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A large reverberation room of approximately 310 m3 (11,000 ft3) used in the air conditioning, heating and refrigeration industry, was in need of improvements to meet the updated requirements of the American Heating and Refrigeration Institute (AHRI) Standard 220. In addition, it was desired to extend the measurement qualification of the room down to the 63 Hz octave band. The initial qualification test results showed that the room did not qualify for the extended low frequency range and also had some irregularities in the 100 Hz third octave band. This paper reports the results of a three-part investigation to correct reverberation room response irregularities in the 100 Hz third octave band, to establish performance that qualifies relative to the most recent standard, and to determine and integrate the means by which its qualification could be extended down to the frequency bands of 50, 63, and 80Hz.

High levels of broadband sound are generally required for sound transmission loss and sound absorption tests conducted within reverberation rooms. However, the sound system components such as loudspeakers are often selected with little consideration or knowledge of the audio engineering principles that govern system operation. This paper will address the selection of a loudspeaker system for producing the required sound level in a reverberation room, starting with the sound level requirements in a test room, and a brief review of the fundamental concepts of loudspeakers, including horn loading and compression drivers, radiation efficiency, directivity, power ratings and limits, thermal compression, crossovers, equalization, and spectral balancing resistors. Loudspeaker manufacturer's specification data, such as 1 watt/meter sensitivity, directivity index Q, and power ratings will then be discussed.

High levels of broadband random noise are generally required for conducting sound transmission loss and sound absorption tests within reverberation rooms. However, the sound system components such as loudspeakers, amplifiers, and other elements are often selected with little consideration of the audio engineering principles that govern device as well as system operation. This paper will explore some of the requirements for reverberation room sound systems starting with the acoustical power spectrum needed to overcome the transmission loss of high performance barrier assemblies, the background noise in the receiving room, the background noise floor of measuring instruments, and air absorption within the reverberation room.

The GM Noise and Vibration Analysis Laboratory (NVAL) was conceived in response to GM's need for a state-of-the-art noise, vibration and harshness (NVH) testing and development facility. This paper examines the construction of the NVAL to help illustrate the process of converting NVH facility design documents into a functioning facility. It features a summary of items learned through the course of the construction effort and outlines issues a technical building owner should consider when embarking on a new facility project. NVH facility construction is unique. The traditional construction approach, emphasizing time and cost reduction, must be buffered with an equal or greater emphasis on performance and the proper sequencing of tasks to allow these integrated facilities to meet their operational objectives.

This paper examines the critical design elements and issues associated with converting facility goals and business objectives into a functional facility. The design of the General Motors Noise and Vibration Analysis Laboratory (NVAL) will be discussed to help clarify key points. A team-oriented design approach is essential to meet the stringent safety, flexibility and operational requirements associated with noise, vibration and harshness (NVH) facilities. The first step is establishing the design team and their respective roles in the process. The challenge of “how to build a facility that meets the specified objectives” is addressed in the programming phase. Operational and financial objectives are reviewed and validated. Upon completion of the programming effort, the team attacks the special technical challenges borne out of that process.

Acoustical laboratories for vehicle testing have specialized requirements which differ from those for most conventional buildings and facilities. As a result, the normal design and building process takes on added dimensions which need to be carefully considered and addressed. This paper presents an overview of the process that starts with conceptualization of the laboratory and ends with the validation and qualification of the laboratory, and includes particular emphasis on the inherent peculiarities. Case studies are provided of several potential perils and pitfalls that may be encountered in the process which can adversely affect the usability of the laboratory as well as the validity and repeatability of test results obtained by that laboratory. The paper concludes with suggested courses of action which will help either to avoid or minimize the compromises that imperil the functional effectiveness of a laboratory.

The paper reports the results of sound absorption verification studies of a rectangular parallelepiped reverberation room that is a dimensionally scaled (miniature) version of a full-size, reference reverberation room. The qualification procedure compares the measurement results obtained in the miniature (mini-verb) room with that determined for the same sample in the reference room, where traditional pressure microphone techniques and decay measurements are employed. The absorption measurements in the mini-verb room, however, are based upon a new technique which relies upon the use of boundary microphones installed in very close proximity to each intersection of three room boundaries (i.e., the eight (8) trihedral corners). An array of boundary microphones, one in each corner, is used in place of a traditional spaced array of pressure microphones, or of a single moving microphone.

Advances in vehicle noise control are leading the automotive industry to place increasing emphasis on weatherseals to block exterior noise. As a result, properly evaluating the acoustical performance of automotive weatherseals is of increasing importance. There is no current specific standard for this testing. Rather, there has been reliance on adaptations of SAE Standard 51400 “Laboratory Measurement of the Airborne Sound Barrier Performance of Automotive Materials and Assemblies” by testing laboratories. However, the 51400 standard addresses testing of flatstock materials and does not readily lend application to pre-formed parts such as weatherseals. For this reason, adaptation of the standard can vary significantly from facility to facility and manufacturer to manufacturer. These differences can be significant and can render comparisons between test results on competing materials very difficult.

The purpose of this paper is to identify various concerns that need to be evaluated prior to the design and construction of a reverberation chamber, such that the chamber can be used for various automotive related acoustical measurements. Some of the concerns involve issues such as room shape and size, the degree of sound and vibration isolation required, the use of conventional building materials versus traditional massive construction, construction cost, and the performance requirements for the test noise generation system. Various uses of a reverberation chamber include random incidence sound absorption measurements, small sample sound transmission loss measurements, vehicle insertion loss tests, dash panel, door, and other “buck” evaluation tests, and sound power level measurements of small automotive components and devices. These uses have differing and in some cases conflicting requirements that compete in the selection of room design parameters.