IMF Transmission Line Stuffing?

Martin most of your designs call for the use of drivers with a small Vas?
Bob Brine has stated this on his website under driver suitability who uses your design program.

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

I.M.Fried did just the opposite in designing all of his oem drivers for T-lines.
A few years after I.M.Fried started Fried products he discontinued the use of the heavy mass Kef bextrene cones which have a large Vas.
Fried had all of the driver cones used in his T-lines sourced to that of a much lighter cone mass but still had a large Vas.
I have stated this many times about the Vas of his 10" drivers being 170-180 liters.
 
My designs do not call for any particular driver or T/S parameter. You pick your driver and model the TL, iterate the design geometry in MathCad to reach your specific SPL response goal. Large or small Vas does not matter, the math is the same and accounts for the driver properties. Hundreds of TLs have been designed using MathCad in the past 15 years with a wide variety of drivers, I am sure all different values of Vas have been successfully used.
 
Martin another facet of the Fried Products design was raising the driver Qts. a considerable amount. This was done by the use of large value air core inductor in the sub to mid bass driver crossover.
When using 10" or 12" 8 ohm sub drivers a 12mh 14gauge inductor was used that added 1 ohm of Re.
Using low Re. iron core chokes would result in a large resonance in the Fried designs.
 
Adding series resistance will raise the effective Qts of the driver. The down side is the loss of SPL/W/m. The baffle step will also lower the bass SPL/W/m so you really need to watch the final system efficiency. All legitimate trade-offs.

I am sure you are aware that the Fried speaker brand has been revived.

http://www.friedproducts.com/

They design the enclosures using my MathCad models.
 
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Bud Fried

Adding series resistance will raise the effective Qts of the driver. The down side is the loss of SPL/W/m. The baffle step will also lower the bass SPL/W/m so you really need to watch the final system efficiency. All legitimate trade-offs.

I am sure you are aware that the Fried speaker brand has been revived.

http://www.friedproducts.com/

They design the enclosures using my MathCad models.

I hope that they are using the same foam to stuff the speakers. Otherwise, Bud will be turning in his grave.
 
Would you show one example of the response curve and impedance curve of a transmission line you built? If you use Dracon etc., I suspect that you will end up with a bass reflex box. No matter what you call it, a twin peak impedance will show that is the bass reflex design.

OK, I have provided the plots that show the use/impact of Dacron fiber in my TL design. Do you feel that what I have shown is truely a TL or is it still a bass reflex enclosure? If you claim that it cannot be a TL, can you provide similar plotted data (empty and stuffed) that demonstrate TL behavior in one of your designs and explain the differences between our two results?
 
Adding series resistance will raise the effective Qts of the driver. The down side is the loss of SPL/W/m. The baffle step will also lower the bass SPL/W/m so you really need to watch the final system efficiency. All legitimate trade-offs.

I am sure you are aware that the Fried speaker brand has been revived.

http://www.friedproducts.com/

They design the enclosures using my MathCad models.

I stated in my previous post that the driver Qts. was raised using large air core inductors. Air core inductors are more linear across the band with and flatten the driver impedance.

I contacted Dennis who designed the series crossover for Jim Salk once I heard about the new Fried speaker model.
Bud Fried never cared for MTM and or D'Appolito designs when I asked him about them. :)
 
Bud Fried never cared for MTM and or D'Appolito designs when I asked him about them. :)

I used to look at the MTM arrangement with extreme skepticism. My logic was that I could buy a better single mid woofer driver for the cost of the required two mid woofer drives for the MTM. A better mid woofer driver had to up the system performance compared to two cheaper drivers.

The down side of the standard T-M arrangement is the lobing associated with the crossover. In my TL design shown above, I went with a side by side arrangement in a mirrored pair of speakers so that I could adjust the toe in to try and place a null created near the crossover point away from the sweet spot. I have driven myself nuts over the years with the destructive interference patterns I predicted for T-M speakers near the crossover point.

The speaker I built last year was an MTM, my first MTM design. In parallel I designed TMM and MTM configurations and then played with crossover simulations to see what worked best. The MTM had some real advantages, it was real easy to get a smooth vertical and horizontal SPL response free of deep nulls. I could also produce a nice linear phase throught the crossover region and looking at the final SPL response you cannot "see" evidence of the crossover in the on or off axis plots.

After 20 years, I think my position has changed with respect to MTM alignments.
 
Is it or is it not a TL?

