Issue Versions of Augspurger Tables

[villastrangiato]

Perhaps this is a rehash, seems pretty obvious to me there's a problem so I'm sure someone else probably noticed it by now - a search on this forum didn't turn up anything though.........in looking over the tables Augspurger published in his AES paper - Loudspeakers on Damped Pipes - I noticed inconsistencies with the table D'Appolito used in the well known Thor (Audio Express) article. Looking at the numbers, the D'Appolito table values appear to be more consistent with values one obtains with King's equations and the more simplistic approach Shultz uses (which were based in part on Augspurger's test data) sooooooo........can anyone tell me if D"Appolito was using a corrected version of Augspurger's table ?- I suspect this is the case because there seem to be numerous addendums and updates that were published by Augspurger after his original paper and symposium.

Anyone out there have a copy of the cd Augspurger sells for about $130? Wonder if that has table values consistent with the D'Appolito published values.....

[JonMarsh]

I think you'd have to contact Joseph to find that out definitively- anything else would be speculation, unless you want to do a lot more background research.

D'Apollito's design for the Thor has been one of the most picked apart and modified endeavors in speaker design I've seen on the web- probably for a number of reasons, including the questionable TL design as well as the crossover filters.

[villastrangiato]

Yeah, I've run across a little "Thor controversy" on here..... :a> ;x( :huh:

The table (table 1 Optimized Alignments) I'm referring to is available to the public online here:

http://diyaudioprojects.com/Technical/Papers/Loudspeakers-on-Damped-Pipes.pdf

The exact version of this is AES vol. 48, no. 5 from May of 2000. But Joe's references include other apparently updated versions. If one just looks at the tables - the numbers just don't seem to make sense - with lower Q, typically more moderately damped and less lossy drivers, Augspurger has the resonant pipe volume going down in relation to the equivalent compliance volume when theoretically, and according to every other TL calculator I've seen, it should be going up. Joe's table's are showing the same apparently upsidedown trend - but not as severe by a factor of 1/3! - :huh:

The formulas themselves that I've seen and used show pipe throat area and pipe volume going down when using higher q drivers - exactly the opposite of what Joe and George's published tables indicate.
Has anyone on here noticed that the numbers appear screwed up in these tables - or at the very least, Joe's tables values aren't consistent with this published version of George's?

As for the Thor, the concerns I have for the methods used in its design relate to the approximations used in combining tapered parameters with offset parameters - while simply adding the driver compliance volumes - seemingly not taking into account how the dynamics of an offset design might be impacted where two drivers are being used. But this thread was not intended to be a b%&tch session on the Thor and I'm sure that ground as you indicate has been tread on mercilessly. I'm just trying to get a handle on whether or not George's publications are really worth the paper (or cd's) they're imprinted upon where their usability for the average TL builder is concerned.

[PhilDSP]

I have Auspurger's CD with modeling software. I never thought the tables had very much value for my own use. I much prefer to first investigate how a prospective driver would sound with a basic configuration in the simulator and then choose 2 or 3 drivers and optimize the results for each.

[villastrangiato]

Looking at his numbers, I can see why. I think it makes sense as a general rule to start with a pipe frequency as Shultz and Augspurger suggest - some where in the vicinity of 1.2 to 1.6 times your driver's resonance - and before you get all hung up on overall pipe volume - plug in a classic 1.5 to 2X Sd value for your throat area to calculate your average cross sectional area in a continuous tapered pipe with the overall specified length. With that, you'll get an approximate pipe volume that you can compare with the "published standards". If you wind up somewhere in the vicinity of their results, I think you have a good starting point. It's interesting how some appear really hung up on throat area (King) while others like Shultz say it's almost irrelevant - Augspurger falling somewhere in the middle talking about his concern for "cross modes". Personally, I tend to put more weight on Shultz' argument that the stuffing material and density will have a lot more impact than slight changes in overall throat area or volume - although I don't think it's safe to reach his conclusion that pipe area is practically irrelevant and that tapering is pretty much unnecessary. To my thinking, tapering should provide an important counterbalance to the reduction in pressure and velocity of the wavefront as it travels through the damping media. In theory anyway, it makes sense to me to have some way of bolstering pressure and velocity as energy dissipates along the pipe - I would think tapering must produce some positive influence in that regard. With the offset design, the amount of tunnel damping necessary to cancel the third and ninth harmonic is significantly reduced - thus the rate of energy absorption and velocity drop-off should be equally reduced. This is one of the reasons I had major issues with the Thor - combining tapering and offset in the same design with very little thought given to the consequences of mixing these very "apples and oranges" approaches. I'm kind of surprised Joe would have done this - even the Augspurger paper he bases his design on cautions against combining different construction methods. :huh:

I think it also bears mentioning that Augspurger and others do not provide an adequate foundation to support the theory of why "quarter wave" resonators work in improving low bass characteristics. I think although it is not quite as detailed, the following paper by Marek Natkaniec, presents a more thorough and reasoned explanation of TL theory - relying more on accurate scientific modelling than trying to make test measurements fit into a damped electrical system model.

http://www.kt.agh.edu.pl/~natkanie/papers/TLS.pdf

The key aspect is the derivation of the pipe frequency. Ideally, you want a resonant structure that resonates at the precise frequency of the exciting element's (driver's) minimum motion point or resonance. So then, why should the pipe frequencies be 1.2 to 1.6 times this frequency. Augspurger, Shultz, and to my knowledge, King fail to address this as Natkaniec does. The simple explanation in his paper is that maximum back wave energy is released at 60 degrees phase (distance) - not 90 degrees as is commonly thought - from the original point of excitation. This can be seen in Natkaniec's rudimentary drawings. According to Natkaniec, this can be derived using vector calculus. So to me anyway, Augspurger's explanation seems misplaced. The pipe length for maximum output should be set at 1/6 the wavelength of the driver's resonance frequency. This corresponds to a ratio of Fp to Fs of about 1.5. I think Augspurger and others should not treat this phenomenon as a magic black box result that has only been discovered through testing. There are mathematical and real world scientific explanations for why it is optimal to set a pipe frequency at roughly 1.5 times the driver's resonance frequency. After all, if you look at the big picture, the entire effort is based on mitigating the negative effects of a driver's resonance whether you use a bass reflex or TL approach. The parameters of an optimal TL design do bear directly on a driver's Fs and there is a direct, scientific approach. No black art here.... :B

[Dennis H]

The key aspect is the derivation of the pipe frequency. Ideally, you want a resonant structure that resonates at the precise frequency of the exciting element's (driver's) minimum motion point or resonance. So then, why should the pipe frequencies be 1.2 to 1.6 times this frequency.

