Need speaker/crossover help - modifying Leslie cabinet?

I have a Leslie 125 that contains a 20W tube amp and a 12" full-range Jensen.

What I want to do is to add a horn to the cabinet in order to get more punch on the high end. I hope to do this without replacing the Jensen, but I will if I need to.

What I don't know how to do is to pick a speaker and crossover that will be correct for the 20W amp and the speaker I currently have. 

Looking for advice in choosing parts to buy. See image for what I want to do

Picture of Need speaker/crossover help - modifying Leslie cabinet?
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Tekameki1 year ago

I have a vintage tremolo unit model 14 L 2S I bought off Ebay from a Lowrey HR 25 organ. What parts, capacitors do I need for making a crossover for it?

gmoon6 years ago
Why no use the Hammond crossover circuit from a leslie with the the horn? Try the 122 for instance: Leslie schematics.

Or even easier, buy a crossover on ebay. I just searched for "leslie crossover" and three are for sale right now...

Good luck btw. Mechanically this will be more of a challenge than electronically (I'd just buy a leslie horn/driver unit).
AndyGadget6 years ago
I was looking at crossover design some time ago and found some pretty useful info HERE with a crossover calculator.  You'll need to know the response of your existing speaker and choose a horn to complement this.
(Are leslie speakers the ones with the rotating baffle?)
henktermaat (author)  AndyGadget6 years ago
Thanks Andy, I'll check out the link. The problem Is I know nothing of response, etc. and don't have the tools necessary to find out.
Hmmm . . . Leslies appear to be pretty complicated beasts and there's a LOT OF THEM. Are you looking to fit a rotating horn?
The existing Jensen should have the impedance on the label, or at least a model number on it (or be traceable from one of the Leslie enthusiast sites) and you should be able to find the impedance from that.
As the Jensen is a full-range speaker, I'd not alter the signal to that, but use  a non-polarised capacitor in series with the horn, which will only let through the higher frequencies.  From THIS table you'd  use a 20uF capacitor to give a rolloff from 1000Hz, which would be reasonable.  The horn would not have to be rated at the full 20 watts as the capacitor limits the power to it.

henktermaat (author)  AndyGadget6 years ago
I hate to say this, but I don't come close to understanding the design of crossovers - it gets really complicated really fast. I am hoping someone can point me to one that will work :)