Single Loudspeaker Research Articles

The cumulative effect on sound levels from multiple underwater anthropogenic sound sources in shallow coastal waters

Summary Underwater anthropogenic sound levels in the ocean are increasing, and the evidence for impacts of sound on marine life is overwhelming. Currently, regulatory bodies require emitted sound from marine renewable energy projects to be assessed in order to infer potential impacts on marine life. Geometric spreading models are sometimes used to assess likely ecological impacts of anthropogenic sound by estimating the propagation of underwater sound without in situ verification. This study investigated the propagation of anthropogenic sound in shallow waters (25–45 m deep) from a single monopole (a single loudspeaker) and twin monopole (two loudspeakers) sound sources replaying tidal turbine sound to approximate anthropogenic sound sources in this environment. Greater sound levels at 100–800, 801–2000 and 2001–20 000 Hz were observed at all observation distances from the sound source for the twin monopole compared to the single monopole. These results suggest that the sound from multiple anthropogenic sound sources installed in one location is likely to be cumulative in the environment where their sound fields overlap. Sound intensities observed in both the single monopole and twin monopole experiments for 0·1–20 kHz were higher than estimates derived from standard geometric spreading models for underwater sound by 3–41 dB across all measured distances from the source. The greatest difference from the theoretical spherical spreading model (41 dB) occurred at the site most distant from the twin monopole sound source, that is, 5 km. Synthesis and applications. The results show that geometric models used by some regulatory bodies may be underestimating the spatial extent to which the anthropogenic underwater sound may be propagating and creating potential ecological impacts. Based on field measurements, we have presented an alternative model which should assist regulatory agencies to better estimate and manage ecological impacts from anthropogenic underwater sound.

A pair of Barred Antshrikes (Thamnophilus doliatus) perched near their nest in French Guiana. Pairs of antshrikes perform vocal duets to defend their territories against rivals. Results of a playback experiment reveal that territorial antshrikes respond more aggressively to duets presented through stereo loudspeakers compared to a single loudspeaker, and that both the male and female display equivalent responses to

A pair of Barred Antshrikes (<i>Thamnophilus doliatus</i>) perched near their nest in French Guiana. Pairs of antshrikes perform vocal duets to defend their territories against rivals. Results of a playback experiment reveal that territorial antshrikes respond more aggressively to duets presented through stereo loudspeakers compared to a single loudspeaker, and that both the male and female display equivalent responses to

Does the ventriloquist illusion assist selective listening?

Driver (1996) reported that the ventriloquist illusion can enhance selective listening of speech. Participants in his study listened to target and distractor words from a single loudspeaker while watching lip movements of the target words on a video monitor either above the loudspeaker or displaced to the left or right. He found that participants were more accurate in repeating the target words when the video was displaced from the loudspeaker than when the video was directly above the loudspeaker. Driver proposed that the ventriloquist illusion dragged the target sounds toward the location of the lip movements, freeing them from interference from the distractor words. However, successful attempts at replicating this finding are rare (we know of only three successful replications from 19 attempts). In five experiments, we found a weak advantage for selective listening from displaced lip movements only when there was a convincing ventriloquist illusion. We conclude that the ventriloquist illusion is necessary to confer the advantage for selective listening from displaced lip movements but that the phenomenon is a fleeting one at best.

Unidirectional Sound Signage for Speech Frequency Range Using Multiple-Loudspeaker Reproduction System

Human safety is the most important issue in disaster management. Speech is a sound signal containing information that is easily and quickly understood by humans. Using speech as sound signage in emergency systems can effectively increase human safety in low or poor visibility conditions such as in smoke-filled situations. However, reflections of sound through walls, floor surfaces, and ceilings will affect clarity of speech. Unfortunately, because of the characteristics of sound reproduction systems, a single loudspeaker propagates sound waves omni-directionally at low frequencies. This paper proposes a simple multiple-loudspeaker system for reproducing sound with uni-directional characteristics. The proposed system consists mainly of a primary loudspeaker for introducing sound in the desired beam, a secondary loudspeaker for reducing gain in the undesired direction, and digital filters. An adaptive finite-impulse-response (FIR) filter is used to produce the controlling sound by implementing a filtered-x least-mean-square algorithm, and a delay filter for adjusting the time alignment of sound propagation between primary and secondary sources at the control point. Several operational conditions for illustrating real situations and reflections were considered in an anechoic chamber. Experimental results show the directivity patterns of the proposed multiple-loudspeaker system for the required conditions. In a low frequency range, the system is able to control unidirectional propagation; there is a sound beam in the desired direction and, conversely, reduction of gain in the undesired direction around the control point.

