No description available.

No description available.

-

Approved for public release; distribution is unlimited / The objective of the STAR project is to test and space qualify a new continuous cycle cryogenic refrigeration system for cooling of sensors and electronics which is based upon the newly discovered thermoacoustic heat pumping effect. The new refrigerator has no sliding seals, a cycle frequency of about 300 hz, and uses acoustic resonance to enhance the overall power density and efficiency. This thesis is concerned specifically with the design and testing of the electrodynamic transducer which is responsible for the electro-acoustic power conversion. A computer model of the driver/resonator system is presented along with the techniques for measurement of the electrical and mechanical parameters used as input for the model. A final driver design (including dimensional drawings) utilizing a modified JBL 2450J neodymium-iron-boron compression driver and associated leak tight electrical feed-throughs, microphone, accelerometer, pressure gage, pressure housing, and resonator interface is provided. Keywords: Electrodynamic loudspeaker, Thermoacoustic refrigerator / http://archive.org/details/electrodynamicdr00fitz / Lieutenant, United States Coast Guard

Microspeakers can overheat and break if not monitored and regulated. This monitoringis usually done by adding a pilot tone that introduces energy to the signal.A problem with this approach is the slow update rate of the temperature estimate.This in combination with a fast temperature rise could result in an audible regulationof the input. By simulating the voice coil temperature these problems couldbe mitigated. In this thesis, two existing grey box models and one novel black boxmodel are estimated for different speakers and evaluated using different signals.The results are promising and indicate that all models can estimate the voice coiltemperature with a mean error below one degree. The tests show that a correctinitialization of the model is crucial. Therefore the suggestion to Cirrus Logic,who hosted this thesis project, is to combine a feedforward model with eithertemperature sensor data from the mobile device or a pilot tone. / Mikrohögtalare kan överhettas och gå sönder ifall temperaturen inte övervakasoch regleras vid behov. Denna övervakning sker med hjälp av en pilotton somtillför energi till högtalarens insignal. Ett problem med denna lösning är att övervakningenär relativt långsam. Detta gör att en snabb temperaturökning kan geen oönskad hörbar reglering av insignalen. Genom att modellera spolens temperaturkan detta problem hanteras. I detta examensarbete tas två fysikaliska modelleroch en konfektionsmodell fram och testas på olika högtalare och signaler.Resultaten är lovande och visar att alla modeller kan skatta spoltemperaturenmed ett medelfel under en grad. Utvärderingen visar att initiering av modellensstarttemperatur är viktig. Därför är förslaget till Cirrus Logic att kombinera en simuleringsmodellsom initieras med antingen temperatursensordata från mobileneller med hjälp av en pilotton.

A coaxial loudspeaker in which the woofer and tweeter oscillate at angular frequencies ω_1 and ω_2 respectively, is known to produce sum and difference frequencies ω_± = ω_1 ± ω_2. The generation of these can be attributed to both the nonlinearity of the equations of motion and the Lagrangian boundary behaviour of the low-frequency transducer. In order to characterize the phenomena of interest a perturbation expansion of the field variables is introduced (sometimes called quasi-linear approximation). After deriving a second-order equation for pressure, from which the intermodulation frequencies are obtained, an attempt is made to justify the dominance of the boundary mechanism over that of the fluid nonlinearity. An exact integral solution is then given for the spatial factor of the ω_± pressure terms. In the special case of a farfield on-axis observer an analytic solution is obtained. Several numerical investigations are performed and compared with experiment.

A coaxial loudspeaker in which the woofer and tweeter oscillate at angular frequencies ω_1 and ω_2 respectively, is known to produce sum and difference frequencies ω_± = ω_1 ± ω_2. The generation of these can be attributed to both the nonlinearity of the equations of motion and the Lagrangian boundary behaviour of the low-frequency transducer. In order to characterize the phenomena of interest a perturbation expansion of the field variables is introduced (sometimes called quasi-linear approximation). After deriving a second-order equation for pressure, from which the intermodulation frequencies are obtained, an attempt is made to justify the dominance of the boundary mechanism over that of the fluid nonlinearity. An exact integral solution is then given for the spatial factor of the ω_± pressure terms. In the special case of a farfield on-axis observer an analytic solution is obtained. Several numerical investigations are performed and compared with experiment.

Semestral thesis is devoted to mapping and verification technologies for the project active loudspeaker crossover using DSP. Three way systém will use open baffle. Design of analog crossover is complex due to the need of compensating for acoustic short circuit and properties of laudspeakers.

The work presented in this thesis can be divided into two main subjects. First, lightweight designs for acoustic devices such as Helmholtz resonators and loudspeakers used for noise control in rocket payload compartments are developed. Second, active control using a hybrid control system (with structural and acoustic actuators) was tested experimentally. Due to the weight limitations for this application, Helmholtz resonators and loudspeakers are re-designed in order to reduce the device weight as much as possible while maintaining performance. For Helmholtz resonators, this is done by modeling the resonator for different structural shapes, wall materials and wall thicknesses using a finite element analysis software. The final design is then compared to the rigid resonators and is shown to perform effectively. These designs are then successfully applied to the full-scale fairing at Boeing facilities. In order to design a lightweight loudspeaker, a comparative approach was used. A standard 12' loudspeaker is taken as the reference loudspeaker and weight reduction solutions are applied to it while maintaining performance. The loudspeaker is characterized using mechanical, electrical and acoustical theories, and an optimization process is applied in order to minimize a defined cost function, which was taken as the total sound pressure output over a targeted frequency range per mass of the actuator. The results are used to build a lightweight loudspeaker together with a lightweight box, and the new designs are tested for comparison with the reference loudspeaker and shown to increase performance by 1.7 dB over 60-200 Hz band while reducing the mass by 78%. The second part of this thesis investigates the performance of a hybrid active control treatment featuring distributed vibration absorbers (DAVAs) and loudspeakers applied on a scale payload fairing. Several aspects such as causality, reference signals, and maximum controllable levels of this feedforward control scheme are the subjects of analyses. The results show that this active control approach can achieve significant amount of interior noise attenuation, and the total actuator weight required to control an external level of 138 dB can be reduced to 9.2kg using lightweight loudspeakers. However, it is shown that the attenuation levels can still be improved further by actuator positioning that gives more effective coupling of the actuators with the structural and acoustic modes and by using multiple references for the control system. / Master of Science

The loudspeakers used in active noise reduction (ANR) headsets are generally identical to loudspeakers used in commercial headphones. Unfortunately, the frequency response characteristics of these loudspeakers are not particularly well suited for open-air active noise control (ANC). Open-air headsets float outside the ear with no contact between the system and the user and allow for regular conversation with others in the environment. This study has identified three limitations on the closed-loop performance of open-air headsets: the distribution of gain and phase in the loudspeaker's open-loop frequency response function, manufacturing variations in loudspeakers that can deviate from design specifications by up to 40%, and the variations in acoustic impedance coupling (ear-to-speaker) among users. This thesis explores the mechanisms that underlie these limitations with the goal of designing open-air headsets that are robust to manufacturing and user variations. Methods are introduced on ways to minimize the effects of manufacturing and user variations and are proven by experiment. With these variations minimized, the controller's design is only limited by the frequency response of the loudspeaker. A comprehensive examination of techniques to model moving-coil loudspeakers is presented followed by detailed studies on how each parameter affects the system's frequency response. A review of frequency domain control system design is then included to help the reader understand loop-shaping techniques. Finally, a compensator is designed for an open-air ANR headset using loop-shaping techniques and the robustness of the closed-loop performance is verified experimentally. / Master of Science