Diffusore acustico a linea di trasmissione
{{W|musica|arg2=ingegneria|agosto 2020}}
{{T|inglese|ingegneria|maggio 2018}}
[[File:TransmissionLineSpeaker.png|destra|miniatura|300x300px|Transmission line enclosure]]
Un '''diffusore acustico a linea di trasmissione''' è un [[Diffusore acustico|diffusore]] con disegno ([[topologia]]) che usa una linea di trasmissione acustica nel suo cabinet, che si differenzia dai classici disegni a sospensione pneumatica (chiusi) o ventilati [[bass reflex]]. Al posto di un riverbero smorzato all'interno del cabinet chiuso, il suono esce dalla parte posteriore del [[woofer]] e convogliato lungo una via lunga (generalmente smorzata acusticamente) all'interno del cabinet, che permette un controllo dell'energia acustica verso le tonalità basse.

All'interno del cabinet della linea di trasmissione (TL), vi è la via di uscita, generalmente ripiegata con anse, in cui il suono si propaga verso l'esterno. La via di uscita è generalmente ricoperta con tipi diversi di isolanti acustici, materiale assorbente acusticamente, e l'uscita può essere libera in aria o anch'essa ricoperta con materiale spugnoso. Usato correttamente tale insonorizzazione evita risonanze e dispersione di energia acustica, con risultante beneficio nel suono, le frequenze vengono assorbite selettivamente per effetto del dotto, o alternativamente emerge solo la parte di energia acustica in fase con l'emissione dell'altoparlante frontalmente, aumentando l'energia emessa alle basse frequenze. La linea di trasmissione è una [[guida d'onda]] acustica, e l'imbottitura riduce le riflessioni e risonanze, riducendo la velocità del suono all'interno del cabinet.

I diffusori TL sono più complessi da progettare, e da costruire in serie, ma i vantaggi acustici sono evidenti. Come di regola, i diffusori TL tendono ad avere eccezionale alta fedeltà nelle frequenze basse, con frequenza che rispondono per un [[subwoofer]], raggiungendo l'[[infrasuono]] (I modelli prodotti dalla TDL Electronics studio monitor negli anni '90 raggiungevano la risposta in frequenza di 17&nbsp;Hz con sensibilità di 87&nbsp;dB per 1&nbsp;W @ 1&nbsp;metro), senza necessità di cabinet separati per subwoofer. I diffusori TL hanno un roll off molto più lento alle basse frequenze, e un miglior controllo rispetto ai bass reflex,<ref>{{Cita web|url=http://www.audio-ideas.com/reviews/loudspeakers/pmc-fb1.html|titolo=Copia archiviata|accesso=30 maggio 2018|urlarchivio=https://web.archive.org/web/20181223073608/http://www.audio-ideas.com/reviews/loudspeakers/pmc-fb1.html|dataarchivio=23 dicembre 2018|urlmorto=sì}}</ref> sono meno sensibili al posizionamento in ambiente, e tendono a creare un'ambientazione da [[teatro di posa|soundstage]].<ref>{{Cita web|url=https://www.soundonsound.com/sos/feb00/articles/pmcfb1.htm}}</ref>

Per contro sono più complessi da calcolare e progettare, rispetto ad altri tipi di cabinet. I parametri di base e le equazioni che descrivono i diffusori con cabinet sigillati reflex sono più facili da capire, rispetto ai diffusori TL, con il risultato finale del prodotto che deve essere sperimentato in fase di realizzazione.

== Descrizione ==
{{citazione|I believe that speakers should preserve the integrity of the signal waveform and the Audio Perfectionist Journal has presented a great deal of information about the importance of time domain performance in loudspeakers. I’m not the only one who appreciates time- and phase-accurate speakers but I have been virtually the only advocate to speak out in print in recent years. There’s a reason for that.}}<ref name="PMC1">{{Cita web|autore=lam seng fatt |url=https://hi-fi-avenue.blogspot.co.uk/2010/09/british-sound-with-unbritish-bass.html |titolo=hi-fi avenue: British sound with 'unBritish' bass |editore=Hi-fi-avenue.blogspot.co.uk |data=6 settembre 2010 |accesso=13 giugno 2015}}</ref>

