Posted by billfort [ 204.191.240.150 ] on July 11, 2005 at 10:35:38:

In Reply to: Re: Great Plains Audio 704-8A - more notes posted by spkrman57 on July 10, 2005 at 13:38:26:

My plan to target 400Hz as the tractrix mouth cutoff is due to me wanting to try an 800Hz cross on the 902 and since the 811 horn is about this size, seems like a good starting point. I will definitely try a higher cross as well.

One place where my plans changed a little was the throat – I measured the 902 exit expecting 1” but found it’s more like .875” so my tractrix throat will start with that dimension. I know it’s not much but I think it might be best to have a smooth transition from driver to horn throat without a .063” step in there.

I know a bunch of the software models say 4 to 5ft3 for flat alignment with these Altecs but in my experience, if you want full range, larger is better. I think you are in the right ballpark with the cabinets BillE is building. What baffle width are you using? As much as they look prettier, I found narrow baffle cabs sounded a little ‘thin’ in the upper bass lower mids with the 604’s and a 26” wide baffle (as used in the 620) yields better balance making that famous ‘604 midrange shout’ a touch less noticeable.

I sure would like to hear a purpose built round wood tractrix on an Alnico Altec 1.4” driver, if I ever find a pair of these at a reasonable price I’ll consider building some but with the price of Altecs these days, I don’t see this happening anytime soon.

No plans for travel anywhere near your place right now Ron, I really have to get down there! Do you ever get anywhere near Toronto? I’d love to have you over.

Replies: