Loudspeaker Performance Research Articles

Broadband Response Diaphragm Materials for Human Acoustics Engineering.

High-performance fiber-reinforced composite materials demonstrate great potential for manufacturing diaphragms in human-engineered acoustic loudspeakers. However, the notable scarcity of high-quality fibers and the uncontrollable nature of the diaphragm structure limit the production of high-quality sound that conforms to human hearing. In this study, a novel composite diaphragm material is devloped by integrating the swelling carboxymethyl cellulose microfiber (CMF) with the hot-melted sheath-core fiber (SCF) based on the "interpenetrating polymeric network" ("IPN") strategy. Simulation methods and Flory-Huggins theory are applied to explain the mechanism of fiber-structure-property interaction in composite diaphragm materials. Owing to the distinct microstructure, this bio-based diaphragm material shows superior mechanical characteristics, including low density (≈0.92gcm- 3), high tensile strength (≈235MPa), and high modulus (≈9.73GPa). Moreover, the loudspeaker mounted with bio-based diaphragm material exhibits enhanced sensitivity (≈82.6dB) and stable performance across a broad frequency spectrum. This study not only elucidates the multiphysics working principles of loudspeakers but also establishes a crucial connection between the physical properties of diaphragms and loudspeaker performance. It opens up new avenues for the design of high-performance bio-based loudspeaker diaphragms in high-fidelity (Hi-Fi) acoustic devices.

Theoretical modeling and parameter identification of balanced armature loudspeakers.

Theoretical modeling and parameter identification are essential for optimizing loudspeaker performance and enabling active control. Although relevant theories for moving-coil loudspeakers are well-developed, accurate theoretical modeling and parameter identification methods for balanced armature loudspeakers (BALs) are scant. This study proposes a model using the equivalent circuit method (ECM) for BALs, with consideration of the armature-suspension coupling as well as the non-piston vibration of the diaphragm. Based on the proposed ECM model, a time-domain identification algorithm utilizing measured voltage, current, and displacement data is established to identify the necessary parameters. Employing the theoretical model and proposed identification method, the model parameters of two different BALs are measured. Comparisons between experimental and numerical results demonstrate the accuracy and effectiveness of the proposed model and identification method in predicting impedance, displacement, and sound pressure responses.

Analysis and Identification of Nonlinear Acoustic Damping in Miniature Loudspeakers

Nonlinear acoustic damping is a key nonlinearity in miniature loudspeakers when the air velocity is at a high amplitude. Measurement of nonlinear acoustic damping is beneficial for predicting and analyzing the performance of miniature loudspeakers. However, the general measuring methods for acoustic impedance, such as the standing-wave tube method or the impedance tube method, are not applicable in this scenario because the nonlinear acoustic damping in miniature loudspeakers is coupled with other system nonlinearities. In this study, a measurement method based on nonlinear system identification was constructed to address this issue. The nonlinear acoustic damping was first theoretically analyzed and then coupled in an equivalent circuit model (ECM) to describe the full dynamics of miniature loudspeakers. Based on the ECM model, the nonlinear acoustic damping was identified using measured electrical data and compared with theoretical calculations. The satisfactory agreement between the identification and theoretical calculations confirms the validity of the proposed identification method.

Analysis of total harmonic distortion of miniature loudspeakers used in mobile phones considering nonlinear acoustic damping.

Total harmonic distortion (THD) plays an important role in the performance of miniature loudspeakers used in mobile phones. Traditional nonlinear models fail to predict THD in the higher frequency domain. Significant discrepancies can be found between the prediction and measurement. In this study, an extended model considering nonlinear acoustic damping is proposed to address this issue. Flow separation occurring near the orifices of the sound port is of particular interest. Two velocity-dependent parameters were derived to model the nonlinear damping effect. Based on the extended model, the dynamics of miniature loudspeakers are described using the state-space method. Experiments and calculations confirm the validity of the extended model. The influence of nonlinear acoustic damping on THD is also discussed.

Research on sound pressure level of graphene loudspeaker with AC and AC/DC excitation

In this work, a graphene loudspeaker is designed using laser scribing technology, and its theoretical model with AC and (AC + DC) excitation is established, which focuses on the effect of different excitations on the performance of graphene loudspeakers. The proposed theoretical model consists of a temperature gradient model and a sound pressure model. The application of (AC + DC) excitation helps to mitigate the frequency doubling effect caused by AC excitation. Sound pressure level (SPL) measurements with AC and (AC + DC) excitations are carried out to verify the theoretical model. The measured results show that the SPL is proportional to the input power and inversely proportional to the measurement distance. The highest SPL produced by the graphene loudspeaker is 53.3 dB with (5 VAC + 5 VDC) excitation. The theoretical model of the graphene loudspeaker with different excitations has a certain reference value for further research on thermoacoustic effects and improving the efficiency of graphene loudspeakers.

High Altitude Performance of Loudspeakers and Potential Impact on Audiometric Findings.

BACKGROUND: The evaluation of how air rarefaction can affect a loudspeaker performance at altitude implies the need for characterization of earphones during hypobaric conditions. The aim of this study was phonometric analysis at different altitudes of the acoustic output of a widely used earphone model, along with its consequences on audiological investigations conducted under such environmental conditions.METHODS: The transfer function of a TDH-39P earphone was analyzed with an artificial ear under nine different altitude levels, from sea level up to 35,000 ft, inside a hypobaric chamber. A specific phonometric system not sensitive to environmental pressure changes was used. Other potentially confounding factors, such as environmental temperature and humidity, were continuously monitored.RESULTS: No relevant temperature or humidity changes were detected. The sound pressure level generated by the earphone under hypobaric conditions was found considerably affected by air density changes. These data produced a correction table aiming at recalibrating the earphone's output at each audiometric octave test frequency within the 250-8000 Hz range. Quite different characteristics of response were observed at different audiometric frequencies. Such findings were particularly evident for altitudes exceeding 12,000 ft.DISCUSSION: The development of a frequency-selective and altitude-related correction factor for acoustic stimuli is an essential aspect when hearing threshold measurements in hypobaric environments are performed.Lucertini M, Botti T, Sanjust F, Cerini L, Autore A, Lucertini L, Sisto R. High altitude performance of loudspeakers and potential impact on audiometric findings. Aerosp Med Hum Perform. 2019; 90(7):655-659.

High-Precision Harmonic Distortion Level Measurement of a Loudspeaker Using Adaptive Filters in a Noisy Environment

The harmonic distortion level (HDL), an important criterion used to evaluate loudspeaker performance, can usually be measured using spectral analysis. However, spectral analysis entails great computational complexity. Furthermore, long measurement times are necessary to measure HDL accurately in a noisy environment. Therefore, we proposed the HDL measurement technique for a loudspeaker using an adaptive filter. This measurement technique can measure HDL as accurately as spectral analysis using fast Fourier transform (FFT). Furthermore, its computational complexity is much less than that of spectral analysis. Nevertheless, this measurement technique requires a long measurement time to assess the convergence of filter coefficients. This paper presents a description of the new HDL measurement technique of a loudspeaker using plural adaptive filters. The proposed measurement technique can measure HDL more accurately than spectral analysis in a noisy environment. We evaluated the performance of the proposed measurement technique using computer simulations. Results based on computer simulations show that the proposed measurement technique is more effective than spectral analysis in an acoustic environment with background noise.