{{citazione|It is difficult and costly to design and manufacture a time- and phase-accurate speaker system. Few of today’s high-end loudspeakers are time- and phase-accurate designs. The audio magazines need to appeal to a broad spectrum of advertisers including many who make speaker systems which are time incoherent. The magazines, and the reviewers who write for them, have ignored or downplayed the issue of time- and phase-accuracy in order to maximize advertising revenue. I am not alone in recognizing this situation.}}<ref name="TNT1">{{Cita web|url=http://www.tnt-audio.com/casse/temperance_e.html |titolo=Newtronics Temperance Loudspeakers listening test [English&#93; |editore=Tnt-audio.com |data= |accesso=13 giugno 2015}}</ref>
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The transmission line (TL) is the theoretical ideal, and one of the most complex constructions, with which to load a moving coil drive unit.
The most common and practical implementation is to fit a drive unit to the end of a long duct that is usually open at the far end. In practice, the duct is folded inside a conventional shaped cabinet, so that the open end of the duct appears as a vent on the speaker cabinet. There are many ways in which the duct can be folded and the line is often tapered in crossection to avoid parallel internal surfaces that encourage standing waves. Some speaker designs also use a spiral or elliptic spiral shaped duct, usually with one speaker element in the front or two speaker elements arranged one on each side of the cabinet. Depending upon the drive unit, and quantity and various physical properties of absorbent material, the amount of taper will be adjusted during the design process to tune the duct to remove irregularities in its response. The internal partitioning provides substantial bracing for the entire structure, reducing cabinet flexing and colouration. The inside faces of the duct or line, are treated with an absorbent material to provide the correct termination with frequency to load the drive unit as a TL. The enclosure behaves like an [[Diffusore acustico|infinite baffle]], potentially absorbing most or all of the speaker unit's rear energies.<ref>{{Cita web|url=http://www.directacoustics.com/lexicon.pdf}}</ref> 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. The physical constraints of the real world, demand that the length of the line must often be less than 4 meters before the cabinet becomes too large for any practical applications, so not all the rear energy can be absorbed by the line. In a realized TL, only the upper bass is TL loaded in the true sense of the term (i.e. fully absorbed); the low bass is allowed to freely radiate from the vent in the cabinet. The line therefore effectively works as a low pass filter, another crossover point in fact, achieved acoustically by the line and its absorbent filling. Below this “crossover point” the low bass is loaded by the column of air formed by the length of the line. The length is specified to reverse the phase of the rear output of the drive unit as it exits the vent. This energy combines with the output of the bass unit, extending its response and effectively creating a second driver.

Essentially, the goal of the transmission line is to minimize acoustical or mechanical impedance at frequencies corresponding to the driver's fundamental free air resonance. This simultaneously reduces stored energy in the driver's motion, reduces distortion, and critically damps the driver by maximizing acoustic output (maximal acoustical loading or coupling) at the terminus. This also minimizes the negative effects of acoustic energy that would otherwise (as with a sealed enclosure) be reflected back to the driver in a sealed cavity.<ref>{{Cita web|url=https://www.scribd.com/full/14966584?access_key=key-mioyzl1d3eydoh4zj26}}</ref>

Transmission line loudspeakers employ this tube-like [[Risonanza (fisica)|resonant]] cavity, with the length set between 1/6 and 1/2 the [[Lunghezza d'onda|wavelength]] of the fundamental resonant frequency of the loudspeaker driver being used. The cross-sectional area of the tube is typically comparable to the cross-sectional area of the driver's radiating surface area. This cross section is typically tapered down to approximately 1/4 of the starting area at the terminus or open end of the line. While not all lines use a taper, the standard classical transmission line employs a taper from 1/3 to 1/4 area (ratio of terminus area to starting area directly behind driver). This taper serves to dampen the buildup of standing waves within the line, which can create sharp nulls in response at the terminus output at even multiples of the driver's Fs.

