Transmision Line ?

[SimplySound]

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...

Good stuff SM... those IPL Kits look nice! Have you built one?

And yeah, PMC is taking a little different approach. Rather than stuff the whole tube, they maintain reflections off of one wall and provide absorption off the other. Not sure if this corresponds directly to what Bailey modeled. :scratch2:

 

[ken kantor]

I said that in response to MJKing's question. The key to the Bradbury model is the derivation of the drag parameters of various kinds of fiber materials. Bradbury conducted the proper experiment to validate his model. MJKing may be an engineer, but he demonstrated that he does not understand the fluid dynamics of air moving in a fiber filled tube. He kept saying that the Bradbury model does not work, and sound speed was not reduced in long fiber wool filled tube. But he never showed evidence that he conducted sound speed measurements, nor show proof that Bradbury did not derive the right model to calculate drag parameters.

All these work by Bailey and Bradbury showed that why ONLY the proper dimensioned long fiber wool provides the right kind of acoustic loading. But mathematical knowledge of linear algebra, complex number etc. is not necessary to design good loudspeakers. But trying to make a simple filter model to descirbe the transmission line enclosure like MJKing did just does not work. I suspect that people built loudspeaker enclosures based on MJKing method will never enjoy the deep and tight bass that the Bailey design can provide. But they should get the bass of a vented, large sized enclosure.

BTW, I am currently using a pair of NHT Super One as the front speakers and argumented by a pair of Wharfedale for the low end. Wharfedale called their bi-amp Monitor M-138 model "transmission line" too, but they are not. It was an aperiodic loaded enclosure with twin 7" woofers. The bass does not go as deep, nor as tight as the Bailey TL. But they are better than many commercial subwoofer boxes on the market. I am an audio hobbyist who likes to experiment with DIY equipments, but my engineer nature sometimes gets in the way. (Sorry that I said I was an engineer again.)

Ken, I respect you because of the sound of the Super One that I hear. It is NOT easy to do it right and keep the cost down.

Thanks! Well, if you like the NHT Super One, you must be correct!

Seriously, I just think that professionals should try and discuss things with mutual respect, even when they strongly disagree. There are many well-known and successful loudspeaker designers who I firmly believe misunderstand very basic aspects of the field. But, it would serve nobody well if I claimed to be the only "real" engineer among us, and it wouldn't be true.

I honestly don't know enough about TL's to pick a side here. (Although I see some elements of the classic Empirical vs. Deductive debate.) But, I do know that Martin has devoted a lot of effort and contributed a great deal to the field of TL speakers, and so I believe he deserves a respectful tone, even if you feel certain he is in error in this matter.

At any rate, Welcome! I look forward to your contributions here.

-k

 

[SimplySound]

Hear, hear, Ken... lots of room for respectful discussion!

I'm learning a lot!!! :yes:

And what's really funny is some guy (or gal) named Shiner shows up here a few months back and gets this ball rolling, and we never hear from them again!

Oh well... like I said, we all get to learn some stuff!

 

[SimplySound]

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

LOL.... I guess the Brits determined it was easier to get wool from out on the Moors rather than having to ship "Coconut Husk" in from the Pacific Isles (or harvest it from the Scotish Shores).

....now what impact does THAT have on the Bailey Model!!!

 

[JimPA]

Good stuff SM... those IPL Kits look nice! Have you built one?
:scratch2:

No as I have previously stated I have built various models of the Fried line and DIY designs over the years.

Here are two side views of the Fried satellite and sub woofer 1/4W T-lines that I have built several pairs over the years and a photo.

I have also included the stuffing density plans for the satellites that show the placement of the foam in the T-line.

http://www.audiokarma.org/forums/attachment.php?attachmentid=473917&d=1386198375

http://www.audiokarma.org/forums/attachment.php?attachmentid=466490&d=1383443485

http://www.audiokarma.org/forums/attachment.php?attachmentid=376738&d=1347904758

 

[keilau]

Thanks! Well, if you like the NHT Super One, you must be correct!

