiling tile, gypsum wallboard, and glass as surface finishes. Materials used in Classroom 008 include linoleum, marker board, gypsum wallboard, and acoustic ceiling tile. Lastly, Multipurpose Rooms 124 and 125, with the greatest total surface area, consists of acoustic ceiling tile, wood, gypsum wallboard, wood on concrete, drywall, mirrors, and metal decking. Background: The features of a room will determine the acoustical performance of that space. The material of the room s surfaces will impact the total sound absorption. Sound quality is unique due to the different set up of each room. Lastly, reverberation time is an important measurement commonly used to achieve the acoustical goal of a space. Every time a sound wave hits a surface it is reflected, absorbed, or transmitted. Absorption is known as the percent of energy that is not reflected, and can be expressed as the coefficient α. Where a perfectly reflective material has α equal to zero, and a perfectly absorptive 2

4 material has α equal to one. Both wavelength and material thickness affect absorption. Higher frequencies are easier to absorb than lower frequencies. Also, at a given frequency, absorption increases as material thickness increases. The amount of sound absorbed can be calculated using A = Sα. Where A represents sound absorption and S represents surface area. Sound absorption is given in units of sabin. The total absorption for a room can be calculated by taking the sum of Sα for each unique surface material. Sound quality and level is dependent on the characteristics of a room. This includes room geometry, volume, and absorptive properties of surface finishes. Every time sound hits a surface, some of the sound is absorbed and the rest is reflected back into the room. As a result, sound does not immediately decay in a standard room. The sound in a reverberation chamber lasts for an extended period of time. The sound in an anechoic chamber is absorbed instantaneously. Sound decay for a given space can be characterized using reverberation time. Which is the amount of time it takes for sound to decay 60 db after it has been shut off. Reverberation is a smooth decline in the energy content of consecutive repetitions. Reverberation time is calculated using the Sabine equation (1) where RT is the reverberation time, B is a constant, V is the volume of the room, ST is the total surface area, and aa is the air attenuation constant. This equation is only valid when calculating the reverberation time of a material with α 0.2. When calculating the reverberation time of a material with α > 0.2, the Norris-Eyring equation ( ) (2) 3

5 where RT is the reverberation time, B is a constant, V is the volume of the room, ST is the total surface area, and aa is the air attenuation constant, should be used. The Sabine and Norris-Eyring equations have several important limitations. These equations will work well for small rooms and not large rooms, such as theaters and concert halls. Also, they work better if the room is relatively diffuse and the absorption is uniformly distributed throughout the room. The placement of absorptive materials is not considered in the Sabine and Norris-Eyring equations. Lastly, when finding the reverberation time of a room with a complicated geometry, acoustic modeling software must be used. This software must also be used when improved accuracy is required. Speech Intelligibility describes the amount of speech that is clearly understood. Reverberation has a major impact on speech intelligibility. Too much reverberation in a room reduces speech intelligibility. However, too little reverberation does not adequately support speech. An optimum reverberation time chart can be used to find the necessary Reverberation Time of a specific room type. Reverberation time should be between s for speech requirements. Results: The Optimum Reverberation Time graph aforementioned can be used by a designer to set reverberation time goals for a specific type of room. The purpose and volume of a space are used to determine a value specifying the reverberation time for 500 Hz (RT 500 ). In the case of this project, each of the three rooms were categorized as speech auditoriums and their individual volumes were used to determine RT 500 for their size. The intersection of a vertical line drawn from the calculated volume of a space with the line for speech auditoriums is used to determine the optimum RT 500 from Graph 1 4

