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
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.
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.
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.
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.
What really determines the sensitivity rating 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
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.
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.
This article discusses 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.
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.
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.
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.
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.
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.
Synergetic Audio Concepts - Tech Topics (2001) about 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.
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 was the original location of NWAA Labs in southern California.
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.
Papers & Presentations (AES, InfoComm, and other invited talks)
This is a YouTube video of a webinar I presented for my friend Fedele De Marco on the topic of Subwoofer Alignment with a Full Range System. This one was
targeted to the situation where it is not possible to disengage the low-pass filter on the subwoofer.
The presentation deals with time alignment in the time
domain. It takes into account time, energy, and frequency. Additionally, the three spatial dimensions are also considered in order to optimize the time
alignment, and the summation in the frequency domain, across the largest audience area possible. Those interested can view the presentation on YouTube
using the link above.
Fedele's introduction is in Italian.
My presentation starts at about 18:30 in the video.
PDF of the slides from the presentation at the 147th AES Convention.
Almost all types of loudspeaker systems will benefit from having a consistent directivity response with respect
to frequency. It is an important contributor for the loudspeaker system to be able to sound good in different rooms with different acoustical properties. This is often
overlooked or relegated in importance in order to give priority to the on-axis frequency response. This seems particularly true when dealing with two-way loudspeaker systems
employing a passive crossover. However, this need not be the case.
This session examined the performance of a product recently evaluated from an overseas ODM / CM. We will detail how software modeling & simulations can be used to
optimize the passive crossover to improve the directivity of the loudspeaker system through the crossover region. A single channel of front-end DSP can then be used to
equalize the overall response of the loudspeaker system. Since the directivity response is more consistent, the equalization can be more effective at improving the overall
sound quality of the loudspeaker system.
PDF of the slides from my 2018 & 2019 AES@NAMM / 2020 AES Academy lectures on how to time align subwoofers with the low frequency section of full-range loudspeakers
Also see the YouTube video of a similar presentation from the 2010 AES
Convention
This is a PDF of the PowerPoint slides I used during the Product Design track talk on "power" ratings for loudspeakers & why they are neither very useful or
accurate. This was presented at the 143rd Audio Engineering Society Convention, October 2017 in New York, NY. It accompanied presentations from Klas Dalbjorn
and Claudio Lastrucci from Powersoft.
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 absence.
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.
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.
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 achieve good
directivity control, specifically horn size and driver spacing. It shows the resultant constant directivity from approximately 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.
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 pattern 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.
This is a PDF of the PowerPoint presentation given during the presentation at the Renkus-Heinz booth for the 129th Audio Engineering Society Convention, November 2010 in San Francisco, 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).
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.
This AES paper details the application of low pass and all pass filters to loudspeaker system using multiple low-frequency drivers to improve the
directivity response 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.
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.
This AES paper details using software modeling (EASE SpeakerLab) to predict the directivity response of a loudspeaker system using the individual driver directivity measurements
and crossover filter transfer functions. This paper was presented at the 123rd Audio Engineering Society Convention, October 2007 in New York, NY.