Seriously, I just think that professionals should try and discuss things with mutual respect, even when they strongly disagree. There are many well-known and successful loudspeaker designers who I firmly believe misunderstand very basic aspects of the field. But, it would serve nobody well if I claimed to be the only "real" engineer among us, and it wouldn't be true.

-k

Ken, Truth is objective, not because I said so.

When Bailey proposed a new enclosure for bass loading, he proved his design by experiment and listening results. Bradbury quantified the reduction of the speed of sound in fiber filled tube analytically and correlated them with test data. All these are objective truth.

I tried to take this off-line by PM you. But you chose not to receive PM.

I did not know who designed the Super One when I got it. I just like the sound very much at affordable cost. They replaced a pair of Tabot home built from the old Falcon Acoustics design from UK.

Regards.

 

[c-atle-79bay]

LOL.... I guess the Brits determined it was easier to get wool from out on the Moors rather than having to ship "Coconut Husk" in from the Pacific Isles (or harvest it from the Scotish Shores).

....now what impact does THAT have on the Bailey Model!!!

The swallows make this process infinitely easier.

 

[ken kantor]

Ken, Truth is objective, not because I said so.

When Bailey proposed a new enclosure for base loading, he proved his design by experiment and listening results. Bradbury quantified the reduction of the speed of sound in fiber filled tube analytically and correlated them with test data. All these are objective truth.

I tried to take this off-line by PM you. But you chose not to receive PM.

I did not know who designed the Super One when I got it. I just like the sound very much at affordable cost. They replaced a pair of Tabot home built from the old Falcon Acoustics design from UK.

Regards.

Well, I am no longer a Logical Positivist, and so I am not fully convinced truth is completely objective. But, I am not talking about truth or falsehood anyway, only about communication and respect.

Yes, I do not use the PM system here. (It is already hard enough for me to keep track of texts, emails and facebooks!) However, you can always reach me at k.k.a.n.t.o.r ~ g.m.a.i.l.c.o.m.

I am very happy to hear that you enjoy your SuperOnes!

-k

BTW- "Base" does not refer to sound. "Bass" is the correct spelling.

 

[HTWillie]

Can you point out where the typo is in the Bradbury paper?

You mention this typo a lot.

If it's significant, I think describing it here could advance the dialogue on this topic.

 

[keilau]

You mention this typo a lot.

If it's significant, I think describing it here could advance the dialogue on this topic.

It is on page 164, Equation (4), the definition of theta.

You will not be matching Bradbury's calculation until you correct this typo. I have been wondering whoelse noticed it. I tried to replucate Bradbury's calculation on a HP programmable calculator after I read the paper and found that I did not get the same numbers as he did in 1976. I found the typo when I went through the derivation of his equations and reconciled the calculation. I concluded that it was a typo made by the Journal of AES, not a mistake by Bradbury.

Through this process, I saw the beauty of Bradbury's work. The typo was a small, but critical one. I will post the detail when I come home from work tonight. Now, I have pointed out where and what the typo is. Anyone wants to beat me to post the detail?

It is one of the most significant and elegant piece of work on the theory of transmission line enclosure. It showed both qualitatively and quantitatively how the sound wave propagates in a long fiber wool filled line by test and analysis. It provided a sound guidance on what to look for if you want a substitue for the long fiber wool. What is your opinion of this paper? (Question to everyone) I have not seen many comment in other posts, except one person who said that it does not work.

Yes, I understand that the Bailey and Bradbury works are NOT complete. They did not model how to couple the driver to the enclosure, thus, leaving the actual design as mostly empirical. The work by Bailey and Jastak (1973 Audio Amateur) filled an important gap.

Trying to model the TL enclosure as a resonant, vented box so that it can be coupled to a driver model is like cutting the foot to make the shoes fit.

 

[keilau]

The complex number equations have a lot of greek symbols. I did not have time to type them up in the proper format today. I will have to put off the detail post I promised to the weekend. Sorry to disappoint you.

 

[HTWillie]

Thanks for contributing the typo detail.

Just scribble the equations onto a piece of paper, and post a photo of it.

 

[keilau]

Thanks for contributing the typo detail.