I think it was Jon Risch who said you shouldn't go by the driver's free air resonance but rather make it equal to the resonance in a sealed box the same size as your TL box. That's a simple explanation for the higher number. With a bit of back and forth, you can close in on an optimum volume and length.

[villastrangiato]

I think it was Jon Risch who said you shouldn't go by the driver's free air resonance but rather make it equal to the resonance in a sealed box the same size as your TL box. That's a simple explanation for the higher number. With a bit of back and forth, you can close in on an optimum volume and length.

Though I think you get directly to the optimal design much quicker without "adjustment" by avoiding (in terms of modelling) an acoustic suspension (sealed) alignment altogether. One of the reasons the TL is viewed as superior is because it is the closest of the three main loading configurations to an infinite baffle in terms of the effect introduced by reflected energy. As a result, there is probably less error in modelling with a TL layout from the get go than with trying to morph a Bass Reflex or Sealed design into a TL. The loading enclosure doesn't generate any energy - it can absorb it and internally reflect it (sealed), absorb and release a narrow band of energy (ported) or absorb and release a broad band of energies (TL). To optimize the level of backwave output of energies (both "unwanted" and "wanted") the length of the transmission line must simply be set at 1/6 the wavelength of the driver's resonant frequency - it's really that simple. Changing the pipe length to anything other than that amount is only going to reduce overall output. The level of attenuation of unwanted frequencies can be altered somewhat with various structural configurations but essentially - that is largely controlled by the density and absorbing qualities of the applied damping material. The two issues really are separate and if you're going to build an optimal design, they should remain that way - in this engineer's ever so humble but strongly held opinion...... :B .....ITEESHBSHO..........

[PhilDSP]

You might want to consider the value of targeting very nearly a one quarter wavelength length of the canal equaling the driver's resonance frequency. That has generally been the classic British approach from the original inventors and innovators such as A R Bailey. With some sacrifice of overall efficiency a much flatter and extended response can be had.

A quarter wave TL design works because it uses the physics of a single open end pipe - the characteristics of that are well known and the differential equation describing its response is simple. Though to properly model the system as a differential equation you'd have to use some additional terms to model the driver.

[villastrangiato]

You might want to consider the value of targeting very nearly a one quarter wavelength length of the canal equaling the driver's resonance frequency. That has generally been the classic British approach from the original inventors and innovators such as A R Bailey. With some sacrifice of overall efficiency a much flatter and extended response can be had.

A quarter wave TL design works because it uses the physics of a single open end pipe - the characteristics of that are well known and the differential equation describing its response is simple. Though to properly model the system as a differential equation you'd have to use some additional terms to model the driver.

The reason I mentioned Natkaniec's paper is that it is the only one I've seen that suggests an undamped pipe/resonant driver system does not resonate with maximum output at the driver's resonant frequency - but at a frequency corresponding to a pipe length of 1/6th the wavelength of the driver's Fs or at a frequency of approximately 1.5 times the driver's Fs. Without offering a mathematical derivation or proof - Natkaniec cites vector calculus as the means for establishing the point. Perhaps someone can provide this derivation. The important principle though that he's trying to establish is that an "ideal" pipe length exists that maximizes pipe energy radiated output . While it may not coincide exactly with the driver's resonance frequency and is not 1/4 of the Fs wavelength, it is in fact related to it's wavelength and is fixed. Modifying the structure from a simple undamped pipe of this length should do nothing other than possibly attenuate certain frequencies while accentuating others. Still - maximum rear wave energy transmission, in theory should never exceed that which is produced by the simple undamped pipe whose length is 1/6 the wavelength of the driver Fs. I've researched every other source I could find online and in texts over the past five years - Natkaniec's paper is the only one I've seen that seeks to establish this point. Everyone else is bogged down with applying electric circuit models to the describe the observed resonant behavior from coupling a driver to an undamped pipe - and thus I think they confuse the issue with too much attention to details involving pipe diameter, taper, offsets, damping material, and the reduction of wavefront velocity. I'd rather see someone start with the idealized basics - produce a strong set of foundation principles - then apply the details - at least that's how I'm used to operating. The primary foundation principle should be to firmly establish the pipe length of an undamped simple straight pipe that maximizes rear wave radiation - thus not necessarily the driver's resonance but the driver/pipe system peak resonance. Natkaniec is the only person I've found thus far examining the situation from this perspective - not to say that others don't exist - I just haven't discovered them or their work yet. Even he seems to confuse the issue half way in his article when mentioning quarter wave parameters and "anti-resonance". If someone can prove that different pipe lengths can produce more total rear radiated energy (actual effective resonance of the pipe/driver system) than that for a simple straight pipe of length that is 1/6 Fs wavelength, then they should produce it and explain the results.

It's seems a little counterintuitive to look for a design that maximizes rear wave energy output - but that is effectively the optimization goal - minimize the effects of the driver's Fs and energy storage behavior. In the process, you should achieve critical damping and maximum rear wave output. Damping of unwanted higher frequencies should be step two or three - and should not be involved in establishing step one. To my way of thinking, it only confuses the issues. An example of this is the wrongheaded (IMHO) approach in the offset design. There you're starting from the beginning by selecting a design that sacrifices rear wave output because you're interested in reducing unwanted upper harmonics - output that in theory could be tamed more precisely without reducing maximum theoretical output of all frequencies.

[Dennis H]

The reason I mentioned Natkaniec's paper is that it is the only one I've seen that suggests an undamped pipe/resonant driver system does not resonate with maximum output at the driver's resonant frequency - but at a frequency corresponding to a pipe length of 1/6th the wavelength of the driver's Fs or at a frequency of approximately 1.5 times the driver's Fs.

That's a good first step to establish the length. Then the total box volume should (in a perfect world) be set to .8*Vas to raise Fb to 1.5*Fs and make the pipe resonate at 1/4 WL at Fb.

Then put it in one of Martin's worksheets and start fiddling with things to see what you'll really get. If only things were so simple that all we had to worry about was Fs. I've been fiddling with tapped horns in Hornresp and I've been amazed at how much the various T/S numbers can change the response when you're looking at a resonant system like a horn or TL.

[Dennis H]

I have to admit I've never fiddled with TLs that much -- not really interested and I just see them as a subset of ported boxes. But if conventional ported boxes are any indication, going for max port output isn't really the best goal if you're going to use it in a room. Room gain makes tuning the port to a lower frequency sound much better. The anechoic response droops down low but room gain gives it back and you end up with flat response extending much lower. I reckon all the same anechoic vs. in-room rules apply with TLs.

[villastrangiato]

If it hasn't already been done, it would be interesting to see how two different designs using the same drivers and crossovers - one a classic bass reflex tuning and the other a "quarter wave" tuning - would compare in actual test results side by side. This would go a long way to settling any significant controversy as to the supposed gains in maximum undistorted output, linearity/damping, and low frequency extension that is attributed to the more elaborate enclosure. I'm building a TL for the Usher 8137a that's coupled to a 51 hz pipe. When it's done I might whip together a cheap ported box of comparable displacement to compare the two. Given that the TL configuration I'm using is set up with the driver on the end of the tunnel - not transverse like most - it should be interesting to see if there's any improvement in mid bass quality as there should be less energy bounced back through the cone. Speaking of which, if you haven't looked at one up close - after holding an 8137a up to a light, it has the appearance of tiny holes in the weave of the cone fibers. Since the clear coating is very thin - it wouldn't surprise me if there actually were "holes" in the cone's surface! :jawdrop:

[MJKing]

I would suggest that you delete Natkaniec's paper from your hard drive, it is totally incorrect in describing how a TL works and how one should be designed. It was written before modern TL theory and simulation software were available. You can easily design a TL that will work as predicted with the tools available today. There are two key facts to remember :

1. Fiber does not significantly slow the speed of sound.
2. A TL closed at one end and open at the other end is a 1/4 wavelength resonant device. The frequency of the resonance is a function of length and taper or expansion of the line's cross-sectional area.

TLs are completely understood and like everything else in audio represent one set of trade-offs, there is no magic involved.

[villastrangiato]

I would suggest that you delete Natkaniec's paper from your hard drive, it is totally incorrect in describing how a TL works and how one should be designed. It was written before modern TL theory and simulation software were available. You can easily design a TL that will work as predicted with the tools available today. There are two key facts to remember :

1. Fiber does not significantly slow the speed of sound.
2. A TL closed at one end and open at the other end is a 1/4 wavelength resonant device. The frequency of the resonance is a function of length and taper or expansion of the line's cross-sectional area.

TLs are completely understood and like everything else in audio represent one set of trade-offs, there is no magic involved.

Martin, - "throw away Natkaniec's paper"? Don't you think that's a little harsh? No one is implying that Natkaniec's view is the "end all, be all" of TL theory. Perhaps it would be a bit wiser to stick to technical observations rather than heated :rant: oriented generalizations like:

"A TL closed at one end and open at the other end is a 1/4 wavelength resonant device. The frequency of the resonance is a function of length and taper...."

If you have hard evidence in the form of response measurements that prove maximum acoustic energy of any driver/pipe system always occurs at a frequency whose wavelength is 4 times the length of the pipe - then produce it. Don't just sling generalizations that have not been backed up with empirical data. Natkaniec suggests in his paper that the coupling of a driver to an undamped pipe results in a shift upwards of the driver/pipe system's resonance frequency from the driver's frequency alone. All the data I've seen - including your own :B appears to back up that observation ( look at the resonance shift on your own graphs posted on your own website.

Look Martin, I didn't start this thread intending to pick on anybody's achievements. You have a right to be proud of your accomplishments and dedication in the field of TL and quarter wave speaker design. Perhaps a little more humility though is in order. You might disagree with Natkaniec's view. I certainly welcome and respect your input. But dismissing Natkaniec's contribution without hard data to back it up is truly beneath you.

[Carl V]

Perhaps if you ask either Jim Salk or Dennis Murphy for their input
thier data & observations might be of some use to you. Their
HT1 has been done as a sealed, simple ported, TL & MLQW.

Best of luck to you in your quest.

[villastrangiato]

Perhaps if you ask either Jim Salk or Dennis Murphy for their input
thier data & observations might be of some use to you. Their
HT1 has been done as a sealed, simple ported, TL & MLQW.

Best of luck to you in your quest.

Cool. Thanks for the info - I'll def hit them up! :T

[MJKing]

Martin, - "throw away Natkaniec's paper"? Don't you think that's a little harsh? No one is implying that Natkaniec's view is the "end all, be all" of TL theory. Perhaps it would be a bit wiser to stick to technical observations rather than heated :rant: oriented generalizations like:

"A TL closed at one end and open at the other end is a 1/4 wavelength resonant device. The frequency of the resonance is a function of length and taper...."

If you have hard evidence in the form of response measurements that prove maximum acoustic energy of any driver/pipe system always occurs at a frequency whose wavelength is 4 times the length of the pipe - then produce it. Don't just sling generalizations that have not been backed up with empirical data. Natkaniec suggests in his paper that the coupling of a driver to an undamped pipe results in a shift upwards of the driver/pipe system's resonance frequency from the driver's frequency alone. All the data I've seen - including your own :B appears to back up that observation ( look at the resonance shift on your own graphs posted on your own website.

Look Martin, I didn't start this thread intending to pick on anybody's achievements. You have a right to be proud of your accomplishments and dedication in the field of TL and quarter wave speaker design. Perhaps a little more humility though is in order. You might disagree with Natkaniec's view. I certainly welcome and respect your input. But dismissing Natkaniec's contribution without hard data to back it up is truly beneath you.

