Orthogonal acoustical factors of a sound field in a bamboo forest

Sakai, Hiroyuki; Shibata, Shozo; Ando, Yumiko

doi:10.1121/1.1354988

Cited by 11 publications

(5 citation statements)

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“…Although the acoustics of forests have been studied previously (e.g. [20], [22]), to date, as cited in [1], only one study has attempted to simulate this reverberant effect. Spratt and Abel's Treeverb is a digital reverberator designed to model the scattering of acoustic waves between a number of trees as might be found in a forest environment [33].…”

Section: A Treeverbmentioning

confidence: 99%

“…For instance, in [21] it was shown that acoustic scattering from the tree trunk is a key factor affecting the behavior of mid-frequency attenuation for sound propagation through trees. Surprisingly, a bamboo forest has good acoustic characteristics for certain types of music [22] and outdoor acoustics also have a connection to concert halls, as shown in a study by Lokki et al who demonstrated that the finite difference time domain (FDTD) technique is suitable for modeling the acoustics of ancient amphitheaters, which are open but can have excellent acoustic properties [23]. A related study, that considered the acoustic characteristics of an historic street, combined impulse response measurement of the existing site and geometric acoustic modeling of the historic environment as part of an analysis of its suitability for dramatic performances [24].…”

Section: Introductionmentioning

confidence: 99%

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Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Stevens

Murphy

Savioja

et al. 2017

IEEE/ACM Trans. Audio Speech Lang. Process.

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Computer games and virtual reality require digital reverberation algorithms, which can simulate a broad range of acoustic spaces, including locations in the open air. Additionally, the detailed simulation of environmental sound is an area of significant interest due to the propagation of noise pollution over distances and its related impact on well-being, particularly in urban spaces. This paper introduces the waveguide web digital reverberator design for modeling the acoustics of sparsely reflecting outdoor environments; a design that is, in part, an extension of the scattering delay network reverberator. The design of the algorithm is based on a set of digital waveguides connected by scattering junctions at nodes that represent the reflection points of the environment under study. The structure of the proposed reverberator allows for accurate reproduction of reflections between discrete reflection points. Approximation errors are caused when the assumption of point-like nodes does not hold true. Three example cases are presented comparing waveguide web simulated impulse responses for a traditional shoebox room, a forest scenario, and an urban courtyard, with impulse responses created using other simulation methods or from real-world measurements. The waveguide web algorithm can better enable the acoustic simulation of outdoor spaces and so contribute toward sound design for virtual reality applications, gaming, and auralization, with a particular focus on acoustic design for the urban environment.

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Section: A Treeverbmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Stevens

Murphy

Savioja

et al. 2017

IEEE/ACM Trans. Audio Speech Lang. Process.

View full text Add to dashboard Cite

show abstract

“…and Cosens and Falls (1984) found that 1 KHz and 3 KHz bands present a minimal excess attenuation because ground effect is reduced and 1 and 2 KHz are good transmission frequencies. Sakai et al (2001) found that in a deciduous forest, reflected sound from ground and direct sound meet up at 40 m from the source.…”

Section: Ground Effectmentioning

confidence: 97%

Habitat Structure, Resources and Natural Enemies: Their Influence on Population Fluctuations of the Kowhai Moth Uresiphita Polygonalis Maorialis (Felder)

