The question I began to explore during the 1987-88 period was whether there was sufficient available information for a do-it-yourself (DIY) audiophile to be able to scientifically design an optimal large line source, true ribbon driver. It rapidly became apparent there was a general paucity of available information, and what information there was available appeared to contain conflicting information. Clearly, building a pair of large ribbon drivers was going to be a very difficult proposition, with a significant investment in infrastructure. My thoughts and intent at the beginning were devoted to 'doing it right.' That is, why not survey the existing literature and design my DIY ribbons on the basis of prior scientific research. There was also a basic curiosity as to what an 'optimal' ribbon design would entail? Could I design and build an optimal large ribbon?
In no case did the available scientific literature at that time seem to contain specific information regarding a 'recipe' for design of large line source ribbon drivers. Later, as the internet became more mature, I was able to access a number of U.S. Patents related to ribbon drivers. Some of those patents were for large ribbon drivers, particularly some of the Magnaplan and Apogee patents [1,3]. Yet a method for scientific design was not evident in those documents. More questions than answers arose from the entire body of literature and U.S. Patents available. This situation persists today.
In 1984 Lampton and Primbsch [2] authored the first DIY article on the design and fabrication of small "simple" true ribbons of which I am aware. At the same time as I was researching ribbon design methods, Thofte [4] published an DIY article on a ribbon design imitating elements of the Apogee ribbon loudspeaker line. Synthesizing a true ribbon design method in 1988 led me to consider a form of 'horseshoe' magnetic circuit as having the greatest potential for maximum sensitivity. As it turned out, attempting to fabricate a large horseshoe magnetic system led to overwhelming amounts of time being spent on hand shaping of steel poles pieces. Ultimately the horseshoe design was abandoned on the basis of advice from David Graebener.
The original impetus to start the project in 1988 was based upon a post-divorce status of not having much money, but having lots of free time to 'hand machine' the steel poles. The project progressed in fits and starts for a number of years, with long periods of hiatus intervening between spurts of progress. After The RD-75 Dipole Baffle Study period passed in 1998 I became engaged in veteran activism and a subsequent class-action litigation against the university where I worked. As a result of that involvement, once again I had large amounts of time available to devote to the exceedingly troublesome fabrication issues.
Three individuals came to my aid during that phase, Leif Aden, Hans Struwe and David Graebener. Without their input and information my ribbons might still not be playing. To date, I do not consider my large ribbons, even thought they have been playing music since January 2000, a completed project. Much research awaits to be done on aspects and elements of the aluminum ribbon itself, particularly corrugation issues. I have tested a unique idea to 'close' the current 'open-circuit' design which seems to have much promise. Implementing that change is yet to come.
As time passed and the internet became a worldwide phenomena I became acquainted with a number of DIY ribbon builders. Europeans, apparently following Thofte's [4] lead, have been creating ribbons of merit and beauty. Their techniques have become rather advanced in my opinion; and, I certainly owe several of them a debt of gratitude for sharing their fabrication techniques. Last year I became aware, in context of membership in the internet Dipole Forum, of a U.S. origin DIY project of a 0.7 inch x 93 inch floor-to-ceiling ribbon based upon the Apogee design. Yet to all appearances, true ribbon building in the U.S.A. is moribund. Frankly, after the effort I've expended this situation is quite understandable.
In no way am I recommending or promoting the fabrication by others of any ribbon design based upon what I have done. Yet, given the limitations of my available information, my 182.5 cm long ribbons maybe be in the running for a position amongst the top five longest ribbons built to date? At least two others have built floor-to-ceiling true ribbons, and there was the Apogee "Full Range" true ribbon tweeter, which I believe was slightly longer? After that? In any event, I can provide significant information on DIY true ribbon design and fabrication that is not yet extent in the public domain. Then there are the 'questions' I have which may be of some interest to those who would consider such a project. I will take the 'loyal opposition' position that large true ribbons are rather difficult to build, and require a costly and significant investment in developing an infrastructure to create the ribbon drivers. There is nothing simple or trivial about the process or the methods.
Cutting to the chase as it were, the concept of an 'optimal' large true ribbon is completely compromised by the necessity to choose between maximum possible sensitivity in the highest regions of the frequency range or maximum possible frequency linearity over a much wider frequency range, but at a significantly lower overall sensitivity level. Furthermore, the ability of the DIY builder to even choose between these options may be moot in terms of an inability to obtain ribbon materials of appropriate mass to implement the choice.
Life is tough for the true ribbon builder.
John R. Whittaker
[1] J.M. Winey, "Line Radiator Ribbon Loudspeaker," U.S. Patent No.
4,319,096, (1982 March).
[2] M.L. Lampton and J.H. Primbsch, "Simple Ribbon Tweeters," Speaker
Builder, vol. 3, pp. 7-13 & 14, (1984).
[3] G.E. Walker, L. Spiegel, A.J. Shuman, and J.L. Kirtley, Jr., "Ribbon
Speaker System," U.S. Patent No. 4,550,228, (1985 October).
[4] O. Thofte, "La Folia: A Kitchen Bench Ribbon Speaker," Speaker
Builder, vol. 1, pp.9-17, (1988).
Considerations on the
Optimal Design of True Ribbon Loudspeakers - Index.
Acoustic Line Source Research - Table of Contents.