Not harsh at all, the paper is pure speculation without any real basis in math or physics. I am not trying to be harsh, I am just providing honest feedback on the paper you referenced. I also recommend deleting the papers by Bradbury and Bailey. There is more bad information out there on TL theory then good accurate information.

I have documented my findings on TL design to the best of my ability, it is backed up by both simulations and correlating measurements. My MathCad simulations match George Augspurger's results when the same case is run through his software. Considering that his modeling methods and mine are totally different, I find this to be a solid confirmation that we are both on the correct physics based path. You have to decide for yourself what to believe and what to discard. Based on the tone of your response, I have no interest in continuing to discuss TLs with you.

Good luck,

[MJKing]

"A TL closed at one end and open at the other end is a 1/4 wavelength resonant device. The frequency of the resonance is a function of length and taper...."

If you have hard evidence in the form of response measurements that prove maximum acoustic energy of any driver/pipe system always occurs at a frequency whose wavelength is 4 times the length of the pipe - then produce it.

Please look in any undergraduate text in acoustics or physics. The equations are solved closed form. Measurements of such systems are provided on many sites on the Internet (my own included). This is one of the fundamental concepts of air vibrating in a column with one end open and the other end closed (like a TL). The geometry cannot produce a 1/8 wavelength, 1/6 wavelength, 1/2 wavelength, or full wavelength resonance. If you cannot buy into the quarter wave nature of a TL then any design sizing you do will have no relationship to the results you get after building the system.

[villastrangiato]

Please look in any undergraduate text in acoustics or physics. The equations are solved closed form. Measurements of such systems are provided on many sites on the Internet (my own included). This is one of the fundamental concepts of air vibrating in a column with one end open and the other end closed (like a TL). The geometry cannot produce a 1/8 wavelength, 1/6 wavelength, 1/2 wavelength, or full wavelength resonance. If you cannot buy into the quarter wave nature of a TL then any design sizing you do will have no relationship to the results you get after building the system.

Martin, I think you're having a forest for the trees moment. The issue is not simply how air vibrates in an undamped pipe, it is how air vibrates in an undamped pipe that is excited by a moving coil transducer with a particular Thiel Small parameter known as Fs (resonance frequency)

The goal in properly loading a low frequency transducer is to offset its energy storing characteristic ( resonance) with a structure that is tuned to said resonant frequency Fs. In order to extract the maximum amount of energy from said transducer, it is necessary to examine very carefully the wavefront within the resonant structure coupled to said transducer. Natkaneic has done this and alleges that maximal back wave energy occurs at a point 60 degrees in phase relative to the point of excitation at the frequency of interest (in this case Fs) If that is in fact the case, than maximal energy output should shift up in frequency from what is output at 90 degrees phase from the point of excitation. In fact, all empirical data (including your own) suggests this to be the case. The point of reference that dictates optimal performance is not the resonant structure coupled to the exciting element - but the minimum motion point (Fs) of the exciting element itself. In order to maximize output overall of the exciting element (thereby minimizing stored energy in the vicinity of resonance Fs) it is necessary to couple said transducer with a pipe that corresponds to the length where maximal energy will appear at the pipe's exit - 1/6 the wavelength of transducer's Fs. Perhaps this is why many who are knowledgeable in the fields of electrical engineering and acoustics place the term "quarter wave" in quotes. :B

[MJKing]

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

[villastrangiato]

For anyone interested in pursuing a proof of Natkaniec's assertion that maximal backwave energy in an undamped pipe excited by a transducer occurs at a distance of 1/6th the wavelength of the frequency of interest (in this case the driver's Fs) - the correct formula to utilize is given at the end of this article:

constans.pbworks.com/f/8.+The+Acoustic+Wave+Equation.docx



The equation of interest is: f_n = (2n-1)c/4L


Although this is used to model a closed end pipe - the net result is essentially the same for pipes open on one end save for time/space shift - THERE ARE AN INFINITE NUMBER OF RESONANCES PRODUCED IN A PIPE EXCITED BY A TRANSDUCER - THE FUNDAMENTAL RESONANCE ONLY BEING ONE!!!!!


This is the simplistic view most people have of resonating structures - they look at the fundamental and forget there are many, many other higher order resonating modes occurring in the system under analysis. If you were to evaluate an infinite series of the above equation, it is highly likely you will prove Natkaniec's assertion that the summed peak of energy produced by these resonating modes is centered about a point that is 1/6 th the wavelength of the applied fundamental away from the point of excitation. While there are other equations that accurately depict the propagation of gas density shifts in space over time - the one cited above is widely accepted as being accurate for defining sound propagation in rigid pipes. On that basis alone, I suspect Mr. Natkaniec, his paper, and his conclusions, should be given the benefit of the doubt before we dismiss them without hard data to support such a position. That kind of respect and good will, after all, is the foundation of progress in modern science. :W

[Deward Hastings]

Why are these things called "transmission lines" at all? The discussion seems to be entirely about resonant enclosures . . .

[MJKing]

Why are these things called "transmission lines" at all? The discussion seems to be entirely about resonant enclosures . . .

Audio slang? It is a naming convention, that may or may not be appropriate, that when used people can picture in their minds a style of cabinet construction. I have seen many heated arguements take place on forums over what constitutes a TL and what doesn't, I stopped worrying about the nit picking of definitions a long time ago. People commonly use TL to cover a wide variety of cabinet designs.

[villastrangiato]

Why are these things called "transmission lines" at all? The discussion seems to be entirely about resonant enclosures . . .

Here's another perspective for you. The original term "transmission line" originated as a description for an electrical power distribution method which used impedance matching to reduce losses associated with transporting electromotive force over large distances.

The analogy to transmission line speakers is the inherent design goal of creating the theoretical equivalent of an infinite baffle that transports acoustical backwave energy away from the source of excitation - minimizing the negative effects of reverberant energy. This lead to a kind of "acoustical impedance matching" whereby the ensuing enclosure design possessed a resonance in association with the fundamental resonance of the exciting element (speaker driver). The unique characteristic of acoustic transmission lines is that they convey through this special enclosure design a broad spectrum of reverberant energy along the line itself - some of it intentionally damped - some of it re radiated as useful low frequency output out of phase with the forward radiated acoustic energy.