Mundaca¹

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The importance of habitat structure has been historically discussed in terms of its influence on diversity, distribution and abundance of living organisms. In this regard, the population fluctuations of any particular species, particularly outbreaking insect species, can be expected to be profoundly influenced by the structure of the habitat. A set of ecological hypotheses, such as, the associational resistance, plant decoy, habitat heterogeneity and resource concentration have implicitly included the structure of the habitat determined by the structure (size, density, physical location) of the host plant and other surrounding plant species. Moreover, type, quality and availability of resources, in addition to the presence of other interacting organisms, e.g. competitors, predators and parasites, have also been considered determining factors in the population fluctuation of outbreaking species. The aim of this thesis is to contribute to the understanding of how the outbreaks of the kowhai moth, U. polygonalis maorialis, relate to the physical structure of the habitat, the availability of resources, specific host plants and to natural enemies. In the first experimental chapter of my thesis I studied the fluctuations of the U. polygonalis maorialis larvae and their impacts on the defoliation levels of Sophora spp. plants. I carried out a survey in urban and suburban areas of Wellington city. I examined levels of defoliation of the host plants and population fluctuations in terms of a set of biotic and abiotic variables. These variables were selected in order to cover a range of measures of habitat structure, resource availability and invertebrate community. I modelled such responses to find which variables better explained the observed defoliation and larval population fluctuations. The best fitted model showed that levels of observed defoliation were explained by the structure of the vegetation surrounding the main host plant (vertical and horizontal) and the species of host plant. Population fluctuations of the kowhai moth were explained by the following predicting variables: density of natural enemies, structure of the vegetation surrounding the main host plant (vertical and horizontal), host plant size, level of habitat disturbance, type of habitat (urban/suburban) and the Sophora spp. In my second experimental chapter, I focused on the importance of availability of resources to explain observed densities of U. polygonalis maorialis and phytophagous insects. In my observational experiment I tested the resource concentration hypothesis and the natural enemies hypothesis, by studying the fluctuations of U. polygonalis maorialis larvae on individuals of Sophora microphylla plants located in gardens across Wellington city. Larval densities were found to be higher on smaller plants than large plants, whereas natural enemies did not show specific responses to plant size. In my manipulative experiment I originally aimed for the establishment of U. polygonalis maorialis in the experimental plots. Unfortunately, these were not colonised by U. polygonalis maorialis, instead I studied phytophagous insects that colonised the plots. I found no differences among the S. microphylla treatments for the levels of establishment of phytophagous invertebrates. On the contrary, the amount of nil records was high and there was an overall high variability among treatments and low rate of establishment throughout the sampling season. Nevertheless, natural enemies were found to occur more often at higher densities in plots with lower plant density in only two specific dates. Uresiphita polygonalis maorialis is the main defoliator of Sophora spp in New Zealand. In this context I studied the feeding and oviposition preferences of the moth for the three most commonly found species of Sophora plants in Wellington city. Sophora tetraptera was the preferred species chosen by the female moth. The same species was also the most palatable and preferred when confronted to S. microphylla and S. prostrata. These patterns observed in controlled conditions are coincident with observations made in the field throughout the study. Within the set of variables determined by the invertebrate community, the influence of natural enemies on an herbivorous population is one of the most important in terms of population regulation. In my last experimental chapter I found a positive correlation among the parasitism by M. pulchricornis and U. polygonalis maorialis larval densities, which opens the possibilities for future research to explore the potential existence of population regulation mechanisms between these two taxa. Overall, the results of my thesis highlight the importance of understanding the influence of the structure of the habitat, types of resources provided by plants and natural enemies in determining the fluctuations of outbreaking insect species.

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Section: Ground Effectmentioning

confidence: 97%

Vocal Communication Within a Forest Bird Community

Azar¹

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This thesis takes a community approach to investigate the acoustics of forest birds in Zealandia sanctuary, Wellington. Initially, the annual changes in vocalisation output of 16 study species and their possible effect on bird conspicuousness were described. Environmental factors that may shape these avian vocalisations were addressed though invoking two key hypotheses, the acoustic adaptation hypothesis, and the acoustic niche hypothesis. In addition, the songs of selected species are investigated: the role of song harmonics in the native North Island saddleback, Philesturnus rufusater, and their role in ranging, change in song dialect through time and space in the introduced song thrush, Turdus philomelos, and temporal change in the song of the native grey warbler, Greygone igata. Vocal activity of the study species varied seasonally, affecting their detectability in bird counts. Some species were mostly first heard rather than seen and viceversa. The results lend support to the acoustic niche hypothesis in that vocalisations within the forest bird community appear to have evolved towards divergence, with native species’ vocalisations being more dispersed within the community acoustic space than those of the introduced species. However, all species concentrated their energy within relatively narrow frequency bands, supporting the predictions of the acoustic adaptation hypothesis. Adaptation to different transmission properties associated with different singing elevations or physiological parameters such as body weight may have an effect on shaping such bird vocalisations. Forests provide a complex acoustic space for sound transmission and a “sound window” may not be a constant property of a given forest. The study revealed that a prominent sound window persists in the lower frequency range that is less affected by habitat. Some high frequencies may have similar average attenuation values to those of low frequency, however, with greater fluctuation in attenuation. Ground effect is a further factor in determining how well different frequency ranges transmit and birds may use acoustic characteristics of their habitat to enhance their signal. Harmonics in North Island saddleback chatter song were found to play a potential role in ranging (estimating the distance of signaller), for playback songs with more relative energy within higher harmonics were evidently perceived as coming from a nearby individual. The repertoire size of the song thrush population studied in Zealandia has apparently evolved to become larger and more varied than the source population of song thrushes in the UK, with more syllables delivered with less repetition than the UK song recordings examined. Over a period of 7 years, syllables in grey warbler song have shifted to a higher frequency, but there was no difference in the temporal structure of the song. Habitat effect, competition on the acoustic signal from reintroduced birds and ambient noise level are considered as possible casual factors.

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Orthogonal acoustical factors of a sound field in a bamboo forest

Cited by 11 publications

References 11 publications

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Habitat Structure, Resources and Natural Enemies: Their Influence on Population Fluctuations of the Kowhai Moth Uresiphita Polygonalis Maorialis (Felder)

Vocal Communication Within a Forest Bird Community

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