811 Fins

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Originally Posted by GM

Greets!

I didn't realize how much they added until I cut out the vane welds and bridged the gap with a GE silicone gasketing product. Ditto adding damping to the sides of the horn. This widened the 'sweet spot' a bit at the expense of some top end 'air' and why historically I've nixed the tweak unless a super tweeter system is added.



GM

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FWIW, if I were only going to do one major tweak it would be to cut the welds out of the vanes and fill the gap with rubber wedges as Altec did in the 500 'C'? variant which was also Aquaplas coated (your sand coating will do similar) or some other damping that sounds best overall, though you want to do the experimenting after EQing the system as flat as practical out to at least 15 kHz. A lot of its ringing is due to the coupling of the two bells combined with the warping that occurs in the welding process and as I previously noted, it mutes (smooths out) the on axis response a bit, though not as much as removing them does.


I'm a bit confused GM.....are you saying that you would cut the welds out & coat the bells....but only if you added a supertweeter??

No, personally I don't recommend completely removing the vanes unless a super tweeter system is used, preferably horn loaded, though I've auditioned small piezos arrayed around the bell that worked quite well too.

GM

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Originally Posted by GM

No, personally I don't recommend completely removing the vanes unless a super tweeter system is used, preferably horn loaded, though I've auditioned small piezos arrayed around the bell that worked quite well too.

GM

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Thanks for clarifying that.

I would leave it. The reason is if Altec went through the trouble to put them in, there must be a reason. It is probably there as as a method of stiffening the horn.

I like the green ones best. ;o)

Hi GM, group,

I have to confess to being a dyed-in-the-wool conical horn enthusiast, as they sound the most clear and open and the "least like horns" to me. I have seen some data for the on-axis hole in h.f. response, but have never been able to measure it myself. This may be due to the drivers and horns that I manufacture, which maintain the same smooth expansion in cross sectional area from phasing plug slit origin to horn mouth. I am not sure what the mechanism of the problematic response would be, as drawing out the horn geometry with a ruler and compass would seem to indicate a portion-of-sphere wave shape that maintains perpendicularity to the horn wall. I do remember Dr. Edgar showing me a book illustration of wave shape of a conical horn that looked pretty messed up, but again I have never heard or measured such effects. I suspect that it may be due to less than ideal driver throat to horn matching causing throat reflections, or a small horn mouth that encourages strong mouth reflections. Conical horns do have relatively poor loading at the bottom of their passband due to the rapidly expanding throat area, which is at least partially compensated for by a longer length and a generous mouth size.

What is neat about conical horns IMO is the degree to which the off axis response mirrors the on axis response. One can feed pink noise to the driver and move a handheld RTA across the mouth. One sees very little change until venturing just beyond the straight side, where the response dies immediately. So, the measured response closely resembles the driver's power response, which of course runs downhill north of the mass corner requiring EQ for flat response. If this is done the nice thing is that the reverberant field has about the same spectral energy as the on axis sound, which mimics nature and sounds natural to the ear.

Getting back to radial horns... I was fortunate to know Mr. A.J. May of RCA, who was John Volkmann's understudy and final design engineer of many of RCA's speaker products. A.J. always spoke glowingly of Mr. Volkmann, and tended to downplay his own accomplishments. He once described Volkmann's radial horn in terms that I cannot recall perfectly, but went something like this... The radial horn is intended to take advantage of the excellent directivity of the conical horn in the important horizontal axis, while maintaining the advantages of exponential expansion by accepting a sacrifice in directivity in the less critical vertical axis by placing all the curvature on the upper and lower horn walls.

One of A.J.s projects was the LC-9A two way loudspeaker. It was intended to compete with Altec's A7 by bettering its chief weakness, poor directivity through the crossover region. Both high and low frequency sections of the LC-9A use 120 degree radial horns, and they blended beautifully at all angles. It is freaky to listen to an LC-9A while standing waaaay off axis, virtually beside the speaker, and hearing very nearly the same response as on axis.

Steve,
Do you have any other info on the LC9A that you could share? It sounds really interesting.
Thanks,
John

J Henry, there is probably more than you ever wanted to know about the LC-9A in this old thread:

RCA ; LC-9A pics

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Originally Posted by Steve Schell

It is freaky to listen to an LC-9A while standing waaaay off axis, virtually beside the speaker, and hearing very nearly the same response as on axis.

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I had a similar freaky experience years ago. 1st time listening to a TAD driver on an Iwata horn. Big Onken box with 416 for bass. Walk around the thing and it was seamless. And the sound never seemed to come from the speaker at all. Even when I could reach out and touch the speaker. Very disconcerting.

Thanks for the RCA kink.

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Originally Posted by Steve Schell

J Henry, there is probably more than you ever wanted to know about the LC-9A in this old thread:

RCA ; LC-9A pics

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Thanks for that.