Transmision Line ?

[SimplySound]

The Bailey designs were almost completely stuffed with wool and did not allow a free flow of air to the line terminus...

The I.M. Fried and R.Wright designs were advertised as using free flow resistive acoustic filters. The use of low density polyurethane open cell foam accomplished this...

I wonder what T-line designs Keilau one of our new forum members has heard?

BTW welcome to AK Keilau.

I have to tip my hat to Keilau... talk about wading into the Karma and taking on two of the sharper minds around here... "Brass Tacks" as they say in "Jolly Ol' England"!

As to your point SM... I do agree the IMF's used open cell foam to better or worse results.

My TDL's though I believe are filled with "Long Fiber Wool"... so this begs the question; Who made the decision to use polyurethane foam in the IMF's, John or Bud? And did John's application of Wool in the TDL's mark a fundamental shift in the way he felt the Bailey Model should be applied or did he have this vision all along? :scratch2:

Now THAT would make for some interesting reading! :yes:

....and whooohooo.... first on Page 5 of this glorious Transmission Line Thread!

 

[c-atle-79bay]

Does anyone have experience with Chapman speakers and his "compression line" version of the transmission line? I spoke with him, was asking if it were the same as a transmission line, and it was a not exactly/its complicated type of response. Beyond that he mentioned he likes rock and that his speakers play rock great. I find that my tlines, early IMF's (The studio) don't do the rock as well as other things.

 

[JimPA]

SimplySound I know that Fried used foam in all of his designs.
All of the Fried Product designs were 1/4W T- lines or aperiodic.

I am not sure who decided the damping material choice used in the IMF designs. Fiberglass is too reactive compared to the foam to use in the Fried designs.
Gary A. Galo also stated this in his Speaker Builder 1-1982 article about 1/4W T-line designs on page 8.
I remember one article where Gary Galo tested many mid bass drivers in T-lines and compared the response curves.

There were several articles over the years in Speaker Builder magazine about the various T-line speakers on the market.
Many authors over the years contributed, Gary A.Galo, Roger Sanders and Robert Spear to name a few about the choice of T-line damping material.

Vance Dickason stated that fiberglass and Dacron will substitute, the results are not as satisfactory. This is from chapter Four about Transmission Line LF Systems of his Loudspeaker Design Cookbook 4th edition. 1994.

Dr. Kevin Blair wrote about the Wright designs using foam in the 2-1994 article on page 58.
Dr. Blair had marketed some of his T-line designs when he established Buggtussel Audio which has since closed.


http://www.stereotimes.com/speak032902.shtml

 

[keilau]

Irving M. "Bud" Fried invented the open cell foam damped TL speakers and believe that he could tailer it better than the Bailey approach. However, he also held his tuning as a trade secret. I met him once when did a product tour to a audio shop in Minnesota. Very personable gentleman.

The beauty of the Bailey design is that everyone can duplicate his result. He did that out of his dissatisfaction with the loosy, boomy bass of vented enclosures. The real, original TL bass may sound thin at first audition. That's why it may not be good for rock music. If you like classical or vocal, TL is for you.

There seems to be still lots of interest for transmission line enclosure. Are there anyone who built the original Bailey design with wool stuffing? Where is your source of the long fiber wool?

I got my long fiber wool from St. Peter Woolen Mill in Minnesota. An one hour drive from the Twin Cities. They knew exactly what I was looking for, but that was 40 years ago. Not sure if they still have the same product. The store is still active.

 

[SimplySound]

If you like classical or vocal, TL is for you.

Don't forget Jazz!!!

Irving M. "Bud" Fried invented the open cell foam damped TL speakers and believe that he could tailer it better than the Bailey approach. However, he also held his tuning as a trade secret...

Keilau... do you know for a fact that Bud drove the Open Cell Foam decision on the IMF's? That is interesting considering that when John Wright took over TDL, it seems he used the "Long Fiber Wool" on the Studio Versions of his TL's!!!

 

[keilau]

I have to tip my hat to Keilau... talk about wading into the Karma and taking on two of the sharper minds around here... "Brass Tacks" as they say in "Jolly Ol' England"!

