Hello

[SoundMods]

Instead of trying to compensate for the horn behavior with a "band-aid" approach you might consider going after the horn driver itself. See photos attached.

Tune the cavity as you would a speaker enclosure, drill two 1/8-inch holes in the back to relieve the cavity resonance by venting the cavity -- and you will find much improved sound quality.

Also, the horn itself can be addresses with constrained layer damping and tying the sectoral blades together.

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[SoundMods]

Here are the images for the horns themselves -- note how the sectoral blades are interconnected. When all else was done the blades themselves were contributing a metallic coloration.

Tying them together with shrink-wrapped steel rods did the trick.

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[J-ROB]

The 511 is a well trodden path. No damping will solve the acoustic ringing. There are some wicked transitions in the throat that are the cause of the problem. It is a poor design. The predecessor WE 1" horns of the late 40s were much much better.

I tried it all and gave up....but go ahead and see if you find something that works. I had a pr encased in a sand filled box... I angle ground out the welds in the vanes and inserted rubber...still nasty. I put 40 packs of dollar store plastic clay on them.

BTE I had a very early 811 that had the rubber inserts in the center of the vanes (and much heavier castings). Didn't like that one much either.

I say start by trying different horns but I am a well-known 511 hater, tis true.

Cogito, your Altec drivers should definitely have the felt insert as pictured by Walt. Some pro models came with a black plastic loading cap over the back of the diaphragm, which won't make much difference at HF but will at 500hz. I made back covers with a much larger volume and really didn't think it was worth doing again but it did create a somewhat softer midrange.

[SoundMods]

The horns can be tamed. The shape of the horn flair is based on logarithms so there is no resonance per-se. But the horns are made from sand-cast aluminum in halves that are welded together.

Damping comes in different flavors. Using coal tar or other similar soft materials does not get the job done. Like I said -- constrained layer. In the example I attached it was not actually finished as the lead sheet alone was not sufficient. I don't have a picture to share, but I later added ceramic tile attached with RTV silicone caulk creating the constrained layer. Tying the sectoral blades together is more important than I thought possible. Part of getting rid of the horn driver cavity resonance is venting. I can't begin to emphasize the importance of the venting.

The crossover, regardless of the capacitors and inductors used needs taming as well with damping resistors across all of the caps and inductors. Somewhere around 400-ohms -- preferably using carbon composition resistors -- or at least non-inductive wire-wound resistors. Am I a quack? Dave Wilson doesn't think so. He confirmed with pulse testing what I confirmed from calculations and ear testing. "Clamping" the reactive components gets rid of series and parallel tuned circuits created by the LC relationships. The electronic ringing imitates mechanical ringing in strange and wonderful ways.

I have a massive respect for all things Western Electric and Altec Lancing. They did wonders with slide rules and guts.

My to cents and I don't expect change.

[Cogito]

Yeah, that is the only graph I could find on short notice, but the sub 8k region looks about right,.

Altec 288s have the same broad peak, addressed in the so called "Hiraga crossover" which adds a series LR in parallel to the standard EQ scheme. See attached schemo.

Anyway, something to consider but if you are happy with what you have, hang out there for a while and learn what it is.

Saw that crossover circuit on Jeff's place. Yes, I will build it as I go along.

Whatever we say 511s, they are very engaging. I will not give up on that quality easily.

[Cogito]

Instead of trying to compensate for the horn behavior with a "band-aid" approach you might consider going after the horn driver itself. See photos attached.

Tune the cavity as you would a speaker enclosure, drill two 1/8-inch holes in the back to relieve the cavity resonance by venting the cavity -- and you will find much improved sound quality.

Also, the horn itself can be addresses with constrained layer damping and tying the sectoral blades together.

In my case, the horn and the woofer (411) are enclosed in the same sealed enclosure. Its not an option unless I move the horn out of the enclosure.

Do you still have modded 511s I can listen to sometime?

Tying the sectoral blades makes sense. They are not needed for the structural integrity of the horn itself. They might have been designed to reduce the vibrations (ringing) of the lips of top and bottom halves of the horn, and by bracing them, you are further reducing the vibrations.

BTW, I met Bruce Edgar in CES in Las Vegas several years ago (his horns were my top choice in the show). He mentioned that he uses truck undercoat to control the resonance of the horns.

