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I'm not sure, it's why I asked. The top end with an 8" driver (most) won't look so pretty. I'd rather a two way in a TL enclosure than a single driver personally.
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Transmission-line speakers
- Thread starter Kvalsvoll
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A dome tweeter with 1 or 2mf capacitor is recommended
Having been co-opted into Marketing frequently I'll partly agree. But isn't at least part of the Nautilus thesis (and others over time) that the internal arrangement of baffling/shape and absorption is superior to a plain parallelepiped? I would sure think so from an acoustic intuition point of view. The rear sound physically cannot just bounce off a parallel rear wall and re-radiate through the cone.
MAB
Major Contributor
There are really cheap ways of making the walls non-reflective. Jute mat does the trick really well. So does a diffuser.
If the Nautilus design does as good a job as simple methods, fine. But the B&W look horrible.
Better watch out for assassin snails, they're coming for you!
I gotta say, beauty is in the eye of the beholder, but the Nautilis definitely look expensive which can have a certain appeal. Or you could get http://www.norh.com/Norh_Loudspeakers/Norh.html
instead...
Vladimir Filevski
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For higher frequencies, yes - it is a good solution, But we are talking about low frequencies, where wavelength is very large, so there will be reflection from the end of the snail tail.
Vladimir Filevski
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Mmmm...yes, very good point! ...then again at very long wavelengths is it really reflection or pressurization? I guess first reflection then pressurization. Anyway less upper frequency crud coming through I would think.
https://audio.com.pl/testy/stereo/kolumny-glosnikowe/59-bowers-wilkins-nautilus#laboratory
"...
This is how most “transmission lines” work, which are indeed largely labyrinth enclosures using the energy of the back side of the diaphragm, but the B&W Nautilus was not to be like that. Unable to realize an ideal transmission line for a woofer and unwilling to accept labyrinth resonances, they opted for an enclosure.... closed.
Yes, it has an internal transmission line design, but ultimately the energy that is not fully damped is reflected from the end of the tunnel. Building a perfect transmission line for the bass is impossible even with the dimensions of the Nautilus, it would require a structure perhaps ten times larger."
"A transmission line type enclosure? In fact, for the woofer we have not been able to create it in the Nautilus, but “only” a closed enclosure with a spiral internal structure. Line or closed enclosure, without active equalization, we do not obtain from such an enclosure, with overdamped characteristics, a sufficiently low cut-off frequency."
A transmission line should transmit, that what it's name says.
That B&W Line is made for absorption in the line and should be named after this.
But according to Wikipedia it's a variation of TML, what leads to further confusion.
That B&W Line is made for absorption in the line and should be named after this.
But according to Wikipedia it's a variation of TML, what leads to further confusion.
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Building a true transmission line speaker is impractical for 99% of the public, that's why the quarter wave has been a successful substitute. The quarter-wave has been successful in large part due to the math done by a few, and understanding what fill is necessary, they're complex designs but practical for a residential environment.
This is what is mentioned in the test - building a TL with full energy absorption of the rear diaphragm is not possible. The bass enclosure in B&W is simply a snail-shaped closed enclosure to - as much as possible - eliminate standing waves.
Circa 25 year ago I bought my PMC GB1 speakers abroad and shipped them home as excess baggage via a small airport. At that more relaxed time than now, the customs officer allowed me behind the curtain to watch them in their boxes going through the X-ray machine. I recall being delighted and a bit amazed to see the labyrinthine carpentry inside the enclosures. I still use these speakers and even though this thread has educated me about the broad and perhaps loose popularized interpretations of transmission line technology, they have performed impeccably for me, and I enjoy the music they make, and am reluctant to change them. They have many virtues beyond their weaknesses. YMMV.
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Looking at the Bailey's 1965 and 1972 articles, that does not appear to be entirely the case. Rather, the available diagrams seem to indicate that the density of the stuffing material along the line was the same. Below is a diagram from Bailey's 1965 article.
From the above diagram, it is apparent that the tightly-packed short-fibre wool was not intended to dampen the line. Instead, its purpose was to reduce significantly the direct reflection of higher-frequency sound from the rear panel of the enclosure. This was specifically mentioned in Bailey's 1972 article: "The folding in the original cabinet design caused sound coloration due to reflections at the bends — particularly the first one at the back of the cabinet."
The initial transmission line loudspeaker that described in Bailey's 1965 article was designed as a sound absorption solution: "The only safe method of removing the rear cone sound energy is by transmitting it down an infinite transmission line. This is obviously impracticable so the nearest approximation was examined." As the title of that article implied, the aim was to create "a non-resonant loudspeaker enclosure design".
However, Bailey's 1965 and 1972 articles both showed loudspeaker designs that evidently did use the vent for sound reinforcement at low frequencies (e.g., see the above diagram). Bailey noted that: "Opening the port had two effects. First, the bass response was improved to become approximately flat and secondly the cone excursion was greatly reduced between 30 and 50 c/s." Also, Bailey stated: "As the wool-filled line acts as a low-pass filter, the radiation from the vent cuts off before cancellation can occur at the higher frequencies."