"Eppur si muove", Galileo Galilei. (1564-1642)

 

[keilau]

Don't forget Jazz!!!
Keilau... do you know for a fact that Bud drove the Open Cell Foam decision on the IMF's? That is interesting considering that when John Wright took over TDL, it seems he used the "Long Fiber Wool" on the Studio Versions of his TL's!!!

No, I do not know that as a fact. Bud Fried (founder of IMF) and John Wright (founder of TDL) formed a joint venture in the early 70's. I still have copies of their product brochures from that era. I saw the foam in the IMF cut-off pictures and assume that it was Bud Fried's idea. I do not remember if the TDL line used foam or not. I suspect that they did not.

I wonder if either one filed a patent disclosure on the use of open cell foam in TL speaker. Someone may want to do a patent search to find out.

 

[SimplySound]

No, I do not know that as a fact. Bud Fried (founder of IMF) and John Wright (founder of TDL) formed a joint venture in the early 70's. I still have copies of their product brochures from that era. I saw the foam in the IMF cut-off pictures and assume that it was Bud Fried's idea. I do not remember if the TDL line used foam or not. I suspect that they did not.

I wonder if either one filed a patent disclosure on the use of open cell foam in TL speaker. Someone may want to do a patent search to find out.

I believe all of the IMF's used foam. Canucker may correct me on that!

The only TDL I have seen is my Studio-4's which as I showed have Long Fiber Wool in the HF area of the Cabinet. I will try to pull my woofer at some point to check it out and verify if it is used there.

What I find intriguing about all of this is the relationship between Bud and John and whether the IMF was really a joint collaboration or whether Bud had more of a hand in it.

The fact that the TDL's more than likely used wool and were maybe truer to the Bailey Design, leads me to believe either John had a change of thought around foam or perhaps always thought wool is what should be used.

 

[SimplySound]

Check out this from PMC...

The main driver is placed at one end of the TL, which is heavily damped with absorbent acoustic material. The most predictable and accurate absorber is a highly specified foam material that took a vast amount of R&D to derive the correct formula of profile, pore size and density of the polymer. The foam, probably the least visually dramatic of the components is tremendously important. It has to absorb all the upper bass frequencies and allow the lower frequencies to exit the vent at the far end of the line in phase with the main driver. It must also be exactly specified to ensure a consistent and balanced backpressure on the driver by interfacing smoothly with the column of air within the line. With too higher damping, the driver cannot move freely enough, and conversely too little damping produces a lack of control and the result is a LF response similar to that of a regular ported design.

When this equilibrium is achieved between length of line and the acoustic absorbency, the air density increases by up to 30% making the 'effective' line length far greater than it's physical length. This backpressure holds the main driver in a vice like grip and the control is effective over a huge frequency range, reducing unwanted cone movement which lowers audible distortion. This lack of harmonic distortion in the LF creates superb midrange clarity as it eradicates the effects of masking. The consistent air loading also facilitates full audible bandwidth at all monitoring levels allowing for extended periods of monitoring without the risk of fatigue.

 

[bare]

I have to tip my hat to Keilau... talk about wading into the Karma and taking on two of the sharper minds around here... "Brass Tacks" as they say in "Jolly Ol' England"!

That's One spin on it.
Those 2 'sharper ' minds are simply that: Sharper.

PS: imo Kef's are substandard speakers, and J. A. was talking thru his hat back as far back as '71.

 

[SimplySound]

That's One spin on it.
Those 2 'sharper ' minds are simply that: Sharper.

So you are saying Kantor and King are smarter than Dr. A.R. Bailey and A.H. Radford? I guess I'm good with that... I mean you having your opinion, whatever it's worth!

 

[SimplySound]

Yanno, what I think get's most of the "Engineers" around here when it comes to TL's, is they can't be modeled very easily.

Yeah, Dave Dlugos lays this out pretty clearly in his site (kudo's to Martin), but I think he even alludes to the fact that there really is some "magic" involved in these designs.

