Pair Of Loudspeakers Research Articles

Audiometers—A Closer Look

Audiometers—A Closer Look

Audio stereo processing method, device and system

The present invention relates to a method and a device for processing and reproducing an audio stereo signal. The method produces a left output signal for transmission to a left loudspeaker in a loudspeaker pair, which is, or is equivalent to, the sum of the mid input signal (M) and the side input signal (S), the method further produces a right output signal for transmission to a right loudspeaker in said pair, which is, or is equivalent to, the sum of the mid input signal (M) and the side signal (S) phase shifted 180° . The method further being characterized in that at least part of the side input signal (S) or the mid input signal (M) is phase shifted approximately 45°-135° relative to the other signal prior to or at the production of the left and right output signals. The invention further relates to such an audio stereo signal reproduction system.

Measurements of Wind Velocity and Direction Using Acoustic Reflection against Wall

The measurements of wind velocity and direction using an acoustic reflection against a wall are described. We aim to measure the spatial mean wind velocity and direction to be used for an air-conditioning system. The proposed anemometer consists of a single wall and two pairs of loudspeakers (SP) and microphones (MIC) that form a triangular shape. Two sound paths of direct and reflected waves are available. One is that of the direct wave and the other is that of the wave reflected on the wall. The times of flights (TOFs) of the direct and reflected waves can be measured using a single MIC because there is a difference in the TOF between direct and reflected waves. By using these TOFs, wind velocity and direction can be calculated. In the experiments, the wind velocities and directions were measured in a wind tunnel by changing the wind velocity. The wind direction was examined by changing the setup of the transducers. The measured values using the proposed and conventional anemometers agreed with each other. By using the wave reflected against a wall, wind velocities and directions can be measured using only two pairs of transducers, while four pairs are required in the case of conventional anemometers.

Image display device with built-in loudspeakers

An image display device has a main display body provided with a thin display unit, a low-frequency loudspeaker (woofer) and two middle and high frequency loudspeakers (tweeters) and a stand supporting the main display body. The stand has a base being just opposite at its top surface to a duct outlet of the woofer, thereby sound emitted from the duct can be constantly absorbed by and reflected from the base. A housing containing the first loudspeaker and a pair of the second loudspeakers has a plurality of through holes formed in a first area corresponding to an aperture of each loudspeaker and a plurality of blind holes formed in a second area surrounding the first area, wherein the second area for the first loudspeaker is different in peripheral shape and/or size from the second area for each of the second pair of loudspeakers.

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.

The binaural performance of a cross-talk cancellation system with matched or mismatched setup and playback acoustics

Cross-talk cancellation is a method for synthesizing virtual auditory space using loudspeakers. One implementation is the "Optimal Source Distribution" technique [T. Takeuchi and P. Nelson, J. Acoust. Soc. Am. 112, 2786-2797 (2002)], in which the audio bandwidth is split across three pairs of loudspeakers, placed at azimuths of +/-90 degrees, +/-15 degrees, and +/-3 degrees, conveying low, mid, and high frequencies, respectively. A computational simulation of this system was developed and verified against measurements made on an acoustic system using a manikin. Both the acoustic system and the simulation gave a wideband average cancellation of almost 25 dB. The simulation showed that when there was a mismatch between the head-related transfer functions used to set up the system and those of the final listener, the cancellation was reduced to an average of 13 dB. Moreover, in this case the binaural interaural time differences and interaural level differences delivered by the simulation of the optimal source distribution (OSD) system often differed from the target values. It is concluded that only when the OSD system is set up with "matched" head-related transfer functions can it deliver accurate binaural cues.

Prediction of sound fields in a long enclosure due to a dipole source

The speech intelligibility in long enclosures is primarily affected by two factors: The reverberation time and the signal to noise ratio. To predict the speech intelligibility, previous studies were mainly focused on predicting either the sound field or the reverberation time in long enclosures. In these predictions, the sound sources were usually assumed to be a monopole source. However, it is well known that many noise sources have distinct directional characteristics. For example, noise radiated from railway vehicles and from ventilating fans is best modeled as a dipole source. This paper presents a numerical model to predict the sound field due to a dipole source in a long enclosure. The numerical model is validated by field measurements. The experimental dipole source was built by using a pair of identical loudspeakers placed at a close distance to each other that generate sound at equal amplitude but opposite in phase. Measurements are conducted at two test sites. Tolerable agreement between numerical predictions and experimental data is obtained.

Active control of drag noise from a small axial flow fan

Noise sources in an axial flow fan can be divided into fluctuating axial thrust forces and circumferential drag forces. For the popular design of a seven-blade rotor driven by a motor supported by four struts, drag noise dominates. This study aims to suppress the drag noise globally by active control schemes. Drag noise features a rotating dipole and it has to be cancelled by a secondary source of the same nature. This is achieved experimentally by a pair of loudspeakers positioned at right angles to each other on the fan rotational plane. An adaptive LMS feedforward scheme is used to produce the control signal for one loudspeaker and the time derivative of this signal is used to drive the other loudspeaker. The antisounds radiated by the two loudspeakers have a fixed phase relation of 90° forming a rotating dipole. An open-loop control scheme is also implemented for the purpose of comparison and easier implementation in real-life applications. The results show that the globally integrated sound power is reduced by about 13dB for both closed- and open-loop schemes. A possible limiting factor for the cancellation performance is found to be the presence of higher order modes of drag noise.