A Secondary Source Configuration for Control of a Ventilation Fan Noise in Ducts

The main noise source in heating, ventilation, and air conditioning systems is usually a ventilating fan. Noise, generated by the ventilating fan is transmitted through the duct into the living and working environment. A typical fan noise spectrum consists of a broadband noise, which is superimposed with pure tones. Different methods are available to reduce a transmission of such noise from the ventilating fan into the living and working environment. In this article it is demonstrated how a feedforward active noise control system can be implemented together with a side branch resonator. Effectiveness of the feedforward active noise control system depends on the quality of a reference signal, which should be in a perfect correlation with the primary noise. An acoustic feedback is the main problem of feedforward active noise control systems in ducts. A combined method uses a single loudspeaker to work as a dipole source and a side branch resonator to reduce the acoustic feedback. A side branch resonator reduces noise transmission in a narrowband frequency range as well. In this article, a theoretical background of a dipole source with a side branch resonator is presented, along with some measurement results and simulations of active noise control.

Analysis and Optimal Condition of the Rear‐Sound‐Aided Control Source in Active Noise Control

An active noise control scenario of simple ducts is considered. The previously suggested technique of using an single loudspeaker and its rear sound to cancel the upstream sound is further examined and compared to the bidirectional solution in order to give theoretical proof of its advantage. Firstly, a model with a new approach for taking damping effects into account is derived based on the electrical transmission line theory. By comparison with the old model, the new approach is validated, and occurring differences are discussed. Moreover, a numerical application with the consideration of damping is implemented for confirmation. The influence of the rear sound strength on the feedback‐path system is investigated, and the optimal condition is determined. Finally, it is proven that the proposed source has an advantage of an extended phase lag and a time delay in the feedback‐path system by both frequency‐response analysis and numerical calculation of the time response.

Evaluating small end-fire loudspeaker array under various reverberations

A compact end-fire loudspeaker array based on the linearly constrained minimum variance has been investigated in various reverberation rooms. In the linearly constrained minimum variance beamformer, the coherent matrix that determines the suppression direction of the radiation sound is important. Therefore, we evaluated the directivities of a loudspeaker array for four different coherent matrices that were calculated using the following methods in which the array will not radiate the sound: (I) for any direction except the reproduction direction, (II) in the direction of several measured room transfer functions, (III) in the direction of several ideal (free field) room transfer functions, and (IV) in the direction of the weighted ideal room transfer functions. To evaluate performance, a 4-element line array of 28-mm-diameter loudspeakers with equal spacing of 48 mm was implemented. The array used loudspeaker units without enclosures to shorten the spaces between the units. The directivities of the prototype loudspeaker array were measured in an anechoic room and three reverberant rooms by using the above four methods. The prototype arrays achieved higher directivity of 6 to 15 dB for wideband frequencies (300 Hz to 3.4 kHz) than the single loudspeaker for all methods. Moreover, the experimental results clarified that the array with method (IV), which did not use prior measured room transfer functions, had efficient performance in comparison with the array with method (II), especially when the reverberation time was 120 ms or less.