An Objective Analysis Method for Perceptual Quality of a Virtual Bass System

Due to the physical size and frequency response constraints of miniaturized and flat panel loudspeakers, low frequency reproduction from these loudspeakers is generally limited and unsatisfactory. The virtual bass system (VBS) enhances the bass performance of such loudspeakers by tricking the human brain to perceive the fundamental frequency from its higher harmonics. Problematically, the additional harmonics from VBS can also introduce perceptual distortion and reduce the audio quality. Therefore, a reliable method to assess the quality of VBS-enhanced signals is necessary in the designing of VBS. Since subjective experiments are often time-consuming and may be inconsistent, it is desirable to develop an objective assessment method for VBS. Earlier studies only utilized some simple objective metrics, which generally do not consider the human auditory model and are unable to accurately predict the perceptual quality of VBS. In this paper, we introduce a perceptual quality-assessment method for VBS based on the model output variables (MOVs) of the ITU Recommendation ITU-R BS.1387. Suitable combinations of MOVs are selected to derive perceptual quality metrics that correlate closely to the subjective quality. A verification experiment is presented to justify the accuracy of the metrics.

THEORETICAL EVALUATION OF LOUDSPEAKER FOR A 10 WATTS COOLING POWER THERMOACOUSTIC REFRIGERATOR

This paper presents a design of moving coil loudspeaker for a 10 W cooling power thermoacoustic refrigerator. An electrical model is presented which simulates the behavior of the loudspeaker. The gas spring system for matching the frequency of the commercially available loudspeaker with the frequency of the acoustic resonator tube for maximizing electro-acoustical efficiency of the loudspeaker is discussed. The optimum back volume for the gas spring system is found to be 59.7 cc, which is about 1.9% of the total resonator volume when the loudspeaker frequency and the acoustic resonator frequency is made equal at 400 Hz with a moving mass of 20 g. The effect of force factor Bl on loudspeaker performance is discussed. Analysis results shows that for better performance of a refrigerator, the loudspeaker should be chosen to have a large force factor and small values for electrical and mechanical resistances. The refrigerator system is tested with DeltaEC software and its results are in good agreement with an electrical model results.

Further Investigations into the Interactions between Cinema Loudspeakers and Screens

Modern-day data-acquisition techniques allow the gathering of high-resolution polar data to assess the detailed performance of loudspeakers. While these techniques are now common in engineering laboratories, they can also be used for acoustic investigation into the in situ performance of loudspeakers. This paper uses modern high-resolution data-acquisition techniques and analysis tools to investigate the complexity of the interaction between a loudspeaker and the screen in a cinema presentation environment. A discussion is presented that explores the effects of three types of screen materials on loudspeaker frequency responses and radiation patterns. These screen effects are explored using a range of loudspeaker-screen distances found in typical cinemas. The impact of the screen on patron listening experience is examined, particularly in relation to the standards for system response set out in SMPTE Timed Text 202:2010.

A Thin Light Flexible Electromechanically Actuated Electret-Based Loudspeaker for Automotive Applications

An electromechanically actuated electret-based loudspeaker made with an organic material membrane is presented, which is small in volume, extremely thin, and lightweight for light vehicle applications. As obtaining good sound quality in a vehicle is a complicated and difficult task, the electrostatic thin-film actuator can be cut into any shape and then assembled into an electret-based loudspeaker for placement at any location within the vehicle. The sound field in a vehicle can be optimized by properly tailoring the electret-based loudspeaker performance and choosing the most appropriate location for the loudspeaker for optimal sound performance. In addition, it is possible to design a novel 3-D sound field. Our newly fabricated 100-mm-by-100-mm electret loudspeaker weighs only 4 g and is 1 mm thick. It only consumes 0.15 mW to generate a sound pressure level at 88 dB at 1 kHz, which is very energy efficient for electric car applications. In summary, our newly flexible electret-based loudspeaker has tremendous potential for future automotive applications due to its excellent advantages over current vehicle loudspeakers.