Here's a link to John Risch's "Classic Page" which is pretty direct to how "trial and error" comes into play.... "tuning" we call it!

Anyway, I guess I'll remain a luddite and will continue to hail the glory of "Long Fiber Wool"!

PS... anyone know who runs this site? Seems pretty detailed for a DIY project!

 

[canuckaudiog]

I believe all of the IMF's used foam. Canucker may correct me on that!

The only TDL I have seen is my Studio-4's which as I showed have Long Fiber Wool in the HF area of the Cabinet. I will try to pull my woofer at some point to check it out and verify if it is used there.

What I find intriguing about all of this is the relationship between Bud and John and whether the IMF was really a joint collaboration or whether Bud had more of a hand in it.

The fact that the TDL's more than likely used wool and were maybe truer to the Bailey Design, leads me to believe either John had a change of thought around foam or perhaps always thought wool is what should be used.

The later IMFs used foam, but the early models used a long fiber wool. Not exactly sure what the material is, though, but it ain't foam. Rock wool perhaps?

On the Kef B110 in my IMF RSPM Mk IVs, they use a long fiber wool, but I believe Doug in the rest of the cabinet, like in my IMFs, you will find foam.

 

[keilau]

That's One spin on it.
Those 2 'sharper ' minds are simply that: Sharper.

PS: imo Kef's are substandard speakers, and J. A. was talking thru his hat back as far back as '71.

So you are saying Kantor and King are smarter than Dr. A.R. Bailey and A.H. Radford? I guess I'm good with that... I mean you having your opinion, whatever it's worth!

The Bailey/Radford and Bradbury papers are still my brass tacks. People are entitled to their opinion as long as they can ignore the scientific facts behind it.

I must admit that audio design, particularly speaker enclosure, are not 100% science yet. Ken Kantor's NHT design are one excellent example of making the right compromise to create the best value product. But trying the wrong science on a computer and blasting the correct science is not right.

 

[canuckaudiog]

The Bailey/Radford and Bradbury papers are still my brass tacks. People are entitled to their opinion as long as they can ignore the scientific facts behind it.

. . .

But trying the wrong science on a computer and blasting the correct science is not right.

Kei Lau, I'm assuming by this comment you are specifically referring to Martin's commentary.

He did indeed build enclosures to specification and in fact, measured the results after. He simply found they did not match up with the intended and calculated performance - in other words, he is saying that you can not simply stick a set of parameters into a calculator and come out with a predictable result (using Bailey's and Bradbury's method) when you go to put the saw to wood.

This is why Martin came up with his own method and software of designing a transmission line so that the results were more predictable. He is not saying the Bailey/Bradbury method does not work, but rather that it is slightly faulty because it isn't totally predictable (and it should be, this is physics after all). I believe his argument was partly due to the fact that there is no slowing of the speed of sound as a result of the fibrous material. This would match up with what I have read and understood about transmission lines, in that people who have tried the Bailey/Bradbury T-line have to do a lot of trial and error in order to get a proper, functioning transmission line.

Martin has also stressed that he's tested and built many enclosures and actually measured them, whereas you simply state you trust your ears. In weighing one's opinion over the other, I'd have to say measurements are 'king' (pun definitely intended here )

Martin, correct me if I'm wrong.

Also here is the article he referred you to.

http://www.quarter-wave.com/TLs/Introduction.pdf

You seem to throw around your 'pedigree' as a way of showing that you have a higher understanding of what's being talked about here, but I think you've missed some key details and instead focused on the wording and terminology. You don't need to be an engineer to communicate.

For the record, I am not an engineer. Just a modest hobbyist.

 

[c-atle-79bay]

I believe ONE earlier material was coconut husk, my IMFS appear to have this.

 

[phivates]

In the revitalized closed box arena the word is that fiberglass is still king, and recycled denim is a contender, but polyester doesn't get it done. Here we have again and again the lust for the one and only best oversimplification of reality. Here's mine: a good TL is better than a good BR or a good CB. Why? Because I say so. That my position is not defended with fancy math is of no concern to me cause I'm just a music lover. Like the rest of you I listen to my beliefs just as devotedly as a mathematician does.