But that's just my perspective, your mileage may vary. :W

[Deward Hastings]

The analogy to transmission line speakers is the inherent design goal of creating the theoretical equivalent of an infinite baffle that transports acoustical backwave energy away from the source of excitation - minimizing the negative effects of reverberant energy.

That is essentially my understanding of the “TL” enclosure, as formed perhaps 40 years ago. It derives from an understanding of transmission lines as typically long relative to wavelength, having a “characteristic impedance” (when properly driven and loaded), and occasionally “tuned” by resonant structures like stubs and baluns to preserve that characteristic impedance over their length. The “TL” enclosure was itself both a “line” and a “stub”, tuned to cancel the resonance of the acoustic driver, and resistively loaded (“damped”) to dissipate higher frequencies. Correct “tuning” was indicated by a reduced impedance hump at driver resonance (often evidence by smaller humps either side of the original indicating the differing Q of the driver and enclosure), and “can’t hear nothing” of any higher frequencies at the terminus of the “line”. The “design goal” was “infinite baffle” or well damped sealed box *without the characteristic driver resonance of either*.

At some point, though, the idea appeared of tuning the stub away from the driver resonance and using the second resonance (and terminus radiation) to augment bass output . . . making the “new” TL just another “reflex” or resonant enclosure. The original (anti-resonant) intent seems to have been lost somewhere along the way (but not the name).

[villastrangiato]

That is essentially my understanding of the “TL” enclosure, as formed perhaps 40 years ago. It derives from an understanding of transmission lines as typically long relative to wavelength, having a “characteristic impedance” (when properly driven and loaded), and occasionally “tuned” by resonant structures like stubs and baluns to preserve that characteristic impedance over their length. The “TL” enclosure was itself both a “line” and a “stub”, tuned to cancel the resonance of the acoustic driver, and resistively loaded (“damped”) to dissipate higher frequencies. Correct “tuning” was indicated by a reduced impedance hump at driver resonance (often evidence by smaller humps either side of the original indicating the differing Q of the driver and enclosure), and “can’t hear nothing” of any higher frequencies at the terminus of the “line”. The “design goal” was “infinite baffle” or well damped sealed box *without the characteristic driver resonance of either*.

At some point, though, the idea appeared of tuning the stub away from the driver resonance and using the second resonance (and terminus radiation) to augment bass output . . . making the “new” TL just another “reflex” or resonant enclosure. The original (anti-resonant) intent seems to have been lost somewhere along the way (but not the name).

You DEVIL - quite the sandbagger you are!!! 8) Thanks for the very insightful analysis - I always appreciate hearing the "old timers" on the subject of TL's - some pretty brilliant people lent their wisdom in the development of transmission lines more than a half century ago and much of the results of their studies remain true today.

[villastrangiato]

Btw Deward,

Based on your observation, I would agree that it's hard to take someone very seriously who designs a "transmission line" or "quarter wave" speaker with a taper of 16 - 20:1!!! Maybe at some point, someone should fill them in on the secret that they actually have a high q bass reflex speaker. But hey, if they want to call it a "transmission line" or "quarter wave" speaker - who are we to argue, right?

:rofl:

[Deward Hastings]

call it a "transmission line" or "quarter wave" speaker -

Well . . . I just call them different things, probably because I'm attached to my original understanding of what a "TL" is. In fact I'm entirely comfortable with the "quarter wave" name for resonant enclosures using pipe resonance (of which a TL as I understand it is a subset) rather than Helmholtz resonance . . . and find it interesting and useful that the theory that describes tuned pipes can be generalized to a broad range of wavelength-dependent tapered "enclosures" (including "H", "U", and even flat baffles of limited dimension). I take discussion of such structures quite seriously, since the analysis points out resonances to be avoided, or to be tuned to cancel other resonances, for more accurate sound reproduction.

[villastrangiato]

I think this argument/analysis calls for a bit of "nit picking" level of detail - don't you?

Here - let's review some of our comrade's findings. Look at page 429 of Augspurger's "exhaustive" analysis - you know, the paper that talks about his experiments where he places a microphone outside the pipe being examined . On that page, George talks about a pipe with a "quarter wave" frequency or resonance of 109 hz resonating at the frequency of the driver (100hz) - and showing resonant peaks at odd multiples of the driver's Fs - imagine that Mr. King - the resonant peaks aren't occuring at multiples of the resonant pipe frequency - but the driver's resonant frequency. But Mr. King declares:

"This is one of the fundamental concepts of air vibrating in a column with one end open and the other end closed (like a TL). The geometry cannot produce a 1/8 wavelength, 1/6 wavelength, 1/2 wavelength, or full wavelength resonance."

-OOOPS!!!

As I noted earlier, the point of reference for determining resonant behavior is not the resonant structure coupled to the exciting element - but the resonant behavior of the element itself. Augspurger's findings, Shultz' findings, and even Mr. King's findings (if he should choose to look at them) bear this out.

Now, let's take this a little step further in Mr. Natkaniec's direction - as clearly our JBL friend did not seem to think it was worthwhile examining sound pressure levels and spectral content at various points within the resonating structure itself.

If you do the math - the first 9 multiples of the resonant frequency for a driver with Fs of 20 are:

1) 20 hz - distance to quarter wave peak 169 inches
2) 40 hz - 84.75 inches to first quarter wave peak
3) 60 hz - 56.5 inches.....
4) 80 hz - 42 inches
5) 100 hz - 33.75 inches
6) 120 hz - 28 inches
7) 140 hz - 24 inches
8) 160 hz - 21 inches
9) 180 hz - 18.75 inches

What's important to keep in mind is - when you get further past the fifth or sixth multiple - numerous full wave cycles will be permitted for each successive multiple to appear in the latter half of the 169 inch long pipe. So the "peaking" contribution will be more evenly distributed across the pipe and less localized peaking will be observed in a specific area (more even distribution as frequency increases) Thus we are left with analyzing the point along the pipe where the primary multiples from first to around the 7th superimpose and produce the greatest amount of energy (amplitude) This condition wouldn't exist if the complete conjecture Mr. King engages in were true - that the pipe length (hence pipe resonant frequency) dictates the frequencies by which the driver/pipe coupled system resonates.