In a transmission line speaker, the transmission line itself can be open ("vented") or closed at the far end. Closed designs typically have negligible acoustic output from the enclosure except from the driver, while open ended designs exploit the low-pass filter effect of the line, and the resultant low bass energy emerges to reinforce the output from the driver at low frequencies. Well designed transmission line enclosures have smooth impedance curves, possibly from a lack of frequency-specific resonances, but can also have low efficiency if poorly designed.

One key advantage of transmission lines is their ability to conduct the back wave behind the transducer more effectively away from it – reducing the chance for reflected energy permeating back through the diaphragm out of phase with the primary signal. Not all transmission lines designs do this effectively. Most offset transmission line speakers place a reflective wall fairly close behind the transducer within the enclosure – posing a problem for internal reflections emanating back through the transducer diaphragm. Older descriptions explained the design in terms of "impedance mismatch", or pressure waves "reflected" back into the enclosure; these descriptions are now considered outdated and inaccurate as technically the transmission line works through selective production of [[Onda stazionaria|standing waves]] and [[Interferenza (fisica)|constructive]] and destructive [[Interferenza (telecomunicazioni)|interference]] (see below).

A second benefit is that the resulting music is time coherent (i.e., in phase). Fried quoted in 2002, a listening test performed and reported in December 2000's ''Hi-Fi News'' (as he believed) in which a high-quality recording was obtained using reputable but non-time-coherent loudspeakers and this recording was then time phase corrected; an expert listening panel "voted unanimously for the superior realism and accuracy of the time corrected output" for high quality sound reproduction.

A transmission line speaker employs essentially, two distinct forms of bass loading, which historically and confusingly have been amalgamated in the TL description. Separating the upper and lower bass analysis reveals why such designs have so many potential advantages over reflex and infinite baffle designs. The upper bass is completely absorbed by the line allowing a clean and neutral response. The lower bass is extended effortlessly and distortion is lowered by the line’s control over the drive unit’s excursion. One of the exclusive benefits of a TL design is its ability to produce very low frequencies even at low monitoring levels – TL speakers can routinely produce full range sound usually requiring a [[subwoofer]], and do so to very high levels of accuracy. The main disadvantage of the design is that it is more labor-intensive to create and [[Accordatura|tune]] a high quality and consistent transmission line, compared to building a simple enclosure. A 2010 Hifi Avenue TL speaker review commented that "One thing I have noticed about transmission line designs is that they create a rather big [[Teatro di posa|soundstage]] and seem to handle crescendoes with ease".

== Storia ==
=== Invenzione e primi usi ===
[[File:Transmission-line.png|destra|miniatura|319x319px|This image is actually an inverted folded horn. You can tell as the throat is larger than near the port opening. A true Transmission Line enclosure is the same width 'vent' throughout.
.]]
The concept was innovated within acoustic enclosure design, and originally termed an "acoustical labyrinth", by acoustic engineer and later Director of Research Benjamin Olney, who developed the concept at the Stromberg-Carlson Telephone Co. in the early 1930s while studying the effect of enclosure shape and size on speaker output, including the effect of "extreme length in a box baffle".<ref>{{Cita pubblicazione|volume=19|doi=10.1109/JRPROC.1931.222439|url=http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1671032&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F10933%2F35025%2F01671032.pdf%3Farnumber%3D1671032}}</ref> A patent was filed in 1934.<ref>[http://www.google.com/patents/US2031500?dq=carlson+labyrinth Original 1934/1936 "Labyrinth" patent, invented by Benjamin Olney and filed by Stromberg-Carlson Telephone]</ref> The design was used in their console radios beginning in 1936.<ref name="Stromberg-Carlson">{{Cita web|url=http://www.radiomuseum.org/r/stromberg_acoustical_labyrinth_837.html}}</ref> A loudspeaker enclosure based on the concept was proposed in October 1965 by Dr A.R. Bailey and A.H. Radford in ''Wireless World'' (p483-486) magazine.<ref name="bailey1965">[http://diyaudioprojects.com/Technical/Papers/Non-resonant-Loudspeaker-Enclosure-Design.pdf A R Bailey, “A Non-resonant Loudspeaker Enclosure Design”], Wireless World October 1965 P483-486</ref> The article postulated that energy from the rear of a driver unit could be essentially absorbed, without damping the cone's motion or superimposing internal reflections and resonance, so Bailey and Radford reasoned that the rear wave could be channeled down a long pipe. If the acoustic energy was absorbed, it would not be available to excite resonances. A pipe of sufficient length could be tapered, and stuffed so that the energy loss was almost complete, minimizing output from the open end. No broad consensus on the ideal taper (expanding, uniform cross-section, or contracting) has been established.