Tailoring the performance of flexible electret loudspeakers by varying cell actuator formation

We present a design of electret-based soft cell actuators which can improve the performance of flexible electret loudspeakers. Electret loudspeakers have advantages over traditional speakers such being thin, lightweight and flexible. They have potential application to 4C products (e.g. computers, communication, consumer electronics, and cars). Flexible electret loudspeakers are composed of an array of small cell actuators. The first mode of each electret cell actuator greatly affects the low frequency of an electret loudspeaker. To tailor the bandwidth of an electret loudspeaker for different applications, the shape and size of each cell actuator can be varied according to the specific requirements. A finite element analysis (FEA) model was used to simulate a vibration mode. An AVIDTM (advanced vibrometer/interferometer device) system and ESPI (electronic speckle pattern interferometry) system were two non-destructive optical detection tools used to detect vibration and the corresponding vibration mode shape of the electret cell actuators, respectively. Our experimental results verified the simulated results. We showed that finite element analysis (FEA) can be used to design flexible loudspeakers. We can tailor the sound characteristics of an electret loudspeaker by varying the size and shape of cell actuators such that flexible electret loudspeaker performance can be dramatically improved.

The harmonic distortion level measurement system of the loudspeaker using two adaptive filters

The harmonic distortion level is an important criterion to evaluate loudspeaker performance. The harmonic distortion level is generally obtained using the power spectrum of the audio signal from a loudspeaker, and a microphone is used to receive the audio signal. It is important to measure the accurate harmonic distortion level for evaluating performance of the loudspeaker. Generally, The harmonic distortion level is measured by the spectrum analysis. However, the spectrum analysis requires large computational complexity. Therefore, we proposed the new technique to measure the harmonic distortion level of the loudspeaker by using the adaptive filter. And we evaluated the performance of the proposed technique by experiment. The proposed technique can measure the accurate level the same as the spectrum analysis, but requires long measurement time to converge the filter coefficient. This paper presents a description of the new technique to measure the harmonic distortion of the loudspeaker by using two adaptive filters. The propose technique improves the accuracy and the measurement time of the proposed measurement technique by using the adaptive filter. We show some results of real-time experiments. The results of the real-time experiments verified that the newly proposed technique improves measurement time and accuracy of measured level.

Audio Projection

The parametric loudspeaker provides an effective means of projecting sound in a highly directional manner without using large loudspeaker arrays to form sharp directional beams. It can be augmented with conventional loudspeakers to create a more immersive audio soundscape. Deployment of parametric loudspeakers in many public places where private messaging can make a difference in attracting attention, conveying messages without needing headphones, and creating private listening zones to reduce noise pollution. Digital signal processing plays a significant role in enhancing the aural quality of the parametric loudspeakers, and array processing can help to shape and steer the beam electronically. In addition, other signal processing techniques can also be applied to add more flexibility and improve the performance of parametric loudspeakers. These developments rely heavily on the latest techniques in acoustics and audio signal processing to overcome some of the current limitations in nonlinear acoustics modeling and ultrasonic transducers' technology. A useful feature in sound projection is to realize a highaccuracy digital beamsteering capability in air using an array of parametric loudspeakers. An in-depth study into the theoretical model of wave steering capability in parametric array in air can provide some hints on how we can best steer the demodulated signal in an efficient manner. As seen from this article, digital signal processing provides the main engine to achieve directional sound projection, and new digital processing techniques will be devised to provide a better quality, controllable audio beaming, and efficient sound focusing device in the future.

A method of characterising performance of audio loudspeakers for linear alternator applications in low-cost thermoacoustic electricity generators

This paper investigates the feasibility of using commercially available loudspeakers as low-cost linear alternators for thermoacoustic applications, to convert acoustic power to electricity. The design of a purpose built experimental apparatus, in which a high intensity acoustic wave is induced by using a high power woofer, is described. The rig is used to excite loudspeakers (referred here as “alternators”) under test, while a pair of microphones and a laser displacement sensor are used to enable acoustic power measurements. The paper presents a case study in which characteristics of acoustic-to-electric energy conversion of a candidate loudspeaker (alternator) – selected from the viewpoint of general performance, as well as parameters such as: high force factor, low electrical resistance and low mechanical loss – are measured. The measurements of acoustic power absorbed by the alternator and the electric power extracted from it by the load resistor, which allow estimating acoustic-to-electric efficiencies, are presented. The alternator has been tested at different operating frequencies, cone displacements and load resistance values. The measurement results are discussed and compared in detail with the calculations based on the linear acoustics model.

