Acoustic Two Ports - Provided by Paul Darlington. These methods take their name from techniques for the analysis of electrical networks having two pairs of wires - or ports - which can be connected to external sources, loads, etc.. The acoustical equivalent is a system having two locations at which acoustic variables (pressure & velocity, or equivalents) are specified. The resulting frequency domain descriptors are incredibly useful in forming models of a wide range of "low ka" acoustic systems. I picked up the basics from David P Egolf when working at the Department of E.E. at the University of Wyoming. Modelling Acoustic Waveguides For example, a uniform lossless acoustic waveguide of cross section S, extending from x=0 to x=L, has the acoustic variables at each end related by a matrix equation: In which k is the wavenumber.
I soon realised that the same two port method can be applied to electroacoustic transducers, and to the acoustic systems in which they are operated. Return to the top of this page. Sound Transduction. Standing Wave Ratio. This animation is almost the same as the one above, except that the red left-going wave is now upside down. This changes the initial shape of the combined sum wave as the two waves begin to pass through each other, but after a short time, the standing wave looks exactly the same. The bottom line is that whenever two waves with the same amplitude and the same frequency are traveling in opposite directions in the same medium, the result is a standing wave.
A traveling wave carries energy and momentum with it as it travels; for a traveling wave the kinetic and potential energy both travel with the wave and have the same value at a specific position at a specific time. In a traveling wave, the potential and kinetic energy do not trade back and forth like they do for oscillation. However, a standing wave (which results from two waves traveling in opposite directions) does not involve the propagation of energy. Beginners' Guide to Electronics, Part 1 - Basic Components Explained.
Copyright © 2001 Rod Elliott (ESP) Last Update 17 Mar 2001Basic Passive Components Articles Index Main Index Contents - Part 1 1.0 Introduction to Part 1 Having looked at some of the alternative offerings on the web, I decided it was time to do a series on basic electronics. Most I have seen are either too simplistic, and do not explain each component well enough, or are so detailed that it is almost impossible to know what you need to know as opposed to what you are told you need. These are usually very different. Basic components are not always as simple as they may appear at first look. This is by no means an exhaustive list, and I shall attempt to keep a reasonable balance between full explanations and simplicity. It must be noted that the US still retains some very antiquated terminology, and this often causes great confusion for the beginner (and sometimes the not-so-beginner as well). 2.0 Definitions The basic electrical units and definitions are as shown below.
Some Wiring Symbols . Sound pressure level 413 particle velocity characteristic specific acoustic impedance Z sound intensity acoustics sound units intensity acoustic characteristic impedance dB SPL calculations pascal audio calculations sound units audio engineering sound rec. The Physical Principles of Sound. An introductory guide to the physical properties of sound and a basic introduction to the acoustics of enclosed spaces. To aid the understanding of any technical matters relating to sound, as often the case with any discipline, it is crucial to understand the fundamental scientific principles of the subject and how they are commonly interpreted. This guide offers an introduction to the basic physics of sound including the build up of sound waves and their properties, the speed of sound, how it is shaped in acoustical environments, and how treatment can be applied to listening rooms.
This document does not, on the whole, provide advice, but presents information for reference with which to aid an overall understanding of sound in a practical working environment. The Physics of Sound Overview At its most stripped back level, sound is the mechanical disturbance of a medium, either gas, liquid or solid. Sound has three stages which affect how it is perceived by a listener. Diagram 1 Diagram 2 Phase. Measuring sounds in Three Dimensions. To explain how we can locate sound sources fixed in space from any observing location, we must diverge a little and consider how sound waves from live sources actually behave. Point sound sources make waves in the air that radiate spherically outward, much as ripples radiate outward from a stone thrown into a pool. Using this pool analogy, ignoring its essentially two dimensional nature and any reflections, if you only saw the waves in the pool at a certain time after starting out from the source, could you work out where the source was – where the stone hit the water?
The answer is yes. At any location and at any observation time (before reflections), we know that the direction of travel of the ripples in the wave front as it expands disclose the source direction. We also know that the height or intensity of the wave drops as it radiates out. But additionally we can see that the curvature of the wave-front contains information on the absolute distance of the source. The Physical Principles of Sound.
Acoustic compliance, inertance and impedance: From Physclips Waves and Sound. The specific acoustic impedance z is the ratio of sound pressure to particle velocity, and z = ρv , where ρ is the density and v the speed of sound. (See Acoustic impedance, intensity and power to revise). So for our duct with cross sectional area A, provided that the wave is strictly one dimensional and travelling in one direction, the acoustic volume flow is just U = Au . For this very special case, we define the characteristic acoustic impedance Z0, where Z0 = p/U = p/Au = z/A so Z0 = ρv/A Of course, there usually are reflections from the other end of the pipe, whether open or closed. So there is a sum of waves travelling to the right and left and quite often these give strong resonances, which is after all how musical wind instruments work.
It is possible to have no reflections, however. Acoustic inertance Acoustic inertance and acoustic compliance introduce two very important special cases. What is the impedance of a short cylinder of area A, and length L << λ? Acoustic Compliance. Introduction to Sound Recording. Radiation from monopoles, dipoles, quadrupoles. If two opposite phase dipoles lie along the same line they make up a Linear Quadrupole source.
A tuning fork is a good example of a linear quadrupole source (each tine acts as a dipole as it vibrates back and forth, and the two tines oscillate in opposite directions). What makes the linear quadrupole interesting is that there is a very obvious transition from near field to far field. In the near field there are four maxima and four minima, with the maxima along the quadrupole axis about 5dB louder than the maxima perpendicular to the quadrupole axis. The near field directivity pattern is shown at right. In the far field there are only two maxima (along the quadrupole axis) and two minima (perpendicular to the quadrupole axis) as shown in the figure below right.
The animated GIF movie at left shows the pressure field radiated by a linear quadrupole. At the center of the picture you can see the quadrupole near field pattern.