TL's vs. Closed Box or Ported

[roddyama]

Hi All,

I've just started to look into TL's as a possible mid-bass configuration and I had a few questions since you can't use "TL" as a search criteria.

Is the responce of a driver in a TL box simular to that of an Infinite Baffle?

How do the T/S parameters differ from the Closed Box or Ported Box alignments?

Is the transient response generally better or worse then a Closed Box or Ported Box?

Thanks for your assistance
Rodd Yamashita

[planet10]

Rodd,

I am currently working a little TL for the Tangband W3-879 which will be used as a mid-tweeter.

A TL can be tuned to roll-off anywhere from 2nd order to 4th order and the phase, transient reponse, bass augmentation, etc will all be affected by your choices hen designing the line. (pretty open-ended answer ).

For a midrange thou you usually aren't trying for bass extension but to gain the advantages of flattening the resonant peak, and minimizing any time smear/reflections from coming back thru the cone (what i refer to as sucking the back-wave down the pipe). In this case you will no doubt what to push the TL towards the aperiodic end of the spectrum which results in FR similar to a sealed box (perhaps a bit better), with a flattened impedance curve, and excellent transient response.

dave

[roddyama]

Originally posted by planet10
For a midrange thou you usually aren't trying for bass extension but to gain the advantages of flattening the resonant peak, and minimizing any time smear/reflections from coming back thru the cone (what i refer to as sucking the back-wave down the pipe). In this case you will no doubt what to push the TL towards the aperiodic end of the spectrum which results in FR similar to a sealed box (perhaps a bit better), with a flattened impedance curve, and excellent transient response.

Exactly. More specifically, I am looking for a way to extend the usable low end of drivers like the TAD 1101H or the JBL 2123H that are made to xover to the woofer at >200Hz. I want to be able to use these drivers down to 70 or 80Hz if possible and xover to a sub-bass.

What type of TL should I use? How long is long enough? Is there a way of predicting the results of a design? After some searching this evening, I noticed that there isn't much quantitative information available beyond wavelength calculations.

Thanks,
Rodd Yamashita

[planet10]

Originally posted by roddyama
What type of TL should I use? How long is long enough? Is there a way of predicting the results of a design? After some searching this evening, I noticed that there isn't much quantitative information available beyond wavelength calculations.

A TL won't give you an octave & a bit -- maybe a half octave, and then only if you tune for bass efficiency.

The best available quantitative tool is Martin King's quarterwave modeling software. (Augspurger's is very close but just not very available)

It started out on my site http://www.t-linespeakers.org/projec...tin/index.html, and now has his own site http://www.quarter-wave.com/. There is also some excellent studies done by Bob Brines.

As well, but not out yet, are some alignments being generated by Rick Shultz (exolinear). Rick has been exploring the huge space of quarter-wave designs that Augspurger & King's models have opened up for exploration and what he is doing (my interpretation) is to set some strict parameters (ie line taper, terminus size, driver placement) and for this subset of quarter-wave space, come up with a brain dead easy way of plugging the T/S parameters in and getting a quarter-wave line out. alphaTL is the 1st (& should be published soon in aXp), i know he is working on more.

dave

[roddyama]

Thanks Dave,

I guess there are new frontiers left to explore, even in a technology as old as this one.

That make you a pioneer.
Rodd Yamashita

P.S.: If you don't mind, I'll have more questions later.

[Pjotr]

Hi,

One of my first big projects was the Rogers Monitor. It produced a lot of dry bas, but I never got it right and it ended in a disappointment for me. Later on the closed box with a Bessel alignment was my favourite, easy to build and a to tune. But in recent years I have heard well designed BR’s that gave cleaner bas response than a CB. To my idea the non-linear spring action of the enclosed air of a CB and the large excursion of the LS unit at lo frequencies are responsible for a load of distortion, harmonic as well as IM.

I am up for building a new set of speakers in the near future. After all those years of DIY speaker building I am still puzzled what topology to use. A TML has still a lot of attraction, because of the low pressures involved in the cabinet, smooth roll-off and low distortion. But I don’t want to go into a long trajectory of “Trial and Error”.

For a TML, I have an eye on the Audax HM170 or the HM210, or maybe one of the top 8” ones from Focal. I am planning a 3-way system with a x-over at app. 125Hz on the low end.

I have ploughed completely trough the articles on http://www.quarter-wave.com/, Good reading, but I have an uneasy feeling this mathematical way is not the way to go. Baily’s original articles are in itself very straightforward and I have the idea that there is no real progress in a methodology of designing a TML, except the work of Augspurger.

As well, but not out yet, are some alignments being generated by Rick Shultz (exolinear). Rick has been exploring the huge space of quarter-wave designs that Augspurger & King's models have opened up for exploration and what he is doing (my interpretation) is to set some strict parameters (ie line taper, terminus size, driver placement) and for this subset of quarter-wave space, come up with a brain dead easy way of plugging the T/S parameters in and getting a quarter-wave line out. alphaTL is the 1st (& should be published soon in aXp), i know he is working on more.

Is there some more reading about this on the internet Dave?

Chaio,

Peter

[planet10]

Originally posted by Pjotr
I have ploughed completely trough the articles on http://www.quarter-wave.com/, Good reading, but I have an uneasy feeling this mathematical way is not the way to go. Baily’s original articles are in itself very straightforward and I have the idea that there is no real progress in a methodology of designing a TML, except the work of Augspurger.

Well given that Augspurger's work and Martin King's work are equivalent to each other i don't know why you would say this. Martin's is a mechanical analog and George's is an electrical analog, but they both generate the same lines from the same data (Rick & Martin have confirmed this). Martin's model doesn't have as much limitation at the higher frequencies as George's.

So if you want to build a TL with confidence, download Martin's software & play. Augspurger's papers are a required read (3 part article in Speaker Builder or the revised version in the AES Journal) because they add some context to Martin's articles.

Is there some more reading about this on the internet Dave?

The bulk is at the 3 sites i mentioned.

dave

[planet10]

Originally posted by roddyama
I'll have more questions later.

That's what we are all here for

dave

[Pjotr]

Thanx Dave,

Well, I just started investigating building a TML a few months ago. Your site and Bob Brines site looks nice as a good start. I have no recent fundamental experience at all with TML’s. It is new adventure.

The reason that I am reserved about doing simulations on such a complex system as a TML is the many variables that are unknown numerically. Like the exact properties of the stuffing and the number of bends and the way the bends are implemented. Simulations never give you an idea how the final thing will sound except you have already a lot of experience with the subject. But you are right, tasting the pudding is in the eating.

On the other hand the rules look simple, the length of the line should be ¼ wave acoustically at the tuning frequency and preferably with no bends at all. To taper or not to taper seems a design choice to me. I will dig up again the JAES articles of Augspurger in the library this week.

Chaio

[Serow]

Thanks for the replies navin. I will probably have other questions for you regarding aperiodic enclosures, but I'll save those for a new thread. I'm leaning towards a aperiodic or no-terminus-output TL.

By the way I'm proposing a new, less cumbersome name for the latter: NOTL or No Output Transmission Line. Unless there is already a name for them that I don't know of.