Transmission-line speakers

[DSJR]

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.
View attachment 381805View attachment 381806View attachment 381807View attachment 381808View attachment 381809

Mission and Gale used to fully 'stuff' their boxes in the 70s too to help tame a 'boxy' sound methinks. A reviewer and one-time friend took all the stuffing out and preferred the sound despite hugely increased colouration. These days, it's all more scientifically done (I hope )

The early to mid 70s IMF transmission lines appeared to have no mechanical damping on the KEF B139 driver, the diaphragm of which wobbled back and forth if pushed and let go. The amps we routinely sold with these were Crown D series and domestically, even the D-60 (45WPC typically at 8 ohms) was more than sufficient to get good levels from them although the D-150 had more headroom on master-grade material, which we had at the time for dems.

 

[DanielT]

Mission and Gale used to fully 'stuff' their boxes in the 70s too to help tame a 'boxy' sound methinks. A reviewer and one-time friend took all the stuffing out and preferred the sound despite hugely increased colouration. These days, it's all more scientifically done (I hope )

The early to mid 70s IMF transmission lines appeared to have no mechanical damping on the KEF B139 driver, the diaphragm of which wobbled back and forth if pushed and let go. The amps we routinely sold with these were Crown D series and domestically, even the D-60 (45WPC typically at 8 ohms) was more than sufficient to get good levels from them although the D-150 had more headroom on master-grade material, which we had at the time for dems.

Aha,

The fact that I mentioned stuffing in TL is because I read ( in this thread?) that in order to remove resomances in a TL, a lot of stuffing may be needed and that in itself leads to quite a lot of reduced efficiency.

My Qln One does not fit as an example because it was an extreme. It must have been the previous owner who filled them. Imagine that you fill to the max. Then you use all your weight to stamp in all the stuffing. Then in with more stuffing and stomp even more and so on. It resulted in a probably completely resonance-free sound but my god what poor efficiency there was with them. Basically 0 bass for example.

 

[Salt]

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.

No.
If at the end of a TML there was no energy left, it wouldn't work.
TML is a resonator (organ pipe), and with closed end it doesn't resonate to the outside, and if filled with damping would work as Helmholtz Resonator (that may be tuned fitting the enclosure resonance frequency), but then it's no TML.

 

[Kal Rubinson]

The early to mid 70s IMF transmission lines appeared to have no mechanical damping on the KEF B139 driver, the diaphragm of which wobbled back and forth if pushed and let go.

Some of us tried a phase-plate in front in an effort to deal with this. Didn't seem to help much.

 

[georgehifi]

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.

@ sergeauckland I'd like your opinion also on this if you could​

Thanks for that, can you say the effect it will have on this measured FR and impedance/phase graph I found on them if I sealed up the TL line.
https://tinyurl.com/24yroz6k
Cheers George

 

[sergeauckland]

No.
If at the end of a TML there was no energy left, it wouldn't work.
TML is a resonator (organ pipe), and with closed end it doesn't resonate to the outside, and if filled with damping would work as Helmholtz Resonator (that may be tuned fitting the enclosure resonance frequency), but then it's no TML.

No it's not! A TL should have no resonance, no reflections, that's why it's called a Transmission Line.

S

 

[Salt]

No it's not! A TL should have no resonance, no reflections, that's why it's called a Transmission Line.

S

Of course every line has a resonating frequency. What you mean is it schould not attenuate this frequency so a lossless passthrough is given.
On the other hand if one side of the pipe is closed it can be used as silencer in ducts, compressors, even in architecture ; may have a look at this for example:

https://www.researchgate.net/public...tering_buildings_through_ventilation_openings

 

[sergeauckland]

Of course every line has a resonating frequency. What you mean is it schould not attenuate this frequency so a lossless passthrough is given.
On the other hand if one side of the pipe is closed it can be used as silencer in ducts, compressors, even in architecture ; may have a look at this for example:

https://www.researchgate.net/public...tering_buildings_through_ventilation_openings

No it doesn't! A line will only resonate if there are reflections that create standing waves. A real TL has no reflections, as the energy is absorbed in the stuffing as the wave progresses down the line. By the time it reaches the end, whether open or closed, there's nothing significant left to reflect back. Any small amounts that may be left are progressively absorbed on the way back, so there's no energy to resonate. A quarter wave resonator is just that. It is NOT a transmission line.

The important thing with a real TL, and what's difficult to get right, is to arrange the stuffing so that it gets progressively more absorbent the further away from the driver, such that there's no back pressure on the driver. As far as the driver is concerned, it sees an infinite anechoic dead space with no reflections. That's why there's no resistance to driver motion, unlike a sealed box or, at resonance, a bass reflex. You can see this clearly from the impedance plot which shows no rise in impedance at low frequencies, unlike the two peaks of a reflex enclosure or the single peak of a sealed box.

