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If not how are those SHORT Transmission lines working? Many are getting results with short stuffed tapered TL speakers but if sound does not slow down how is it workin?
Follow Ups:
Yes it does and not!
A negative taper 4:1 will lower the fundamental as much as extending a straight pipe by 40-50%. The harmonics on the other hand will not be lowered by the taper!
Example straight pipe
Fundmental 40 Hz 3rd harmoic 120 Hz 5th 200Hz
A tapered pipe of the same lenght
Fundemental down to 30 Hz or so but the haronics still arount 120 and 200.
Thanks guys for all the input and tapered pipe gives lower resonance vs straight from Mr King.
not sure about the technobabble, but i've been using tl speakers for 35 years, and still haven't heard bass to compare with these - they are certainly not high efficiency though!!
"When the going gets weird, the weird turn pro." -HST
.
Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.. . .Oh!. . .Remember: Modifying things voids their warranty.
can't you just hear the low end?
"When the going gets weird, the weird turn pro." -HST
Sound propagation involves complex angled reflections off
the side walls, added to simple reflections from the ends.The combined wavefront of these reflections creates the
illusion that inside waveguide, the phase of a wave may
stretched out and appear to travel faster than the speed
of sound. Then again, I could be smoking crack...Perhaps the stuffing prevents these sidewall reflections?
In any case, I don't think it slows the speed of sound.
But it might just prevent phase velocity from speeding up.Or perhaps its some lag of thermal storage and release
in the stuffing's mass that causes the effect?
A tapered pipe will have a lower resonant frequency compared to a straight pipe of the same length, that is the "trick" for getting a short tapered pipe to have a lower then expected tuning frequency. That is also the "trick" that caused people to believe that the speed of sound had dropped significantly in a stuffed TL.The classic formula f = c / (4 x L) only works for a constant area straight TL, it is not accurate for a tapered TL (1/4 wavelength frequency will be lower) or an expanding TL (1/4 wavelength frequency will be higher). It is not accurate for a TL with a choked or ported open end.
Fiber stuffing only slows the speed of sound very slightly, the lowest value I use is 320 m/sec for 1 lb/ft^3 of stuffing density compared to a free air value of 344 m/sec.
Did you ever read the articles in Speaker Builder magazine? They had some good articles on short transmission lines called short lines. I built a short line using JBL LE14A's in a four foot line with a 11.75" x 11.75" cross section area. You have to stuff the line right or it is too boomy. If you think you over stuffed it you need to put in more stuffing. You read that right, stuff it more. To me that is the key to it. It is a short line so even with a lot of stuffing it is still efficient for a transmission line. Mine sounds smooth and sails down to 20hz with no problems. I don't cross it over any higher than 1000hz and I find it very smooth. I usually use it as a sub woofer and point the drivers in the corners and cross over at 50 to 80hz.
Some say it is not a transmission line at all, but I say with the right amount of stuffing, length and cross sectional area, it slows the speed of air down to a 1/4 wavelength.
Some also say they won't handle power, but that isn't right either. It is not like a traditional transmission line as it is not tapered or as long.
At least, not enough to matter.
I built several dozen different transmission lines, many of them "short", and never once got a short one to work well.
Duke
Ever try a non ported TL?
Non-ported? Do you mean, as in no opening at the end? Or, no tuned port at the end?
All of my transmission lines except for one had a mouth of roughly the same cross-sectional area as the last section of the line. That one had a woofer at each end of the line, and it sucked.
I think Dick Shahinian builds transmission lines with a passive radiator at the end of the line, so I assume the enclosure is a transmission line/reflex hybrid. Buggtussel also built TL/reflex hybrid enclosures, but didn't use a passive radiator.
I do think that it's possible to build a transmission line that sounds superb, but none of the short-cuts I tried worked. Wait a minute - one did, but I'm keeping that one under my hat for now.
So far I haven't tried a Martin King Spreadsheet quarter-wave line, but the ability to model the line is something that we couldn't begin to do back in the "old days" of TL DIYing.