=== "Classici" ===

: '' Source for much of this section: Loudspeakers: for music recording and reproduction (Newell & Holland, 2007)''&nbsp;<ref name="modern transmission lines"/>

The birth of the modern transmission line speaker design came about in 1965 with the publication of A R Bailey’s article in Wireless World, “A Non-resonant Loudspeaker Enclosure Design”, detailing a working Transmission Line. Radford Audio took up this innovative design and briefly manufactured the first commercial Transmission Line loudspeaker. Although acknowledged as the father of the Transmission Line, Bailey’s work drew on the work on labyrinth design, dating back as early as the 1930s. His design, however, differed significantly in the way in which he filled the cabinet with absorbent materials. Bailey hit upon the idea of absorbing all the energy generated by the bass unit inside the cabinet, providing an inert platform for the drive unit to work from; unchecked, this energy produces spurious resonances in the cabinet and its structure, adding distortion to the original signal.

Shortly thereafter the design entered mainstream [[Alta fedeltà|Hi-Fi]], through the works of Irving M. "Bud" Fried in the United States, and a [[Britannici|British]] trio: John Hayes, John Wright, and David Brown. Dave D'Lugos describes the period that followed (approx. 35 years until the start of the 21st Century) as a period when the "classical designs" were created.

Fried was exposed during his time at [[Università di Harvard|Harvard University]] to high fidelity audio reproduction, and later became an importer of audiophile items. Under the [[Marchio registrato|trademark]] "IMF" (his initials), from 1961, he eventually became involved with many advancements in [[Audiofilo|audiophile]] equipment: cartridges (IMF – London, IMF – Goldring), tone arms (SME, Gould, Audio and Design), amplifiers (Quad, Custom Series), loudspeakers (Lowther, Quad, Celestion, Bowers and Wilkins, Barker, etc.).<ref name="norton">{{Cita web|url=http://www.hometheater.com/content/coda-irving-m-fried}}</ref> In 1968 he met John Hayes and John Wright, who had already designed an award winning tone arm in the UK and had brought along a transmission line speaker designed by John Wright - described by Hayes as "fanatical regarding quality"&nbsp; - in order to promote and demonstrate the tone arm at a New York hifi show. Irving unexpectedly received a number of orders for the unnamed speaker, which he dubbed the "IMF". The British pair, along with Hayes' colleague David Brown, agreed to form a UK company to design and manufacture speakers which would be sold by Irving in the United States. John Hayes later wrote that:

: ''Of course, Bud, had called it the IMF, and therefore, perhaps mistakenly we registered IMF and formed an IMF company... At no time did Bud Fried have any input on the designs. We sold him speakers and he was the US Distributor...''&nbsp; [...] ''Bud Fried was never a Director or shareholder of IMF Electronics. IMF electronics were the only company manufacturing the transmission line speakers. The name IMF was adopted because Bud Fried had demonstrated the first prototype speakers at the New York hi fi show, and because of the publicity and the fact that he had used his name on the then unnamed speakers, we stuck with the name which was a mistake on our part. It was never his company. After our lawsuit he called his speakers Fried''.

The relationship broke down acrimoniously when Irving began to make his own, poorer quality speakers, also marketed as "IMF", and refused to cease until a court agreed that the UK business had the right to the trademark IMF for loudspeakers. Following the split, Irving in the USA (under the [[Marca (commercio)|brandname]] "Fried") and the three founders of IMF Electronics in the UK (via a [[joint venture]] with driver manufacturer Elac under the name TDL), both became well known in audiophile circles for many years as major advocates of transmission line speaker design. TDL closed after John Wright's gradual failing of health and death in 1999 from [[Neoplasia|cancer]]. He was described in his 1999 obituary as "one of the most important figures on the British hi-fi scene since the mid-1960s... best remembered for his transmission-line loudspeaker designs".<ref>{{Cita web|url=http://www.stereophile.com/news/10468/index.html}}</ref> The brand was acquired by Audio Partnerships (part of retailer group Richer Sounds). Freid died six years later, in 2005.<ref>{{Cita web|url=http://www.soundandvision.com/content/coda-irving-m-fried}}</ref>