OK, I have provided the plots that show the use/impact of Dacron fiber in my TL design. Do you feel that what I have shown is truely a TL or is it still a bass reflex enclosure? If you claim that it cannot be a TL, can you provide similar plotted data (empty and stuffed) that demonstrate TL behavior in one of your designs and explain the differences between our two results?

There are a few unique features that defines a Bailey transmission line.
  1. The stuffing is supposed to make the TL a half wave length tube at the woofer Fs. There should be a single impedance peak at around 27 Hz for the Focal.
  2. The stuffed tube is supposed to make a phase inverter at the Fs. The sound attuation should be decreasing as the frequency goes down.
  3. The sound pressure at the TL opening is supposed to be similar to the front sound and 180 degrees out of phase.
  4. Overall, the TL is designed to have a -3 dB poiont around the Fs.

Did I see those classic TL responses? No. Instead, the responses resemble an infinite baffer, of a moderate size woofer installed in an oversized, heavily stuffed cabinet. The 45 Hz impedance peak and across board attenuation at the TL box outlet seem to confirm that.

The transmission line responses were well documented by Bailey and Bradbury in their original papers. I do not have the equipment to duplicate their effort.
 
My early Studios on at least the final stage use really long fibeer wool and some sort of mat type stuffing.
 

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There are a few unique features that defines a Bailey transmission line.
  1. The stuffing is supposed to make the TL a half wave length tube at the woofer Fs. There should be a single impedance peak at around 27 Hz for the Focal.
  2. The stuffed tube is supposed to make a phase inverter at the Fs. The sound attuation should be decreasing as the frequency goes down.
  3. The sound pressure at the TL opening is supposed to be similar to the front sound and 180 degrees out of phase.
  4. Overall, the TL is designed to have a -3 dB poiont around the Fs.

Did I see those classic TL responses? No. Instead, the responses resemble an infinite baffer, of a moderate size woofer installed in an oversized, heavily stuffed cabinet. The 45 Hz impedance peak and across board attenuation at the TL box outlet seem to confirm that.

The transmission line responses were well documented by Bailey and Bradbury in their original papers. I do not have the equipment to duplicate their effort.

The geometry of a classic TL is a pipe, which may be straight or tapered, with the driver mounted near or at the closed end and the far end open. The one dimensional wave equations requires different boundary conditions at each end. At the driver end the velocity is zero and the pressure is a maximum and at the open end the velocity is a maximum and the pressure is zero. That is basic physics that can be found in almost any acoustics textbook. As a result of these boundary conditions the natural frequencies and standing wave mode shapes can be determined, they are all odd harmonics of quarter wavelengths (1/4, 3/4, 5/4, ....). Any pressure or velocity profile in the pipe can now be expressed as a linear combination of these mode shapes, this has to be true and is called modal analysis by mechanical engineers. There is no way you can have a half wavelength mode shape with or without distributed stuffing or foam lining, it violates the fundamental physics boundary conditions.

So your items 1, 2, and 3 are all physically impossible. This pretty much undermines most of everything else you are saying. Just as an aside, if you look at the geometry of Bailey's TL and the wave equation solution used by Bradbury (which applies the boundary conditions I stated above to solve the equations of motion) you will find that they are not compatible. I will let you figure that out on your own.

Bottom line from my perspective, your understanding of the physics of how a TL works is extremely shallow. You have been sucked in my the rhetoric and mystique that surrounded TL design for decades. There were some very good TLs produced in this time period which were the result of the natural insight of the designer, luck, and trial and error building and not based on any sound engineering design methods or equations.

The "art" of TL design has moved forward significantly to more of a sound engineering approach with several different software packages available for simulating and designing the geometry and the placement of fiber materials. You have your mind so closed that you cannot question your own beliefs or probe to see what makes sense and what is pure technobabble. We really have no common gound to discuss TLs, the forum members can decide who to follow for themselves.
 
Have either of you tried, both approaches side by side? I mean really, dudes.

So back to STUFFING, we have different types of foam, loosely connected fibers, some sort of mat that looks like a role out product. So in terms of stuffing, many different types look to have been used.
 
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Have either of you tried, both approaches side by side? I mean really, dudes.

So back to STUFFING, we have different types of foam, loosely connected fibers, some sort of mat that looks like a role out product. So in terms of stuffing, many different types look to have been used.

I have used both approaches. I started with computer models using Bradbuy's equations. I made a test line and measured the impedance and SPL responses of an empty TL and then stuffed with different densities of Dacron or long fiber wool, the fiber results were almost identical and niether matched predictions based on Bradbury's equations. The hole moving fiber and slowed speed of sound theory of Bailey and Bradbury is completely incorrect, it is a myth. So I removed the moving fiber assumption and redid the fiber damping models. It worked and is documented on my site. George Augspurger did the same type of work in parallel using different math models and our results match, his work is documented in the AES journal.