 

[trikster]

Not to derail the current conversation but I have a question...

I have heard a few of these style of speakers and have really enjoyed the sound. I am curious if these types of speakers only shine on tube gear? I have a lower wattage Marantz receiver that I am restoring and wonder how a set of these speakers would sound on it (the unit is a model 2015, cir 1974, doing a recap on it for starters). The speakers I liked had a 5 1/4 inch driver by Fostex I believe in a folded horn design. I am thinking of doing a smaller bookshelf size speaker and for the lows, a powered 10" sub. So I need the speakers to play down to about 100 or 80Hz. Is this doable or should I look at a different speaker design.

 

[keilau]

Kei Lau, I'm assuming by this comment you are specifically referring to Martin's commentary.

He is not saying the Bailey/Bradbury method does not work, but rather that it is slightly faulty because it isn't totally predictable (and it should be, this is physics after all). I believe his argument was partly due to the fact that there is no slowing of the speed of sound as a result of the fibrous material.

Please, read Martin King's comment in his earlier post. The reduction of the speed of sound in long fiber wool filled tube was a well established scientific research results as published in many scientific journals. I do not believe Martin King even replicated the test that Bradbury did, nor understand how to do it. (He made the statement that it could be easily done at home with borrowed test software.)

What Bailey and Bradbury missed was the impact the tapered TL had on the tuning frequency. There was no significant reduction in the speed of sound due to the fiber stuffing. I have done the math starting from Bailey and Bradbury models and they do not work, predictions and measurements do not agree. Many others have arrived at the same conclusion.

Bradbury showed excellent comparison between his test results and analytical calculations. I am talking about Figures 5 and 6 on page 166 of Journal of The Audio Engineering Society, Vol 24, #3, April 1976. Yes, the comparison were NOT perfect. The experimental data points did not lay on top of the line. But in engineering, these are execellent comparison in trend and in magnitude.

You keep bad mouthing the work by Bradbury. What problem did you find with his test methodology? You stated that you "rederived all of the equations and replicated the numerical results". Can you point out where the typo is in the Bradbury paper? Did you calculation showed same result as Bradbury once you corrected the typo? You do not need a PC to do this. It can be done on a piece of paper. You do need to have some working knowledge of linear algebra and complex number.

I am still waiting for Martin King's answer on my last question. When he rederives the equations in Bradbury's paper, he will find excellent calculation results in agreement with what Bradbury did, both experimentally and analytically.

 

[JimPA]

Check out this from PMC...

The main driver is placed at one end of the TL, which is heavily damped with absorbent acoustic material. The most predictable and accurate absorber is a highly specified foam material that took a vast amount of R&D to derive the correct formula of profile, pore size and density of the polymer. The foam, probably the least visually dramatic of the components is tremendously important. It has to absorb all the upper bass frequencies and allow the lower frequencies to exit the vent at the far end of the line in phase with the main driver. It must also be exactly specified to ensure a consistent and balanced backpressure on the driver by interfacing smoothly with the column of air within the line. With too higher damping, the driver cannot move freely enough, and conversely too little damping produces a lack of control and the result is a LF response similar to that of a regular ported design.

When this equilibrium is achieved between length of line and the acoustic absorbency, the air density increases by up to 30% making the 'effective' line length far greater than it's physical length. This backpressure holds the main driver in a vice like grip and the control is effective over a huge frequency range, reducing unwanted cone movement which lowers audible distortion. This lack of harmonic distortion in the LF creates superb midrange clarity as it eradicates the effects of masking. The consistent air loading also facilitates full audible bandwidth at all monitoring levels allowing for extended periods of monitoring without the risk of fatigue.

Simply Sound the PMC T-line model in that picture uses a much lower volume of stuffing density compared to the IMF and Fried Products designs.
IPL has used a similar stuffing density layout like PMC in some of their designs.

http://www.iplacoustics.co.uk/S3tl Rib CP.htm

Foam is easier to measure and cut then secure in the T-line and remains in place once it is glued compared to wool.