=== Nuova era ===
In the early 21st century,{{when|date=November 2014}} [[Modello matematico|mathematical models]] that seemed to approximate the behavior of real-world TL speakers and cabinets, began to emerge. According to the website t-linespeakers.org, this led to an understanding that what he termed the "classical" speakers, designed largely by "trial and error", were a "good job" and the best that was reasonably possible at those time, but that better designs were now achievable based on modeled responses.

== Principi ==
[[File:TL_Phase.jpg|destra|miniatura|Fig. 1 - Relationship between TL length and wavelength]]
[[File:TL_measurement.jpg|miniatura|Fig. 2 - Frequency response (magnitude) measurement of Drive unit & TL outputs]]
Phase inversion is achieved by selecting a length of line that is equal to the quarter wavelength of the target lowest frequency. The effect is illustrated in Fig. 1, which shows a hard boundary at one end (the speaker) and the open-ended line vent at the other. The phase relationship between the bass driver and vent is in phase in the pass band until the frequency approaches the quarter wavelength, when the relationship reaches 90 degrees as shown. However by this time the vent is producing most of the output (Fig. 2). Because the line is operating over several octaves with the drive unit, cone excursion is reduced, providing higher SPL’s and lower distortion levels, compared with reflex and infinite baffle designs.

The complex loading of the bass drive unit demands specific [[Parametri di Thiele & Small|Thiele-Small driver parameters]] to realise the full benefits of a TL design. Most drive units in the marketplace are developed for the more common reflex and infinite baffle designs and are usually not suitable for TL loading. High efficiency bass drivers with extended low frequency ability, are usually designed to be extremely light and flexible, having very compliant suspensions. Whilst performing well in a reflex design, these characteristics do not match the demands of a TL design. The drive unit is effectively coupled to a long column of air which has mass. This lowers the resonant frequency of the drive unit, negating the need for a highly compliant device. Furthermore, the column of air provides greater force on the driver itself than a driver opening onto a large volume of air (in simple terms it provides more resistance to the driver's attempt to move it), so to control the movement of air requires an extremely rigid cone, to avoid deformation and consequent distortion.

The introduction of the absorption materials reduces the velocity of sound through the line, as discovered by Bailey in his original work. L Bradbury published his extensive tests to determine this effect in an AES Journal in 1976 <ref>L J S Bradbury “The Use of Fibrous Materials in Loudspeaker Enclosures” Journal of the Audio Engineering Society April 1976 P404-412</ref> and his results agreed that heavily damped lines could reduce the velocity of sound by as much as 50%, although 35% is typical in medium damped lines. Bradbury’s tests were carried out using fibrous materials, typically longhaired wool and glass fibre. These kinds of materials however produce highly variable effects that are not consistently repeatable for production purposes. They are also liable to produce inconsistencies due to movement, climatic factors and effects over time. High specification acoustic foams, developed by manufacturers such as PMC, with similar characteristics to longhaired wool, provide repeatable results for consistent production. The density of the polymer, the diameter of the pores and the sculptured profiling are all specified to provide the correct absorption for each speaker model. Quantity and position of the foam is critical to engineer a low pass acoustic filter that provides adequate attenuation of the upper bass frequencies, whilst allowing an unimpeded path for the low bass frequencies.

=== Mathematical equations, modelling, and design process ===

: ''The [[Transmission line loudspeaker#External links|external links]] section of this article links to a number of resources that detail the mathematical principles, models, and DIY calculations, as well as extended practical design material, related to transmission line speakers.''

