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Damping 511B ringing: Whats your experience? [message #41227]

Mon, 05 May 2003 10:34

AstroSonic
Messages: 58
Registered: May 2009

Baron

The stock cast aluminum/welded Altec 511B horn rings quite audibly on playback in comparison to more recent non-metal horns such as the JBL 2380 which I also have. On some selections the sound even becomes 'shouty'. The excited range of frequencies is like those emitted when the horn is tapped or gently brushed. At this point I have reviewed the archives here (horn damping and 511b damping) and several suggested fixes were turned up.
1) De-stress the horn by separating/cutting the dividers.
2) Apply a few layers of paint and sand until the ringing is inaubible,
3) Apply a thick layer of window puty,
4) Apply a thick layer of duct sealant,
5) Apply a 'layer' of constrained layer' damping material (like Dynamat), and
6) Build a box around the horn and fill with sand.

My guess is that all of these methods provide some audible/beneficial improvement. I would like to do the most effective reasonable modification. The sand-filled box is out because it is just too heavy. I was favoring doing #1, but decided to investigate a bit further.

I got a 50 # bag of 'playsand' and filled a total of 18 zip-lock sandwich bags. These were placed, first on the lips (above and below). I noticed an obvious but minor improvement. Interestingly, my wife commented favorably right away. I then added sand bags above and below the body of the horn, and this made a huge improvement (to me). This does suggest that the sound benefits from damping the body of the horn, as well as (more than?) the lips.

The sand bags on the body of the horn can stay, but the bags on the lips have a very low WAF and must be replaced with an alternative. Anybody had experience with one or more of the above approaches? I am especially curious about the 'constrained layer' technology.

TIA,
AstroSonic

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Re: Just say no to dope [message #41230 is a reply to message #41227]

Mon, 05 May 2003 18:00

bmar
Messages: 346
Registered: May 2009

Grand Master

Cutting the fins will help but not damp the entire horn. do this in addition.

I used a box filled with sand. This makes a nice presentation of your horn when its installed into a cabinet so to speak. Fill the box with sand from the back and close it up.

The painting layers thing will eventually work (i presume) but when to you think its properly damped vrs you got used to the ringing sound.

The putty, caulk, foam, dope and sealant approach is just too gross to even think about. If you want that shit all over your horns, then by all means!

I am to understand the "bed Bath and Beyond pillows are the nuts!

lastly, wood horns.

Enjoy the Altecs. Nice stuff arn't they. just dont goop em up

Bill

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7)sell on ebay [message #41233 is a reply to message #41227]

Tue, 06 May 2003 04:32

Sam P.
Messages: 307
Registered: May 2009

Grand Master

...you are not worthy :) Buy wood horns. Sam

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Re: Just say no to dope [message #41243 is a reply to message #41230]

Wed, 07 May 2003 07:49

AstroSonic
Messages: 58
Registered: May 2009

Baron

Bill, Thanks for replying. I want to do as little 'damage' as possible to these awesome horns. Based on my sand-bag experiment, I think they can be effectively damped and provide superb sound quality. I too would prefer a solution with minimal aesthetic damage. The box that you built around the back of the horn - was it built up to the flange or did it go up to/over the lips. If not the latter, do you hear any remnant ringing possibly coming from them? Did you cut the fins?

Also, are you using your 511B's with a VOTT style cabinet or other type. What type of crossover are you using? Any HF compensation?

Regards,

AstroSonic

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Love'm or leave'm! [message #41245 is a reply to message #41233]

Wed, 07 May 2003 08:19

AstroSonic
Messages: 58
Registered: May 2009

Baron

Sam, Thanks for replying. You tried cutting the fins on your 511B's. Did that adequately damp the ringing (by itself)? Did you try any damping on the lips or body of the horn?

At this point I don't think that the ringing I currently have with the sand bags is unlivable. Fact is, the sound quality is incredible, and in most respects, better than I have ever had in my home. However, I want to get the best sound quality that I can from my equipment. I enjoy building and tweaking, and the improved sound quality that results (eventually...most of the time). I may at some point try wooden horns but I am enjoying the 511B's too much to make the change now.

Thanks for emailing the details of the fin cutting. Seems like that can be done with minimal aesthetic impact. After receiving your emails I picked up a sawzall. Have not done the deed yet, but did cut down some overgrown bushes!

Regards,

AstroSonic

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Re: Damping 511B ringing: Whats your experience? [message #41254 is a reply to message #41227]

Wed, 07 May 2003 13:27

djn
Messages: 16
Registered: May 2009

Chancellor

Do like I'm doing. Take your horns, with the driver attatched, to a local university engineering department and talk to the NVH prof (noise, vibration, and harshness) and have do an "experimential modal analysis" on the horn and driver. That with tell you the resonent frequency of the horn/driver and from there they can tell you what freq your dampening stuff should be and were to get it. With this method you can make a horn/driver combo as dead as concrete (which by the way has a resonent freq but is to low to notice)

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Re: Damping 511B ringing: Whats your experience? [message #41255 is a reply to message #41227]

Wed, 07 May 2003 15:04

tdc
Messages: 34
Registered: May 2009

Baron

Just to share what I did with 811b which does not ring quite like a 511. I cut the fins and filled the gaps with hard rubber cut from a tire. Poly cord and steel belts sound the same. Be sure to use radial tires with all radial horns. Then I sprayed the outside of the horn with automoble sound damping material. This comes in a spray can and is like undercoating. That looks bad but the next step takes care of that. Then I built a box to hold the horn with a heavy wood face plate. Use all the mounting holes to screw the horn face to the wood ( use t nuts) and clamp it tight. You can also a a washer made from an inner tube.That is the most help. A bell rings from the edge. Bolt it to a wooden plank and you get a dull thud.The box also serves a small baffle which allows you to cross over closer to the horns bottom line. I use 850 hz 12db with the 811b but will try both 1000 and 1200 later. Problem is the woofer starts to break up a little above 500 but is not bad a 800. At full range about 1600hz it is a bit rough. I also use JBL 2345 and 2370 horns. They need none of the above treatments. tdc

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more on fin cutting [message #41256 is a reply to message #41255]

Wed, 07 May 2003 16:35

tdc
Messages: 34
Registered: May 2009

Baron

You only cut the weld between the vertical fins. Its about 4mm thick. You don't remove or cut out the entire fin. When you do you release a lot of pressure that was applied to bring the fins together for welding in the first place. I got the trick over the phone from altec engineers before the company went out of business. I believe altec sold the last runs of 811 and 511 horns with the fin welds removed so they really believed in it. tdc

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'Nother question on fin cutting [message #41262 is a reply to message #41230]

Thu, 08 May 2003 05:59

JLapaire
Messages: 156
Registered: May 2009

Master

Bill, is there a downside to cutting the fins off and grinding them flush? Do they serve a purpose if the flange is bolted to a cab?

Thanks,
John

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Anyone tried Dynamat? [message #41263 is a reply to message #41227]

Thu, 08 May 2003 09:11

AstroSonic
Messages: 58
Registered: May 2009

Baron

Has anyone tried constrained layer damping like Dynamat Xtreme (from Dynamic Control) or 3M 2552? This stuff comes in sheets with adhesive backing and is used to damp metal panels in machinery, aircraft and automobiles. Both appear to be effective between about 100 Hz and 10,000 Hz at room temperature. They can be cut to shape with scissors. If you have tried either of them what results did you get? Both companies have pdf data sheets: www.dynamat.com and www.3M.com/industrialtape.

AstroSonic

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