I tried some of John Cockroft's shortlines, and was disappointed in the results. Apparently others have been happier with them than I was, but I was spoiled by having listened to IMF speakers at a local high-end shop, so that was my standard for comparision when it came to transmission lines. Only two of my probaby four dozen were what I'd call "successful", and they both followed the same (unorthodox) pattern that I may some day try to turn into a commercial product.
Duke
When I was at madisound a few back I was talking with Larry the owner we where looking at a few books on audio design one on TLs stated only true TL is non ported vented etc. The TL line is long fully damped but not vented.I have tried such as have the good folks at madisound this type of TL works very well.
Very interesting - I wouldn't have thought that a closed-ended TL would work any better than a sealed box. Thanks for the information!
Duke
The Hegeman that HK sold was a sealed TL.
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That morrison x-mission line was sealed but had 4 different path lengths, so instead of 1 large impedence peak, there were 4 smaller ones.
I've been drawn to sealed transmission lines but hadn't found much on them.
Any idea to make one ?
Norman
The design he did for HK had three lengths.
Hegeman's "Contrabombarde" for Shahinian was open with two floorfiring slot vents - wheezed in my larger room. BP4 with 1-4" ID vent played about as well or better - it did sound pretty good in a small room
when the original article on transmission lines was writte I believe it mentioned closed lines. Theoretically a line should be infinitely long so since it can't be you have to cut it off. opening it or not doesn't matter line-wise. But if you cut it at the right point and open it you get a second base source which is why most lines are open. Why waste the extra bass?
Just thinking out loud, the idea of a TL is to get rid of all the back energy which is virtually impossible except perhaps at higher frequencies. So one tries a line to have length to slowly absorb energy as much as possible with reduced reflection compared to boxes. and then ends the line. So to me neither open or closed is a true TL but both have some affect. The closed line looks like a closed box looking at the impedance curve with the single box peak and most open lines look like a bass reflex with two peaks and I believe ultimately 24 db/octave roll off very low. The only exception to the double peak is if there is enough damping to supress it as in the D'Appolito Thor in which case I suppose you have a cross between a variovent and TL and you get no port output.
Interstingly Bud fried always felt the variovent or line tunnel as he called it was the second best loading after the TL though his speakers never combined them. Coincidentally the Dynaco A25 made by his best friend's company(David Hafler and Dynaco) and perhaps the best selling speaker of all time used the variovent principle.
"the idea of a TL is to get rid of all the back energy"
Not at all. The idea of the TL is to make use of the 1/4 wavelength resonance to enhance bass output. The easy way to do so is via a simple pipe enclosure. The problem with a plain pipe is that a series of resonant response peaks are created. The trick of a good TL is to suppress the all the resonant peaks except the 1/4 wavelength. Methods of so doing include, but are not limited to, driver placement, stuffing and tapering of the pipe.
Some of the descriptions in this thread of closed 'TLs' in fact refer the Acoustic Labyrinth concept, which was in its original form intended to totally absorb the backwave, though I've seen the name applied to vented boxes as well.
Bud Fried always said the idea was to get rid of all the energy but that it couldn't be done prctically in a real TL so the next best thing was to tune the line to use the energy not absoebed to extend the response of the line.
And I still think, though Bud wouldn't have agreed it was a very special, sophisticated bass reflex like device acoustically. It certainly has the double impedance peaks of a reflex.
"Bud Fried always said the idea was to get rid of all the energy"
But Bud didn't invent the TL. That honor probably belongs to Olney circa 1936, though he called his damped pipe an Acoustic Labyrinth, not to be confused with the later Stromberg-Carlson products and other non-vented cabs. Voigt's TQWP weren't stuffed, but they were vented. Bailey's 1965 TL was a stuffed vented pipe, as were those of his disciple Bradbury a decade later. It may all be a matter of semantics, but the word 'transmission' intimates that something is transmitted from somewhere, and in the case of the TL that's generally accepted as bass frequencies transmitted by the vent.
