In the last several parts of this continuing series, I've written about why speakers need enclosures to make bass, instead of just for cosmetic appeal. In the course of that, I've written about enclosure types ranging from just a simple huge board to sealed boxes both of the previous being, if the board or the box are big enough, called "infinite baffles" ; to small sealed boxes "air" or "acoustic" suspension systems ; to bass-reflex systems of various kinds simple, "tuned-port" and "distributed port" and "resistive port" systems that act more like leaky sealed boxes than bass-reflex systems.
In the course of that, I've mentioned - and even promised to write about - "transmission line" "TL" enclosures a number of times, but never yet actually done so. One of the reasons for that was simply that there was so much other information that had to be delivered to put the transmission-line enclosure in perspective and to make it comprehensible both in terms of how it works and as relative to other speaker enclosure designs.
The other reason was, as I told you last time, that there are at least two different kinds of enclosures that -- despite their design and functional differences - have been given that same name. Or, if you'd prefer, two different names "Transmission Line" and "Acoustic Labyrinth" have been given to similar but differently-functioning enclosures.
As to how TL enclosures work, that's really quite unusual and explains why I had to tell you about bass reflex and resistive port enclosures first - because one of the two types is reminiscent of the operation of a bass-reflex enclosure and the other is more similar to a sealed box enclosure with a resistive port.
Let's take a look at the one more like a bass-reflex enclosure first. In that form of "transmission-line" a long "maze-like" path usually called a "duct" is structured within the enclosure for the back wave from the driver to follow and is always vented to the open air. This duct is similar in internal complexity to a folded horn we'll talk about horn enclosures in another installment but, unlike a horn, there is no direct need for it to "flare" grow greater in cross-section as it grows longer and, although some designs may, in fact, be flared, the duct may also remain constant in cross-section or even, as the designer specifies, grow progressively smaller over its length.
Unlike a horn, the flare is not the critical factor but instead, it's the length of the created air column that is most important. In this type of transmission-linealthough the purpose of the duct is still, as with a bass-reflex enclosure, to "flip" the polarity of the energy appearing at the end of the duct the "vent" so that it will add to the front wave off the driver, the sound that comes out of the vent is actually the driver's original back wave and not some resonant construct.
Where the length of the duct comes in is that, although TL enclosure design has historically been "iffy", and nowhere near as easily predictable or formulable as some other kinds of enclosure, one quarter of the wavelength of the fundamental resonance of the driver has been a pretty common choice and can provide the same kind of enhancement that port and box resonances do in bass-reflex designs.
The difference is that it is not a resonant effect, but, by matching duct length to frequency, it allows for optimum driver loading, minimum enclosure resonance, and minimum acoustic impedance at the vent, for reduced back wave reflection back to the diaphragm and improved coupling to the air outside the enclosure.
Although the critical thing about the duct is its length, other aspects of it do matter. For example, it's almost always stuffed to a greater or lesser degree, depending on the specific type of TL, the materials chosen, and how they're applied with one or more kinds of damping materials Dacron, long-fiber wool, etc. The purpose of this is to absorb all but bass frequencies and to reduce or eliminate both unwanted cabinet resonances and unwanted upper frequencies that might interfere with the other non-bass aspects of the sound that gets to the listener's ear.
The other type of transmission -line enclosure also uses a long duct for the back wave and that duct is also stuffed with damping material. Where it differs is that the duct may or may not be vented to the open air because its intent is not to pass, but to, as completely as possible, absorb the back wave from the driver.
A theoretically perfect TL would absorb all frequencies entering the line from the rear of the drive unit but remains theoretical, as it would have to be infinitely long. One famous subwoofer, the Shahinian " Contrabombarde ", designed by Stewart Hegeman the same man who invented the omnidirectional speaker and designed Harman-Kardon's original "Citation" series electronics used just two 8" woofers in a double open-ended transmission-line setup two side-by-side transmission lines in the same box with output only through the ventsthat was claimed to be "flat" to 17Hz and as told to me by Skip Weshner, who was my friend and a tight buddy of Hegeman to have usable, and possibly even "world-destroying" bass down to 8Hz.
As I remember it, the Contrabombarde used two different lengths and thus two different tunings for its transmission lines, which allowed it to TL load both the front and back waves off its drivers so that the sound from both came out in-phase and hugely powerful at the vents. A similar "load-both-sides-of -the-driver" approach has been taken by no less than Bose, and is mightily impressive. I'll tell you about it and other things next time. For more information about AudiophileReview.