6 Graph 1: Optimum Reverberation Time graph Volume and Purpose of a space can be used to determine RT 500 with this graph RT 500 is used as a starting point for Figure calculating Architectural the optimum Acoustics, reverberation Principles and Design times for other frequencies. According to the project description, RT 500 is to be used for the 1,000 Hz octave band, a time 15% longer for Hz octave bands, and 10% shorter for the 2k-4k Hz octave bands. These percentage adjustments were applied to the RT 500 values and are summarized in Table 1. Discussion: The sound absorption, for each surface finish, used to calculate absorption and reverberation time is located in Table 1. These values were taken from Appendix H of the textbook. Reverberation time values calculated for the original design of each room is located in Table 2. Plot 1 displays the reverberation times for all three rooms. Reverberation time for Conference Room 101L, located on the main level, was calculated using data about the room s surface finishes, volume, and total surface area. The surface finishes in this space included acoustic ceiling tile, 1/8 carpet tile, 5/8 gypsum wallboard, and less than ¼ thick glass window. Conference Room 101L has a volume of 2,389 ft 3 and a total surface area of 1,133 ft 2. The optimum reverberation time for Conference Room 101L at 500 and

7 Hz is 0.38 s. Conference Room 101L did not meet this requirement at 500 Hz with a reverberation time of 0.62 s. However, at 100 Hz Conference Room 101L had a reverberation time of 0.40 s. Reverberation time for Classroom 008 was also calculated using the room s surface finishes, volume, and total surface area. Classroom 008 contained acoustic ceiling tile, 5/8 gypsum wallboard, linoleum, wood doors, glass windows, and page board over 25mm fiberglass board. This space has a volume of 13,442 ft 3 and a total surface area of 4,189 ft 2. The optimum reverberation time for Classroom 008 at 500 and 1000 Hz is 0.55 s. Classroom 008 met this criterion at 1000 Hz; however, at 500 Hz the space had a reverberation time of 0.82 s. Lastly, Reverberation time for Multipurpose Room 124 and 125 was calculated using the volume, total surface area, and surface finishes of the space. The surface finishes of Multipurpose Room 124 and 125 included acoustic ceiling tile, 5/8 gypsum wallboard, 1-1/2 acoustic deck, wood floor on concrete, glass windows, ¼ or thicker glass pane, and wood doors. Multipurpose Room 124 and 125 has a volume of 91,377 ft 3 and a total surface area of 19,864 ft 2. The optimum reverberation time for Multipurpose Room 124 and 125 is 0.65 s. Multipurpose Room 124 and 125 met this criterion at 1000 Hz but had a reverberation time of 0.82 s at 500 Hz. Due to the fact that none of the spaces met the optimum reverberation time criteria, all three rooms were altered. One alteration was the addition of ALPHASORB wall panels to the walls. Also, ALPHASORB cloud panels were added to the ceiling tiles. These two additions were applied to all three spaces in order to correct the reverberation time values. The multiple alternatives for Classroom 008 consisted of- changing the floor to the carpet used in Conference Room 101L, changing the glass wall to gypsum wall board, adding ALPHASORB wall panels to the walls, adding Sonex Classic Acoustical Foam to the walls, and adding ALPHASORB 6

8 cloud panels to the ceiling. The addition of ALPHASORB cloud panels and ALPHASORB wall panels were chosen because they lower the reverberation time the most, are the most absorptive, and can be easily be manipulated with respect to area. For the addition of the ALPHASORB wall panels, the area of the wall had to be subtracted out. Since the ALPHASORB ceiling panels are hanging, the acoustic ceiling tiles were not removed. Summary: Reverberation time was used to set and reach acoustic goals for Conference Room 101L, Classroom 008, and Multipurpose Room 124 and 125. Room characteristics such as volume, surface area, absorption coefficient, surface finishes and absorption were used to calculate reverberation time. With all three rooms categorized as speech auditoriums, the volumes were used to determine an optimum reverberation time. In conclusion, Conference room 101L, Classroom 008, and Multipurpose Room 124 and 125 did not match the optimum reverberation time values and required adjustments. Classroom 008 had the worst reverberation time out of the three spaces. The main goal when redesigning these spaces was to calculate reverberation times that were closer to the target reverberation times. The task was to find reverberation times within ± 0.05 s of the target reverberation time for the Hz octave bands and ± 0.10 s for the remaining octave bands. In order to accomplish these goals, ALPHASORB Cloud Panels and ALPHASORB wall panels were added to the existing spaces to lower reverberation times. These products are from Acoustical Solutions, and can be found in the Appendix. The gypsum wall board was exchanged for ALPHASORB wall panels because of their absorptive properties. The ALPHASORB wall panels have higher sound absorption coefficients than the painted gypsum wall board. The Multipurpose room proved most difficult to adjust. Ultimately, 7

