A true ribbon loudspeaker is possibly the simplest electric motor. Yet in my experience a large ribbon driver is one of the most time consuming, expensive and even excruciating projects for a Do-It-Yourself (DIY) amateur builder to attempt to design and build. Others assert that DIY ribbon design and fabrication can be easy [1]. Wherein lies the disparity of experience? Much has changed in the past 15 years in regards the potential for DIY large ribbon design and fabrication. My purpose here and in the sections to follow will be to delineate the evolving design process I began about 15 years ago in 1988-89; and, to detail the myriad fabrication and construction issues which delayed achieving operational status of my pair of 1 cm x 182.5 cm (3/8 inches x 6 feet) drivers until January 2000.
Prior to March 1999, at this website, a number of photographs and short
explanations related to the creation of my ribbon building infrastructure and fabrication process
were shown here under the title of
"The True Ribbon Diversion." That ongoing process came to an end after March 1999 due to my
leadership of a class-action litigation
against my employer, California State University, Long Beach, with a number of other Vietnam era
veterans for discrimination and retaliation. After July 2001 when I retired from the university
as a result of a settlement adjudication of "discrimination/retaliation" against the university,
the Acoustic Line Source Research website was moved to Bob Stout's "Snippets.org" site.
My large ribbons have been playing for over three years now, since January 2000, in a presumed 'undeveloped' state using so-called 'flat ribbons' of un-corrugated aluminum foil. There has been an opportunity for much subjective observation of the ribbons' operation and performance since that time. A few limited measurements were also made about a year ago for the Dipole Forum.
Today my ribbon-building infrastructure is almost rebuilt/restored, and I have obtained a new high-performance 24/96-measurement system, Liberty Instrument's "Praxis". Furthermore, a new book on DIY ribbon design and fabrication is being finalized for publication at this time. Last year, at the request of its author, I provided him copies and explanation of my prior methods, means, and references. I have declined his offer to participate in the book as a secondary or guest author. While I do acknowledge that a simple small ribbon might be 'slapped together' in the garage over a weekend's time, what if one wants to pay lip service to 'scientific' optimal design? What are the stages and considerations of design for a large ribbon driver?
Personal computer technology has advanced enormously since 1988, and as a result of that advance, and other achievements in the academic explanation of the computation of primary ribbon parameters [2], the situation is vastly different today than just 15 years ago. Engineering is the exploration of compromises. That understanding applies in the matter of optimal ribbon design. A ribbon loudspeaker cannot be or do all things. Limits apply. Indeed, recent observations of the operation of my 1cm x 182.5cm true ribbons in context of the dipole acoustic environment created by my new pair of line array 'woofer' systems have proved quite troubling. (See A New Line Array for 2003.)
In this regard, consider the 'answer' Siegfried Linkwitz has provided his "Phoenix" loudspeaker FAQ 'question #25' in regards his non-use of dipole ribbons for his "Phoenix" dipole loudspeaker: Q25 - Why do you not use a rear firing tweeter or a dipole ribbon tweeter?
He states therein, "The large amount of air movement due to the close proximity of the 8" drivers might modulate the movement of the low mass ribbon and lead to further distortion. I have not used a ribbon driver, because the ones that I am aware of do not seem to fit this application." Siegfried Linkwitz.
Extremely large excursions of my un-segmented ribbons have been observed, when driven or
un-driven, in context of equally large excursions of the adjacent drivers of the line array. In
context of the high
volume velocity environment created by the close proximity of the line array, the large ribbon's
performance potential appears to be compromised due to external modulation. This is obviously
going to be an area for
further research and attempts at quantification. Previously the large excursions had been noted
in context of separated subwoofers, but the connection was not so grossly apparent as now with the
adjacent line arrays. On the basis of correspondence with a number of other ribbon makers it is
apparent that the large ribbon excursions is an oft-noted phenomena, which have
perplexed others as they have me. As you might imagine, distortion-causing external acoustic
modulation of a ribbon's ouput is not a general topic in commericial ribbon loudspeaker literature
and advertisements.
Obviously a long ribbon might be segmented by use of, say, silicone grease 'dots' to anchor the ribbon at points along its length to attempt to restrict its susceptibility to external modulation. Yet this method/technique must alter the performance potential of the ribbon negatively due to restriction of maximum excursion capability; and also, by creating multiple interfering sources where originally there was only one. Many opportunities for research come to mind to document these effects.
Despite whether a true ribbon is easy or hard to design and fabricate, a ribbon's relative fragility and seeming gross susceptibility to external acoustic modulation may be a limiting factor in large ribbon design or small ribbon design for that matter. In the pages and sections that follow I will attempt to present a comprehensive description of the chronology of the design and fabrication processes I developed and evolved during the creation of my ribbons.
There are three individuals whom I must acknowledge here at the beginning for their unselfish help and assistance - as I was being driven mad by fabrication problems. Without their help, I might still being looking for answers on fabrication issues. Leif Aden, of Sweden, told me what sort of tool to use to cut ribbons from aluminum foil. Hans Struwe, of the Netherlands, told me how to affix the aluminum foil to a cutting mat (The Struwe Wet-Processed Ribbons). David Graebener, of the Bohlender-Graebener Corporation, a designer and manufacturer of the RD-75 magnetic-planar line source driver, provided valuable intellectual information about the design of magnetic circuits and a special type of adhesive appropriate for gluing magnets to steel.
Sections and pages which follow may not appear in strict chronological sequence due to the availability of previously prepared materials which can be posted without substantial preparation.
John R. Whittaker
[1]. J.V. Verhagen, "Ribbons Made Easy,", AudioXPress, vol. 32, no. 5, pp. 56 - 63, (2001 May).
[2]. S.P. Lipshitz, T. Scott & Bruno Salvy., "On The Acoustic Impedance of Baffled Strip Radiators," J. Audio Eng. Soc., vol. 43, no. 7/8 (1995 July/August).
Considerations on the
Optimal Design of True Ribbon Loudspeakers - Index.
Acoustic Line Source Research - Table of Contents.