A Control Source Structure of Single Loudspeaker and Rear Sound Interference for Inexpensive Active Noise Control

Active noise control systems of simple ducts are investigated. In particular, open‐loop characteristics and closed‐loop performances corresponding to various structures of control sources are compared based on both mathematical models and experimental results. In addition to the standard single loudspeaker and the Swinbanks′ source, we propose and examine a single loudspeaker with a rear sound interference as a novel structure of control source, where the rear sound radiated from the loudspeaker is interfered with the front sound in order to reduce the net upstream sound directly radiated from the control source. The comparisons of the control structures are performed as follows. First, the open‐loop transfer function is derived based on the standard wave equation, where a generalized control structure unifying the three structures mentioned above is considered. Secondly, by a comparison of the open‐loop transfer functions from the first principle modeling and frequency response experiments, it is shown that a certain phase‐lag is imposed by the Swinbanks′ source and the rear sound interference. Thirdly, effects on control performances of control source structures are examined by control experiments with robust controllers.

How Much Residual Hearing Is ‘Useful’ for Music Perception with Cochlear Implants?

Aim: To compare performance on a song recognition task of bilaterally combined electric and acoustic hearing (bimodal stimulation) with electric or acoustic hearing alone. Methods:Subjects were 14 adults with cochlear implants (CI) who continued to use a hearing aid (HA) in one/both ears. Subjects were asked to identify excerpts from 15 popular songs, which were familiar to them, presented in a random order via a single loudspeaker. Presentation conditions were fixed in order: bimodal, CI alone and then HA alone. Musical excerpts were presented in each condition with and then without lyrics. Results:In a subgroup of subjects (n = 8) with better low-frequency residual hearing (thresholds <85 dB hearing level (HL)), mean scores for bimodal stimulation were significantly greater than for CI alone. In addition, mean ‘no lyrics’ scores for HA alone (59.7%) were significantly greater than for CI alone (38.8%). All of these subjects considered bimodal stimulation to be the most enjoyable way to listen to music. For the remaining subjects (n = 6) there was no benefit from using bimodal stimulation over CI alone, and the majority of these preferred to listen to music using CI alone. Conclusions:Bimodal stimulation provides better perception of popular music, particularly melody recognition, compared to CI alone when low-frequency residual hearing is better than 85 dB HL.

Auditory-guided reaching movements in the peripersonal frontal space

Previous studies on auditory localization processes have shown that humans can localize sound sources accurately, including distance in certain situations. Few studies have examined auditory localization by binaural mechanisms in the peripersonal space. Numerous studies have examined auditory localization through verbal report or various pointing movements. This study examines the precision of hand "reaching" movement towards an auditory object. An experimental platform (semicircle, radius 1m) was constructed with 35 small loudspeakers placed under an acoustically transparent grid. Blindfolded subjects were seated within the platform at table height. Test protocol consisted of a brief audio stimulus presented via a single loudspeaker followed by the subject placing their index finger (preferred hand) at the location of the sound object. Optical finger tracking was used during the course of the experiment. Two test variables were investigated: different audio stimuli, Gaussian noise bursts varying the number and the duration of each burst; room acoustic conditions, with and without acoustical damping for reflection suppression. Preliminary results show precision of localization does not grow indefinitely with the number of burst repetitions but reaches a limit. Azimuth precision remains accurate, even with short burst conditions, contrary to the distance perception which increases with the stimuli duration.

Active Noise Cancellation for Ventilation Ducts Using a Pair of Loudspeakers by Sampled‐Data ℋ∞ Optimization

We deal with the design of active noise control systems for ventilation ducts with a pair of loud‐speakers based on sampled‐data ℋ∞ optimization, in order to improve our previous study with a single loudspeaker. The resultant controller requires lower computational complexity for the implementation, compared to the standard time‐varying adaptive controllers, since it is time‐invariant and the order is comparable. Moreover, the effect of Swinbanks′ source is automatically recovered by the ℋ∞ optimization. The benefit of the proposed method is also confirmed from experimental results for a real house, where the achieved noise attenuation level is about twice as much as that of the single loudspeaker case.