S

 

[Salt]

Sorry, but you are messing up "resonating" and "resonance frequency RF" (f0).
A line is transductive for it's basic RF and the multiples of it. So sound energy that is directed into the line would exit unattenuated at the other end (if not closed ), thus using the backfiring energy of the woofer for bass support. Energy of input = energy of output (idealised).

What's undesired is the harmonics that pass the line too, and those are ideally damped as far as possible to be inaudible.

 

[sergeauckland]

Sorry, but you are messing up "resonating" and "resonance frequency RF" (f0).
A line is transductive for it's basic RF and the multiples of it. So sound energy that is directed into the line would exit unattenuated at the other end (if not closed ), thus using the backfiring energy of the woofer for bass support. Energy of input = energy of output (idealised).

What's undesired is the harmonics that pass the line too, and those are ideally damped as far as possible to be inaudible.

I'm not messing up anything. A TL loudspeaker enclosure has a very absorbant line so nothing exits, it is ALL attenuated. That's why for a real TL, it doesn't matter if the line is open or closed. B&W's Nautilus has a closed line for just that reason.

The backfiring energy is all converted to heat in the line stuffing.

S

 

[Salt]

No. Thus it would be same as highly damped CB. Some facts (and I'm out here now):
http://diyaudioprojects.com/Technical/Papers/Loudspeakers-on-Damped-Pipes.pdf

 

[sergeauckland]

No. Thus it would be same as highly damped CB. Some facts (and I'm out here now):
http://diyaudioprojects.com/Technical/Papers/Loudspeakers-on-Damped-Pipes.pdf

I refer you to the conclusion. Bailey's transmission lines had stuffing at variable densities, lighter at the start and heavier at the end. His designs also provided for the pipe to be tapered, i.e the reverse of a horn, and they didn't use the vent for reinforcement, so mattered not whether the vent was open or closed.

However, they were big, and internally complicated so expensive to manufacture.

S

 

[617]

I refer you to the conclusion. Bailey's transmission lines had stuffing at variable densities, lighter at the start and heavier at the end. His designs also provided for the pipe to be tapered, i.e the reverse of a horn, and they didn't use the vent for reinforcement, so mattered not whether the vent was open or closed.

However, they were big, and internally complicated so expensive to manufacture.

S

Serge what should we call speakers with an acoustic line designed to create 1/4 wave augmentation? I agree the term transmission line is not descriptive but that's the term I've seen over the years.

 

[Vladimir Filevski]

Bailey's transmission lines had stuffing at variable densities, lighter at the start and heavier at the end. His designs also provided for the pipe to be tapered, i.e the reverse of a horn, and they didn't use the vent for reinforcement, so mattered not whether the vent was open or closed.

Wrong. If you close vent of such TL, the low frequency output will drop. If it didn't matter, why Baliey left vents open?

 

[sergeauckland]

Serge what should we call speakers with an acoustic line designed to create 1/4 wave augmentation? I agree the term transmission line is not descriptive but that's the term I've seen over the years.

I would call that a 1/4 wave line. I agree that these have been erroneously called Transmission Lines, but that's for marketing reasons, and isn't a correct technical description.

 

[sergeauckland]

Wrong. If you close vent of such TL, the low frequency output will drop. If it didn't matter, why Baliey left vents open?

Why? There's nothing coming out of the vent in a real TL, it's ALL absorbed in the line.

S

 

[Vladimir Filevski]

Could you please state which Transmission Line loudspeaker (brand and model) has no output from the vent? Thanks.

 

[sergeauckland]

@ sergeauckland I'd like your opinion also on this if you could​

Thanks for that, can you say the effect it will have on this measured FR and impedance/phase graph I found on them if I sealed up the TL line.
https://tinyurl.com/24yroz6k
Cheers George

If the line is not long enough, and/or there's not enough absorbancy, then there will be significant output at low frequencies. Blocking the vent then will reduce the LF output. This is so with most so called TLs as commercially, few are big enough to be true TLs. The B&W Nautilus is one exception.

S

 

[sergeauckland]

Could you please state which Transmission Line loudspeaker (brand and model) has no output from the vent? Thanks.

The B&W Nautilus, as it doesn't have a vent, and is a true TL.
S

 

[Vladimir Filevski]

My question contains word "vent", so closed boxes (including B&W Nautilus) are out of question.
I asked which TL loudspeaker with vent has no output from the vent?