Talk:Acoustic transmission line

There is a reflection from an open ended pipe - try Frank Fahy's book "Foundations of Engineering Acoustics" and look up pressure release. How could there be a resonance of the pipe if there was no reflection?

Also, cavitation is the process of bubbles forming in a liquid. Although I understand your metaphor, i think the use of this terminology in this context is misplaced/confusing. — Preceding unsigned comment added by 62.189.28.130 (talk) 11:25, 8 February 2012 (UTC)

Another question along those lines, ask yourself, can a tube of fixed length with any open or closed end configuration exhibit standing waves? If so, how can this occur without a reflected wave of some non-zero magnitude and some phase offset? I like the revision as of 17:10, 19 November 2010 best, and think that the page should either be restored to that point, or references regarding cavitation and claims that transmission line theory doesn't apply should be replaced with correct information, backed-up with references from technical journal articles, such as Keefe, Journal of Acoustic Society of America, 1984, or other such academic material that makes use of the wave equation. The main problem here is that this article's scope embodies (1) a loudspeaker design concept design for music listening and (2) a broader applied engineering and theoretical analysis topic that may apply to ultrasound, or test and measurement. -SJP

-- — Preceding unsigned comment added by 62.189.28.130 (talk) 11:21, 8 February 2012 (UTC) A number of non experts (Mardis) have contributed to this page insisting that "reflections" are occurring at the end of an open pipe (open ended acoustic transmission line). This common misconception misplaces Helmholtz resonance for the special case of open pipe resonance in which a loudspeaker seals off one end of the pipe or transmission line duct. They are not equivalent phenomena. Helmholtz resonance requires constant radial displacement of air at the open end of the pipe - resulting in a build up of pressure within the cavity which is subsequently purged in accordance with the time required for a specific volume of air to fill said cavity and then exit. By contrast, the acoustic transmission line is excited by a transducer with oscillating axial air flow pulses. This results in resonances and anti resonances at the terminus which are a function of the transducer's resonance - not the fixed dimensions of a sealed cavity. George Augspurger's data confirms that open pipe resonance is centered upon the exciting transducer's fundamental resonance. Altering the length of the pipe only conceals (attenuates) or reveals (accentuates) the harmonic multiples of resonance (odd ordered harmonics) and anti-resonance (even ordered harmonics). If the transmission line terminus were closed, then peak resonance would occur at odd ordered harmonics of the pipe's fundamental with peak anti-resonance occurring at even ordered harmonics of the pipe's fundamental. The roles of the transducer and pipe would then reverse - with the transducer serving to accentuate resonances where its fundamental (Fs) or odd ordered harmonics thereof happen to coincide with the pipe's fixed dimensions. When the driver's odd ordered harmonics don't fit evenly within the pipe's fixed dimensions, resonances are attenuated to the extent by which wave peaks are generated up to a quarter wavelength away from the pipe's rigid boundary. In other words, open pipe resonance is primarily a function of the exciting element's fundamental resonant characteristic while closed pipe resonance is primarily a function of the pipe's fundamental resonant characteristic. The notions of "reflection" occurring at the open end of an acoustical transmission line demonstrate substantial misunderstanding of the fundamentals of acoustics which require a sizable change in media density for reflection to take place. Anyone who intends to contribute a point of view that is contrary to this most basic understanding should be required to cite experimental data demonstrating this phenomenon of open ended "reflection". —Preceding unsigned comment added by 66.31.194.18 (talk) 16:36, 19 November 2010 (UTC)

I have a few problems with the list of transmission line attributes

1. virtually no sound emanating from the enclosure except the loudspeaker;

That is OK, but applies even more to a closed box.


 * ''I don't think that is correct. The port in a TL is tuned such that the port output is highest where the second electrical impedance peak is reached. Whatever this frequency is, most of it is then heard at the port. This contradicts #1, and a closed box would likely have more sound, not less, coming from the cabinet due to standing waves.
 * ''Desmoid (talk) 18:57, 7 January 2008 (UTC)

2. precisely defined imaging, particularly in the bass region and vocals;

This is not a function of transmission line loading. This is to do with the detailed design of the speaker, particularly for vocals which are generally above the band where TL operation becomes dominant.

3. precicely timed bass without echo or reverberant 'booming';

Bass timing is a function of many factors, of which the box is just one. Any speaker is resonant and a TLS is no less so than any other. As for reverberation, that does not apply in a space so small and well damped as a speaker enclosure.

4. excellent transient response and uncompressed dynamics;

Transient response is a function of the upper part of the response curve, not the bass. So things like crossovers and phase matching with tqweeters determine transient response. Dynamic compression has absolutely nothing to do with transmission lines. That is a function purely of the driver design.

5. typically, extended bass below a half wave frequency of the reflected line length e.g. 30Hz=8foot length;

No. The bass extension depends solely on the resonance frequency of the driver, provided the TL is long enough.

6. typically, even loudspeaker-impedance, from the unchanging consistent load(no reflection resonances);

Again no. A good TL will leave the resonance of the driver unchanged. That means a large resonance peak at the primary driver resonance. Reflection resonances will occur with a TL speaker to just as great an extent as any other, since it must couple power to the room.

