An easy to build classic horn?

[dabbler]

This is just for fun really. I have a pile of foamcore sheets at home and was thinking of making some large horns with easy to build profiles, like the altec mantaray horn.

If I dont like it I can toss it, no harm done. Any other easy horn designs out there that would be worth a try? Up to 500mm (20 inches) wide and deep would be ok and 600-700 hz crossover would be nice.

 

[revintage]

fabrication1

Can also be made rectangular. The templates is easy to get from HR.

 

[dabbler]

Hi Revintage, not sure where HR is?

I'm also thinking something like an 8 petal conical could be easy to make. Anyone have experience with such horns? Any programs available for modelling?

 

[dabbler]

I think i'll start very basic and work my way up: A square conical horn. Is there a quick formula / ratio for calculating cut-off?

I'll smooth the throat transition with some putty...

 

[revintage]

Use HR=Hornresp! It also has templates for four and up petals. You should also use Hornresp to model the horn whatever flare you want, Tractrix, Expeonential etc, etc. You get the templates after you have modelled the horn.

 

[dabbler]

Ah okay thanks. I did try hornresp but had no idea where to start. Can't see anything on conical horns or petals etc. That GUI is for smarter chaps than me!

 

[revintage]

Without the flares and templates you can forget about building the horn. But if you decide how you want it, Fs, At(driver-area), type(Tx, Exp, etc) , number of petals(from four), I will make it for you. Go for a square Tractrix!

 

[Brett]

This is just for fun really. I have a pile of foamcore sheets at home and was thinking of making some large horns with easy to build profiles

Why not just conical then?

 

[dabbler]

Without the flares and templates you can forget about building the horn. But if you decide how you want it, Fs, At(driver-area), type(Tx, Exp, etc) , number of petals(from four), I will make it for you. Go for a square Tractrix!

Thanks for the help, I had a look through the HR help manual and it makes sense now, so I should be able to get something happening on my own! I will eventually build a tractrix and le cleach but I will start with a square conical, simply because it is easy to build with stiff foamcor.

It seems that cutoff frequency cannot be entered for a conical horn (F12). Why is that? I can enter it for tractix and le cleach without a problem....?

 

[revintage]

Did you really check the conical horns frequency response on/off-axis? Constant directivity is useless for high-or mid-horns. The low end drops early which means you have to make it very big to go down to your prefered XO-point.

 

[dabbler]

Yes i've noticed that the conical gets very big in order to get sufficient for a low cutoff, like an OSWG. See the SPL plot attached for a 30cm long horn (50 degrees) which shows drop off at 800hz then a bump 400 before it drops off steeply. Could we say that the cutoff is at 800? If so should I double the frequency to 1600hz for the crossover point as is done with tractrix and le cleach horns?

Tractrix does have good "bang for buck" in terms of size vs cut-off. Will be interesting to compare the sound to my OS waveguide.

 

[David McBean]

It seems that cutoff frequency cannot be entered for a conical horn (F12). Why is that?

Hi dabbler,

A conical horn does not have a specific theoretical cutoff frequency. To illustrate:

Attachment 1 shows the normalised throat acoustical impedance of an 'infinite' exponential horn having a cutoff frequency of 100 hertz. Notice how the resistance (black trace) falls abruptly to zero at 100 hertz.

Attachment 2 shows the normalised throat acoustical impedance of an equivalent 'infinite' conical horn. In this case there is no sharp reduction (or cutoff) in resistance at a particular frequency.

Kind regards,

David

 

[dabbler]

Hi David, thanks for the explanation and for your program.

 

[dabbler]

I am trying to export a tractrix horn design as a rectangular tractix flare however from the dropdown list I can only see the Conical, Exponential and Uni flares?

 

[David McBean]

I am trying to export a tractrix horn design as a rectangular tractix flare however from the dropdown list I can only see the Conical, Exponential and Uni flares?

Hi dabbler,

The Con, Exp and Uni options relate to how the width of the rectangular horn is flared. The rectangular cross-sectional area itself still expands as required for a tractrix horn.

Uni is probably the option to choose, unless perhaps you wish to use Con to achieve some degree of constant directivity in the horizontal plane.

Kind regards,

David

 

[dabbler]

Thanks David, I'll give the Uni option a try.

 

[revintage]

Noticed you still use "Constant Directivity" in your sims. This will not help you very much in a mid or high horn. A good starting point is 10 degrees off axis.

 

[dabbler]

Hi Lars, not sure exactly what you mean by "you still use "Constant Directivity" in your sims". My latest design is a tractrix horn, I am not aware of how to change directivity other than selcting a conical flare for export. I have used the "Uni" option.

 

[revintage]

Its in "SPL response"! When in that window go to Tools/Directivity/Response and choose 10 degrees. This shows the predicted response for horns above basshorns.

 

[dabbler]

Thanks Lars, gotcha now. Ive attached a CAD drawing of the square 400hz tractrix which will be made of card. I'll slide in the throat tranistion piece shown at the end.