For most of the 20th century, transmission line design remained more of an art than a science, requiring much trial and error. Jon Risch states in an article on classic transmission line design, that the hard part was finding the best stuffing density along the line's length, because "the line stuffing affects both the total apparent line length AND the total apparent box volume simultaneously". He summarized the state of design at the time as:<ref name="risch">{{Cita web|url=http://www.t-linespeakers.org/design/classic.html}}</ref>

: "The classic transmission line bass enclosure has never been completely and successfully [[Modello matematico|modeled]] such that it can be built from a pat set of [[Equazione|equations]]. Some claim to have done this, but it doesn't seem to allow a first time build without adjustments, so the models have enough wrong to require a fudge factor..."&nbsp;

Dave D'Lugos, founder of fan site t-linespeakers.org, comments that this reflects the "classical" designs from the 1960s until Risch's writing, during which period "TL design was seat of the pants".<ref name="rmf">{{Cita web|url=http://www.t-linespeakers.org/readme1st.html}}</ref>

However from the 21st century, Martin King and George Augspurger (both separately and referencing each other's works), produced models which show these to be "generally less than optimal" designs which "did a good job of approaching what was possible in their day". Audio engineer Augspurger had modeled TL using an electrical analogy, and found it to agree closely with King's existing work, based on a mechanical analogy. D'Lugos concluded in his overview of TL modeling and design theory: "I think that using modern drivers & tools such as King's software you can build a better TL easier today".
-->

== Principali costruttori ==
Pionieri:

* Benjamin Olney - con la sua idea originaria di "acoustic [[Labirinto|labyrinth]]", mentre lavorava alla [[Stromberg-Carlson]] come acoustic engineer e studiò l'aspetto fisico del fenomeno.
* Bailey e Radford - svilupparono assieme un disegno di diffusore nel 1965.
* [[John Wright (audiophile designer)|John Wright]] assieme a John Hayes e David Brown, con la IMF Electronics Ltd (ovvero [[TDL Electronics]]) - Wright, disegnò un braccio per giradischi e per provarlo nella sua superiore qualità audio si recò a New York per prendere un diffusore Tl non commerciale. Decisero così di produrre diffusori acustici con tale principio vincendo anche premi (1968). TDL venne sciolta dopo la morte di Wright nel 1999 e il marchio comprato da Richer Sounds.
* [[Irving M. Fried|Irving M. "Bud" Fried]] - incontrò Wright e Hayes nel 1968, e commercializzò i diffusori di questi negli USA. Più tardi creò lui stesso un'azienda costruttrice.
* Martin King e George Augspurger - ricercatori.

Altri:

* [[Lentek]], Newtronics (Temperance line), Gini B+ (Bass Extenders line), T+A Electronics (Criterion line), J M Reynaud,<ref>{{Cita web|url=http://www.jm-reynaud.com/jmr_us/produits.html|titolo=Copia archiviata|accesso=30 maggio 2018|urlarchivio=https://web.archive.org/web/20150906185032/http://www.jm-reynaud.com/jmr_us/produits.html|dataarchivio=6 settembre 2015|urlmorto=sì}}</ref> [[PMC Ltd.|PMC]], Salk Sound, [[Rega (fiume)|Rega]] (their RS7), Adelaide Speakers, TBI Audio Systems LLC (subcontracted by Asis to research and design smaller TL speakers suitable for embedding into [[Computer portatile|laptops]]),<ref>{{Cita web|url=http://www.tbi-asia.com/zh/news.html}}</ref> [[Marantz]] (Karoke range), Merkel Acoustic Research/Jeff Merkel,<ref>{{Cita web|url=http://merkelacoustics.com/about-2/|titolo=Copia archiviata|accesso=30 maggio 2018|dataarchivio=8 gennaio 2018|urlarchivio=https://web.archive.org/web/20180108014148/http://merkelacoustics.com/about-2/|urlmorto=sì}}</ref> Decibel Hifi (also kit manufacturer),<ref>{{Cita web|url=http://www.decibelhifi.com.au}}</ref> Albedo (Helmholine range), Transmission Audio,<ref>{{Cita web|url=http://www.transmissionaudio.com/}}</ref> Audio Reference (Acoustic Zen line),<ref>{{Cita web|url=http://www.audioreference.co.nz/product/acoustic-zen-adagio-floorstand-2w-transmission-line-speakers-burr-maple|titolo=Copia archiviata|accesso=30 maggio 2018|urlarchivio=https://web.archive.org/web/20180312012150/http://www.audioreference.co.nz/product/acoustic-zen-adagio-floorstand-2w-transmission-line-speakers-burr-maple|dataarchivio=12 marzo 2018|urlmorto=sì}}</ref> Radford,<ref>{{Cita web|url=http://www.t-linespeakers.org/classics/radford.html}}</ref>