The First Damped Frequency with Maximum Sound Pressure of a Miniature Loudspeaker for Cellular Phones

ABSTRACTFor improving the performance of a miniature loudspeaker, engineers have been pursuing a goal of lowering its first damped frequency to have a broad and smooth region of its sound-pressure-level response. This article applies the approach of electro-mechano-acoustical analogy to study the first damped frequency of a miniature loudspeaker used for cellular phones. Using the analogy approach, the authors derive an explicit formulation for the sound-pressure-level of a typical miniature loudspeaker of dynamic type. The veracity of the derived formulation is verified by comparing with the experimental result recorded by B and K apparatus. The derived formulation is further simplified by neglecting factors that are either irrelevant or insignificant for the first damped frequency. Through basic algebraic and calculus operations, this article also presents an explicit form of the first damped frequency. This work has laid the platform for engineers to tailor the design in pursuit of improving the performance of miniature loudspeakers.

120 アクティプ制御による音忠実再生の研究 : 薄肉スピーカ筐体の音質改善検証(音響制御(2))

This paper concerns the improvement of loudspeaker performance by shaping acoustic waveform in time domain using active control technique. In the audio-video equipment with thin-panel, the drive for ever thinner speakers typically results in shortcomings in sound quality compared with conventional box speakers. Because of unnecessary sounds radiated from speaker unit and box, it's impossible to reproduce the original sound perfectly. Then, the authors propose a method employing an adaptive impulse response control system with secondary speaker. This method is applied to the thinner box speaker and audio-video equipment of a thin type. The sound reproduction performance is verified on the basis of experiments.

The loudspeaker as musical instrument: An examination of the issues surrounding loudspeaker performance of music in typical rooms

The loudspeaker is the most important and one of the most variable elements in the electroacoustic music performance process. Nonetheless, its performance is subject to a ‘‘willing suspension of disbelief’’ by listeners and its behavior and variability are usually not accounted for in assessments of the quality of music reproduction or music instrument synthesis, especially as they occur in small rooms. This paper will examine the aesthetic assumptions underlying loudspeaker usage, the general timbral qualities and sonic characteristics of loudspeakers and some of the issues and problems inherent in loudspeakers interactions with small rooms and listeners.

Robust control of a sensorless bass-enhanced moving-coil loudspeaker system

Moving-coil loudspeakers generally exhibit poor response in the low-frequency range because the diaphragms are unable to produce sufficient volume velocity. To alleviate the problem, this study focuses on enhancing the low-frequency performance of loudspeakers by means of modern control techniques. A self-sensing velocity observer is utilized for producing the cone velocity signal required by the controller. Feedback H∞ robust control and feedforward H2 model matching control are employed to simultaneously achieve robust stabilization and tracking performance. The proposed controller is implemented using a combined digital signal processor and operational amplifier circuitry.

Robust design of a sensorless bass-enhanced moving-coil ANC actuator

Loudspeakers have been employed by far as the major ANC actuators. However, the responses of moving-coil loudspeakers are generally poor in low-frequency range because the diaphragms are unable to produce sufficient volume velocity. To alleviate the problem, this study focuses on enhancing the low-frequency performance of loudspeakers by means of modern control techniques. Both magnitude and phase of the frequency response are optimally compensated. A self-sensing velocity observer is utilized for producing the cone velocity signal required by the controller. Feedback H∞ robust control and feedforward H2 model matching control are employed to simultaneously achieve robust stabilization and tracking performance. The proposed controller is implemented using a combined digital signal processor and operational amplifier circuitry.