An active headrest for personal audio

There is an increasing need for personal audio systems, which generate sounds that are clearly audible to one listener but are not audible to other listeners nearby. Of particular interest in this paper are listeners sitting in adjacent seats in aircraft or land vehicles. Although personal audio could then be achieved with headsets, it would be safer and more comfortable if loudspeakers in the seat headrests could be actively controlled to generate an acceptable level of acoustic isolation. In this paper a number of approaches to this problem are investigated, but the most successful involves a pair of loudspeakers on one side of the headrest, driven together to reproduce an audio signal for a listener in that seat and also to attenuate the pressures in the adjacent seat. The performance of this technique is investigated using simple analytic models and also with a practical implementation, tested in an anechoic chamber and a small room. It is found that significant attenuations, of between 5 and 25 dB, can be achieved in the crosstalk between the seats for frequencies up to about 2 kHz.

Head rotation and sound image localization in the median plane

The effect of head rotation on median plane sound source (or image) localization is studied. It is suggested that, at low frequency, the change of interaural time difference (ITD) caused by head rotation supplies information for determining sound source direction in the median plane. Based on the suggestion, the summed sound image localization equations for multiple loudspeakers arranged in the median plane are derived. Especially, for a pair of loudspeakers arranged front-back symmetrically in the median plane, the localization equations are similar to that of stereophonic sound in horizontal plane. A sound image localization experiment was carried out to prove the theoretical analysis. The results of this paper are not only available to virtual spatial auditory, but also supply a quantitative validation of the hypothesis that head rotation is a cue for sound source localization in the median plane at low frequency.

Stereophonic reproduction maintaining means and methods for operation in horizontal and vertical a/v applicance positions

Display apparatus including a display and an orientation sensitive interface mechanism is disclosed. In an exemplary embodiment, the orientation sensitive interface includes first and second loudspeaker pairs. The first loudspeaker pair includes first and second loudspeakers and the second loudspeaker pair includes the second and third loudspeaker. The first and second loudspeaker pairs are disposed along transverse directions to each other. The display apparatus comprises a switch which switches between the first loudspeaker pair and the second loudspeaker pair. By providing the respective loudspeaker pairs, and switching between them, it is possible to orient the display apparatus in transverse directions corresponding to respective loudspeaker pairs, yet maintain a substantially stereophonic reproduction for each orientation.

映像情報が音像の方向定位に与える影響について

The purpose of this paper is to clarify the effects of visual information on corresponding auditory information when they are presented simultaneously in a wide frontal area (180 degrees) on a horizontal plain. Sound localization experiments were carried out both with and without visual stimuli associated with sound stimuli. In the experiments, four different visual images of a human speaker and the four corresponding speech sounds were used as the visual and sound stimuli, respectively. The visual stimuli were projected on a half-cylindrical shaped screen in five directions (-60, -30, 0, 30, 60 degrees), and the corresponding sound stimuli were reproduced in 13 directions (-90, …, -15, 0, 15, …, 90 degrees) via loudspeakers placed in each direction or transaural reproduction using a pair of loudspeakers (±30 degrees). The degree of sound localization accuracy was evaluated according to a five-grade system in cases where visual stimuli were absent. The results obtained showed that a sound image far away from its corresponding visual image (maximum 150 degrees) was affected by the visual image, and that a sound image having a relatively low degree of localization accuracy tended to be strongly affected by the visual image. These results show that, in addition to the relative position of visual and sound stimuli, the degree of sound localization accuracy is one of the important elements in auditory-visual interaction on a wide frontal area.

Acoustic coherence imaging through the atmosphere

The process of making images of acoustic scenes through the atmosphere has been investigated. Representations of the acoustic power with angle and the power spectrum with angle can be formed. The performance of interferometric imaging methods based on the Van Cittert–Zernike theorem has been evaluated using data collected in a series of field experiments. An array of microphones received the far-field emissions from a pair of large loudspeakers that reproduced broadband random noise signals. Both the loudspeakers and the array are located near the ground. All imaging is done in the horizontal plane. Pairs of microphones in the array are correlated to form measurements of the complex coherence. An image is then formed via an inverse Fourier transform operation. The field data show that making accurate acoustic images outdoors is difficult due to the effects of turbulence. The image distortion, signal-to-noise ratio, and variance associated with the coherence measurements were calculated as a function of the average wind speed. Even at moderate wind speeds (6 m/s) turbulence can cause an order of magnitude increase in the variance of coherence measurements. Guidelines were drawn that define the expected performance based upon the observed wind speed. Methods for image enhancement are discussed.

