Will rounding out some of the visible edges of the Dallas II horn affect the sound?

[hugz]

Hey everyone.

Many years ago I have built the Dallas II speakers, and the Firstwatt F2 amplifier. Alas, I seem to have some kind of psychological inability to finish my projects once they become functional. The amp amplifies, but is uncased. The Speakers sound , lovely, but are unpainted and rough around the edges (literally).

Now that I come to finish the speakers, I realise that i will have to cover a lot of the outside with thin plyboard to level out rough patches where panels join at right angles. I though that since i'm doing this already, i could use the plyboard to round out some of the sharp edges that form part of the acoustic horn but potentially detract from the appearance.

Below is a drawing skillfully done in paint, showing in BLUE where the rounding would go.

Would this affect the sound at all? Upon further consideration, the bottom part could be even MORE rounded (now shown in GREEN). note that in this version there is an air gap between the rounded plyboard and the solid mdf of the speaker. is this problematic?



http://i.imgur.com/LoH0J.png

[dave w p]

Rounding off sharp edges is always something to aspire to. If you can imagine air flowing over these surfaces there is potential for disruption of the air flow (i.e. eddys). Air always flows at bass frequencies and the smoother its passage the better. What you've got to be careful with is the overall tapering and not to introduce bottlenecks. It appears from your drawing that the green line may be a tad excessive, but if you increase the curvature to meet the blue line that should be better. You need to do some careful measuring at various angles along the bottom of the cabinet to ensure a smooth and gradual taper.
I've bent plywood for speakers and it can be tricky, although you can buy bendy ply and that should do the job nicely.
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[picowallspeaker]

Hi ! I was was thinking when reading the title ,that you were talking about some plastic or steel horn for tweeter duty . And I would say : yes ! Go for it !
Gently flowing from round to linear (baffle ) with the right angle is also eye-pleasing . But I don't think it might be the same for LOW freq .If (wave length )size matters , specially near the mouth of the horn ,no more nor less than the designed expansion should be used . Wave doesn't care ( I think ) ...just like sea waves near a beach and a reef ,they just go ahead . Different thing is the space near the throat of the horn ,when a low-pass action is done by the compression chamber and the start of the horn ,so a Higher air pressure in smaller ducts -segments and relative folds must be taken in consideration. In fact in the design shown by Hugz the first two narrow turns are rounded,not in the mouth area ,and changing for example the last segment into two (or more ,meeting a circle)angled segments would change the geometry of the horn . I do not say that Rough is better (but I like it !).
Also the bandpass action of the horn as designed for determined frequencies that result in the end to give the desired sound in combination with the drivers' front emission ,comma , can produce some nasty interferences if the frequency is not too low-below 100 Hz I think- so it might be better to keep it low (long and big horn ) and keep in mind how walls vibrate ...