headers work on the principle of a collumn of hot gas shrinking as it cools flowing in a tube . gas has mass and velocity there is a negative pressure after the end of the collumn and the the length and the diameter of the tube is calculated so that an optimum velocity of the gas column has a vacuum behind it timed to pull the next gas collumn behined it tuned to a certain rpm to develope the most volumetric efficiency in concert with camshaft timing...most of us don't realize exhaust has mass and kenetic energy...
I don't know where this came from but I know where it's going>>>
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I don't know where this came from but I know where it's going>>>
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I forgot headers are tuned to work at a specific RPM(frequency) range and are tuned specifically for the application,just like pipes in a pipe organ...
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From my "learned" (possibly some may disagree and I am always ready to be educated) position I thought TL speaker concept had little to do with a transmission line as it applies to a wire and a whole lot more to do with directing the back wave from the back of the transducer down a lossy closed duct of some kind such that all energies from the back of the speaker were converted to heat rather than any being allowed to radiate back into the listening environment. Suppose the concept of the terminated wire which is terminated into its' characteristic impedance resulting in no reflections has a conceptual similarity to the TL speaker in that no wave (energy) is ever reflected back out the driver or "leaks" out of any opening in the TL type loud speaker. In essence, a glorious way to get rid of the radiation from the back of the speaker without changing the resonance of the raw driver.
This is much easier to say than to do. In practice the lossy line which absorbs the energy and is supposed to not leak has appeared very difficult to achieve. Real TL cabinets that do not leak unfortunately become very large so almost all seen are truncated TL design. Further in practice because it is very difficult to maintain tuning of such short lines because acoustic materials are unstable and slight changes is velocity of sound with humidity and temperature along with a host of other factors (looses its' accurate tuning) makes the truncated transmission line often behave like a ported speaker resulting in the two classic electrical resonant peaks.
The most effective truncated TL I have personally ever seen had this complex shaped duct off the back of the driver with a hole series of side ducts of different lengths which the builder had individually tuned (a la Helmholtz) with damping to interfere with with the progression of the wave down the main duct In the end this worked okay but was pretty large (9 feet long and 20"x26" more or less at the big end with all the tunable side ducts sticking straight up some several feet themselves). Anyway, it worked okay but was not really any better than a very solid sealed box which was much smaller.
Somewhere in this thread someone said a horn is a directivity control device. Actually a horn is an acoustic transformer which transforms the low amplitude high pressure at the diaphragm to the higher amplitude lower pressure suitable for radiation into free air. An impedance match throat to mouth. Modern horns have change the shape of the matching element to control directivity and in the process change the impedance away from that of the straight elliptical horn. Even though the modern horn with constant directivity does not offer constant impedance at the throat the impedance seen by the driver is within the operational limits of the diaphragm design (usually) so they work fine. Reflection back down the throat of the horn occur when the match at the mouth in not equal to the impedance of the free air at the mouth. By far the biggest offender of this is the dual rate horn with always bad sound and always lots of reflections. To minimize reflections horn mouth really needs to be at least 1/2 wavelength at the lowest frequency used and really should be the wavelength of the lowest frequency used. So you may see the dual rate horn has a mouth the size of where the rate changes and is therefore limited to narrow band operation. And please note that is the mouth minimum dimension if the mouth is not round. This means (using the 1/2 wave rule) a horn mouth of 4 inches is only good down to 1700Hz absolute minimum. This means there is no such thing as a good small horn.
This is much easier to say than to do. In practice the lossy line which absorbs the energy and is supposed to not leak has appeared very difficult to achieve. Real TL cabinets that do not leak unfortunately become very large so almost all seen are truncated TL design. Further in practice because it is very difficult to maintain tuning of such short lines because acoustic materials are unstable and slight changes is velocity of sound with humidity and temperature along with a host of other factors (looses its' accurate tuning) makes the truncated transmission line often behave like a ported speaker resulting in the two classic electrical resonant peaks.
The most effective truncated TL I have personally ever seen had this complex shaped duct off the back of the driver with a hole series of side ducts of different lengths which the builder had individually tuned (a la Helmholtz) with damping to interfere with with the progression of the wave down the main duct In the end this worked okay but was pretty large (9 feet long and 20"x26" more or less at the big end with all the tunable side ducts sticking straight up some several feet themselves). Anyway, it worked okay but was not really any better than a very solid sealed box which was much smaller.
