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I've seen a couple of full stop transmission lines built into the foundation of houses, that's dedication, lol. Please post your driver and final numbers, thanks.
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Transmission-line speakers
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DanielT
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RonSanderson
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I wouldn't wake up this old thread, except I think there is still more that has been missed.
Irving M. (Bud) Fried was the original importer of IMF speakers (note his initials), and later produced his own under the Fried name. He was a firm believer in transmission lines - I have two models, the IMF Studio III from 1972 and the Fried Studio V from about 1995. They are still in daily use.
I have most of his marketing newsletters from 1961 to around 2000, where he discusses how transmission lines work and why he used them. The attachment "The Virtuous Transmission Line" is most relevant to this thread.
I am attaching the brochure for his System H, which may be one of the first, if not the first, subwoofer / satellite system. For those in a hurry, sections IV and VII are most relevant here. This system must be at least 50 years old by now. (Edit: introduced in 1975.)
A few decades later his enthusiasm for TL's had not wavered.
One assertion is that the back wave from the speaker is attenuated and delayed by placing resistive materials in the line. The goal is to match it to the direct output from the speaker, but coming out from the bottom front vent. He asserts that this creates a coupling between the front and rear speaker energy that produces a planar wave front for the bass, which is much larger than the wavefront produced by the speaker cone alone. He also asserts that this reduces room interaction compared to that produced by a single point source.
"Transmission lines: By their nature, as described in a 1970 article written in "Hi Fi News" by an English associate and myself, lines appear in rooms as planar sources, with much less energy going randomly to the walls (as in "spherical source" loudspeakers). Thus, there is much less room interaction with lines, and purer response no matter where situated in the room."
I also attach some of the marketing materials and newsletters about the Studio V. In the printed blurb at the beginning of this file he discusses the difference between using a transmission line in the bass and what he terms a "line tunnel" for the midrange. There is other stuff in the PDF file that is not relevant to this thread. Sorry, but I had it all bound into a single unit. There is, however, a picture of the transmission line in a cutaway drawing.
Finally, I attach two pages discussing the design of the Studio V in which he further discusses TLs. "The Virtuous Transmission Line" is a blurry copy of an article from "Hi-Fi Heretic", a publication I never heard of!
I hope this sheds some light on the views of an insider and one of the transmission line's biggest proponents.
Irving M. (Bud) Fried was the original importer of IMF speakers (note his initials), and later produced his own under the Fried name. He was a firm believer in transmission lines - I have two models, the IMF Studio III from 1972 and the Fried Studio V from about 1995. They are still in daily use.
I have most of his marketing newsletters from 1961 to around 2000, where he discusses how transmission lines work and why he used them. The attachment "The Virtuous Transmission Line" is most relevant to this thread.
I am attaching the brochure for his System H, which may be one of the first, if not the first, subwoofer / satellite system. For those in a hurry, sections IV and VII are most relevant here. This system must be at least 50 years old by now. (Edit: introduced in 1975.)
A few decades later his enthusiasm for TL's had not wavered.
One assertion is that the back wave from the speaker is attenuated and delayed by placing resistive materials in the line. The goal is to match it to the direct output from the speaker, but coming out from the bottom front vent. He asserts that this creates a coupling between the front and rear speaker energy that produces a planar wave front for the bass, which is much larger than the wavefront produced by the speaker cone alone. He also asserts that this reduces room interaction compared to that produced by a single point source.
"Transmission lines: By their nature, as described in a 1970 article written in "Hi Fi News" by an English associate and myself, lines appear in rooms as planar sources, with much less energy going randomly to the walls (as in "spherical source" loudspeakers). Thus, there is much less room interaction with lines, and purer response no matter where situated in the room."
I also attach some of the marketing materials and newsletters about the Studio V. In the printed blurb at the beginning of this file he discusses the difference between using a transmission line in the bass and what he terms a "line tunnel" for the midrange. There is other stuff in the PDF file that is not relevant to this thread. Sorry, but I had it all bound into a single unit. There is, however, a picture of the transmission line in a cutaway drawing.