Binaural sound reproduction in a stereo dipole system

A new transaural system referred to as a ‘‘stereo dipole’’ reproduction system using a closely spaced pair of loudspeakers in front of a listener has been introduced recently. Computer simulations using theoretical models, in which the listener’s head is assumed to be a perfectly rigid sphere, revealed that sound field equalization by the SD system including inverse filtering and also for the virtual source reproduction can be achieved in a wide range of area relative to the standard loudspeaker arrangements. This paper will deal with a further investigation of the SD system in terms of the controlled acoustic field around the head. The theoretical model used in the computer simulation is extended so that one can calculate an impulse response at any point while considering the influence of a rigid sphere. This model is used to compare the sound field around the spherical obstacle due to the SD system with one by the ordinary transaural system.

Subjective investigation of a new sound reproduction system (stereo dipole)

Recently, a new transaural sound reproduction system, referred to as a ‘‘stereo dipole’’ (SD) reproduction system, has been proposed, in which a closely spaced pair of loudspeakers is located in front of a listener. Theoretical investigation was carried out by computer simulations and it was reported that the SD system would be capable of providing a relatively large equalized area to the listener and robustness with respect to a listener’s head movement compared with those given by the standard loudspeaker arrangements. This paper deals with a subjective investigation of the SD system. It is known that the ordinary transaural system has a disadvantage in the quality of reproduced sound; that is, the reproduction of unnatural and antiphase virtual sound from the psychoacoustic point of view. Therefore, subjective listening tests were carried out, which aimed to compare the SD system with the ordinary system. The significance of the SD system on reproduced sound perception is suggested.

Design of a filter matrix used for stereo dipole transaural systems

A new transaural system, referred to as the ‘‘stereo dipole’’ reproduction system (hereafter the SD system), using a closely spaced pair of loudspeakers in front of a listener, has been introduced recently. In this paper, the deconvolution techniques used in the SD system, in which a 2×2 matrix of digital filters is used to compensate for the response of the loudspeakers and to create virtual sound sources, are dealt with. The deconvolution method is based on the analysis of a matrix of exact least-squares inverse filters. Two kinds of design techniques are developed. One is a very fast FFT-based deconvolution method; the other is a time-domain counterpart to the FFT method. The well-known principles of least-squares optimization and regularization are introduced in both the design methods. The relationships between the characteristics of the deconvolution filters and loudspeaker arrangement are investigated. In particular, the theoretical analysis is concerned with the locations of poles and zeros and the required dynamic range of the filter. Computer simulation reveals that the SD system offers the robustness of the sound image and a wide range of equalization area relative to the ordinary loudspeaker arrangement system. Finally, the subjective effects of the filter characteristic are also discussed.

Subjective Annoyance Response to Diesel Engine Sound During Idling Conditions.

Subjective annoyance response to diesel engine sound during idling conditions was evaluated by 80 participants. Eight different sound spectra were presented to the participants at a constant level of 80 dB(A) in a paired comparison procedure. Stereo-recorded sound stimuli were played back through a pair of loudspeakers in an anechoic room. Four objective parameters of loudness, sharpness, impulsiveness, and roughness were found to be the determining factors that cause subjective annoyance. An annoyance prediction model for the test stimuli of an idling diesel engine was developed on the basis of these factors. The objective parameters and their interactions have a significant effect on the annoyance prediction model. The spectral distribution indicated by test participants to be pleasant can be used as a basis for appropriate modification of engine sound. A single microphone measurement in free field conditions can be used to estimate objective parameters for defining the cause of annoyance.

Demonstration of room acoustic parameters using a digital multieffects processor

Digital multieffects processors is a useful tool to study and demonstrate room acoustic parameters. Live and prerecorded speech and audio program will be processed through a multieffects device and reproduced through a pair of loudspeakers. The listeners will be allowed to hear the effect of varying a number of acoustic parameters that occur in natural spaces. These include: reverberation time, echoes, diffusion of sound, high frequency decay rate, initial time delay gap, spaciousness, and depth. A brief explanation of each parameter will be given before its audible demonstration. The means in which an architectural acoustician designs an acoustic space with these parameters in mind will also be discussed.

Distortion reduction in loudspeakers

A loudspeaker includes a pole piece that is transversely divided into magnetically coupled, but electrically isolated first and second sections. The first pole piece section is surrounded by the voice coil and is magnetically coupled to, but electrically isolated from, the loudspeaker bottom plate. Other versions include pairs of loudspeakers with reversed polarity magnets and magnetic intercoupling for offsetting distortion produced therein.

Multi-channel sound simulation system

A multi-channel sound simulation system for processing a stereophonic signal having a high frequency component for use with at least a pair of primary loudspeakers and a pair of secondary loudspeakers includes a receiving member for receiving the stereophonic signal and for producing a first primary channel signal and a second primary channel signal. The first and second primary channel signals are adapted to be respectively applied to a first primary loudspeaker and a second primary loudspeaker. The receiving member is further adapted to divide the input signal into a first secondary channel signal and a second secondary channel signal. The first and second secondary channel signals are fed through a roll-off member which inhibits the high frequency component of the signal, thereby producing inhibited first and second secondary channel signals. These inhibited signals are adapted to be respectively applied to the first and second secondary loudspeakers to supply ambiance information to a listener in a home audio/video system. The listener thus receives a fuller, more realistic sound in his/her own home.