Using a signal cancellation technique to assess adaptive directivity of hearing aids

The directivity of an adaptive directional microphone hearing aid (DMHA) cannot be assessed by the method that calls for presenting a "probe" signal from a single loudspeaker to the DMHA that moves to different angles. This method is invalid because the probe signal itself changes the polar pattern. This paper proposes a method for assessing the adaptive DMHA using a "jammer" signal, presented from a second loudspeaker rotating with the DMHA, that simulates a noise source and freezes the polar pattern. Measurement at each angle is obtained by two sequential recordings from the DMHA, one using an input of a probe and a jammer, and the other with an input of the same probe and a phase-inverted jammer. After canceling out the jammer, the remaining response to the probe signal can be used to assess the directivity. In this paper, the new method is evaluated by comparing responses from five adaptive DMHAs to different jammer intensities and locations. This method was shown to be an accurate and reliable way to assess the directivity of the adaptive DMHA in a high-intensity-jammer condition.

A Compact Active Control System for Tonal Noise Reduction in Axial Fans

The objective of this paper is to show the feasibility of active control of tonal noise from automotive engine cooling fans using a single unbaffled loudspeaker in front of the fan. A simplified model is described for preliminary design using this configuration. A single input single output (SISO) filtered X-LMS has been implemented to control the first tones in real time. At the error microphone, the sound pressure attenuation at blade passage frequency (BPF) and its first harmonics are reduced down to the broadband noise level. At low frequency, for large sound wavelength compared to the fan radius, the sound radiation is reduced in all directions, since the dipolar directivity of the secondary noise emitted by the unbaffled loudspeaker is similar to the directivity of the primary noise emitted by the fan.

Efficient Multichannel NLMS Implementation for Acoustic Echo Cancellation

An acoustic echo cancellation structure with a single loudspeaker and multiple microphones is, from a system identification perspective, generally modelled as a single-input multiple-output system. Such a system thus implies specific echo-path models (adaptive filter) for every loudspeaker to microphone path. Due to the often large dimensionality of the filters, which is required to model rooms with standard reverberation time, the adaptation process can be computationally demanding. This paper presents a selective updating normalized least mean square (NLMS)-based method which reduces complexity to nearly half in practical situations, while showing superior convergence speed performance as compared to conventional complexity reduction schemes. Moreover, the method concentrates the filter adaptation to the filter which is most misadjusted, which is a typically desired feature.

Effect of Type of Noise and Loudspeaker Array on the Performance of Omnidirectional and Directional Microphones

Differences in performance between omnidirectional and directional microphones were evaluated between two loudspeaker conditions (single loudspeaker at 180 degrees; diffuse using eight loudspeakers set 45 degrees apart) and two types of noise (steady-state HINT noise; R-Space restaurant noise). Twenty-five participants were fit bilaterally with Phonak Perseo hearing aids using the manufacturer's recommended procedure. After wearing the hearing aids for one week, the parameters were fine-tuned based on subjective comments. Four weeks later, differences in performance between omnidirectional and directional microphones were assessed using HINT sentences presented at 0 degrees with the two types of background noise held constant at 65 dBA and under the two loudspeaker conditions. Results revealed significant differences in Reception Thresholds for Sentences (RTS in dB) where directional performance was significantly better than omnidirectional. Performance in the 180 degrees condition was significantly better than the diffuse condition, and performance was significantly better using the HINT noise in comparison to the R-Space restaurant noise. In addition, results revealed that within each loudspeaker array, performance was significantly better for the directional microphone. Looking across loudspeaker arrays, however, significant differences were not present in omnidirectional performance, but directional performance was significantly better in the 180 degrees condition when compared to the diffuse condition. These findings are discussed in terms of results reported in the past and counseling patients on the potential advantages of directional microphones as the listening situation and type of noise changes.

Control of tonal noise from subsonic axial fan. Part 2: active control simulations and experiments in free field

