Tractrix info?

[bobhayes]

Helloooo...

Can any helpful soul tell me how to calculate the lower and upper cutoff frequencies for a tractrix horn, or guide me to relevant information?

Cheers,

Bob

[planet10]

Is it covered in Dinsdale? (assumming you have the articles)

dave

[bobhayes]

Dinsdale recommends avoiding tractrix flares for mid/treble loading with a comment that they can be used if the mouth perimeter is reduced to 1 wavelength of the lowest frequency.
The three articles written for wireless world are based solely on exponential flares for the front horn (there are tables etc for tractrix bass horns), and are somewhat simplified to throat areas of sd/4 for back horns, and sd for mid/treble horns.
Unfortunately, Dinsdales tables do not correspond at all well to the simulations I have run on the Ishtek java applet, and I seem to get lower cutoff values considerably lower than Dinsdale suggests in his tables.
It looks like it's gonna be another case of trial and error!
Fortunately, I have finished the cabinets with the option to mess about with the front horn to some extent.

[Scottmoose]

Hell's teeth Bob! Impressive.

[bobhayes]

Thanks Mr. Moose.

[GM]

Greets!

Tractrix loads to within a 1/2 octave of its mouth cutoff, so if you want it to load all the way to Fc you'll need a bigger horn than if expo, but then you defeat some of the purpose of using it. Like any horn, its HFc will be a function of St and its wall angle, but I've never seen a formula for it, though it may be in Edgar's articles: http://www.volvotreter.de/dl-section.htm. Not being a fan of them per se, I've never bothered to pursue them beyond a comparison test I did ages ago. FWIW I've read that Hornresp does pretty accurate sims.

Nice woodworking BTW, I envy ya'll's patience!

GM

[bobhayes]

Thanks for the link GM... Very useful downloads!

I'm gonna spend a while trying different things out WRT the front horn. The flat side panels currently approxiomate to an exponential flare, with radii provided by the cabinet above and below the driver. I reckon the changable sides give me a little scope for experimentation, although it will never be ideal as I decided to make the throat height large enough to remove the driver from the front without stripping the cabinet.
I was reckoning that I could pick an appropriate x over f, play with compliance volume to align the bass horn to around -3dB at said f, then adjust the front horn to blend (mouth size and length for LFc, throat size for HFc around 2kHz where the whizzer starts to dominate).
The panels at the sides can overlap the driver to a degree, in order to reduce the throat area to maximise HFc, if required, but I reckon it is unlikely to be necessary for 2kHz.
Making up the side panels is a pain, as each one has to be trimmed to fit closely, and now I'm thinking curves... it will be worse still!
Never mind though, I'm sure it will be worth it.

If anyone has any further comments, suggestions or advice are most welcome.

Bob