Solid horn - work in progress

[rendoman]

Hi all!
I'm building the second horn for my RCF Nd1710 mt3 audio driver, 1" exit , 108db/w/m, 1-20khz range, titanium diaphragm and strong magnet.

The big boy is a 130mm round bar, normal aluminum that melt on tools

I chose tractrix contour, I tried it many times in the past, it works perfectly for home use for middle and high frequency.


Probably I will buy a good finishing tool


Some pictures of the horn , still work in progress

Saluti
Stefano

[rendoman]

Aluminum streamers today!

The raw profile of the horn is done, with the lathe at limit. My endowment of boring bar is limited, for this tool I have no new carbide tips. Unluckily the only right tool I have, it's short and tiny, not enough for this job but I do what I can.
Now it's time to use the files, lot of sand paper and finally wool and polish!

I'm having some trouble about vibration using boring tool and up to 20° angle, have some good advice in order to have a good smooth surface?
thanks
Stefano

[Tuomas]

Wow. Nice.

[rendoman]

Thank you Tuomas!

[Frank S]

It is a crying shame that the true acoustics of your builds can never be experienced coming from the speakers or headphones of our computers.
I liken these to that of trying to experience the effects of a performance in a symphony hall from an ear bud on a 2 transistor am radio.

[rendoman]

You're right Frank! I hope I will be able to describe the sensations!
The good thing is that with only one watt you can have 108db at 1 meter, so even a tiny amplifier with no caps and few components can make the difference

Ps: I'm close to sand paper work!

[rendoman]

Ready to polish the inside of horn… unluckily I can't use cotton wheels and normal paste.
I'm trying to make a "grease" paste with powder, I hope it will be good!

[Frank S]

If you can't find any jewelers rouge then a wad of lambs wool on a stick and tooth paste usually works for me.

[rendoman]

Some work of adjustment, lot of sand paper needed, lot of passion.
I prepare a second special recipe for the polishing paste with lithium grease and oil, it should work fine, at least it can stick better to surface. The trouble is that I can't push so much to increase heat, like with cotton wheels. Another trouble this soft aluminum is a crap to polish compared to ergal, scratch are behind every corner.
I'm thinking about the next step, Last time I build brass long feet from solid bar (H frame), maybe I will machine a couple of rods fixed directly to the horn.

[rendoman]

Hi all!
Lot of time with sandpaper, from 60 to 1500 grit, about 5 hours to polish both, I still need half an hour, the abrasive mix with grease and oil is hard to clean inside the horn, in first picture there is the veil on the surface.
I have to finish the adaptor, and thinking about the pedestal, I found 25mm solid brass round bar that seems perfect for the purpose, I'm still undecided if make a stand alone unit or fix to the horn through screws.