If you take a simple average of the distances to the first amplitude peaks of the first seven multiple's - you get 62 inches. Now if you take into account the width of the pulses - I'm sure you can see where Mr. Natkaniec's assertions would be pretty darn accurate - that the sum total of peak amplitudes are centered in the vicinity of 60 degrees phase of the fundamental - not as the ridiculously oversimplified view of 1/4 wave or 90 degrees phase would suggest. This is precisely the point where scientific measurements meet estimated modelling - sometimes our estimates aren't accurate and the fudging we apply to the math breaks down when we're asked to explain all the "nit picking" details associated with a given phenomenon.
ops:

[Deward Hastings]

I think this argument/analysis calls for a bit of "nit picking" level of detail - don't you?

Yes . . . and no. There is always room for analysis, but the insulting tone you have chosen to take adds nothing to that. I will be interested in continuing this discussion with you only if you stop it.

There are several "nits" that you might consider in your analysis. Coupled resonant systems are never simple, and never (by definition) independent. The driver will typically "pull" the passive (it's where the energy comes from, after all), and the "tuning" of a pipe is not determined by length alone.

More important in regard your analysis, however, is the assumption that the harmonic standing waves on which it is based are present at all, and thus contribute to the pressure distribution in the pipe. This is not necessarily the case in a simple pipe, and is certainly not the case in a properly damped transmission line. As might have been hinted in my previous post my interest in the TL type enclosure is limited to its use to buck, or null, the driver resonance (given that backwave absorbtion can be accomplished in almost any enclosure), and I'm failing to see how your harmonic structure analysis bears on that. Also interesting would be a discussion of the effect of different placements of the driver along the line, a matter which may complicate any discussion of internal pressure waves.

[ThomasW]

If the provocative language and personal insults don't stop this thread is going to be locked.

[villastrangiato]

Yes . . . and no. There is always room for analysis, but the insulting tone you have chosen to take adds nothing to that. I will be interested in continuing this discussion with you only if you stop it.

There are several "nits" that you might consider in your analysis. Coupled resonant systems are never simple, and never (by definition) independent. The driver will typically "pull" the passive (it's where the energy comes from, after all), and the "tuning" of a pipe is not determined by length alone.

More important in regard your analysis, however, is the assumption that the harmonic standing waves on which it is based are present at all, and thus contribute to the pressure distribution in the pipe. This is not necessarily the case in a simple pipe, and is certainly not the case in a properly damped transmission line.

I see no conditions to support "standing waves" - if the opposite pipe end were closed - that would be a different matter. All testing results (including George's casual measurements noted above) establish that resonant modes (particularly at odd multiples of the fundamental) are very much present at the output. Within the more narrow band of driver resonance - there is a continuum of spectral output - as exists throughout nature. The resonance characteristics of the driver (even with drivers of very high q) do not exhibit a discrete set of frequencies but rather a distribution - hence the need to address the resonating cavities effect on a spectrum rather than just one particular frequency - that being the fundamental.

Btw, I respect your feelings about the snarky references - they were reintroduced into this discussion to drive home a point that I fear many have not adequately absorbed. The devil is indeed in the details - and as Robert Fripp once pointed out many years ago - the details can be very humbling. I enjoy and respect your input as you clearly approach the subject with more sensitivity and respect than the average person. However, I think the point has been made - and there clearly will be no more need for "snarky" comments - if there ever was a need for them in the first place. Point well taken.

Side Note: It should be pointed out that this analysis is not mine - proper credit should go to Mr. Natkaniec and his fellow university staff/students. I'm merely expressing my agreement with the theories and observations he has put forth - defending his point of view if you will.

[ch83575]

I see no conditions to support "standing waves" - if the opposite pipe end were closed - that would be a different matter.

I am hesitant to contribute to this thread because I do not like the general tone, but I just finished physics 1 (so I am far from an expert on the subject) and one of the questions on the final was to calculate the first and second frequencies that produce standing waves in a pipe with one closed end and one open. The standing wave occurs due to the reflection back into the pipe from the impedance missmatch at the open mouth. The first (fundamental) frequency is 4 times the length of the pipe (1/4 wavelength) and the second is 4/3 the length of the pipe (3/4 wavelength) and so on.

Just thought this was a good place for a little PHY 117 review.

[MJKing]

I am hesitant to contribute to this thread because I do not like the general tone, but I just finished physics 1 (so I am far from an expert on the subject) and one of the questions on the final was to calculate the first and second frequencies that produce standing waves in a pipe with one closed end and one open. The standing wave occurs due to the reflection back into the pipe from the impedance missmatch at the open mouth. The first (fundamental) frequency is 4 times the length of the pipe (1/4 wavelength) and the second is 4/3 the length of the pipe (3/4 wavelength) and so on.

Just thought this was a good place for a little PHY 117 review.

Nicely done, I would give you an A in physics. The impedance mismatch is exactly correct and leads to a reflection of the sound wave at the open end.

[villastrangiato]

I am hesitant to contribute to this thread because I do not like the general tone, but I just finished physics 1 (so I am far from an expert on the subject) and one of the questions on the final was to calculate the first and second frequencies that produce standing waves in a pipe with one closed end and one open. The standing wave occurs due to the reflection back into the pipe from the impedance missmatch at the open mouth. The first (fundamental) frequency is 4 times the length of the pipe (1/4 wavelength) and the second is 4/3 the length of the pipe (3/4 wavelength) and so on.

Just thought this was a good place for a little PHY 117 review.