DIY kit:

* UK - [http://www.iplacoustics.co.uk IPL Acoustics] ([https://web.archive.org/web/20141029003346/http://www.tubedistinctions.co.uk/ipl.htm article]), [http://www.falconacoustics.co.uk/drive-units-1/seas-drive-units/seas-diy-loudspeaker-kits-speakers.html Falcon Acoustics] "Thor"
* USA - [http://gr-research.com/n3.aspx GR Research] {{Webarchive|url=https://web.archive.org/web/20180529173147/http://gr-research.com/n3.aspx |date=29 maggio 2018 }} "N3"
* Australia - [http://www.redspade.com.au Red Spade Audio] {{Webarchive|url=https://web.archive.org/web/20170726000337/http://www.redspade.com.au/ |date=26 luglio 2017 }} "LSK TL6", "Etude TL", etc, [http://www.decibelhifi.com.au/diy-speaker-kits Decibel HiFi]
* USA - New York Acoustics, loosely associated with New York Audio Labs [http://www.meta-gizmo.org/index.html], kits and plans for 8" and 10" driver TL speaker cabinets, active in the mid 80's.

== Note ==
<references />

== Voci correlate ==
* [[Diffusori acustici]]
* [[Risposta in frequenza]]

== Altri progetti ==
{{interprogetto}}

== Collegamenti esterni ==
* [http://www.t-linespeakers.org/ Transmission Line Speakers Pages] – TL projects, history & more
* [http://www.quarter-wave.com Quarter-wave.com] – by Martin J King, developer of TL modeling software; also includes design calculations for professional and DIY TL speaker creation.
* https://web.archive.org/web/20180510080408/http://www.loudspeakerdesign.co.uk/transmission_line.php
* http://www.perrymarshall.com/articles/industrial/transmission-line/ - mathematics of the TL speaker, Perry Marshall
* [https://web.archive.org/web/20091027112701/http://geocities.com/rbrines1/Articles.htmlBrines Acoustics Articles] ([ Archived] 2009-10-24) – Application, tips, essays
* [https://web.archive.org/web/20061207142016/http://www.diracdelta.co.uk/science/source/q/u/quarter%20wave%20tube/source.html Quarter Wave Tube - DiracDelta.co.uk] - description of operation, equation and online calculation
* [http://www.directacoustics.com/lexicon.pdf Loudspeaker Handbook and Lexicon, Windslow Burhoe, 1978 (revised 1995/95/97)] - has a sizeable section on TL speakers.

; Articoli scientifici
* [http://diyaudioprojects.com/Technical/Papers/Non-resonant-Loudspeaker-Enclosure-Design.pdf A Non-resonant Loudspeaker Enclosure Design] - Bailey's original 1965 paper
* [http://diyaudioprojects.com/Technical/Papers/Transmission-Line-Loudspeaker-Enclosure.pdf The Transmission-Line Loudspeaker Enclosure: A re-examination of the general principle and a suggested new method of construction] - Bailey's 1972 follow-up paper
* Papers and documents related to Olney's original "Acoustic Labyrinth":
** [http://scitation.aip.org/content/asa/journal/jasa/8/2/10.1121/1.1915883 Acoustic Society of America paper, 1936]
** [http://p10hifi.net/planet10/TLS/downloads/Acoustic-Labyrinth-Olney.pdf Followup paper, 1937]
** [https://www.google.com/patents/US2031500?dq=carlson+labyrinth 1934/1936 "Labyrinth" patent, filed by Stromberg-Carlson Telephone Manufacturing Co.]
** [http://beta.worldcat.org/archivegrid/collection/data/871407477 Archive of Olney's papers at Rush Rhees Library, University of Rochester]

{{portale|musica|ingegneria|scienza e tecnica}}

[[Categoria:Ingegneria acustica]]