1. Conceptualizing and Constructing the Smart Speaker: Designing a power-limiting device for the common 2-way loudspeaker. Presented by: Ryan Gwinn – Project Advisor: James Hedrick Senior Project –Electrical Engineering – 2009 The goal of this project is to design a governor that limits the power reaching a loudspeaker’s drivers regardless of the input signal connected to its external terminals. This system, not meant to be an add-on, but part of a speaker’s design will be created using the parameters of two drivers’ physical/material limitations. To accomplish this, a two driver enclosure complete with a 2-way passive crossover will be designed and constructed. Individual limiting circuits will then be placed between the crossover and each driver within the loudspeaker. Limit the power reaching the loudspeaker’s drivers regardless of the input signal. React to the input signal within 15 milliseconds. Function with a changing audio file containing significant dynamic range. When not active, the device must have minimal effect on the loudspeaker’s performance parameters (frequency response etc.). Results and Future Work Loudspeakers surround us all in our everyday lives – for some they represent a livelihood, and for many, a passion. Their failures can be incredibly costly and while numerous systems exist to protect speakers, nearly all function within the amplifiers. The protection of loudspeakers must begin to consider the speakers themselves. Clip-protection, gain controls, and signal processors are not enough. Abstract Motivation Design/Performance Specifications The Basic Design Limiter to be implemented three ways: 1)As a feedback system (to the amplifier). 2)With an active switch. 3)As a passive element. It is important to remember that a 2-way loudspeaker is already a system. The block diagram to the left is an alteration of this system. This project had several successes. First, two loudspeakers were designed and constructed. One (the control) modeling the BR-12 by Paul Holsopple. It was designed following the criteria outlined in Speaker Building 201, and tested according to Joseph D’Appolito’s Testing Loudspeakers. The second speaker was slightly altered with the crossover removed from the cabinet as seen on the left. This allows for easy access when adding additional circuitry. Because of limitations in acoustical testing equipment, both speakers were tested for frequency response using a program developed for this project within MATLAB. Currently a system using feedback is being developed, though it is not fully operational. Moreover, certain design issues were realized preventing the incorporation of active switching, and a passive approach. Developing an active switch requires an additional power source, and has many boundaries preventing it from not effecting regular performance. The ideal passive system is currently inactive as of now due to the inability to dissipate excess variable ac signal power as well as problems such as over-heating. However, a test system has now been created (including test programs) that in the future can serve both as a learning tool and a first step of reaching this project’s final goal. A MATLAB line-level signal (sine sweep, then audio file) is sent to a power amplifier. Next the speaker level signal enters a 2-way passive crossover, which acts as two band-pass filters in order to send the proper frequency range to each driver. Each (independent) speaker-level signal enters its respective limiting device, which attenuates the signal if over the predetermined cut-off voltage. The signal then reaches the drivers, ideally with no loss in quality.