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Transmission line loudspeaker
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Just wondering about the advantages or disadvantages of each. Swerd Audioholic Spartan. Last edited: Aug 15, TLS Guy said:. The other confounding problem is that I think consumers have become accustomed to resonant bass reproduction at least to a degree.Tips and Tricks.
What is the difference between a transmission line and a bass reflex system? Due to their complex design and associated higher production costs, the transmission line is rarely found today. At the same time, this concept is said to produce a distinct and clean low bass with unproblematic impedance progression. In addition, a well-designed transmission line efficiently reduces resonances of the speaker enclosure. Similar to the operation of an organ pipe, the length of the tube of a transmission line running inside the box must be exactly one quarter of the wavelength of the bass frequency that one wishes to support.
In purely mathematical terms, this would be approximately three meters of pipe length for 30 hertz. Therefore, a transmission line tube is folded in the box. The predominantly rectangular sound outlet opening in the housing is usually calculated so that it corresponds to the size of the membrane surface of the bass speaker.
A bass reflex system also makes use of the backward sound radiation of the woofer. The volume of air stimulated in the interior of the box housing, together with the air at the outlet opening of the bass reflex tube, creates a vibrating system, which is also called a Helmholtz resonator. If the bass diaphragm moves inwards, air is expelled by the bass reflex tube with a time lag phase shift by degrees.
Right in between, at 90 degrees, is the resonance frequency, here the sound emitted to the front gives maximum support to the sound emitted from the rear, as a result the bass is perceived as fuller and deeper. Poorly tuned bass reflex systems often suffer from poor impulse response and rapid level drop.Volvo s40 front lip
Back to Tips and Tricks. Skip to content Tips and Tricks. Transmission Line and Bass Reflex. T ransmission line:. Bass reflex:. Close Menu.Forgot your password? This kind of goes with myths and lies. Here I am trying to figure out why some insist on a port box for spl? Is there a specific reason why? The reason I see the transmission line is better is x max is reduced so when you add 8, watt burp to a 2, watts rms sub the tinsel leads do not come apart as easily.
The t lines can be tuned the same as a ported for high output.Mlad sin jebe zrelu mamu spavanje
So why go ported? Sorry as for goal it's spl. I just bought a mach5 audio spl 12 for the box it says L at hertz. I will be running it off a saed for now till i can get a bigger amp maybe even two amps like the sazd strapped. If you have a T-line that is more efficient than a 4th order vented alignment, chances are it isn't a T-line. The whole point of a T-line is to be very flat in amplitude response, it is about as good of a choice for SPL as a 2nd order sealed alignment.
Tlines have more control over the cone within it's tuned freqeuncy, but if u go below or above it, it drops faster then a ported box. But the mechanical power handling drops, because if u go out of the tuned freqeuncy the excursion will be bigger. A Tline or a quarter-wave enclosure is more efficient than a 4th order bandpass.
You are tottally wrong about efficieny of a Tline, they are more efficient then a lot of other enclosures. By the way, i have a Tline and i had a well designed ported box before and the Tline walks over a ported box without a doubt.
The 4th order bandpass could get louder, because power handling is better then in a ported box, and Tline was waay more efficient then any of those boxes. I'm pretty sure for a T-line to be as efficient as a bass reflex design, the box has to be MUCH larger. How are you defining efficiency though? The problem with a question like this is that it makes it obvious you shouldn't even think about it.
If you sit down and truly look at the response and math of T-lines you'd never even ask. Add that to the fact that you won't ever nail the build on the first attempt it is surely not what you should use.
Even if you didn't have to ask the question the answer you'd come up with would be to not bother as there is no benefit for you. I know, it is obvious from his kirill 2nd post that he didn't understand that a 4th order vented box is not a bandpass I never even mentioned bandpass and that he completely missunderstands how a T-line works look into the use of the word "tuning".
Pretty much everyone who believes this, and believes they have built a T-line when in fact they have build a ported box with a huge port will go on and on about it The whole point of a T-line is NON-resonant behavior and flat response with an enhanced low end.
A proper T-line will never be more efficient except the last octave, in which case they accell, but this doesn't help car audio SPL in the least than a proper 4th order vented alignment It is also appratent when someone post a picture of a "T-line" only to find that in fact, they have not built one at all.Forums New posts Search forums.