Somewhere in this thread someone said a horn is a directivity control device. Actually a horn is an acoustic transformer which transforms the low amplitude high pressure at the diaphragm to the higher amplitude lower pressure suitable for radiation into free air. An impedance match throat to mouth. Modern horns have change the shape of the matching element to control directivity and in the process change the impedance away from that of the straight elliptical horn. Even though the modern horn with constant directivity does not offer constant impedance at the throat the impedance seen by the driver is within the operational limits of the diaphragm design (usually) so they work fine. Reflection back down the throat of the horn occur when the match at the mouth in not equal to the impedance of the free air at the mouth. By far the biggest offender of this is the dual rate horn with always bad sound and always lots of reflections. To minimize reflections horn mouth really needs to be at least 1/2 wavelength at the lowest frequency used and really should be the wavelength of the lowest frequency used. So you may see the dual rate horn has a mouth the size of where the rate changes and is therefore limited to narrow band operation. And please note that is the mouth minimum dimension if the mouth is not round. This means (using the 1/2 wave rule) a horn mouth of 4 inches is only good down to 1700Hz absolute minimum. This means there is no such thing as a good small horn.
Just so I have it straight... If all the tubes are of the same diameter, that would mean they'd need to be equal in length to have the same volume...?...correct 😉. I'm certainly not saying they don't exist, but I've never seen a header that used varying sizes (diameter) within it's construction.
Thanks for the clarification.
Gentlemen, may I remind you that when we go off topic, we miss out on the stimulating intercourse of acoustic transmission lines.
Yes, I agree headers are an issue of volume rather than length. Makes it easier to design them to fit under a hood.
Oops.
Yes, I agree headers are an issue of volume rather than length. Makes it easier to design them to fit under a hood.
Oops.
Equal volume is not absolutely necessary. Both you and smokinghot have applied blanket statements to describe hard rules that don't exist either in the automotive industry or in racing (the example I used). Factually, there is a good deal of science that goes into the timing and sizing of exhaust pulses in a high performance exhaust system. For a brief overview, you can look here:
Summary of Exhaust Theory - Exhaust System Basics - Sport Truck Magazine
I know what I'm talking about because I've seen the designs up close both in high performance ski boats and at Formula 1 races spanning back 25 years. The pulses generated in an exhaust system mirror what happens in a TL in many respects. The issues of time and distance are key in establishing optimal performance.
I didn't see any reference to driver Fs in table 1.
I think I may be approaching this problem from a different angle - I believe before other aspects of a transmission line can be considered - the pipe length should be established based on the driver's frequency dependent impedance profile alone. Augspurger's experimentation sought to establish very basic foundation principles with a simple undamped pipe. To be able to make the claim of full optimization, you have to start simple - clearly define what is "optimal" with the most basic changes to configuration - then proceed to the more detailed or nuanced. For me, this means - establish pipe length - not based on driver area or throat area or whether you've chosen an offset or a coupling chamber design or continuous tapered pipe. Just a simple undamped straight pipe. Alter the length until you get maximum total backwave output and maximum suppression of the driver's impedance curve. From there, play with throat area, taper, offsets - all the other various parameters to your heart's content. I don't necessarily buy into a specific design methodology - whether you want to label it classical or otherwise. My methodology is and always has been focused on knowing the contribution of every aspect to the end game. And as far as I'm concerned, you can't proceed to a pipe length with just throat and terminus area alone. The driver's Fs is the point of reference - not because I'm saying it is - but because the extensive test data (as obtained by Augspurger) says it is.
This is where you and I fundamentally disagree Martin. I don't like making any assumptions whatsoever. If I'm going to model something, I have to know that if I vary parameter x - it's going to produce a change in result y every time. If I'm starting out of the starting gate with a bunch of assumptions off the bat, I can't really conclude with certainty that my model is ultimately worth a darn or that I'm leaving anything substantial out that could send me in a better, more optimal direction.
In the process of building headers header volume is measure directly by filling the tube with water. Yes the length matters for other reasons like resonant tuning and so on such as an organ pipe. When it comes down to actually building the header the water volume is the final measure of the correct tube fabrication. If the volume at length is to small a larger tube is used. Mandrel bending the tube changes the cross sectional area of the tube dramatically.
So how many high performance header systems have you put out on the track? I have done about 10 first hand.
Similar errors are made in many things audio where what one believes is the prime criteria is actually not really the item of interest such as this transmission line thing. Wrote just a bit ago about the difference in transmission line concerning wire and truncated TL loudspeaker cabinet. Often it is the case we measure something that has nothing to do with what our actual test interest are and we end up making a bad conclusion from the measurement of some thing that has little to do with the effect we see. Aargh! Audio and its subversive hidden details of mysterious actions...
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I've seen many TLs up close, and grasp the logic... However I'm not so pretentious as to claim I understand the advanced math behind them.
As Cal has suggested. Can we focus the discussion back on the topic we think we know.
As Cal has suggested. Can we focus the discussion back on the topic we think we know.
Interesting, interesting...
I know Planet10's credentials, and gedlee's work is widely known. Other posters critical of the "strangiato approach" have presented some background in the field.