This paper deals with the global control of engine cooling fan noise in free field at the Blade Passing Frequency (BPF) and its first harmonic. The aim of this paper is to investigate the feasibility of using a single loudspeaker in front of the fan to cancel the tonal noise. A simplified model of fan noise, which only takes into account the most radiating circumferential mode of the forces acting by the fan on the fluid, is first combined with an unbaffled loudspeaker model to predict the residual sound field for various sensor configurations. Metrics for global control such as sound directivity or sound power attenuation reveal that the control is effective with this simplified model in the whole space at low frequency, depending on the number and location of the error sensors. However, for non-homogeneous flow, other circumferential modes may contribute to the sound radiation and then, the inverse model described in the companion paper is used to provide a more accurate extrapolated sound field from the reconstructed unsteady aerodynamic forces acting by the fan on the fluid. Simulation results demonstrate the global control in the downstream half space of the blade passing frequency and its first harmonic using a single error microphone and a single control source. A single-input–single-output (SISO) adaptive feedforward controller is implemented experimentally to drive the control loudspeaker. The tones at the BPF and at its first harmonic are attenuated by up to 28 and 18 dB, respectively at the far field error microphone.

Development of a Test Environment to Evaluate Performance of Modern Hearing Aid Features

This article describes a new test environment and materials with the potential to measure performance differences among different hearing aid signal processing methods and features. Normative data suggest a linearly predictable increase in difficulty on a speech-in-noise task as the masker changes from random noise to multiple-talker speech, and the number of talkers increases. Data collected with normal listeners revealed no differences across four test sites for the single loudspeaker (Noise-Front) results and some differences across test sites for the multiple loudspeaker results. Room dimension differences among audiometric test enclosures and diffusion (or lack thereof) of the maskers in the vertical and horizontal dimensions of the sound fields appear to account for performance differences for the multiloudspeaker arrays, confirming the need to limit maskers to aperiodic signals in rooms with controlled ceiling height or to establish norms for each test environment such that results obtained in different enclosures can be compared.

The effect of stimulus bandwidth and subject position on horizontal-plane localization with virtual source images

In an anechoic chamber normal-hearing subjects performed a localization task in the frontal horizontal plane. The stimulus was a 200-ms burst of filtered noise. Within a block of trials, half of the presentations (randomly determined) were ‘‘real’’—presented from single loudspeakers—and the other half were ‘‘phantoms’’—produced by the simultaneous activation of two loudspeakers at ±30° using a virtual source imaging technique [Takeuchi et al., J. Acoust. Soc. Am. 109, 958–971 (2001)]. Both phantom and real sources spanned the azimuthal range ±80°. When the stimulus was a 4 kHz low-pass filtered noise, rms error was only slighly higher for phantom (D̄=7.1°) than for real (D̄=5.5°) sources. For 8 kHz low-pass filtered noise, performance remained about the same for real sources, but increased for phantom sources (D̄=11.5°). Data will also be reported for conditions in which the subject’s position is systematically varied outside the ‘‘sweet spot.’’ Results will be discussed in terms of robustness of the virtual imaging technique to stimulus and position factors and its potential usefulness as a tool for the investigation of human auditory spatial perception in static and dynamic environments. [Work supported by NIDCD.]

The effect of background noise on the perception of auditory distance

Five-ms broadband noise bursts were played and recorded through a KEMAR manikin from 6 different distances in a reverberant room. Distances ranged from 4 to 9 feet, and all recordings were 500 ms in duration. A single loudspeaker sat atop a table, and was moved to each distance prior to recording. During testing, stimuli were presented over headphones to listeners seated in a sound-attenuating chamber. In one condition, the ambient sound of the room was mixed with the stimuli, and served to fill in the silent gaps between stimulus presentations. Previous results have shown that distance judgments improve significantly when the silent gaps are filled with ambient noise. In the other conditions on-line noise, which was filtered to approximate the spectrum of the ambient noise, was added instead. Three levels of attenuation were used, −5 dB, 0 dB, and +5 dB, relative to the background noise level. The task was to judge the distance of the sound. A repeated measures design was employed, and listeners ran in only one condition on a given day. Preliminary results suggest that judgments are significantly improved with ambient-room noise, as compared to on-line noise. Additional findings and significance will be discussed. [Work supported by NIH.]

Simple drive system for Mössbauer spectroscopy

A simple driving system for generating photons with flat energy spectrum by the Doppler effect is described. The classical double-loudspeaker design with electronic feedback is replaced with a single loudspeaker and smart driving electronics, that uses low cost microcontrollers and DACs.