9 the solution was found by removing the current design s acoustical ceiling tiles and replacing them with the ALPHASORB Cloud Panels. The current design of the IM Building could benefit from changes made according to these recommendations. Appendix A: Tables Table 1: Sound absorption coefficient used to calculate absorption and reverberation time. Taken from Appendix H in Architectural Acoustics, Principles and Design 8

10 Table 2: Current and proposed design reverberation time. Appendix B: Graphs Graph 1: Optimum Reverberation Time graph Volume and Purpose of a space can be used to determine RT 500 with this graph Figure in Architectural Acoustics, Principles and Design 9

11 Appendix C: Plots Plot 1: Compares the reverberation times of the current design to the proposed design Reverberation Time (s) Frequency (Hz) Legend Conference Room 101L Multipurpose Room Classroom 008 Conference Room 101L Multipurpose Room Classroom 008 Appendix D: Manufacturer Data Information SEE FOLLOWING PAGES Appendix E: Hand Calculations SEE FOLLOWING PAGES 10

12 PRODUCT ALPHASORB NAME WALL PANEL Main Product Image DESCRIPTION AlphaSorb Fabric Wrapped Wall Panels are your answer to your acoustical and aesthetic needs with their strong sound-absorbing performance, durability and eye-pleasing appearance. These panels are available in a wide variety of sizes, shapes and colors. They allow you to create an effective sound control treatment that is distinctly designed for your environment. Standard color options are the Guilford of Maine Fabric FR701, Style Other designer fabrics are available upon request. ALPHASORB WALL PANELS TECHNICAL CHARACTERISTICS Sizing Thicknesses 1, 2 Colors Custom Sizing up to 4 x 10 Wide Variety, See Color Chart FEATURES Class 1 Fire Rated NRC Ratings.85 to lb. Per Cubic Foot Density Various Mounting Systems Options for Beveled, Mitered or Radius Edges Octave Band Frequencies (Hz) NRC Sound Absorption Coefficient MOUNTING OPTIONS & EDGES Z-Clip Fasteners Impaling Clip Fasteners Velcro Fasteners Installed (Available on Sizes 4 x 5 or Smaller) Chemically Hardened Edges 1 Thick Thick Radius, Mitered or Beveled Edges Expedite Fee APPLICATIONS Houses of Worship Teleconferencing & Videoconferencing Classrooms Broadcast & Recording Studios Home Theaters Multipurpose Rooms 11

13 PRODUCT ALPHASORB NAME CLOUD PANEL Main Product Image DESCRIPTION AlphaSorb Ceiling Clouds are perfect for the reduction of sound in ceiling areas. These panels are suspended horizontally with eye hooks (for panels up to 4' x 4') or with T-Grid attachment. They are available in a wide variety of sizes, shapes and colors to allows you to create an effective sound control treatment that is distinctly appropriate for your environment. These panels come in standard or custom sizes, up to 4' x 10' in 1" or 2" thickness. Standard color options are the Guilford of Maine Fabric FR701, Style Other designer fabrics are available upon request. TECHNICAL CHARACTERISTICS Sizing Custom Sizing up to 4 x 10 Thicknesses 1, 2 Colors See Color Chart FEATURES Class 1 Fire Rated NRC Ratings lb - 7lb per Cubic Foot Density Eye Hook Mounting (up to 4 x 4 panels ) or T- Grid Mounting Installed at the Factory Options for Beveled, Mitered or Radius Edges APPLICATIONS Restaurants Lobbies ALPHASORB CLOUD PANELS Octave Band Frequencies (Hz) NRC 1 Thick Sound Absorption Coefficient 2 Thick ALPHASORB CLOUD MOUNT PANELS Product Size Thickness AlphaSorb Cloud 2 x 4 1 AlphaSorb Cloud 2 x 4 2 AlphaSorb Cloud 4 x 4 1 AlphaSorb Cloud 4 x 4 2 AlphaSorb Cloud 4 x 8 1 AlphaSorb Cloud 4 x 8 2 PANEL EDGE OPTIONS 12