Just scribble the equations onto a piece of paper, and post a photo of it.

I most likely will just do that.

 

[SimplySound]

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.

Nice C-atle... never heard of Chapman, and now I have! See we all learn things!!!

I read this review of the T8 and this guy mentions the Bass from his "metal/rock" perspective. The Bass in the T8 only goes down to 28Hz +/-2 so my first response was that maybe they don't go as low in that "Bottom Octave" as a TL, but they sound like they are still pretty dynamic.

This is an interesting subject! In his review he talks about the difference between the "Front Firing" Tetons and the "Side Firing" Chapmans. In my write up of the comparison of my TDL's to my KEF 107's, I noted that the Bass seemed more dynamic from the front firing TDL's, but that the KEF's seems to have more control and presence in the real low stuff. The KEF's, as many may know, are a Coupled-Cavity design, and my sense is they are NOT a "Dynamic Bass"!

Now, my definition of "Dynamic" and "Presence" in this case is that the TDL's seem to come at you with the Bass, whereas the KEF's just seem to "envelope" you with it. You don't quite know where it is coming from and it doesn't strike right at you, but aurally it's all around you and at the right times and notes seems to penetrate you with resonance. That's "the magic" of the big KEF's!

Thanks again for the Chapman reference... and if anyone can shed light on C-atle's question on what constitutes a "Compression Line", please enlighten us all! :thmbsp:

 

[phivates]

This is not an objective comment. I doubt that any comment by a human is completely objective. As for the transmission line: I got the bug in the 70s when I learned that I could get an affordable 8" driver to go as low as an AR2 just by building a box with more than 6 pieces in it. And if I put a 10 inch driver in one I got all the way to a solid 40 hz and could still do a two way so the problem of a successful three way crossover was avoided. The one note echo of a vented box just never worked for me. There's more to this than LF extension, a lot more, so I'll summarize: a good TL is the best compromise. Now if SPL at the expense of accuracy is the goal, well you Reflex Boys can keep your delayed excursions and other non musical artifacts to yourselves. Nowadays we have long excursion subs and silly big power amps to counter you with. Got one of those in my van. It plays all the low notes, not just its favorites.

 

[JimPA]

Mysterious Ways from U2 Achtung Baby is a good song to hear what T-line bass is all about.

https://www.youtube.com/watch?v=TxcDTUMLQJI

 

[keilau]

You mention this typo a lot.

If it's significant, I think describing it here could advance the dialogue on this topic.

Ok. Here they are. In picture 1 is the original text in the AES Journal. In the definition of theta just under equation 4(b), both arctangent terms should be negative. The typo is missing the first "-" sign.

I was puzzled that I could not repeat Bradbury's computation at first and found the typo by duplicating his derivation.

In order to perform numerical calculation, you need to convert the complex number in equation (3) into real and imaginery parts. Picture 2 shows how I duplicated Bradbury's derivation. You convert the complex numbers into polar form to do the division in equation (3). Then convert it back to real and imginery parts of equation 4(a) and 4(b) for the calculation. Very simple operation for students of linear algebra or engineering mathematics class.

 

[HTWillie]

I never would have caught that. (even in a hundred years) Thanks for demonstrating this point though.

Hopefully some of the earlier posters will return and weigh in. I'd like to hear their take on it.

 

[keilau]

I never would have caught that. (even in a hundred years) Thanks for demonstrating this point though.

Hopefully some of the earlier posters will return and weigh in. I'd like to hear their take on it.

Before we hear from others, let us hear from Dr. A. R. Bailey on his objective in designing the Transmission Line Enclosure and why he called it as such.

By far the largest number of current loudspeaker cabinets are based on the" bass reflex" cabinet design'. (This is shown in Fig. 1 as a sectional view) This cabinet appears to have only a relatively short path-length between the back and the front of the cone and would therefore be expected to give relatively poor l.f. response. In fact the response at low frequencies can be quite large, this being due to the cabinet having a Helmholtz air column resonance at about the lowest frequency being reproduced. In the reference given previously, the theory is well explained.