7. high efficiency.

The efficiency of a speaker is determined solely by the design of the driver. You cannot change it with the cabinet loading design.

—Preceding unsigned comment added by 81.174.169.10 (talk) 07:48, October 2, 2007

Some answers for these numbers from my personal point of view:

1. One idea of a transmission line is that the driver will not cause enclosure resonances as in a closed box.

2.&3. Yes, but a transmission line design is part of the design of a speaker, of course there are other details.

5. I guess it is meant that the bass is extended because the output of the line (from the rear of the driver) is added to the front output of the driver in phase if the length is half the wave length. BTW, the resonance frequency of a driver depends on the enclosure.

6. It is meant that there is no reflection onto the rear of the driver from the inside of the cabinet as in a closed box. Therefore a closed box leads to additional resonances of the driver causing uneven impedance curves.

7. No; of course the efficiency depends on the enclosure, see e.g. horns.

--Cyfal (talk) 21:04, 30 March 2009 (UTC)


 * I get the feeling the unnamed person who wrote that list has never heard a good transmission-line speaker. They do not sound the same as conventional woofers. This difference is usually ascribed to overdamping, which (sorry!) improves the driver's transient behavior. (This invalidates remarks #4, #5, & #6, suggesting that the unnamed contributor doesn't understand the resonant behavior of drivers.) The overdamping is also one of the reasons for extended response.


 * I seem to remember some Australian researcher producing a (claimed) valid model of transmission-line systems several years ago. (I have no reference.) Regardless, T-L systems have long been controversial. This article needs more work. WilliamSommerwerck (talk) 08:51, 7 June 2013 (UTC)

speaking tube
Amended introduction to include perhaps the most direct acoustic analog of a transmission line, the old fashioned speaking tube used widely in offices, ships, and elegant homes. Also pointed out wind instruments additional functions of production, modulating, and radiating sound in addition to transmission line function.

A clear explanation of the similarities and differences between transmission line theory of longitudinal acoustic versus transverse electromagnetic waves would be in order, but I don't know enough to supply it.CharlesHBennett (talk) 11:58, 16 September 2011 (UTC)

Article should be longer?
I think this is a good article, but i felt that it ended abruptly. I only have a passing knowledge of this material but I was just starting to understand what was being said when the article ended. — Preceding unsigned comment added by Longinus876 (talk • contribs) 17:07, 29 December 2011 (UTC)

The article does not go with the title of this Wiki page
This article, in my opinion, "hijacks" the subject of acoustic transmission lines. The first short paragraph of this article is fine, but instead of going into the theory and usefulness of modeling a tube as a transmission line, the article goes directly into a description of a type of audio speaker. People interested in modeling acoustics may be interested in the theory of acoustic waves in waveguides, and how the electrical analogy of a transmission line is used in lumped-element acoustics modeling. However, if one searches on acoustic transmission line, one gets this page about audio speakers. I was a senior research engineer at one of the largest audio speaker companies in the world, and we used the term "acoustic transmission line" to mean just that - it was never used to describe a type of speaker. — Preceding unsigned comment added by Ad000000 (talk • contribs) 22:59, 1 October 2013 (UTC)

i completely agree with this. i came to this page specifically to read about acoustic transmission lines, which need more detailed explanation than provided in the introduction. additionally, the material which should belong in an article on TRANSMISSION LINE SPEAKERS is not only awkwardly inserted and awkwardly worded, but its (apparently) lone author seems to be at odds with most people who write on the topic. i would suggest the article needs to be written in a style that is more harmonious to multiple viewpoints (isn't the reflection of an infinite number of impulses mathematically equivalent to the oscillation of a captured gas? isn't cavitation the formation of gas bubbles in a liquid and irrelevant to the discussion?) to avoid the appearance of being written by a green inker. acoustics is one of those fields like relativistic physics where dedicated amateurs frequently wander in and get confused on basic concepts while declaring they have eclipsed the experts. can we get an actual credentialed expert to pass judgment? and either way, if this can be separated into the appropriate two articles then it will be easier to isolate and fix difficulties (and maybe i will get to read about impedance changes in transmission lines) — Preceding unsigned comment added by 110.175.57.184 (talk) 08:39, 14 March 2014 (UTC)

Accuracy of 'older descriptions section is disputed - Dec 2015
Flagged the 'older descriptions' section as disputed, as discussed by others above. The section about the absence of any reflection from the open end of a pipe is completely wrong. Very basic physics tells us that a large impedance discontinuity will cause a reflection, and this is exactly what causes the resonance in an open pipe. I agree with others above, there seems to be a general lack of acoustics expertise in this and related articles.

'older descriptions' has been removed
See discussion above. I have particular expertise on this topic, but unfortunately not much free time at the moment. I'm hoping to find some time in the near future to 'fix' this article to fit it's more general title, explain the theory in detail and provide more reliable information about transmission line loudspeakers.

Qnivqu14 (talk) 09:53, 14 April 2016 (UTC)