Designing for grille and diffuser noise is of paramount importance. Neil Jarman looks at the data currently provided by manufacturers and provides some design tips.
As active noise control systems begin to penetrate the market place, are the days of the passive attenuator numbered? Andrew Brister looks at the likely future for anti-noise.
Is fighting sound with sound the future for noise control? James Macneil hears how active noise technology is slowly being fine-tuned for commercial use.
The sound insulation provided by similar types of windows varies considerably. This paper describes experiments on a number of elements which affect sound insulation, including the sealing of openable panes, the type of frame material, the size of the window panes, and the spacing of panes in multiple pane systems. It identifies the main factors and lists the potential insulation values for various types of window. This paper will be of interest to architects, planners and acoustic consultants.
Office noise affects the productivity of every person in every office. Companies have woken up to the detrimental effects on productivity of stale air pumped out by air-conditioning systems, and they are replacing these with natural ventilation systems. However, air-conditioning provides a useful by-product: the steady masking of background noise. Tom. Dawn considers the options for creating a better acoustical environment.
The acoustic environment was investigated in an office building with a history of occupant complaints. A scoring system was developed for rating occupants' sick building symptoms. High scores were associated with the occurrence of high levels of infrasound (< 20 Hz) in the rooms, und low levels with low scores. The infrasound came from the ventilation system as airborne noise, rather than structural-borne vibration. Levels of infrasound were often amplified in the tightly sealed rooms, and could be higher at work stations than at supply grilles.
The issue of sound quality in offices and other occupied spaces has been of continuing interest since the 1950s. Existing assessment methods do not adequately account for the Low-frequency background sound ( < 250 Hz) produced by operating heating, ventilating, and air-conditioning (HVAC) systems, in particular, Low-frequency rumble. This paper discusses the results of ASHRAE-sponsored research in which more than 75 HVAC noise samples were collected, normalized, and categorized in terms of sound quality.
Fans and their associated ventilation ducts are amongst the major sources of airborne noise encountered within a submarine. Health & Safety Standards require that the ship's crew are not exposed to unnecessary high levels of noise and have a suitable environment free from intrusive noise in order to work and rest. The problem with noise emitted from fans and ducts in submarines can be categorised as follows:
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