Impulse
Publications

Patents

US 8,887,862 - PDE Phase Plug Device

Issued - 18 November 2014
This patent the details a phase plug that produces a rectangular planar wave front, or one with a defined curvature.  This type of phase plug is well suited for use in line arrays or conventional horns
Licensing opportunities available! Please contact us for additional information.

US 8,467,557 - Coaxial Speaker System with Improved Transition Between Individual Speakers

Issued - 18 June 2013
This patent details a coaxial loudspeaker system with a low frequency driver employing a flat diaphragm to minimize detrimental reflections of sound originating from the high frequency driver.

US 8,041,061 - Dipole & Monopole Surround Sound Speaker System

Issued - 18 October 2011
This patent is the basis for a compact 5-channel surround sound loudspeaker system housed in only 3 distinct enclosures and placed in front of the listener (GT 5051) produced by Altec Lansing.

US 7,260,228 - Optimum Driver Spacing For a Line Array With a Minimum Number of Radiating Elements

Issued - 21 August 2007
This patent is the basis for a small line array loudspeaker system (FX 6021) produced by Altec Lansing.

US 6,059,069 - Loudspeaker Waveguide Design

Issued - 9 May 2000
This patent is the basis for the Quadratic Throat Waveguide produced by Peavey Electronics.  An AES paper detailing the design and performance of this design method was presented at the 107th Audio Engineering Society Convention, September 1999 in New York, NY.

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.

Loudspeaker Sensitivity   (2009-03; 0.3 MB)

What really determines the sensitivity reating of a loudspeaker? How does this relate to the SPL from a given loudspeaker with some specified source material? These are a couple of questions that are, hopefully, answered in this article. If this article is helpful you might also want to check out the Loudspeaker Target SPL and Amplifier Size article

Loudspeaker Target SPL and Amplifier Size   (2009-08; 0.2 MB)

Have you ever wondered what size power amp is needed driver a particular loudspeaker to a target SPL? It depends on a couple of things that are detailed in this article. A few equations are also given to help calculate the required power rating of the amplifier. This is a good companion / follow-up article to the Loudspeaker Sensitivity article.

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.
  • The relative bandwidth of the subwoofer and the full-range system (crossover)
  • The relative output level of the subwoofer and the full-range system (gain)
  • The relative arrival time of the signal from the subwoofer and the full-range system (delay)
It is this last item that is perhaps the most challenging. This is the one that we will primarily investigate.

Understanding Horn Directivity   (2009-11; 0.3 MB)

This article explains some of underlying principles that govern the directivity of horns. It details the frequency dependent nature of horn directivity as it relates to the size of the horn. Several typical horn mouth shapes are investigated and used to illustrate how "pattern flip" can occur.

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.

Using Limiters to Help Protect Loudspeakers   (2008-08; 0.1 MB)

This article details the use of a limiter and processing of its side chain input to help minimize over excursion of a loudspeaker driver. This is an alternative to the use of an high pass filter.

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

Progressive Degenerate Ellipsoidal Phase Plug   (2015-10; 1.4 MB)

This AES paper details the concepts and design of a new phase plug. This device can be utilized to transform a circular, planar wave front to a rectangular, planar wave front.  Such functionality can be very useful for line array applications as well as for feeding the input, or throat section, of a rectangular horn from the output of conventional compression drivers.  The design of the phase plug allows for the exiting wave front to have either concave or convex curvature if a planar wave front is not desired.  One of the novel features of this device is that there are no discontinuities within the phase plug.  This paper was presented at the 139th Audio Engineering Society Convention, October 2015 in New York, NY.  Due to an illness, Don Keele presented the paper in my absense.

Sound System Modeling   (2015-06; 1.8 MB)

This is a PDF of the PowerPoint slides present at the Ask The Experts session at InfoComm 2015 in Orlando, FL (June 2015)

Measuring Loudspeaker Systems   (2014-10; 6.9 MB)

This is a PDF of the PowerPoint slides I used during the Product Design track tutorial detailing various aspects of measuring loudspeakers.  This was presented at the 137th Audio Engineering Society Convention, October 2014 in Los Angeles, CA.

Subwoofer Arrays & Applications   (2011-10; 3.8 MB)

This is a PDF of the PowerPoint presentation given during the Live Sound seminar, LS7, on Subwoofer Arrays & Beam Steering which featured Jim Risgin (chair), Charlie Hughes, Doug Fowler, and Bennett Prescott.  It details end-fire and cardioid arrays as well as how to broaden the coverage of a straight line array of subwoofers using delay.  EASE models of several example applications are given showing SPL maps on the audience and stage areas with different arrays.  This was presented at the 131st Audio Engineering Society Convention, October 2011 in New York, NY.

Audio System Coverage   (2010-11; 3.5 MB)

This is a PDF of the PowerPoint presentation given during the Audio System Coverage Workshop, W18.  The panel included Kurt Graffey (chair), Floyd Toole, Peter Mapp, Brian McCarty, and Charlie Hughes.  This presentation details some key items to consider at the design phase of a loudspeaker system in order for it to acheive good directivity control, specifically horn size and driver spacing.  It shows the resultant constant directivity from approximatley 100 Hz - 16 kHz for a compact line array loudspeaker system using these principles.  It also details using delay between devices in a cluster design to improve the overall directivity response and coverage of the cluster.  This was presented at the 129th Audio Engineering Society Convention, November 2010 in San Francisco, CA.

Subwoofer Array Directivity   (2010-11; 3.8 MB)

This is a PDF of the PowerPoint presentation given during the Live Sound seminar, LS6, on Subwoofer Array Directivity which featured Charlie Hughes (chair), Dave Rat, Bill Gelow, Steve Bush, and Ales Dravinec.  It illustrates directivity as a function of source size and wavelength.  It also shows the effects of steering an array electrically.  This leads into wave front shaping and the broadening directivity patern from the output of a large "line array" of subwoofer using variable delay.  This was presented at the 129th Audio Engineering Society Convention, November 2010 in San Francisco, CA.

Alignment of Subwoofers and Full-Range Loudspeaker Systems   (2010-11; 2.1 MB)

(See the video of this presentation on YouTube)
This is a PDF of the PowerPoint presentation given during the presentation at the Renkus-Heinz booth for the 129th Audio Engineering Society Convention Convention, November 2010 in San Fronacisco, CA.  It covers all of the time domain alignment issues, but time for the presentation did not permit us to go over the frequency domain alignment issues.  These issues are covered in the presentation given at the 127th AES (see link below).

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 in New York, NY.

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 in San Francisco, CA.

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 in San Francisco, CA.

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 in New York, NY.

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 in New York, NY.

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