14 SONEX CLASSIC ACOUSTICAL FOAM Main Product Image DESCRIPTION Sonex Classic acoustical foam is an extremely popular foam because of its design, acoustical effectiveness and its economical price point. Sonex Classic Acoustical Foam is extremely popular because of its design, acoustical effectiveness and its economical price point. Sonex Classic features a modified anechoic wedge design for cost -effective yet impressive sound control. TECHNICAL CHARACTERISTICS Available Sheet Size 2 x 4 Thickness 2 Melamine Colors FEATURES Class 1 Fire Rated per ASTM E-84 Density.7lb. Per Cubic Foot Flame Spread Natural 5 Smoke Density Natural 45 White or Light Grey SONEX CLASSIC ACOUSTICAL FOAM Octave Band Frequencies (Hz) NRC Sound Absorption Coefficient 2 Thick APPLICATIONS Broadcast & Recording Sound Studios & Home Studios Home Theaters Offices Residential Industrial Commercial, Retail & Corporate, Restaurants Industrial 13

15 16 Acoustic Properties of Perforated Steel Deck June 2004 Introduction Steel deck is generally a structural product designed to resist gravity loads. However, from the time it was first commercially introduced, there have been successful attempts to utilize deck to perform more than one function. Acoustic roof deck is one example of using the decking material to perform multiple functions with very little increased cost. The acoustic deck provides a finished ceiling with noise reduction capabilities while still providing the required vertical and horizontal load resistance. The noise reduction is achieved by the perforations and the acoustical insulation or material shown in Figure 1. The sound penetrates the deck through the perforations and is absorbed by the insulation. The perforations in the deck do cause a small reduction in strength and stiffness. The reduction varies from 5 to 10%. You should consult your deck supplier for the exact capacity. Noise Reduction Table 1 shows the minimum sound absorption data at various frequencies for typical acoustically treated roof deck. This data is obtained by conducting the ASTM C423 test, with mounting conforming to ASTM E795, at an accredited acoustical laboratory. The sound absorption coefficients represent the percentage of noise that the tested surface converts to other energy forms which does not reflect as sound. The usual tested frequencies are 125, 250, 500, 1000, 2000 and 4000 Hertz and the Noise Reduction Coefficient (NRC) is the average is rounded to the nearest Because of the measurement methods, the sound absorption coefficient for a particular frequency can be greater than 1; but, for any specific use at that frequency the value should be taken as 1. The sound absorption at any particular frequency and the NRC is a function of the total construction. Higher NRC values can be obtained by using fiberglass insulation board for the insulation material on top of the deck system in lieu of the commonly used foam board insulation. Consult individual CSSBI member companies for their recommendations and be aware that insulation board selected for its thermal characteristics will not have the same NRC as fiberglass board. Substitution of Figure 1: 1-1/2 and 3 acoustic roof deck 1-1/2 Acoustic Deck 3 Acoustic Deck FREQUENCY (HERTZ) Table 1: Sound absorption coefficients for acoustic steel deck (Canadian manufacturers) NRC Bishop St. N., Unit 2A, Cambridge, Ontario N3H 4V6 Tel.: (519) Fax: (519)