The late Irving “Bud” Fried (1920–2005) blazed a trail through high-end audio’s formative years, first as an importer of classic British gear and later, starting in the 1970s, as a manufacturer of transmission line (TL) speakers under the Fried name. His strongly held beliefs about loudspeaker design were based, as he put it, upon the inexorable laws of physics, and he wasn’t afraid to promote and defend his ideas within the audiophile community. Fried maintained that the ideal loudspeaker would preserve the audio signal’s time coherency, which explains his fondness for the non-resonant bass response of TL designs. However, his pet preference for series, rather than parallel crossover networks, seems a bit quaint today after 40 years of progress in this field.
Fried Products Corporation, owner of the Fried and IMF brands, approached Salk Sound during 2012 with the idea of designing and marketing a TL speaker under the Fried name. This seemed like a natural fit as Salk Sound was already manufacturing TL speakers, and Jim Salk, founder of Salk Sound, decided to take up the challenge. Suffice it to say that the Fried/IMF brand names are now licensed exclusively to Salk Sound. The first speaker in the new line, says Jim Salk, “is very similar to our SongTowers. It plays deeper since it has 7" woofers, and we used a series crossover rather than a parallel one. Other than that, both speakers are based on roughly the same concept.”
Jim Salk described for me the Fried Tower’s design considerations: “A team of people were involved in this first Fried project. I knew Bud used Hiquphon tweeters in the past and chose a tweeter model that was originally developed by Oskar [Wrønding] for him. I next looked for a moderately priced woofer with good performance characteristics. The Peerless model we chose was very reasonably priced, but used a lot of copper in all the right places. It was an excellent performer for the money. I asked Paul Kittinger to come up with a transmission-line cabinet for this model. Paul has done quite a few TL cabinet designs for us and looked at various TL formats. My initial request was that he develop a standard folded TL design. While this modeled fairly well, he also looked at a mass-loaded quarter-wave design similar to that used in our SongTowers. As happens on occasion, the mass-loaded design modeled in a slightly superior fashion. So we had a quandary. Do we assume Bud would have opted for the slightly superior enclosure or do we stick with the type of TL cabinet he was best known for? In the end, while it was not necessarily the approach Bud would have taken (tools to model these designs were not available in his day), we opted for the slightly superior mass-loaded design.”
“Once we had a cabinet design, we turned the project over to Dennis Murphy for crossover design. Dennis developed a standard parallel crossover for the speaker, which optimized the capabilities of the drivers. Once we had optimized this design, he took on the task of converting the design to a series crossover more in keeping with what Bud would have done. The resulting slopes were steeper than with Bud’s ideal loudspeaker design, but certainly consistent with some of the crossover designs he offered (we were supplied with all previous lab notes and crossover schematics). In looking over Bud’s lab notes, he had quite a few strongly held theories, but his designs did not always conform to his definition of the perfect loudspeaker (based on his white papers). These speakers obviously take some liberties with Bud’s ‘ideal’ design philosophies as well.”
The Tower’s cabinet is definitely not a classic TL in the tradition of A.R. Bailey’s folded line or Robert Fris’ DALINE (Decoupled Anti-Resonance Line), whereby the rear chamber housing the woofer is vented into a folded line. I’m certain that Bud Fried would have had difficulty in correctly identifying the Tower’s as a TL. And that’s because a mass-loaded transmission line (ML-TL) is a hybrid design in which an acoustically damped line is terminated through a bass-reflex-style vent. No wonder this design is often identified as just a tall bass reflex with no independent significance. But that clearly isn’t the case, as Martin King, who popularized this design, has shown. I used Armin Jost’s excellent AJHorn software to model two versions of the Tower cabinet. The first, as a normal bass reflex, and the second with the internal volume stretched out as a one-meter-long quarter-wave resonator. In both cases, the net interior volume was assumed to be two cubic feet and the box tuning frequency was set to 30Hz. The simulation results were similar, but did highlight two advantages of the ML-TL model. Damping in the deep bass was improved relative to that of a standard bass-reflex box, and the line appeared to distribute the port output more evenly in the bass region, as upper-bass energy (70 to 200Hz) was shifted to the midbass to give a smoother overall response.