Case study 8

A demonstration field-research study reveals that aircraft noise measured at two one-story houses is ∼9dB less attenuated from measured outdoor levels than is street traffic noise, and, found in other studies, ∼14dB less than railway noise. Comparable differences are found between these noises from the application of basic acoustical formulas for quantifying attenuations that occur on site of one- and two-story houses. Reasonably consistent with those findings are results from attitude surveys showing that daily exposure levels of aircraft must be ∼8dB less than levels of street traffic noise, and ∼13dB less than levels of railway noise to be perceived as an equal cause of annoyance and related adverse effects. However, USA government guidelines recommend that equal exposure levels of noise measured outdoors from vehicles of transportation should be considered as being equally annoying. Changes in present USA noise-measurement procedures and noise-control guidelines are proposed that provide more accurate...

Acoustical, sensory, and psychological research data and procedures for their use in predicting effects of environmental noises.

The Schultz [(1978). J. Acoust. Soc. Am. 64, 377–405]; Fidell et al. [(1991). J. Acoust. Soc. Am. 89, 221–233] and Finegold et al. [(1994). Noise Control Eng. 42, 25–30] curves present misleading research information regarding DENL/DENL levels of environmental noises from transportation vehicles and the impact of annoyance and associated adverse effects on people living in residential areas. The reasons are shown to be jointly due to (a) interpretations of early research data, (b) plotting of annoyance data for noise exposure from different types of transportation vehicles on a single set of coordinates, and (c) the assumption that the effective, as heard, levels of noise from different sources are proportional to day, night level (DNL)/day, evening night level (DENL) levels measured at a common-point outdoors. The subtraction of on-site attenuations from the measured outdoor levels of environmental noises used in the calculation of DNL/DENL provides new metrics, labeled EDNL/EDENL, for the calculation of...

Acoustical model and theory for predicting effects of environmental noise on people

The performance of reflectors and diffusers used in auditoria have been
evaluated both objectively and subjectively.
Two accurate systems have been developed to measure the scattering
from surfaces via the cross correlation function. These have been used to
measure the scattering from plane panels, curved panels and quadratic residue
diffusers (QRDs). The scattering measurements have been used to test
theoretical prediction methods based on the Helmholtz-Kirchhoff integral
equation. Accurate prediction methods were found for all surfaces tested. The
limitations of the more approximate methods have been defined. The
assumptions behind Schroeder's design of the QRD have been tested and the
local reacting admittance assumption found to be valid over a wide frequency
range. It was found that the QRD only produces uniform scattering at low
frequencies. For an on-axis source the scattering from a curved panel was as
good as from a QRD. For an oblique source the QRD produced much more
uniform scattering than the curved panel.
The subjective measurements evaluated the smallest perceivable change
in the early sound field, the part most influenced by reflectors and diffusers. A
natural sounding simulation of a concert hall field within an anechoic chamber
was used. Standard objective parameters were reasonable values when compared
to values found in real halls and subjective preference measurements. A
difference limen was measured for early lateral energy fraction (.048 ± .005); .
inter aural cross correlation (.075 ± .008); clarity index (.67 ± .13 dB); and
centre time (8.6 ± 1.6ms). It was found that; (i) when changes are made to
diffusers and reflectors, changes in spatial impression will usually be larger than
those in clarity; and (ii) acousticians can gain most by paying attention to lateral
sound in auditoria. It was also found that: (i) diffuse reflections in the early
sound field are not perceived differently from specular reflections; and (ii) the
initial time delay gap is not significant to listener preference.

Objective and subjective evaluation of reflecting and diffusing surfaces in auditoria

Some preliminary acoustical considerations in the design for the proposed Wellington (New Zealand) town hall

Investigation of aircraft overflight and ground vehicle noise around a general aviation airport provided the opportunity to measure the frontyard to backyard noise reduction afforded by residential structures for these two types of noise sources. The measured average noise reduction for two residences using passing street vehicles as noise sources was found to be 17 and 21 dBA. For aircraft overflights using identical measurement instrumentation and microphone locations, as were used for the street traffic noise, the average measured noise reduction (i.e., difference between frontyard and backyard noise levels) was found to be 0.2 and 0.4 dBA. The results of the measurements show that acoustical factors around residences are such as to generally cause substantial frontyard to backyard noise reduction for street traffic noise, but not for the noise from aircraft overflights.

Comparison of aircraft and ground vehicle noise levels in front and backyards of residences

An array of electroacoustic equipment is designed to present to a listener a series of acoustical events essentially similar to the occurrences in a real auditorium. Direct sound, first side‐wall reflections, and the growth and decay of reverberant stored, are independently generated and individually controllable. Thus the ratios of direct/environmental/reverberant sounds can be adjusted by the subject to suit his taste for the program samples. The system and its components are described. It handles either recorded material or live performance, which can be played into the system operating in continuous real time.

Auditorium Synthesis—A Research Tool

The importance of early reflected sound from side wall and ceiling reflecting panels in auditoria and other spaces used for musical presentation has been recognized for some 25 years. Quantitative data on the size, shape, and orientation of reflecting panels to achieve wideband spectral reflections have not been widely available. This paper presents some results on the effect of size and aspect ratio on the reflection characteristics of hard panels measured using scale modeling techniques.

Measurement of panel reflection using acoustical scale modeling techniques—Part II: Measured results

It is imperative to investigate the acoustical properties of roms with the aid of models prior to construction. Two sound sources have been developed to facilitate these investigations. An air jet utilizing four intersection jets provides a nondirectional random noise, over a frequency range of 2400 cps to over 100 kcps for the study of the steady‐state properties of rooms. A repeating spark generates an acoustical pulse having a rise time of less than 2 μsec and a duration of 20 μsec, providing a source for the study of the reflection of pulses within a room. These sources, with a 14‐in.‐diam microphone, are used in 1/50 scale models. Results utilizing these acoustical tools are illustrated by data on the absorption of direct sound over a sloping audience surface, reflection of sound from a canopy, side‐wall reflections, and the acoustical performance of an orchestra enclosure.

Jose C. Ortega

Papers

Comparison of aircraft and ground vehicle noise levels in front and backyards of residences

Auditorium Synthesis—A Research Tool

Measurement of panel reflection using acoustical scale modeling techniques—Part II: Measured results

Acoustical Modeling in Architectural Acoustics