811 Fins

[SOOTSHE]

Need some advice on removing the fins from a pair of 811's.....or rather, why I should remove them. I've been trying to come up with a valid reason why this would make them sound better, but my head keeps saying "why is this so".

I assume Altec fitted them to make them stronger for possible pro applications but wouldn't they also provide bracing from the top to the bottom of the flare? Much the same as you would brace a speaker cabinet from front to back or from side to side. In the speaker cabinet scenario this prevents resonances from occurring, so why doesn't the same apply to the 811? Wouldn't the fins brace the top & bottom together making the whole assembly more rigid.

I've read posts where the fins are broken at the weld with rubber wedges inserted or black silicone applied....wouldn't this make the horn less rigid?

MAybe I'm way off here but I just can't seem to make sense of this.

[Old Guy]

Opinions are like...

I have heard then with and without can't hear a difference

You will ruin any resale value:doh:

IMHO wasted effort

Make sure damped well and forget it

[bowtie427ss]

You will ruin any resale value:doh:

IMHO wasted effort

Make sure damped well and forget it

QFT = quoted for truth.

[Steve Schell]

J Henry, you have posed an interesting question. Just what function do the fins serve on the 811 (and 511) horn?

Certainly they are not for pattern control, and being obstacles they would degrade the pattern slightly if anything. Perhaps they were intended to stiffen the structure, though the horn is still plenty stiff without them.

I think there might be other reasons: styling and product differentiation. The first version of the 811, the H-811 or 1952 or so, was a stylish thing. It was a one piece casting with a curvy appearance to the mouth, and the fins gracefully arched outward. It must have been a bear to cast, as it was replaced within a year by the two piece welded 811A.

The RCA MI-9594 (60 degree) and MI-9595 (90 degree) cast aluminum theatre horns had been introduced in about 1950. RCA produced the first radial horns, as the radial horn had been invented by RCA engineer John Volkmann. The Altec modified radial horns were obviously inspired by Volkmann's work. Perhaps the fins were intended to differentiate the look of the Altec product from the RCA horns, which did not use fins.

Another reason may have been to maintain a visual continuity with the earlier Altec horns. Altec Lansing had produced only multicellular horns until the introduction of the H-811, and the fins served to visually divide the mouth area, providing an evolutionary appearance change rather than a revolutionary one.

[Old Guy]

Pretty much 100% with Steve here, just adding the fins make them resemble multicells, Altec's bread and butter.

Jim Lansing didn't like multicells, but JBL later was forced to buy Vitavox multicells thru DuKane in order to bid on jobs where there was a specific muticell spec.

[GM]

Certainly they are not for pattern control, and being obstacles they would degrade the pattern slightly if anything.

Have you measured or seen polar plots of them with/without? In theory they should affect it just as is shown in Cohen's book.

GM

[zelgall]

Have you measured or seen polar plots of them with/without? In theory they should affect it just as is shown in Cohen's book. GM

I don't have plots but I do have several 811's and I did cut the fins out of one. I also filled in the casting radii between the top and bottom halves on a pair. I found no audible difference between the fin / no fin versions within normal listening distances. I listened to both config's and really didn't notice much differnce between them. Checking by ear is always a crap shoot anyway.

[bfish]

...Just what function do the fins serve on the 811 (and 511) horn?

Perhaps they were intended to stiffen the structure...

I think there might be other reasons: styling and product differentiation... Perhaps the fins were intended to differentiate the look of the Altec product from the RCA horns, which did not use fins...

Another reason may have been to maintain a visual continuity with the earlier Altec horns. Altec Lansing had produced only multicellular horns until the introduction of the H-811, and the fins served to visually divide the mouth area, providing an evolutionary appearance change rather than a revolutionary one.

I guess Western Electric must have never gotten that memo.

"The horn is sectoral in form and integrally cast partitions are provided to reduce reflection effects within the sound passage."




courtesy HiFilit.com

I don't know the production dates of the pictured KS series, but W.E. did have fins in sectoral horns that pre-dated the 811.

[Steve Schell]

Scathingly brilliant, bfish! I had forgotten all about the W.E. horns. Altec had received the rights to manufacture them in 1949 along with the speaker and microphone designs. Altec built them through most of the 1950s, some continuing until much later.

[GM]

........W.E. did have fins in sectoral horns that pre-dated the 811.

Actually, the few I've seen were true sectoral horns, i.e. the 'vanes' extended all the way back to the throat to create a cast multi-cell whereas the later 311/511/811 appear to be a manufacturing compromise to at least get some of the earlier design's HF gain, though over a narrower arc.

GM