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Thread starter herbu Start date Aug 15, I have a little understanding of passive radiators, and a little of folded transmission lines, but not much. It seems people often generally equate the sound of the Phil3s to the SS8s, but it appears the design is quite different. Just wondering about the advantages or disadvantages of each.
Swerd Audioholic Spartan.Resources saved on this page: MySQL Show 50 post s from this thread on one page. I'm looking to build an efficient speaker to be powered by my Bottlehead Stereomour 2A3 Amp.
Transmission Line and Bass Reflex
Unfortunately, the one thing I failed to check was the size - what I had designed would in no way fit in my living room. SO - back to the drawing board. It seemed that another logical option might be looking at a quality full-range driver in a larger cab, perhaps horn loaded or in a transmission line. I stumbled across the Tang Band W, which appears to be a fantastic driver and by most reviews, iswell suited for a larger bass-reflex or t-line enclosure.
I decided to attempt a transmission line design. I've designed the cabinet using Martin King's alignment tables unfortunately it appears the MathCAD program is no longer available for modelling, so I couldn't do much actual testing. Here are the specs: Tuned to 40hz. Approximately Use Leonard Audio Transmission Line program for modeling. It is based on Martin Kings work.
Transmission line loudspeaker
You can find the link on Mrtin Kings webpage. Worth your while to discuss your needs with Bob. Look at some of the FAST designs on this website i.
Much better to let the full range driver work best within it's natural range 2. Thank you for all the suggestions - some of those links I had not come across in my research, incidentally, so they're proven to be helpful in my search. The depth can be stretched as can the height, but I'm not looking to add anything into mys system aside from a more efficient speaker than I'm currently driving with my 2A3 tube amp. If I find it absolutely necessary in the future I will add in a separate powered sub, but for now I like to listen to vinyl at pretty reasonable levels in an otherwise pretty small living room.
I don't have home theater hooked up to this system, so it's exclusively for music. Mostly I'm looking for simple, even if it is at the expense of some clarity. And I want some really good looking speakers - I'm an architect, and honestly the look matters about as much as the sound, which shifts my criteria a bit. I have also modeled this as a bass reflex in winISD and can get a pretty reasonable f3 38Hz with a L cab, a sentiment and design I've heard reflected elsewhere.
In your opinion, what would be the advantages of doing something like a tapered TL or MLTL vs a bass reflex for a driver like this? I've seen those Pure Audio Project speakers before and they are gorgeous; unfortunately, they won't fit in my living room :. The suggestion about a bookshelf paired with a sub is something I will definitely look into - I very much appreciate the suggestion!
Page 1 of 3. Jim Griffin.Transmission line, ported and vented designs are three different concepts on how to load the bass driver in a speaker enclosure. Transmission lines and sealed boxes have a 12dB per octave roll off after the resonant frequency, while a vented box has a 24dB per octave roll off.
Ported speaker are the most common as they are cheap to build and easy to design, though the quality of the bass reproduction is questionable in many designs and such a steep roll off can have knock on problems further up the frequency range.Application of sr latch as switch debounce
Sealed boxes have a similar roll off to transmission lines, however the efficiency of such systems is lower due to the inward radiating energy not being utilised by the cabinet. Distortion also occurs as the air in the box is compressed and expanded adiabatically as the cone moves in and out, the force required to move the cone changes non linearly with respect to the cone excursion.
Both sealed and vented designs require careful absorption to avoid rear radiating sound bouncing off the cabinet walls, and passing through the bass driver causing boxy resonances. Transmission line by contrast sound very natural because there is no build up of pressure behind the bass cone, with the rear radiating air being forced through an internal labyrinth to reinforce the bottom end of the frequency band.
This also means no rear sound is re-radiated through the bass driver. The other advantage is that the air in the transmission line loads the bass driver and lowers its resonant frequency. This allows for the extended low end response and keeps the bass driver well damped, requiring less excursion than sealed or ported speakers to produce the same output.
PMC has painstakingly developed their own advanced transmission Line ATL and has taken loudspeaker design to new levels, by using a cabinet construction and highly specified drive unit and crossover components.
If you have a question that's not listed here, please contact us. Latest News Events Reviews Awards. Events Reviews Awards. Skip to main content. PMC 'How do transmissions lines differ from ported and vented speakers? This action is not possible due to your location! Find a retailers Please use our 'Where to buy' section to find your local retailer. How do transmissions lines differ from ported and vented speakers?
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