604 series improved replacement horns!!

[Roland N R]

Most agree that the small multicell horn in the 604 series could be improved upon. A round tractrix or CD type like Urei's horns would be an improvement.

The question is how large..how low the horn cutoff can be made for the 604 series??
The small format compression driver can easily be loaded to 800Hz or lower freq. Then the limiting factor seems to be hindering the output of the LF driver by the large horn. GM recently suggested that a ROUND 800 Hz horn may not significantly affect LF performance because LF output is not very beamy if the LF driver is crossed about 800 Hz. Granted this size horn would protrude forward outside of the cone and be cosmetically unacceptable for some. But imagine the performance of XO at 800 Hz instead of 1600Hz. These would be point source model 19 like speakers!! In actuality the horn cut off would be lower than 800Hz to allow actual XO at 800 Hz.

Then the question is how large can a round tractrix or exponential horn be made to fit the 604s without affecting LF output. (Large rectangular horns like CDs would likely affect LF output and are not considered here for that reason)

Months ago, last time I checked on tractrix horn calculators, for the throat opening of 1.4" (really 1.5" at horn entrance) I got close to 800 Hz cut off for a horn depth that would not protrude forward of the cone itself. The horn mouth diameter as I remember was close to 8". Granted you will need to XO above the 800Hz and the output will get beamy off axis. But for home use, where you have a sweet spot and HF coverage is not critical, quality of sound will be better than the 1600 Hz multicell.

Two questions remain:

1) LF interference by the large horn???
2) Will Iconic or other consider producing:

This round tractrix in two possible versions protruding 800 Hz XO and nonprotruding with higher XO.

And also the Urei type CD horn for the 1.4" throat 604s.

All these would likely be A DIY replacements

[David Deratany]

604B's have a true multicellular horn, and the early ones crossed over at 1000. Does anyone know why the crossover frequency was raised and why that horn was abandoned?

[Jim D]

The original 604 horn was expensive to build. The original 604 crossover was not right and the speaker had some midrange problems. The then cheif engineer of acoustic's, Alexis Badmieff, who was always trying to make things less expensive and get a wider market, redesigned the horn to get more horizontal dispersion. Because of the "wider' dispersion, the crossover had to be raised. The newer multicell (C-D-E-G), which I call the eggcrate, is not a true multicell and is in this authors opinion, a disaster. While it may be true that the "B" model multicell actually needed a somewhat higher crossover, maybe 1200Hz, it is still a far better horn. The "B" horn mold is long gone, too bad. JIM

[Roland N R]

Bill at GPA has access to the Urei horn mold. We'll see if he can get some made. Also trying to convince him to make 802G pole pieces to update the older alnico small format to tangerines. If enough interest is shown it may go!!!!

[GM]

Really, the only LF limit considerations is the driver and how much phase delay can be electronically dialed in, and the lower the better WRT any potential LF masking. Fold a complementary horn around it and you have a ~tractrix variant of the 9864/9894.

GM

[David Deratany]

I, too, found the mids bothersome and difficult to tame on my 604b's but bi-amping helped tremendously, and crossing over at 1200 helped yet more. They hold their own quite well as compared with 511/802's in place of the internal horn.

[Albert Allen]

I might just have to run the calcs for an 800HZ tractrix and try one out on my Eminence/Altec Hybrids, I think making one out of wood on the lathe might look pretty spiffy protruding out of the middle of a 15 inch driver!

[Fitts]

Why not get really far out and design a folded tractrix HF horn that uses the woofer cone as a 15 inch diameter HF horn opening. Properly designed, you could probably get down to 500hz.

Just a wacky thought but you know what they say, "nothing verntured nothing gained."

[GM]

Yeah, it would. FYI if you don't already know is that to get a solid 800Hz loading you have to make it longer/bigger than 800hz due to the flare, so it needs to be built to ~565Hz.

Hope to read some first impressions soon!

GM

[Albert Allen]

Roland, that is good to hear about the square horns. I have racked my brain trying to think of any way to make a round horn easily and even though they are easy to model in CAD they are very difficult in reality. I have played around with making solid models of square horns in CAD and it looks like once I develope the flat patterns from the CAD data it should be fairly easy to produce them. the only problem would be the transition from round at the driver mounting to square, I would guess this would be the critical area.

Is there a calculation program available for the exponential? (I am a design engineer and I still hate doing calculations)