Yes a TL (as we usually see them) is a quarter-wave.
The term TL is commonly used to talk about the subset of lines that are like those in the past, and in a much wider sense that includes most if not all quarter-wave (or half-wave) designs. This can (and does) cause some confusion.
dave
The term TL is commonly used to talk about the subset of lines that are like those in the past, and in a much wider sense that includes most if not all quarter-wave (or half-wave) designs. This can (and does) cause some confusion.
dave
A true "backhorn" is not reliant on quarterwave resonances, though most constructions face this as a challenge due to the box style builds often used. Many backhorns are not horns at all but hybrid TL/BR/Horn devices.
The 1/4 wave or 1/2 wave resonance are both undesirable results of the TL and or rear horn. The concept is delay and the reflection induced resonances are a necessary evil.
True enough, haha, yes i should expect both odd and even harmonics aplomb, and again yes, a mess i should think. im thinking it MAY be possible, although i have not tried doing the math and seeing if it is practicable or not. i just figured that MAYBE the sectional resonances could be used to dampen some of the undesirable harmonics generated by the total pipe length, in a similar way to which some designers use helmholtz resonators:
http://www.visaton.de/bilder/zeichnungen/gross/vib130tl_tz1.gif
At least, i know it COULD be possible haha, maybe......
ah ha! ok... lol i think i misunderstood......i agree, they should be suppressed..or avoided if at all possible.
I would say no that is not accurate. The l/4 resonance is what makes a TL work as well as a vented design and is required; the behavior is completely analogous. The l/2 resonance is detrimental in that it causes response irregularities.
Perhaps symantic, but the concept of TL as I understood it was to delay the rear to be in phase with the front. This does not require a resonance at all. That the design could be configured to see a benefit from a resonance is quite possibly true.
I should probably stay out of this discussion since I am not an expert on TL designs and what works and what doesn't. I long ago stopped caring much about specific LF tunings and designs since I see the solution to LFs in room to be the use of multiple sources and "bass managment" - how the individual sources are designed is a distant secondary concern IMO. To me, they will most likely all work the same once properly setup.
The delay model is old, first promoted by Bailey as I recall, and perhaps a few other papers in the 1960s or 70s. It was inaccurate based on the well established theories and what is seen in experimental models.
With regard to all the confusion concerning the walls of the pipe, people need to consider the time varying pressure and volume velocity profiles down the line. These are analogous to voltage and current in the electrical analogy. Simple question, what does a rigid boundary provide - the volume velocity must be zero at the walls because no air can flow through the boundary. The radiated output is a function of the volume velocity at the port and cone, the total system output is the vector sum of the two.
People questioning this need to read a basic text on acoustics, Beranek or perhaps something more basic. The OP questioning end correction demonstrates that he also has not read a basic text on acoustics.
And trust me, my paper would not have been accepted if the electrical analogy was not a precise analogy - it is.
People questioning this need to read a basic text on acoustics, Beranek or perhaps something more basic. The OP questioning end correction demonstrates that he also has not read a basic text on acoustics.
And trust me, my paper would not have been accepted if the electrical analogy was not a precise analogy - it is.
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I thought that in a traditional tapered TL there would be close to no output from port opening, hence the low efficiency
Isnt it merely a design to get very tightly controlled high mass coupling, thus very low tuning of driver
Shouldnt the deep bass come from driver, due to the low tuning, and not from port
Isnt it merely a design to get very tightly controlled high mass coupling, thus very low tuning of driver
Shouldnt the deep bass come from driver, due to the low tuning, and not from port
Normally, pass band efficiency for direct radiator systems has little to do with the box that you put the driver in. There are a few things that can make a TL have lower efficiency, mass loading which does not occur at all frequencies, and if heavy damping is placed directly behind the driver it can also cause increased mass loading and more acoustical resistance for an effectively lower Qms and therefore Qt.
You mention tapered, do you mean the slightly tapered style used in the old IMF TLs? Let's take those as an example. I have heard the version with a single KEF B200 (8") per side shake a room with powerful low bass. Test reports on those designs, the version with the KEF B139 for example, showed an amplitude response that was only a few dB down at 25 Hz, and distortion that was significantly lower than nearly any other home design of that time. Keep in mind that most systems are 10 dB or more down at 25 Hz.
Do you think a single 8" or the B139 has enough volume displacement to accomplish this without port augmentation? No, most of the output comes from the line in the deep bass, just as it does from the port of a vented design. Bailey also claimed that there was virtually no output from the port and I have never seen this in any TL even with heavy fill. Such low frequencies are difficult to attenuate completely. I have to wonder if Bailey actually measured anything.
Perhaps I'll start a new thread explaining how a lumped vented system works and how it is analogous to a l/4 TL. I have a feeling that there is a lot of confusion about vented systems also.
So, what is the magic behind a TL? Consider the huge boxes used in the IMF designs, imagine if you built a traditional vented design with a B139 for example in something like 4 cu ft with a very large port (for minimal compression) tuned to 25 Hz. The large box and large port will provide much more output at port tuning than say a 1-2 cu ft box. To be more specific design something around a B4 or B6 alignment with a B139 and run the sims, now, double the size of the box run the sims again. You should see 4 to 6 dB more output at Fb. This is tremendous, 6 dB is like having 4 times the acoustical output. This is most of what is going on with those big old TLs - this and a few more considerations.
You mention tapered, do you mean the slightly tapered style used in the old IMF TLs? Let's take those as an example. I have heard the version with a single KEF B200 (8") per side shake a room with powerful low bass. Test reports on those designs, the version with the KEF B139 for example, showed an amplitude response that was only a few dB down at 25 Hz, and distortion that was significantly lower than nearly any other home design of that time. Keep in mind that most systems are 10 dB or more down at 25 Hz.
