Excessive Reverberation Research Articles

Excessive Reverberation Time for Organs?

Whether or not organists and organ builders are demanding excessively reverberant environment is posed as a problem for consideration. The point is brought up that too long reverberation periods could result in an undesirable coloring of what is heard.

Use of Selective Equalization for Feedback Suppression

The paper summarizes results of measurements and observations made in about 200 rooms with sound re-enforcing systems. Behavior of sine-wave room response near major feedback modes is described. The effect on feedback of broad-band equilization is shown. The role of narrow-band filters relative to control of ring modes and excessive reverberation is set out. The existence of a limit to system gain before feedback, set by the geometry of the situation and other parameters, is discussed, along with the concomitant change in the nature of the feedback modes as the limit is approached. The observed effect of temperature on the frequency of feedback and ring modes is reported. The degree of nonlinearity between the irregularity of room response at these modes and the insertion loss of a filter to eliminate the irregularity is described.

Examples of Unusual Sound-Reinforcement Systems

Several examples are selected to illustrate solutions of unusual or extreme problems, such as excessive reverberation, high-level ambient noise, disproportioned theaters, large-group conference, indoors-to-outdoors, the large amphitheater. All solutions are devised to achieve high intelligibility, naturalness, and apparent source localization.

Sound Propagation in Urban Areas

Outdoor sound communication systems for urban areas have been traditionally designed using relatively few sources of sound, located high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block by-block coverage system using many sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound-propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound refraction effects were observed over distances of a city block or two when sound was propagated from a source 10–20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation.

Investigation of Sound Propagation in Urban Areas

Outdoor civil-defense alerting and voice-warning systems for urban areas have been traditionally designed. using relatively few sources of sound high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block-by-block coverage system using many directive sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound-propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound-refraction effects were observed over distances of a city block or two when sound was propagated from a source 10 20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation. [Work supported by the U. S. Office of Civil Defense.]

Acoustics of Shaheed Smarak Hall at Jabalpur

AbstractThe paper relates to investigations made regarding the acoustics of the hall and the measures adopted to improve the same.The three main factors responsible for acoustic condition, namely (a) the reverberation time, (b) the distribution of sound pressure level and (c) the noise level, were studied. Measurements were taken when the hall was completely empty. The intelligibility was found to be poor, the main cause being the excessive reverberation. Based on these results, an estimate was made of the reverberation time that may be expected after furnishing it with the chairs and with audience present. Attempt was made to provide as much of the additional absorption necessary, as was possible with such objects as carpets, curtains, hangings, etc. Only the remaining amount of absorption was provided by treating with acoustical tiles, without affecting the architecture of the hall.Several sets of measurements were taken under different conditions of the hall during the execution of the suggestions and ...

Modern Schoolroom Acoustics

Many teachers are faced with conducting classes in buildings that were obsolete thirty years ago. Others are or soon will be teaching in new schools which are in no way modern in some of their basic construction details. A classroom, laboratory, or auditorium is fundamentally a shelter in which the basic functions are seeing and hearing. Daylight provides satisfactory seeing a large part of the time. In spite of this, about $1.50 per square foot is the average investment for auxiliary lighting, while satisfactory acoustics is often completely overlooked or is the target of severe economy measures. Architects today are often eliminating or seriously compromising on the acoustical treatment expenditure while spending lavishly for less important materials. Eighty-five percent articulation will usually result in satisfactory hearing for adults because the context supplies the transitional ties. For children, however, especially the very young, each word and every syllable is important. Excessive reverberation time or poor sound distribution may create conditions which seriously handicap the students and teachers alike. Modern medical methods have shown that poor eyes and poor hearing are often responsible for backward children who are really average or above average in mental ability. It is inexcusable to add to their natural handicaps those of poor architecture and poor engineering. Good acoustics is as fundamental as lighting and ventilation, and much more attention should be paid to this phase of school design.