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Gliding Dutchma
02-12-2008, 04:13 AM
Here they are - in a shabby condition without drivers... what model is this and what drivers do you suggest using with them?

http://i195.photobucket.com/albums/z54/glidingdutchman/AltecHorns-Mid.jpg

Seems I am getting myself into a heap of trouble... :blink:

The Gliding Dutchman

PS - Hello from sunny South Africa!

spkrman57
02-12-2008, 06:44 AM
90 degree dispersion and flare rate of 300 hz.

I had a pair of 311-60's that I liked very much. (60 degree dispersion)

These are very heavy cast aluminum and coated with some type of "aquaplas" to deaden the horns from ringing.

The throat on these are 1.4" and were used with Altec 288, 291, etc drivers.

Nice find! They sound very good crossed over at 800hz for home audio if your room is large enough for good loading!

Hope this helps!

Ron

Gliding Dutchma
02-15-2008, 01:17 AM
Thank you Speaker Man!!

GD

spkrman57
02-15-2008, 05:27 AM
http://www.audioheritage.org/vbulletin/showthread.php?t=18301&highlight=latest

Ron

Steve Schell
02-15-2008, 10:56 PM
Gliding Dutchman, you have some very fine horns. They were designed by Bill Hayes at Altec, probably sometime in the 1960s. They are radial horns, a type invented by John Volkmann of RCA in the late 1930s. The most used RCA radials were the MI-9594 (60 degree) and MI-9595 (90 degree) midrange/high frequency horns. Mr. Hayes saw fit to design similar horns for Altec, the 60 degree 311-60 and 90 degree 311-90.

The radial horns were designed to optimize directivity in the horizontal pattern, at the expense of collapsing directivity in the less important vertical axis. The exponential expansion is achieved through the curvature top and bottom, which causes the vertical pattern to narrow increasingly at high frequencies. The straight side walls permit the excellent pattern control vs. frequency of a conical (straight sided) horn in the horizontal axis.

Mr. A.J. May designed the RCA horns in about 1950 while working under John Volkmann's direction. He also experimented quite a bit with pure conical horns (straight on all four sides) and he really liked their near perfect directivity control. They were never produced by RCA though, as they had to be so physically large for a given low frequency cutoff. The radial horns were the best compromise, as the exponential flare provided good low frequency loading in a reasonably sized horn. The RCA systems often used bass enclosures with a radial front horn. These bass enclosures (often referred to by the slang term "Ubangi") matched the horizontal directivity of the midrange horns almost perfectly. RCA felt that they had a significant performance advantage over Altec because of this feature, but alas it never translated into large sales due to Altec's marketing might.

With care you can assemble a really terrific hi fi horn system using the 311-90s. You may want to apply some additional damping, as even with the coating they can sound a bit ringy. Bags of sand sitting on top may be just the trick. If you use Altec 288 drivers with correct aluminum diaphragms, a passive 6dB/oct. crossover can be EQed up on the top end with a small value capacitor that bypasses the padding usually applied to pull the level of the 288s down to match the bass system.

Skywave-Rider
02-16-2008, 08:43 AM
Hi all,
Sorry to barge in here, but in looking at Gliding Dutchman's horns, I noticed a "vane" near the throat. I have only an 811B to compare it to, which doesn't have that. Is this design a direct predecessor to the 511/811 horns? And what does that smaller vane do -- dispersion? I like Ron's setup with this horn.
Thanks

Davester
02-29-2008, 03:48 PM
Skywave-Rider... if memory serves me correctly, what appears in the picture to be a "vane" near the throat is actually more of a "rod," probably strictly for mechanical stiffening of the horn structure (and actually closer to the midpoint of the horn casting).

That's a very nice description Steve gave of the RCA 9594, 9595 and Altec 311-60 and 311-90 horns. One tidbit to add: a former Altec employee told me back in the 1980's that the 311-60 was the "worst horn Altec ever built." He liked the 311-90, but added that the 60-degree version was simply 2/3 of the 90-degree, without a proper exponential flare... causing frequency and directivity anomolies. Then he went on to say the RCA 9594 was the best 60-degree radial ever made. My old high school auditorium had one of Dr. C. P. Boner's "early" designs; in that one ("fan" shaped) he spec'ed a pair of the RCA 60-degree horns with Altec 288C drivers on them. The sound was absolutely excellent!

With good drivers (such as the 288C), Dutchman's 311-90's ought to sound superb.

--Davester