Do you think a single 8" or the B139 has enough volume displacement to accomplish this without port augmentation? No, most of the output comes from the line in the deep bass, just as it does from the port of a vented design. Bailey also claimed that there was virtually no output from the port and I have never seen this in any TL even with heavy fill. Such low frequencies are difficult to attenuate completely. I have to wonder if Bailey actually measured anything.
Perhaps I'll start a new thread explaining how a lumped vented system works and how it is analogous to a l/4 TL. I have a feeling that there is a lot of confusion about vented systems also.
So, what is the magic behind a TL? Consider the huge boxes used in the IMF designs, imagine if you built a traditional vented design with a B139 for example in something like 4 cu ft with a very large port (for minimal compression) tuned to 25 Hz. The large box and large port will provide much more output at port tuning than say a 1-2 cu ft box. To be more specific design something around a B4 or B6 alignment with a B139 and run the sims, now, double the size of the box run the sims again. You should see 4 to 6 dB more output at Fb. This is tremendous, 6 dB is like having 4 times the acoustical output. This is most of what is going on with those big old TLs - this and a few more considerations.
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interesting..i have often wondered if that were the case with a ported system, although i was always (lead to believe at least) that a larger than 'optimal' Vb would lead to poor power handling, (high Vb/Vas ratio) and i have thus avoided experimenting with it.
and yes the analogy of a TL or many speaker types is readily compared to an electrical circuit,m and is acurate enough. In the case of the TL its a great deal better than the haphazard method used early on, although without these then the current theory wouldnt exist i guess.
and yes the analogy of a TL or many speaker types is readily compared to an electrical circuit,m and is acurate enough. In the case of the TL its a great deal better than the haphazard method used early on, although without these then the current theory wouldnt exist i guess.
Lets please remember that these "circuit" type analogies are limited to LFs. Even at the first resonance of the TL these electrical circuits analogs are no longer valid. And as far as the total bandwidth of our hearing goes, circuit models only work for a very small fraction of it. A portion, in fact, where the room effects dominate any model of the enclosure itself. IMO, Circuit analogs are way overblown in how useful they are.
Your claim that "Even at the first resonance of the TL these electrical circuits analogs are no longer valid" is entirely wrong; what is the basis for this claim?
Small fraction of our total hearing? A woofer itself only covers a small fraction of our hearing so what are you talking about? The breakup modes? So tell me what analysis would you use that would cover the low bass _and_ the breakup modes? The fact is that it is completely reasonable to treat these independently and measure the breakup modes because there is no way to easily predict them.
You throw in the room to invalidate the analysis; so what type of analysis do you suggest as an alternative, one that would include Max SPL predictions? The simple answer to use multiple subs that you repeat over and over and want to sell people? To take you seriously would be dismissing all the work of Thiele and Small and those that followed modeling even more complex systems.
You write "IMO, Circuit analogs are way overblown in how useful they are". The fact is that they are incredibly powerful particularly due to the fact that the methods and mathematics for analysis of electrical circuits is well developed. Your an expert in the field; show us your TL simulator based on your methods that would be so much better and more accurate. The fact is that you just demonstrated a few posts back that your understanding is based on one paper from the 1960s.
One thing that I dislike about people who are misleading on the Internet is that there are students who might actually believe what someone like you writes and then spout off similar erroneous claims.
Sometimes it is hard to believe the things people say on the Internet! But then you want to sell multiple subs ....
Small fraction of our total hearing? A woofer itself only covers a small fraction of our hearing so what are you talking about? The breakup modes? So tell me what analysis would you use that would cover the low bass _and_ the breakup modes? The fact is that it is completely reasonable to treat these independently and measure the breakup modes because there is no way to easily predict them.
You throw in the room to invalidate the analysis; so what type of analysis do you suggest as an alternative, one that would include Max SPL predictions? The simple answer to use multiple subs that you repeat over and over and want to sell people? To take you seriously would be dismissing all the work of Thiele and Small and those that followed modeling even more complex systems.
You write "IMO, Circuit analogs are way overblown in how useful they are". The fact is that they are incredibly powerful particularly due to the fact that the methods and mathematics for analysis of electrical circuits is well developed. Your an expert in the field; show us your TL simulator based on your methods that would be so much better and more accurate. The fact is that you just demonstrated a few posts back that your understanding is based on one paper from the 1960s.
One thing that I dislike about people who are misleading on the Internet is that there are students who might actually believe what someone like you writes and then spout off similar erroneous claims.
Sometimes it is hard to believe the things people say on the Internet! But then you want to sell multiple subs ....
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Depends on how they are done. T-matrix models are an order of magnitude more acurate than lumped parameter, but still lack the accuracy to cover the bandwidth of hearing, or even get to the critical range of 1-3 kHz.
Rooms are than "important", they dominate the LF regime. Everyone accepts this, its not just me.
You really need to be more specific here. The lumped model is valid and accurate for all frequencies where the wavelengths are long compared to the dimensions of the acoustical elements. Usually good below 200 Hz, and much higher for a small bookshelf or mini monitor.
Also, consider the intent for these lumped models, which was to model very low frequencies! The fact that they are often good to 200, 300, and sometimes 500 Hz (for very small systems) is just a bonus. How else would you model the very low end and apply all the well known characteristics of classical filter theory?
Know your tools, understand their limitations.
Guys,
Discuss the idea, not the person. I have just had to delete a number of posts, some decent technical discussion was collateral damege. Feel free to repost technical stuff.
dave
Discuss the idea, not the person. I have just had to delete a number of posts, some decent technical discussion was collateral damege. Feel free to repost technical stuff.
dave
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