[Cogito]

This ebay ad claims Altec supplied some 511Bs with factory applied AquaPlas Damping.

http://www.ebay.com/itm/Rare-Early-Altec-Lansing-511B-horn-w-Factory-Applied-AquaPlas-Damping-/182169486844?hash=item2a6a25c5fc%3Ag%3A290AAOSwq5pXP01e&nma=true&si=lZxeiDgyTsSc6iYID3IYL9Hr%252B64%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

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[SoundMods]

As far as the venting is concerned the sealed enclosure will not impact the vented horn drivers. The "vents" are not unlike restrictors in a pneumatic control system.

[J-ROB]

The problem with the Altec 511 is that it goes from round to square throat very abruptly--WHY?, very roughly cast especially in the throat where it matters most, and then opens up to a wide expo flare very abruptly which is a diffraction generator.

The throat should be smooth and regular ideally. This is a super high compression area and geometry and surface regulariity matters.

Mechanical ringing is a secondary issue and simply bolting the 511 to a baffle solves a lot of that.

The issue I'm hearing is acoustic.

The earliest 811s had the vanes cut (or rather never welded) and they stuck in some rubber to damp bell effect. You can see the fossil of this idea in the earlier 511s where most of the slot still remains, but it is welded instead.

I am a huge Altec fan...been using the stuff since 1985 continuously, I published articles on Altec before it was cool, I started the Altec users Group...and still I must rag on the 511. It was designed for cheap production, which is not necessarily bad, but there are deficiencies in the fundamental design.

What needs to be done is to fill the throat and rebore it to a more accommodating geometry and surface and there is still the refractive throat/bell transition. Hopeless.

But they do have a certain liveliness... and high intelligibility in paging applications.

When I say they are fair at best, but that is in comparison to many better horns. There are also far worse.But some of the very good ones were current within a decade of the introduction of the Altec sectorals, so they should have known better. Probably comes down to manufacturing economics somehow. They spent the cash on the driver and cheaped out on the horn.

Late model 511s look like they were cast and welded in India. Rough welds and flash inside, Niot precision instruments... but OK for generic PA, perhaps.

Now here is a good 500hz horn, the Emilar EH -500. Designed by Jonas Renkus after he left Altec and intended as a bolt on retrofit/upgrade for the 511. It is a heavy casting. Very smooth throat that gradually opens...in fact without the 1" adapter, there is no throat extension on the horn for a 2" driver. You can see the diaphragm, as it were, from any point inside the coverage angle of the horn.

The later Renkus Heinz horns were like this too, and the RH and Emilar drivers had only about 1" of throat. between the phase plug and the horn mouth. The throat is a trouble spot. Renkus minimized it.

I don't talk about these horns too much. Word is already out somewhat, but you are my DCDIY bros...and Joseph Esmilla will probably tell the world next week anyway

Sadly, they are not super common, especially with the 1" adapter.

Sorry about my ugly toe in the pic!

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[Cogito]

Thanks, I will be on the lookout for i32s and Emilar EH-500s.

I came across an this article, Taming the ALTEC A5 Classic for Domestic Use by John Stronczer, in which he explains the issue.

Why doesn’t the stock crossover work in this type of speaker?

That is really quite simple. For theater use the crossover is designed to be as lossless as possible, efficiency is everything when trying to fill a large space with intelligible speech and music.

In a small room for music listening you need at least 12 dB of HF attenuation and you can let the higher harmonics come in better. These horns sound remarkably sweet in the upper frequencies and can even seem overly soft until some real HF energy comes in and startles you with its presence and detail. When EQed correctly, they have a very natural bloom and energy with very low distortion giving a sweet yet detailed sound.

Distortion of this speaker above 100 Hz at 100 dB out will be typically less than 0.05%! This level of distortion is even less than that provided by the 30 watt Orfeo amp which is around 0.07% at 1 watt out. I would guess that most people have never heard a loudspeaker with as low distortion as these. This contributes greatly to the naturally detailed sound and dynamics that approach those of live music.

Evidently Altec shipped Santiagos and Valencias with 30904 EQ circuit. My speakers did not have a crossover built in. I purchased standard Altec Crossover N-500D, which is why when I added the 30904 EQ, the speakers sounded so much better.

BTW, I do not hear any ringing, but then, I havent compared with other horns, so I may be missing it. Atleast there is no obvious and noticeable ringing.

http://wajonaudio.webs.com/Voice%20of%20the%20theatre.pdf