Everything I have done is on my site under TL Theory.
 
Martin I have never had the opportunity to listen to one your designs.
I know that with the Fried designs some very low bass exits the line terminus of the enclosure.
This is why Fried referred to his designs of being an expanding sound source since the low frequencies expand once exiting line terminus.
Do a lot of the low frequencies exit the line terminus of your designs?
 
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The depth and amount of low frequency that is produced is a function of the line length and the geometry (tapered, straight, or expanding). You can tune the design as low as you like, you can tune well below the driver fs if that is desired. The summed SPL response, driver and terminus, can be flat or slowly rolled off below the driver fs depending on the cabinet design. My approach does not provide a single TL alignment for a given driver, you iterate the geometry in the software to design the entire low end response to meet your needs.
 
There are a few unique features that defines a Bailey transmission line.
  1. The stuffing is supposed to make the TL a half wave length tube at the woofer Fs. There should be a single impedance peak at around 27 Hz for the Focal.
  2. The stuffed tube is supposed to make a phase inverter at the Fs. The sound attuation should be decreasing as the frequency goes down.
  3. The sound pressure at the TL opening is supposed to be similar to the front sound and 180 degrees out of phase.
  4. Overall, the TL is designed to have a -3 dB poiont around the Fs.

So your items 1, 2, and 3 are all physically impossible. This pretty much undermines most of everything else you are saying. Just as an aside, if you look at the geometry of Bailey's TL and the wave equation solution used by Bradbury (which applies the boundary conditions I stated above to solve the equations of motion) you will find that they are not compatible. I will let you figure that out on your own.

Bottom line from my perspective, your understanding of the physics of how a TL works is extremely shallow. You have been sucked in my the rhetoric and mystique that surrounded TL design for decades. There were some very good TLs produced in this time period which were the result of the natural insight of the designer, luck, and trial and error building and not based on any sound engineering design methods or equations.

The "art" of TL design has moved forward significantly to more of a sound engineering approach with several different software packages available for simulating and designing the geometry and the placement of fiber materials. You have your mind so closed that you cannot question your own beliefs or probe to see what makes sense and what is pure technobabble. We really have no common gound to discuss TLs, the forum members can decide who to follow for themselves.

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

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 built the original Bailey design more than 30 years ago following the recommendation by Jastak in the Audio Amateur (1973, 1:3). I used the Philips 10100 10" woofer. The HF section was two Janszen 2-panel electrostatic, crossover at 1K Hz. An execellent system for my small apartment room and very affordable for a graduate student. It replaced the Larger Advent's that I had before them. The cabinet went into storage when the Philips driver deteriorated due to age and I could not find a suitable replacement. (I have recently purchased a pair of Peerless CSX 850146 and may rebuild the TL sometime.)

"The Bailey designs were almost completely stuffed with wool and did not allow a free flow of air to line terminus". And the non-linear effect of flow resistance (frequency dependent) threw a lot of people off balance. The mathematic is only based on linear algebra which most upper class undergraduate students should have taken. (An "extremely shallow" understanding of the mathematics is sufficient, but required.) Prof. Bradbury at University of Surrey (UK) published an elegant paper on this topic and proved the foresight of Dr. Bailey. 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.

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.

Mr. Martin King, you keep bad mouthing the work by Bradbury. What problem did you find with his test methodology? You stated (in another post) 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's 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. Did you ever try to duplicate his experiment with the proper dimensioned long fiber wool? (I suspect you never read the Bradbury paper. BTW. Bradbury showed how fiber glass would respond and why it is not a good TL stuffing material too.)

It is wrong for you to say the genius work by Bailey, Bradbury and Fried as "physically impossible" without showing any proof. The non-linear nature of the low frequency response of the TL design is not "rhetoric and mystique that surrounded TL design". They are based on sound science and engineering work. You can replace the linear algebra equations with your simple linear wave equations, but your equations do not describe how sound wave propagate in the Bailey TL.

Personally, I have done NO original work (experimental or analytical) on transmission line bass loading. But I have lots of respect for the work that the trailbrazer did because they had results that can be heard. I asked you the same questions on an earlier thread on "Transmission Line" and you never answer. I don't expect you to this time either.
 
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Can anyone ID the type of fiber material pad used in the IMF Studios?

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