Finally, I attach two pages discussing the design of the Studio V in which he further discusses TLs. "The Virtuous Transmission Line" is a blurry copy of an article from "Hi-Fi Heretic", a publication I never heard of!
I hope this sheds some light on the views of an insider and one of the transmission line's biggest proponents.
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OT: Those Brüel & Kjær print-outs (mid '70s) you posted bring back much sweet memories, as a young EE.
We were working on a contract for the original digitization of analog ... at the tip-of-the-technology - secure (encrypted) voice communications @2.4kbps - of the era.
The [ummm...] contracting agency had drop-shipped us set of two 8-foot rack fulls of Brüel & Kjær test equipment and a pallet of ancillary hardware.
We were told to perform some exotic "audio intelligibility testing" on the terminals (secure phones) as a part of our contract.
No one in our engineering department had realized that we may had gotten ourselves in deep doodoo << because we did not even know (or had ever used) such a compilation of buttons on test equipment.
It took few of us grunt EEs nearly a month, inside some hi-security lab's anechoic chamber (30'x30'), to get proficient with the hardware and audio measurements.
Fortunately, we managed to impress [ummm....] our customer that [ummm...] all things considered... [deplorable] 2.4kbps voice-digitization was 'intelligible' ... at least, when it came to pangrams that were drilled into our brains continuously for 3 straight months.
The supporting documentational reams of Brüel & Kjær plots/graphs/print-outs for [ummm...] our customer measured in 'pounds' and not in 'pages'.
In hindsight: Us punk-EEs were thinking we were invincible for conquering what is now done at the press of a button on some "cheap" AP...
Thanks for the memories.
I've just built some TLs - parallel duct, 1/4 wavelength, rear-top exhaust. 1.16 x 0.3 x 0.3 m. It predicably and repeatably, resonates in the lower register, and there is a significant (-12 dB) attenuation at around 89 to 90 Hz. The tweeter, which is sealed, also has significant resonances, whereas the spec sheet shows a flat response. However, trying some temporary DSP EQ, it was a shock to discover that I could get the response flattened to a reasonable level, and the sound improvement was significant. The trouble with resonating type speakers is that the bass doesn't 'belong' to the music - maybe because the bass waveform takes time 'to resonate'? With my TLs, the bass is tight - and it is deep. I'm now making a hardware version of the EQ (it needs high-Q responses).
The impurities induced by the summation of out of phase bass from the back of the cone being combined with the front by means of a port or transmission line pale in comparison to the chaos created by our rooms.
I am a big fan of traditional loudspeaker design, but I think our collective understanding of bass reproduction has moved on from worrying about bass alignments too much - Geddes for example in his speakers said he didn't worry about the 'thiele small stuff' and put his midwoofers (12"+ pro sound woofers) in sealed enclosures of arbitrary size, and the subwoofers he used to sell were bandpass solely to get the desired output.
This seems to be a conflation with like a line array of speakers as used in many PA systems. I like transmission lines...still look on eBay etc for a set of Celestion 300s...but the source is still a woofer and a "port"* which does not make it into a line source at all.
I recall George Augspurger wrote a program for calculation TL enclosures; I think I still have it somewhere. What I don't recall seeing is any TL systems actually measured, let alone compared to sealed and ported. ?!?!?!?
*what DO we call the open end of a transmission line?
Doesn't that make it a 1/4 wave TL? Which I'm not recalling how effective that really is.
And now, it is time to mention the Bose Acoustic Wave Cannon! Perfect sound forever, and we've made your amplifier twice as powerful! (ha ha when I once met Richard Small at Harman in Indiana he was a bit embarrassed about that latter statement. Although actually when the Power Cube came along later, perhaps he shouldn't have been!)
A really good question Head_Unit. I called it the exhaust once. According to AI - In church organ pipes, it's called the "Mouth", or technically, the "Antinode" for a 1/4 wave etc., if it's the open end of the pipe, opposite the sound source.
Matt_Holland
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I was given a pair of PMC DB1+ small bookshelf speakers. I’m seriously considering to block up the rear port.
Yes, electrical data transmission lines have 'Terminators' to stop/reduce reflections (i.e. to stop the wave bouncing back) - which has the same function as an open duct - so 'terminus' seems related...
