Tannoy DC2528 Transmission Line build.

[Macca]

Working then?

[Marco]

Like it so far, Dunc, I shall be following this with interest!

Marco.

[struth]

Need to get you to make me up a flat pack dunc super job

[Ian Walker]

"Oh God ! What have I Created?"

Dunc...Are you alright there?

Has one just run across the room and eaten you!!

[danilo]

Had my interest until you said 1/4 wavelength.
http://www.quarter-wave.com/index.html

[Reffc]

Had my interest until you said 1/4 wavelength.
http://www.quarter-wave.com/index.html

Nothing wrong with a decent 1/4 wavelength design. Castle Acoustics with design leadership from Andy Hill are probably best known for their very successful implementation of the 1/4 wave design starting with the Chester Mk1 in 1988 (or thereabouts) and the Harlech, Howard and Winchester loudspeakers. Great sounding designs if you've ever managed to hear any.

[ScottL]

There is absolutely nothing wrong with a quality quarter-wave speaker, other than the fact that there is about a metric ton of myth and nonsense that has been attached to them. FWIW, a few basic points:

• 'Transmission Line' is in the majority of cases something of a misnomer. It has become a convenient catch-all phrase for all QW enclosure types, which means you can see it being trotted out for enclosures that are functionally opposites of each other. Since it's been ingrained into hi-fi terminology now, it's too late to get rid of it. Technically it comes from the electrical transmission line, so if the definition is applied strictly, it should be a line that is designed with the sole object of providing the flattest possible impedance, with zero other considerations. Of course, as noted, it's almost never used so narrowly. Bailey employed it in the title of his old '68 Wireless World article, and caused a massive amount of confusion by then proceeding to describe a line that was in fact partially resonant.
• A TL / QW type speaker is not a bass reflex. It differs in that the dominant resonant mode is derived from standing waves / eigenmodes not Helmholtz cavity resonance. If we compare the physics of (for example) a mass-loaded transmission line (MLTL) to a BR, the practical transition from one to the other can be said to occur when one dimension of the enclosure is stretched sufficiently for the eigenmodes generated to modify the enclosure alignment away from what would be obtained from the same Vb and vent dimensions under Helmholtz conditions (which assumes an internal uniform air particle density and no standing waves). Most MLTL designs are quite highly forced (significant mass loading) to keep the dimensions in check, but they still generate & exploit standing waves to an extent.
• Internal stuffing material does not significantly slow the speed of sound. It does a bit, but not much. That was Bradbury's theory -a very nice, elegant piece of maths, based on aerodynamic drag. Unfortunately it was wrong, as Augspurger, King & a number of others have subsequently illustrated. Naturally, different materials have different absorption properties, so stuffing densities tend to need to be adjusted on this basis, and some of the details will differ a little.
• The fundamental resonant frequency of a line is a function of axial length and taper, so simply taking c / (desired Fp / 4) only works for untapered pipes, and only then when you have factored in end-correction etc. A tapered pipe (narrowing toward the terminus) will have a lower fundamental than an untapered pipe for the same physical length. An expanding pipe (horn) will have a higher fundamental than an untapered pipe of the same physical length. In both cases, how much lower or higher depends on the degree of taper.
• Line cross sectional area has no functional relationship to driver Sd. Unfortunately that's one myth that has got itself particularly ingrained, and is arguably the cause of more unsuccessful QW enclosures than anything else, since it often ends up causing an insufficient internal volume.
• Tuning to the driver free air resonant frequency F0 is rarely optimal; like any other type of enclosure, line tuning depends on your particular objectives and the driver characteristics. Another one that's responsible for a lot of poor performing QW / TL boxes.

Rgds
Scott

[walpurgis]

Good quote Scott.

Having built several very effective 1/4 wavelength tapered TLs (and 1/4 w/l horns) I'd agree with what is said.

[danilo]

Erm OK.. Have any obtained and Tried... Martin Kings' worksheets ?
He's a Mathematician... his developed modelling/design formulas are More than simply good. State of the Art imo.
He claims/proves that once at 8" drivers, a 1/4 w and or a folded tube variant IS effectively a BR box.. with the attendant Math.

Nothing less than naive to design a 1/4 w or Folded line contraption.. without consulting Kings' works
They are a Proven design tool... learn the programs (easier said than done TBH ) and the results are as predicted.
A genuine 'cut once' solution to an Old problem
Those were Freely available.. until recently.
Sadly he has, due to persistent abuses removed the Free aspect.
Still available, if you ask nicely and pay a 'reasonable' fee.

Just trying to help here

[walpurgis]

I was perfectly happy using principles described by G A Briggs over fifty years ago.