An example of such a loudspeaker, the IMF TLS80, is shown in the diagram below. The enclosure dimensions were approximately 97.8cm high, 40.6cm deep, and 45.7cm wide (gross enclosure volume of 182 liters).
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Irving "Bud" Fried! And the racetrack woofer, first before KEF? Or was it a KEF woofer?
The early version of the TLS 80 used the KEF B139 “ractrack” woofer. Later versions of the TLS80 (and some other IMFs) used the IMF 128/20 woofer which also featured a racetrack shape.
1. It was a KEF.
2. It was John Wright, not Fried, who implemented it.
The early IMF speakers used KEF B139 and B110 midrange drivers. Sometime in the early 80's they switched to Elac drivers. The same racetrack chassis outline for the bass driver, but with a fibreglass over foam construction rather than the aluminium foil over foam of the KEF. The actual casting was different too. The mid driver changed as well, again with the same general construction and dimensions as the KEF, but with a noticeably thinner surround. Way back then I discovered that the IMF dealer was offering an upgrade kit - to upgrade the KEF drivers to the new Elac ones. And the upgrade kit was really cheap. When I asked if I needed to prove I to owned a pair of IMF speakers in order to purchase a kit, I was told that I didn't. So, having been impressed by the IMF MkIVs in the showroom, and like many, seeking to emulate them, I bought an upgrade kit with the intent of building a clone. I never got around to it, and eventually sold the upgrade kit to a local IMF enthusiast who wanted to actually upgrade a pair of speakers. The upgrade also included a few new capacitors to change the crossover slightly and a set of very open reticulated foam plugs that were supposed to go in the external openings of the line.
The origional KEF B139 bass drivers had some evil breakup behavior, so the new Elac design may have helped. Careful crossover design was needed to avoid nasties otherwise. Like may of the time I built a pair of Concertos from a KEF kit. They were pretty good for the time, but many years later I reworked the crossover for just this reason, with very good effect.
There was something quite appealing to the sound of those old IMF speakers. IMHO a lot of it has to do with the upper bass, and the lack of box resonances. The trouble with almost all the discussions I have seen over the decades about transmission line designs is that they all fous on the lower bass performance, and the littany of wierd claims that were, and in some quarters continue, to be made about how they work. Eventually they are well modelled as a 4th order vented system with loss in the vent. About it really. The lossyness makes the response look a bit different. The quote above about the bass driver having significantly reduced amplitide when the line was opened is something of a giveaway here.
Someting that people miss on the cutaway diagrams of the IMF speakers, the mid-range is also placed at the head of a damped line. How much of a difference this makes is hard to know, but clearly the intent was there.
One claim that seemed to continue to crop up was that the vent stuffing so reduced the speed of sound in the pipe that it became a half wavelength long, and that was why the low bass improved. Measurements showing the end of the line 180 degrees out of phase with the driver were touted as proving this. Pointing out that that was how a 4th order system would behave didn't help.
Eventually those early TL speakers were empirically designed. There was little to no analysis, just a lot of testing to obtain something that measured well with the tools they had and sounded good to the designers.
The origional KEF B139 bass drivers had some evil breakup behavior, so the new Elac design may have helped. Careful crossover design was needed to avoid nasties otherwise. Like may of the time I built a pair of Concertos from a KEF kit. They were pretty good for the time, but many years later I reworked the crossover for just this reason, with very good effect.
There was something quite appealing to the sound of those old IMF speakers. IMHO a lot of it has to do with the upper bass, and the lack of box resonances. The trouble with almost all the discussions I have seen over the decades about transmission line designs is that they all fous on the lower bass performance, and the littany of wierd claims that were, and in some quarters continue, to be made about how they work. Eventually they are well modelled as a 4th order vented system with loss in the vent. About it really. The lossyness makes the response look a bit different. The quote above about the bass driver having significantly reduced amplitide when the line was opened is something of a giveaway here.
Someting that people miss on the cutaway diagrams of the IMF speakers, the mid-range is also placed at the head of a damped line. How much of a difference this makes is hard to know, but clearly the intent was there.
One claim that seemed to continue to crop up was that the vent stuffing so reduced the speed of sound in the pipe that it became a half wavelength long, and that was why the low bass improved. Measurements showing the end of the line 180 degrees out of phase with the driver were touted as proving this. Pointing out that that was how a 4th order system would behave didn't help.
Eventually those early TL speakers were empirically designed. There was little to no analysis, just a lot of testing to obtain something that measured well with the tools they had and sounded good to the designers.
IMF was definitely a firm dedicated to testing. I was acquainted with the fellow who headed up IMF USA back in the day and he worked with the IMF technical leads in the UK. As a result I was able to hear a succession of RSPM designs.
The replacement of the B139 in the RSPM resulted in improved bass handling. I recall the Telarc CD of Copeland’s Fanfare for the Common Man would easily bottom the B139s in my RSPM Mark IV whereas a friend’s Mark VIIs (using the replacement woofer) could handle the same track. Incremental improvements based on operational test and evaluation.