It's not an impedance mismatch - it is a slight pressure expansion along with an associated slight deformation at the edge of the density profile of the wavefront itself - both of which are absolutely miniscule. The amount of "reflection" is so utterly small as to be inconsequential - certainly not detectable as a high level signal. The outputs that have been documented over and over again show very clearly a rapid decay of upper resonant mode multiples - generally occurring at around the 7th multiple. Take any low frequency driver - like any driver PE sells with CLIO data documenting the impedance profile. You will see very clearly a curve that peaks around the Fs and asymptotically degenerates in the region around the fifth to seventh resonant mode multiple. And to a significant degree, the energy storage/energy dissipation profile is not always clearly represented or evident in impedance profiles. Most people with reasonable experience in speaker building have seen at one time or another a remarkable shift in frequency response from very slight ripples in the impedance curve. If you would like, I can provide dozens of examples of this phenomenon. My father worked at MIT more than 40 years ago - and he's suggested to me on several occasions that resonant modes in speaker drivers were very well understood back then - these concepts are nothing new. If you have a specific case study from a major lab or university that shows high signal level resonant modes resulting from "pipe exit reflections" (within a few db's of center frequency reference level) - I'd love to see them.

[Deward Hastings]

It's not an impedance mismatch

It most certainly *is* an impedance mismatch, and the resulting reflection is exactly what one would expect from an unterminated transmission line, be it a pipe or length of coax.

It is also why an open organ pipe makes a tone rather than just wind noise from the fipple . . .

[villastrangiato]

It most certainly *is* an impedance mismatch, and the resulting reflection is exactly what one would expect from an unterminated transmission line, be it a pipe or length of coax.

It is also why an open organ pipe makes a tone rather than just wind noise from the fipple . . .

Oh, I didn't know there was a "fipple" on the other end of the pipe George was testing. Maybe it's just a hunch but my guess is organ pipes aren't straight pipes with big holes at the end. Transmission lines aren't Hemoltz pipes. They aren't organ pipes either. It would be wise to consider these details before engaging in wild extrapolation. The point of excitation, the exit configuration, and most importantly, the nature of excitation itself make all the difference in the world. Does a transmission line "sing" like an organ pipe or Hemoltz pipe? Please, let's get real and stop grasping at straws here. Let's stick with one geometry first - and try to understand every aspect, every nuance before we draw analogies to something entirely different. Yes, a Citroen Deux Chevaux and a Ferrari Berlinetta Boxer both have four wheels - but in every other aspect they are worlds apart.

As for the "impedance mismatch" you're referring to, no one is denying that a shift takes place from confinement of the wavefront to open space. You can call it an impedance mismatch - I prefer to call it a boundary or shift in the environment. Either way Deward, as you noted earlier - it's terminolgy - we're both referring to the same thing. What we clearly disagree on is what's going on at that boundary. I am convinced that any conceivable pressure or density disruption at that boundary offers very little resistance to the passage of other wavefronts escaping the pipe - particularly in comparison to the scenarios you are presenting that use fixed, hard boundaries to establish standing waves.

If you want to gain a clear understanding of sound wavefront interaction or lack thereof - look here particularly at figure three:

http://www.meyersound.com/support/papers/line_array_theory.htm

[villastrangiato]

I am hesitant to contribute to this thread because I do not like the general tone, but I just finished physics 1 (so I am far from an expert on the subject) and one of the questions on the final was to calculate the first and second frequencies that produce standing waves in a pipe with one closed end and one open. The standing wave occurs due to the reflection back into the pipe from the impedance missmatch at the open mouth. The first (fundamental) frequency is 4 times the length of the pipe (1/4 wavelength) and the second is 4/3 the length of the pipe (3/4 wavelength) and so on.

Just thought this was a good place for a little PHY 117 review.

As a refresher with regard to the "standing waves" you're referring to, look here:

http://www.iop.org/activity/education/Projects/Teaching%20Advanced%20Physics/Vibrations%20and%20Waves/Superposition/file_4299.doc

If you read it carefully, you will find that the only "standing waves" that are allowed in a pipe system with one end open are the waves that have an anti-node at the open end. "Anti-node" means "null". Now I don't know your specific audio background, but in my experience a "null" is something you can't hear very well. Furthermore, these anti-nodes or nulls at even multiples of the fundamental are dealt with in Natkaniec's paper which seems to be the focus of this thread's current discussion. Perhaps you should review the Physics 117 text once more for a more thorough understanding.

[MJKing]

As a refresher with regard to the "standing waves" you're referring to, look here:

http://www.iop.org/activity/education/Projects/Teaching%20Advanced%20Physics/Vibrations%20and%20Waves/Superposition/file_4299.doc

If you read it carefully, you will find that the only "standing waves" that are allowed in a pipe system with one end open are the waves that have an anti-node at the open end. "Anti-node" means "null". Now I don't know your specific audio background, but in my experience a "null" is something you can't hear very well. Furthermore, these anti-nodes or nulls at even multiples of the pipe fundamental are dealt with in Natkaniec's paper which seems to be the focus of this thread's current discussion. Perhaps you should review the Physics 117 text once more for a more thorough understanding.

I suggest you reread your reference, in particular the answers on page 3. The answers confirm what everybody is telling you about quarter wave pipes. Clearly you do not understand the theory. Even worse, you do not seem to be able or want to read the reference material and understand what it is telling you about pipes and resonances. Instead you insult and attempt to talk down to anybody offering the correct explanations.

The young man who I am assuming is young and taking his first Physics class in college (my appologies if I have over assumed) understands more then you do about pipe resonances. To be honest, he understands more then I did at that point in my engineering education which was well over 30 years ago.

All the derivations of TL behavior are available on my site. They are backed up by my own calculations and measurements which correlate extremely well as seen in the plots. My results match George Augsperger's results very closely, we each worked independently using different modeling methods over the same period of time, which is further confirmation. My best estimate is that over the past 10 years thousands of TL enclosures have been built using these methods and simulation tools and have worked exactly as predicted. TL design is no longer an art, it is a well understood science.

So your choice is to read and learn about TL theory and design, or remain clueless and continue making off the wall and insulting forum posts. Your decision, your credibility, I am comfortable with whatever you choose.

[villastrangiato]

I suggest you reread your reference, in particular the answers on page 3. The answers confirm what everybody is telling you about quarter wave pipes. Clearly you do not understand the theory. Even worse, you do not seem to be able or want to read the reference material and understand what it is telling you about pipes and resonances. Instead you insult and attempt to talk down to anybody offering the correct explanations.

