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In Reply to: RE: Transmission lines... posted by mkuller on January 30, 2015 at 22:36:54
Agreed although I refer to them as John Wright's speakers. After the Bailey article in Wireless World stimulated lots of DIY interest, JW had one in HiFiNews (linked below) describing the development of a commercial model (IMF) which greatly influenced me. I built several.The IMF was not the first commercial TLS as Arthur Radford had already produced a few and Stromberg-Carlson had marketed several similar "acoustic labyrinth" models here in the US. Currently, PMC markets such designs.
A later analysis in Wireless World demonstrated that the TLS was not more effective than a similar but simpler ported speaker but enthusiasts (such as I) have felt that the quality of the bass (whatever that is) was superior.
Lots of info on this can be found at: IMF
BTW, I was a proud owner of JW's "wireless" mercury contact unipivot arm that he marketed as the Audio+Design M9BA M9BA
Edits: 01/31/15Follow Ups:
I think at the time it was easier to tune a line than a reflex by varying the damping to get bass control. But once Thiel/Small was published and especially with computer implementation of Thiel/Small control of the bass design became orders of magnitude better and lines weren't worth as much.
By the way, Bud Fried actually believed that the most important implementation of a transmission line was in the mid-range. The model G was a great example of this with a stuffed port bass design but a line for the mid-range and in the last version of the G the line was longer and folded and was an obvious improvement over the shorter front to back lines used in the 1st Gs.
I completely agree with you about the changes wrought by Theile/Small. After years of building TLs, I jumped on an article in "Audio" which offered a clear and logical series of equations for reflex design based on the Theile/Small work. I implemented them in a MS Basic program and never looked back.
As for the mid, he was right because it smoothly extended the FR and made the Xover design easier. KEF showed a prototype midrange with a dedicated flexible line. From Martin Colloms' book: "Covering a 250 Hz to 4 kHz range, this latter driver employed a 65 mm hemispherical dome formed in a rigid polystyrene/neoprene polymer, and was fitted with a double suspension and loaded by an 0.8 m pipe filled with long-fibre wool, for absorption."
I knew about the KEF mid line. They only built a few I think. It held up the completion of John Crabbe's second set of built in bass horns(down to 25 Hz) because he waited for it to be the mid-range. He finally gave up and adapted the mid/tweeter combo from the IMF monitor.
> It held up the completion of John Crabbe's second set of built in bass
> horns(down to 25 Hz) because he waited for it to be the mid-range. He
> finally gave up and adapted the mid/tweeter combo from the IMF monitor.
I was lucky enough to spend an evening listening to John Crabbe's bass
horn-based speakers before he sold the house. They did indeed sound fine.
But they were outclassed by a friend of John's. who had constructed a pair
of horizontal bass horns under the floor of his listening room, running the
full length of the room and venting under the main speakers.
John Atkinson
Editor, Stereophile
Thanks John.
Those were exciting times as one expected to see innovative products appear regularly. I miss that.
I loved them the first time I heard them.
E
T
According to Bud Fried Radford promised a lot for years(Bud was going to import his speakers)and produced very little which is where John Wright and IMF came in. Bud announced his line speaker for a show based on Radford's promises which fell through. John Wright suggested using a KEF Concerto kit(B139, B110, T27) and putting it into a transmission line box. As the speaker evolved the T27 was replaced with a Celestion HF1300/HF2000 tweeter/super tweeter combo seen on the classic IMF Monitor.
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