Now shut me up if this has been broached and I just missed it somewhere...
But what are villastrangiato's professional/academic accreditations? One must ask... I'm only an accredited Carpenter and farter so I'm no snob to be sure. But surely the time has come to ask?
Are you a P. Eng? Or Ph. D?
I'm all for lively debate but it seems unfair that one side of the argument has it all on the table and the other is a sole anon hyperlinking wikipedia lr&c.
I know Planet10's credentials, and gedlee's work is widely known. Other posters critical of the "strangiato approach" have presented some background in the field.
Now shut me up if this has been broached and I just missed it somewhere...
But what are villastrangiato's professional/academic accreditations? One must ask... I'm only an accredited Carpenter and farter so I'm no snob to be sure. But surely the time has come to ask?
Are you a P. Eng? Or Ph. D?
I'm all for lively debate but it seems unfair that one side of the argument has it all on the table and the other is a sole anon hyperlinking wikipedia lr&c.
Hey I never got a truncated TL to work all that well as I always ended up with the two peaks resonant tuned port like effect. Then I started messing with small drivers and the truncated transmission line with a great variety of variations. With a driver resonance of 500Hz the line got manageable in size and was able to show "yes, this can actually work" in an empirical sort of way, based on math models of course. I ran the numbers to replace my 20Hz subs based on the successful 500Hz lab experiments and said "Holy smokes that is a BIG cabinet." That was the end of that extrapolation.
Long story short... now using very solid sealed box with Q in box less than 0.5 and electronic EQ. Within my experience this has been the all around best so far.😀 Getting 103dBa at 30Hz and less than 3% THD. Of course with that low Q in the box overshoot and flab in the bass are non-existent.
Long story short... now using very solid sealed box with Q in box less than 0.5 and electronic EQ. Within my experience this has been the all around best so far.😀 Getting 103dBa at 30Hz and less than 3% THD. Of course with that low Q in the box overshoot and flab in the bass are non-existent.
You're kidding, right? I'm being challenged by a picture of a stuffed doll and a guy with a hard hat to prove my credentials? LOL!!
Look, I started this thread to support key aspects of a published paper and coordinate it with certain aspects of other published papers. Why does everything on these boards have to degenerate into a peeing match of people's qualifications? Do my posts in this forum or the other forum that will remain nameless suggest to you that I just fell off the turnip truck? The moderator of this board suggested I play the ball - not the man. I intend to do that and I hope you will do the same. As for my identity, just consider me an avid Rush fan who happens to know a thing or two about acoustics. The fact that most of you are Canadian and not one of you mentioned my screen name suggests very strongly to me that a good percentage of you are hostile. Under such circumstances, how would telling you my life story benefit me?
In the spirit of "real expert or just self proclaimed" perhaps villastrangiato would like to back up his claims with some measurements of real speakers -- SPL, impedance, etc. I'm not terribly concerned with academic credentials, the ability to speak tech babble, etc. Some of the smartest people I know in audio are self-taught. To quote the old commercial, "where's the beef?"
The numbers across the top of the table... 1st step in using the tables, Fs gives you a length (which is also a function of taper ratio)
dave
No not at all. Of course you don't have to divulge who you are and what your background is in order to bring forth an argument. I think that sometimes when your arguments don't gel with the mainstream, some will want to know more about you in order to have some sort of validation, that's all.
Which do you like more, the west or the east?
1st Wikipedia hit -- i'm not a Rush fan...
Rush instrumentals - Wikipedia, the free encyclopedia
dave
I couldn't care less what you're user name represents. Mine is an ongoing joke amongst friends, and the pic is film character who gets high on sugar and makes my daughter laugh... Who cares.
I'm only curious about your credentials, if any, because you claim to know quite a lot, and I'm certain you can't be an authority on everything. For all any of us know, you could be one of those enlightened genuises that doesn't have any letters after their name, but can set up a septic system one day and redefine the laws of physics the next. Or some random guy that just loves audio, especially TL theory.
So, without any hostile intent.... Mr.Villastrangiato, may I ask in what field your expertise/knowlegde lays...?
I'm only curious about your credentials, if any, because you claim to know quite a lot, and I'm certain you can't be an authority on everything. For all any of us know, you could be one of those enlightened genuises that doesn't have any letters after their name, but can set up a septic system one day and redefine the laws of physics the next. Or some random guy that just loves audio, especially TL theory.
So, without any hostile intent.... Mr.Villastrangiato, may I ask in what field your expertise/knowlegde lays...?
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From what I've seen so far you keep mistaking the man for the ball.
Almost every participant in this thread has politely pointed this out to you.
Here's a last official warning:
This pub has friendly open minded people, eager to learn from whoever presents his view in a mature way. You better cope with that.
All: lets talk TL. 🙂
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