The young man who I am assuming is young and taking his first Physics class in college (my appologies if I have over assumed) understands more then you do about pipe resonances. To be honest, he understands more then I did at that point in my engineering education which was well over 30 years ago.

All the derivations of TL behavior are available on my site. They are backed up by my own calculations and measurements which correlate extremely well as seen in the plots. My results match George Augsperger's results very closely, we each worked independently using different modeling methods over the same period of time, which is further confirmation. My best estimate is that over the past 10 years thousands of TL enclosures have been built using these methods and simulation tools and have worked exactly as predicted. TL design is no longer an art, it is a well understood science.

So your choice is to read and learn about TL theory and design, or remain clueless and continue making off the wall and insulting forum posts. Your decision, your credibility, I am comfortable with whatever you choose.

Martin, we all know pipes have resonant characteristics. But the characteristics you cite for simple pipes don't address the specific data that's being generated. For your information, the young man advising me to read physics 117 got it wrong. An open ended pipe cannot resonate at frequencies corresponding to 3/4 of the pipes length - that would put a node where an anti node belongs.

George Auspurger's data agrees with Mr. Natkaniec's paper - the observed upper resonant modes at the output of the undamped pipe excited by a transducer of resonant frequency Fs are in fact multiples of Fs - not the pipe's wavelength - it's really that simple. I'm trying very hard not come off as lecturing people - but if people would actually read a little before spouting - we might actually achieve a higher degree of understanding. No matter what you say, you have not explained why the upper resonances are based upon the driver Fs - something that Mr. Augspurger clearly states in his findings. Until you address this core problem in your reasoning - I really don't want to hear any more of YOUR insults - either directed at me or Mr. Natkaniec.

[MJKing]

George Auspurger's data agrees with Mr. Natkaniec's paper - the observed upper resonant modes at the output of the undamped pipe excited by a transducer of resonant frequency Fs are in fact multiples of Fs - not the pipe's wavelength - it's really that simple.

That is because they typically set the pipe's length to match the driver's fs. This is done for the same reason as a bass reflex enclosure tuned to fs, to dramatically attenuate the driver's motion near fs. For a straight pipe the calculate length as follows.

L = c / (4 x fs)

Please note this equation does not work for a tapered or expanding pipes (that was the mistake made by Bradbury and Bailey). As a result the higher harmonics are approximate multiples of fs. The higher harmonics will not be nice multiples for a tapered or expanding geometry. If the length of a straight TL was sized for a frequency above or below fs, the harmonics would be a function of that frequency and not fs. It is that simple.

[villastrangiato]

Martin, are we talking about what someone typically does or are we talking about a controlled experiment to achieve empirical data? Augspurger obtained data that proves:

- REGARDLESS OF WHAT YOU SET THE TRANSMISSION LINE PIPE LENGTH TO - THE RESULTANT SYSTEM RESPONSE CONTAINS RESONANT MODES THAT ARE MULTIPLES OF THE FUNDAMENTAL RESONANCE OF THE TRANSDUCER THAT'S EXCITING THE RESONANT PIPE - NOT THE PIPE'S FUNDAMENTAL RESONANT FREQUENCY

Look, I'm really getting tired of all your double talk, the obsfuscations and worse yet, the insults to both myself and just about anybody who's ever been involved in the development of Transmission Line Theory. I would appreciate it if you refrain from attempting to force your views any further in this thread. If you continue, I will have no choice but to ask that this thread be locked. Thank you.

[MJKing]

- REGARDLESS OF WHAT YOU SET THE TRANSMISSION LINE PIPE LENGTH TO - THE RESULTANT SYSTEM RESPONSE CONTAINS RESONANT MODES THAT ARE MULTIPLES OF THE FUNDAMENTAL RESONANCE OF THE TRANSDUCER THAT'S EXCITING THE RESONANT PIPE - NOT THE PIPE'S FUNDAMENTAL RESONANT FREQUENCY

I am not sure where you got that quote from, or is this something you have typed yourself? My copy of Augspurger's AES preprint, page 2 of Part 2 says :

"With no stuffing, a pipe resonates at odd multiples of its fundamental
quarter-wave resonance. The speaker cone is heavily loaded at these
frequencies so that speaker output is attenuated and pipe output is
accentuated. To complicate the picture, the two are alternately in
and out of phase at even multiples of the fundamental, resulting in
highly irregular system response."

I think that is what most of us have been saying to you in this thread.

[Deward Hastings]

Maybe it's just a hunch but my guess is organ pipes aren't straight pipes with big holes at the end.

That's exactly what they are.

Does a transmission line "sing" like an organ pipe or Hemoltz pipe? Please, let's get real and stop grasping at straws here.

Undamped that's exactly what they do.

Let's stick with one geometry first - and try to understand every aspect, every nuance before we draw analogies to something entirely different.If you want to gain a clear understanding of sound wavefront interaction or lack thereof - look here particularly at figure three:

"Transmission line" and "line array" do both have "line" in their names, but they do not have "one geometry". Not least of the differences is that one is deliberately resonant (which is what we were/are talking about) and the other is not . . .

[villastrangiato]

That's exactly what they are.

Undamped that's exactly what they do.

"Transmission line" and "line array" do both have "line" in their names, but they do not have "one geometry". Not least of the differences is that one is deliberately resonant (which is what we were/are talking about) and the other is not . . .

Deward, most organ pipes I've seen have fixed, hard boundaries at either end with an opening set at a precisely determined point along the length of the pipe where sound is emitted. The standing waves in the pipe vibrate back and forth and the opening siphon's a portion of the pressure wave out into the intended listening area. This is not to say that open ended pipes don't "resonate" - but their resonance is more directly tied to the source of the excitation - whether that be Louis Armstrong's lips or the reed of a woodwind instrument. One design "rings" at a predetermined frequency - the other (open ended) is not intended to ring monotonically - thus it's resonance characteristics are completely different. Again, we're comparing apples and oranges here. If I'm discussing the superiority of a racing engine's air operated valve train versus a mechanical version in the 12,000 rpm range - your mentioning that Briggs and Stratton lawn mower engines operate on the same 4 cycle principle doesn't really advance the discussion much, does it?