Fried on Series Networks
FRIED ON SERIES NETWORKS
By Irving "Bud" Fried.
In Kalman Robinson's review of the OLS Karma Ceramique CE-2.0 loudspeaker (Stereophile Oct 2000 p209) he refers to the designer's description of the network as a "subtractive" crossover network of the series type.
I have been a longtime proponent of series networks, of which I was apprised over 20 years in my researches in Denmark. (My article on this subject is available from me for $2.50)
I am happy, therefore, to note that the subject of series networks has been brought up: they are generally considered to be "mysterious" and not to be discussed by the profession of speaker designers. I would like to make it several points regarding them and why they are virtually ignored by the profession.
First of all, Kalman recites, they are more difficult to design:, or you have to be able to visualize &endash; ie. have a brain. (My article points out that Peter Walker has often mentioned the dearth of first-class minds in speaker design. Peter, who created the Quad Electrostatic, has a first class mind!)
Second, while there are formulas for designing series crossovers (David Weems gives such in his book), there are no computer programs available, as there are for parallel networks.
Third, they are "self-balancing" as OLS assets, meaning that small variances in parts values does not destroy them (as in sharp parallel filters); rather it merely shifts the transition point up or down. Only if there is a very large error do bad things happen -- ie, presenting a capacitive or inductive load to the amplifier.
Otherwise, series networks present an "resistive" load to the amplifier. That is good, because amplifiers prefer such loads to the highly reactive loads of sharp-filter parallel networks -- the networks that are used all too frequently in supposedly high-end loudspeakers today.
Kalman in his listening, pointed to the merits of series networks, when he commented how the mid, woofer, and the tweeter seemed much more integrated than that to which he was accustomed. This is because series networks, done with the proper drivers and with the proper parts, are much more in-phase at the crossover points. Indeed, when one is accustomed to a properly operating series network loudspeaker, when one goes to another loudspeaker with parallel networks, no matter what the slope rate, the first shock is to notice that the drivers all seem to be separate -- what has been called "woofer/tweeter" sound.
Why is this? Several theories have been evolved regarding this phenomenon. I will list them briefly, and suggest that further elaboration can come from that article of mine.
Better phase on dynamic variations -- the sound is more "together".
Greater dynamic range of reproduction (my article cites laboratory data on this, illustrations of the effect to various expert listening groups, and actual measurements made), thus more of the "transient dynamic linearity" of Richard Heyser, the late genius who postulated that this is the primary difference between "live" and "reproduced". Peter Walker also states this as the primary difference between "live" and "reproduced". (Peter is another genius)
The "reverse Doppler" effect, much mentioned in the "Diaural" literature. (Yes, the Diaural is a simple series network). Simply stated, the parallel network produces an artificial division between lows, mids and highs, whereas in nature, what the ear perceives is a modulation of each range by the other. Only a single diaphragm speaker (such as a Lowther) or a series-connected multi-way loudspeaker can preserve the relationships as we hear them in person -- thus the "naturalness" of the series connected loudspeakers!
Why aren't series networks more popular? This is most fascinating to me. I list several possibilities.
Ignorance or, as some of my confidants tell me, "stupidity" among designers.
Fear of the unknown -- or, everyone else uses parallel theories, so they must be o"Conspiracy" theories. I can cite one case, of a rival loudspeaker company that I talked into trying series networks. He did, this engineer, and called back to say, "they are better" -- as if I didn't know that. A week or so later, he called back again to tell me that he had said the same to another loudspeaker engineer, who then pleaded with him not to convert to series networks! he said there seemed to be a conspiracy of silence in the industry, (David Weems, in his book, suggests the same.)
The obsession with "flat frequency response," rather than the nature of the wave fronts -- which, after all, is what music is. Most loudspeakers reflect that obsession, while physicists such as Nobaru Tominari, professor at the University of Tokyo (he likes it called the "Harvard of Japan"), suggests is all wrong.
The phenomenon of "cognitive dissonance" also covered in my article: ignoring evidence that does not fit one's conceptual frame.
The almost universal lack of intimate acquaintance with the sound of live instruments and live performance values among the "Hi-Fi" public
Forgive me for going on and on, but series networks are better, and all you have to do is compare them to parallel networks speakers!
Irving M. (Bud) Fried
Fried Loudspeakers
Philadelphia, PA