Bailey did mention closed lines in his article if I recall correctly, though I've rarely seen it used except in shorter mid-range lines, by IMF and Vanderstein in the model 5s among few others.
Bud certainly didn't invent TLs. Henever claimed that> In fact he expected to import TLs built by Radford(Arthur Haddy of Decca advised him to look into these). But Rad ford kept putting off producing them and Bud was forced into making his own, the first of which was essentially a KEF Concerto kit in a TL box that later evolved into the IMF Monitor series. And I believe ther was a 2 way TL with a 12" paper cone and Kelly-Decca ribbon.
In my experience the strongest reinforcement comes at the frequency where the line is 1/2 wavelength long due to the backwave adding in-phase with the frontwave. But unfortunately there will also be a dip in the response at the frequency where the line is 1 wavelength long, as now the backwave energy emerges out-of-phase with the frontwave. By stuffing the line the energy that causes the 1 wavelength dip is attenuated, but so is the energy that is beneficial down at lower frequencies. Too much stuffing and you will not get usable bass extension down to the 1/4 wavelength frequency. So, it's a juggling of tradeoffs.A transmission line enclosure with the line closed off at the end (instead of open) is really just a well-braced sealed box. I do recall reading that the theory was based on the idea of an infinite line length (probably in Bailey's original article), but don't think that was much more than talk. The idea all along was to use the backwave energy to reinforce the bass - as you very correctly point out, why waste it? I wouldn't be surprised if the misnomer "transmission line" stuck mainly because it sounds so cool.
Duke
Greets!
"A transmission line enclosure with the line closed off at the end (instead of open) is really just a well-braced sealed box."
Yes, and no. If the same net Vb as the typically proportioned sealed cab is turned into a high enough aspect ratio closed pipe it will be long enough to damp the driver's impedance peak much more, which was considered a big deal back when low power, high output impedance systems was the norm. For even more damping, taper it back to a point. With today's typically vanishingly low output impedance systems it only makes sense IMO to use these cab alignments in higher cut off passive ones, though as always YMMV.
GM
Loud is Beautiful if it's Clean!
> > I wouldn't be surprised if the misnomer "transmission line" stuck mainly because it sounds so cool.
Yea, but Mass Loaded Transmission Line sounds even cooler, no?
æNormal is just a setting on my dryer.
____
"A transmission line enclosure with the line closed off at the end (instead of open) is really just a well-braced sealed box."
Quite right. If there is no vent there is no transmission. Likewise, if the vent is restrictive it's not a TL. A TL is by definition non-resonant except at the quarter-wavelength frequency, with stuffing employed in sufficient density to suppress any other resonant peaks arising in the line. If the size of the vent is restrictive, creating a resonant peak below the quarter-wavelength resonance, it's a reflex box, albeit a very long one.
Is that a port, a line, something else?
I wouldn't know what to call it. The website provides virtually no useful information about the product, no SPL charts, no impedance charts, no cutaway views. It's as if they don't want anyone to know what they're getting for their money, other than unsubstantiated hype.
faked Druid
hey Duke - heres a 10ft line outdoors (not best data due to winter wind) with regular vent, larger area Fulmer vent and vent blocked
Freddy
Hi Artesmio
see link below for theory
mass loading with a port or similar can adjust the resonant frequency.
The Zu druid always looked a bit on the short side to me to work as claimed, but mass/floor loading of the port may make the difference.
regards Philip
It does, but in order to do what some claim it would have to be slowed by a few hundred feet per second, and that ain't happening. If a pipe is getting significant port output at frequencies below a quarter wavelength it's via reflex action. Most of those 'too short to be true' TLs are curiously lacking in both measured response charts and, more important, measured impedance charts that would tell what's really going on.
Sound does indeed move at different speeds through different mediums.
Once the density of the packing material and the acoustical properties of the fiber is known, a taper of shorter length may be constructed. The one thing that will change with more stuffing though is an attenuation of the tuned frequency.
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