*Shrugs as well.
"Terminus" sounds like a comic book character-soon coming to a big screen near you!
Hmmm, maybe instead of building a custom listening room, I should be focused on building a pavilion in a large farmer's field!
We went to the wonderful Upscale Audio...where speakers are more in the middle of very large, treated rooms. Yes stuff sounds more wonderful. At home...not quite so. Then again that should not deter us from improvement, like the folks who say audio is wasted in a car or a boat or whatever. Er, the sound will never be as pristine, but that doesn't mean you can't improve it to sound really enjoyable.
100% agree.
georgehifi
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Can one of the TL experts tell me what happens to the parameters of the bass if you seal up the port of a 1/4 wave length TL line??
Like this one https://castle.uk.com/avon-2/
1: how much higher will the -3 or 6db point be?
2: efficiency is it higher, lower or the same?
3: what is the "rate of roll off" per octave compared to being open?
Cheers George
Like this one https://castle.uk.com/avon-2/
1: how much higher will the -3 or 6db point be?
2: efficiency is it higher, lower or the same?
3: what is the "rate of roll off" per octave compared to being open?
Cheers George
A transmission line with a sealed terminus is a sealed cabinet. It will be identical to a sealed cabinet with slightly better attenuation of midrange energy coming back reflected through the cone, maybe. This is the design principle of the BW Nautilus speaker.
DSJR
Major Contributor
I grew up with hearing and demming the big IMF models of the mid 70's. the way the RS, PM and TLS80 at least balanced it was, according to 'Choice and other tests done at Hirst Labs (where IMF I believe also did their measurements) to accepot the cancellations in the large models around 100 - 150Hz and then pull the midrange and top down to largely match it. This meant the sub 100hz frequencies were boosted up to 5dB and using a sweep sine wave, the Pro Monitor III went down to a door rattling 17Hz (inaudible but one could sense the pressure waves). The mkIV in neutral state, rolled the sub 50Hz bass off gently, but the perception was of an extended but much 'tauter' balance. I don't recall seeing measurements of the Mk7 and Reference Standard. Below an early scan from early 70s Hi Fi Sound -How speakers used to be tested over here - I have other scans, but risk deluging you with them.
Interesting how the bass rise shown in the slightly smaller TLS80 isn't shown here. the Mk III 'Improved' had a slightly livelier sound, not that you'd probably notice today.
Interesting how the bass rise shown in the slightly smaller TLS80 isn't shown here. the Mk III 'Improved' had a slightly livelier sound, not that you'd probably notice today.
I think this is wrong. With a true TL, it doesn't matter whether there's a vent or not, as there's no energy left by the time it reaches the end of the line, so nothing is reflected back. B&W's Nautilus is a prime example of a real TL, not a sealed cabinet. In a sealed cabinet, the cabinet is pressurised by the cone movement, and this pressure acts as part of the cone suspension. Sometime they're called Acoustic Suspension. A TL doesn't pressurise the cabinet.
S.
DanielT
Master Contributor
Then it is a question of whether the specific driver is suitable for the volume of the closed box/cabinet.
Regarding the efficiency. One factor to weigh in about it depends on how much the current TL box is stuffed compared to how much stuffing is appropriate with the closed box. Open up your speakers and check. They can be massively, tightly stuffed, or not.
I have a pair of sealed Qln One speakers where the manufacturer had pressed in lots of stuffing. Really pushed in as much as possible, with a lot of force. It killed the efficiency I can say. Okay, it might be the previous owner who did it. I find it hard to believe that a recognized good manufacturer would do something so idiotic, but hey you never know.
Stranger things can be seen in the HiFi world.OT. I am now rounding the baffle corners on my Qln One. I intend to mount tweeter SB26ADC-C000-4 or Dayton Audio ND25FW-4 together with
woofer: SB15NBAC30 in my Qln One boxes.
Crossover will be my active LD Systems X 223.
...
Hm, I'm not satisfied. I will round off the baffle corners more. It is easier to see when you have painted them that it is needed. In any case it is easy to do with the grinder.
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