Publications

Articles

Alternative Ways of Viewing Polar Data   (2001-05; 0.8 MB)

Synergetic Audio Concepts - Tech Topics (2001) about a my MATLAB program PolarSum.  This details a different way to view directivity data.  It also describes processing the data with filter functions and adding multiple sources to calculate their combined directivity response.

Crossovers   (1997)

How using textbook crossover filters with typical non-ideal loudspeaker drivers can affect a loudspeaker's performance in the real world.

EASE Focus - Line Array 2D Aiming Software   (2006-04; 2.2 MB)

A Synergetic Audio Concepts Newsletter (2006) article detailing the features and operation of EASE Focus.

EASERA - Calibration for Absolute Levels   (2006-07; 0.3 MB)

A brief procedure for calibrating EASERA to display measurements with correct absolute levels.

EASERA - Overview and Operation   (2006-04; 0.9 MB)

A relatively quick glance at the acoustical measurement and analysis features of EASERA.

EASERA SysTune - Overview   (2008-11; 0.5 MB)

A general overview of the features and functionality of SysTune: a relatively new software for the alignment and tuning of sound systems.

Filter Summations   (1999-11)

Graphs of popular crossover filter alignments and how they sum together.

Impedance Measurements   (2007-05; 0.4 MB)

A process is described for measuring impedance of loudspeakers at higher drive levels common of typical usage.  Most often impedance is measured at very low drive level which may not reveal some problems.  This is done with standard, off-the-shelf software and hardware that is relatively inexpensive.

TEF Impedance Measurements   (2006-04; 0.1 MB)

A short article on how to do small and large signal impedance measurements with a TEF analyzer. Waterfall (3D) impedance measurements showing how impedance resonances behave as a function of time are also mentioned.

Microphone Directivity   (2001-02)

A brief explanation of different pick-up patterns of microphones.

Phase   (1998)

A brief explanation of phase.

Phase Response & Propagation Delay   (2007-08; 0.2 MB)

There are always questions about the "correct" phase response when measuring a loudspeaker or some other band pass device.  In this article I examine the correct phase response of a text book device (a band pass filter).  I then describe a method to determine the correct propagation delay for an arbitrary device under test so that its true phase response may be measured.  This is a great companion / follow-up to the Subwoofer Alignment article.

ProSoundWeb Chat Transcript

Transcript of Charlie's ProSoundWeb chat from April 2, 2001.

Square Waves & DC Content   (2006-10; 0.2 MB)

Does a square wave, or any clipped wave form, contain DC?  I examine a square wave and see what causes it to have its square shape.  This leads into an easy to understand explanation of phase and its effects in the time and frequency domains.  This is a very general introduction to Fourier analysis and the correlation between the time & frequency domains with no math cited.

Subwoofer Alignment with a Full-Range System   (2007-03; 0.2 MB)

I have heard the question "How do I align a subwoofer with a full-range loudspeaker system?" asked many times. I thought it might be interesting to delve into this to see if I could come up with an answer. The task of adding a subwoofer to a loudspeaker system to increase the low frequency bandwidth should typically entail three primary items. It is this last item that is perhaps the most challenging. This is the one that we will primarily investigate.

Using All Pass Filters to Improve Directivity Response   (2007-11; 0.5 MB)  

This article discuss the use of all pass filters to improve the directivity response of loudspeaker systems employing multiple woofers. The techniques presented are also applicable to multiple midrange drivers.

White Papers

How Accurate is Your Directivity Data?   (2005-10; 0.7 MB)

A white paper on the anechoic chamber modifications and calibration that were necessary to accurately measure the complex data of directivity balloons of loudspeaker systems.  The facility detailed in this paper is operated by NWAA Labs in southern California.

Quadratic Throat Waveguide - White Paper   (2000-03; 0.4 MB)

John Murray gives a very good explanation of the Quadratic Throat Waveguide without a lot of the math.  This also covers some of the history of the development of conventional constant directivity horns.

AES Papers & Presentations

Alignment of Subwoofers and Full-Range Loudspeaker Systems   (2009-10; 4.7 MB)

This is a PDF of the PowerPoint presentation given during the Live Sound seminar, State of the Art of Loudspeaker Design.  It details methods for determining the correct arrival time of the sound energy from a subwoofer and how to properly align this, in both the time and frequency domains, with the sound energy from a full-range loudspeaker system.   This was presented at the 127th Audio Engineering Society Convention, October 2009.

Loudspeaker Directivity Improvement Using Low Pass & All Pass Filters   (2008-10; 0.6 MB)

This AES paper details the application of low pass and all pass filters to loudspeaker system unsing multiple low frequency drivers to improve the directivity resposne of the system.  The filter parameters are based on the spacing of the low frequency drivers and the desired coverage angle free of off-axis lobes within the pass band of the LF drivers.  This paper was presented at the 125th Audio Engineering Society Convention, October 2008.

Loudspeaker Directivity Improvement Using Low Pass & All Pass Filters   (2008-10; 2.1 MB)

This is a PDF of the PowerPoint used during the presentation of the AES paper referenced immediately above.  This was presented at the 125th Audio Engineering Society Convention, October 2008.

Simulating the Directivity Behavior of Loudspeakers with Crossover Filters   (2007-10; 1.0 MB)

This AES paper details using software modeling (EASE SpeakerLab) to predict the directivity response of a loudspeaker system using the individul driver directivity measurments and crossover filter transfer functions.  This paper was presented at the 123rd Audio Engineering Society Convention, October 2007.

Quadratic Throat Waveguide   (1999-09; 0.6 MB)

A new concept in horn design.  This paper was presented at the 107th Audio Engineering Society Convention, September 1999.