Audio Systems Group, Inc.
Over the years, we've authored a number of articles and application notes to explain design concepts, help our clients understand complex issues, and help users get the most out of their sound systems. Here are some of them. More recently, we've been devoting energy to issues relating to various forms of interference to audio systems from both power and radio frequency (RF) sources. You'll also find applications notes for Amateur Radio Operators (Hams).
New Additions and Updated Materials
RFI, Ferrites, and Common Mode Chokes For Hams Most recent update 5 May 2010. This tutorial is directed specifically to RFI in ham radio applications. It includes an extended discussion of the use of common mode chokes as transmitting baluns, and extensive measured data on ferrite chokes. A chapter on audio and computer interconnections in ham stations shows how to make bulletproof connections between a computer sound card and ham rigs for SSB, RTTY, PSK31, and SO2R contesting without expensive interface boxes, using nothing more than simple cables with the right connectors on each end.
160M Antennas for a Small Lot (and for Larger Lots Too!) NEW! October 2012 This is a pdf of the Power Point for my recent presentation at Pacificon.
Using Sim Smith to Improve Antenna Matching NEW! October 2012 This is a pdf of the Power Point for my recent presentation at Pacificon.
RFI and Ham Radio NEW! May 2011 This is a new pdf of the Power Point for a tutorial on RFI I've done for several ham clubs.
This is the Power Point for a tutorial lecture I presented at the Stanford Jazz Workshop on Sound And Acoustics For Jazz Musicians .
This is the first draft of an in-progress tutorial on Coax and Stubs for use on the HF bands . Comments are appreciated.
This is an applications note on a variety of Power Line RF Filters that I've found at a local electronics surplus house, HSC, also known as Halted. Unfortunately, they are not listed in their internet catalog, so you've got to go to the store to buy them. They're also widely available from industrial electronics suppliers like Allied and Newark.
Antennas for Limited Space I've spent most of my time in ham radio operating from small city lots. This article shares some ideas that have worked out very well for me. And here are the Power Point slides for a somewhat expanded presentation of these ideas at Pacificon last fall.
Sound Reinforcement for Jazz and Other Acoustic Music These are my Power Point slides for a tutorial session held at the 2008 Fall Convention of the Audio Engineering Society in San Francisco. These are my slides -- other members of the panel presented other concepts and other elements of the problem.
RF Interference in Audio Systems These are my Power Point slides for a tutorial lecture held at the 2008 Fall Convention of the Audio Engineering Society in San Francisco. The presentation describes the fundamental mechanisms by which RF interference occurs, then shows how interference can be avoided by proper system design and how it can be eliminated from existing systems. The next item listed on RFI for Hams covers much of the same material and more, can be studied as a text to go with the Power Point.
Computer to Radio Interfacing - You Don't Need An Expensive Interface! Most recent update 15 Apr 10. Most hams (including authors of some ARRL publications) believe that transformers, expensive boxes, or even optical isolators are needed to connect computers and other gear to transceivers without hum and buzz. This is sadly (and expensively) wrong, and so are many of the solutions offered. An unshielded transformer or an improper shield connection may CAUSE hum, buzz, and RFI! This Power Point for a presentation to the Northern California Contest Club shows simple and effective solutions, involving no more than a few feet of copper braid and properly wired cables that can connect anything to anything, without transformers, interface boxes, or optical isolators. Audio connections are addressed first, followed by rig control, sending CW, PTT, and RTTY. This material is also covered in tutorial fashion in Chapter 7 (Solving Problems in the Shack) and Appendix 6 (Audio For Ham Radio) of the RFI Tutorial.
Transmitting Chokes Most recent update 23Apr10. This is an expanded Power Point for presentations I've done to several ham clubs (PVRC, Pacificon, NCCC, NCDXA, REDXA, and Visalia) that extends my research on ferrites to the design and application of greatly improved common mode transmitting chokes, also known as "current baluns." See also RFI, Ferrites, and Common Mode Chokes For Hams for the tutorial text that goes with this Power Point, including my "Choke Cookbook."
Coax Chokes on Low Loss Toroids New 5May08 This short research note summarizes and analyzes some recent measurements of chokes wound on Fair-Rite #61 toroids.
Comparing Verticals and Dipoles New 9May08 This applications note takes a closer look at the relative performance of wire dipoles and verticals for the 160M, 80M, and 40M ham bands..
Transmission Lines at Audio Frequencies, and a Bit of History The behavior of cables at audio frequencies is widely misunderstood. This tutorial attempts to shed some light and bring some sanity to the discussion.
Giving Back An unpublished piece I wrote for the SynAudCon Newsletter a year or so ago.
Acoustics and Sound System Design
Why Churches Buy Three Sound Systems, and How You Can Buy Only One Most churches are so afraid of buying sound systems that they do it three or four times before they finally end up with one that works well enough to meet their needs! Here's how you can do it right the first time.
Acoustics and Sound Systems in the Contemporary Church The contemporary church is built around communication - verbal, musical, and emotional - as well as worship. The minister communicates with the congregation by preaching, leading prayers, and announcing church activities. Music attempts to communicate ideas and concepts while it simultaneously enhances the worship experience through emotional involvement. The acoustics of the worship space have a profound effect on all of these functions. This article explains these complex issues in plain English for the non-technically inclined.
The Revitalization of a Community Landmark - The Greensburg Palace Theater The 1200-seat Palace Theater is an anchor of this small town on the western slopes of the Alleghenies just off the Pennsylvania Turnpike east of Pittsburgh. This blow-by-blow description of an historic renovation is a textbook example of how to do it right. We're very proud of everyone involved in this project!
Mixing for Three Channel Sound Reinforcement Two and three channel sound reinforcement is a concept whose time has finally arrived. Two and three channel systems are being successfully used in performance and worship spaces, on Broadway. and in theme parks. A well designed two or three channel system can blow the pants off of a monophonic system which uses significantly more powerful equipment. While this article (published in the March 1998 issue of Sound and Communications) was specifically commissioned to address mixing for these systems, it addresses our design philosophy for these systems as well.
The Acoustics of Sound Systems for Baseball was an invited paper presented to the annual meeting of the Acoustical Society of America in Chicago in June 2001. There is a lot of good information here about how sound behaves outdoors and when traveling long distances. Much of it also applies to sound indoors, especially in larger spaces. And here is a Power Point (97) presentation with a lot more graphs and graphics to go with it.