Unfortunately, this resonance in the cabinet causes coloration in the bass output of the system. This “ringing" of bass transients can be very noticeable, particularly on such instruments as string bass.

In addition the cabinet itself is frequently unlagged and consequently the sound is still emerging long after the original signal has stopped. Very heavy lagging is necessary to stop this effect and in so doing the cabinet "Q" is reduced so that the bass reflex action is lost.

Sine wave testing does not necessarily show up the defects of a speaker system. Rapid cut-off at the edges of a flat response can make it sound far worse than a slower rate of fall at the edges of a system with apparently a poorer bandwidth. (This is shown in Fig. 2.)

The effect of the abrupt change in slope of the amplitude/frequency characteristic is to give "ringing" at the frequency where the slope change takes place. This effect is unavoidable and is the necessary price to pay for the extension of bandwidth by the use of resonance effects. It is for this reason that loudspeaker systems can sound very "boomy" in the bass, even though the measured amplitude response shows no resonant peaks.

One method of testing that has not apparently been widely used is that of impulse-testing of loudspeaker cabinets. This method is very powerful and is described later on. For the moment it is sufficient to state that it confirmed that normal loudspeaker enclosures are not very good.

It is now apparent that it is the sound waves produced at the rear of the cone that have to be absorbed if delayed output and resonances are to be avoided.

Acoustic labyrinths" have been used in the past in an attempt to "lose" the sound down multiple paths. (Such an enclosure is shown in Fig. 3), but the size needed is excessive. Unless there is adequate internal lagging, then these cabinets will also possess pronounced energy storage and the consequent lack of sound clarity.

Transmission line approach

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.

I will let the reader to look up of rest of Bailey's 1965 article to get the detail of what he did. He tested fiber glass, short fiber wool and long fiber wool for the design and showed only the last works as required. He did not test polyester fiber (Dracon is one of the trade name) which is popular with speaker stuffing for other designs. Richard Small once questioned the wisdom of using polyester stuffing because his test showed that the stuffing has little or no impact of the tuning of vented enclosure (citation needed).

Bradbury's 1976 paper is interesting because he actually measured the speed of sound and sound absorption in fiber glass and long fiber wool. His test and analysis collaborated with the Bailey design, but Bradbury did not break new ground in the design approach.

From information on the internet (sine wave measurements), a quarter wave length enclosure filled with polyester fiber may sound just like the "Helmholtz air column" that Bailey tried to avoid. But it may just be the type of bass some user prefers and it is very subjective. However, such a design does not have any "transmission line" effect or benefit.

 

[JimPA]

Before we hear from others, let us hear from Dr. A. R. Bailey on his objective in designing the Transmission Line Enclosure and why he called it as such.


I will let the reader to look up of rest of Bailey's 1965 article to get the detail of what he did. He tested fiber glass, short fiber wool and long fiber wool for the design and showed only the last works as required. He did not test polyester fiber (Dracon is one of the trade name) which is popular with speaker stuffing for other designs. Richard Small once questioned the wisdom of using polyester stuffing because his test showed that the stuffing has little or no impact of the tuning of vented enclosure (citation needed).

Bradbury's 1976 paper is interesting because he actually measured the speed of sound and sound absorption in fiber glass and long fiber wool. His test and analysis collaborated with the Bailey design, but Bradbury did not break new ground in the design approach.

From information on the internet (sine wave measurements), a quarter wave length enclosure filled with polyester fiber may sound just like the "Helmholtz air column" that Bailey tried to avoid. But it may just be the type of bass some user prefers and it is very subjective. However, such a design does not have any "transmission line" effect or benefit.

Keilau another good thread on damping material in the link below.

http://www.audiokarma.org/forums/showthread.php?t=189662

I.M. Fried chose drivers in his T-lines that have a large Vas. which contradicts the guidelines of others in the link below of DRIVER SUITABILITY.
The various 10" drivers I.M.Fried used have a Vas of 170-180 liters, a low mass cone, low Qts. and a decent Xmax approximately 8-10mm.

http://brinesacoustics.com/Pages/Quarter_Wave_Resonators.html