Mick Bell Posted January 14, 2005 Share Posted January 14, 2005 My Altec 811s have been around the block a few times! Would painting them alter the acustic properties? Mick Bell Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 14, 2005 Share Posted January 14, 2005 That depends on how thick of a coat you use! I would think a glossy coat on the inside would be best, the thinner, the better. Just to be safe. I've heard of horn afficianados painting the insides of their respective bass horn with high-gloss paint to reduce friction. DM Quote Link to comment Share on other sites More sharing options...
sunnysal Posted January 14, 2005 Share Posted January 14, 2005 I seem to remember the originla coating was rather rough on those horns. I also seem to remember that smooth is not the best for reducing drag, that is why golf balls have dimples, if they were smooth they would fly less far...tony Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 14, 2005 Share Posted January 14, 2005 Are you sure about the dimples? I suspect they're there to increase the amount of elasticity of the ball surface, giving it a bigger kick off the club. If rough was smoother, swimmers would wear dimpled suits instead of smooth, sandpaper would be course for finish work, you get the idea. The issue of coating a horn is probably that of dampening than of air movement. Then again, lots of people put dampening materials on the outside of their horns on purpose. Any comments on this? Quote Link to comment Share on other sites More sharing options...
Marvel Posted January 14, 2005 Share Posted January 14, 2005 The dimples on golf balls is to provide lift. Just don't ask me to explain it. Marvel Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 14, 2005 Share Posted January 14, 2005 I think the dull black is just so they don't shine behind the gossimer grill cloth. Rick Quote Link to comment Share on other sites More sharing options...
michael hurd Posted January 15, 2005 Share Posted January 15, 2005 There are dimples on a golf ball to reduce the boundary layer friction, and allow more distance. This was discovered when it was found that balls with scuff marks and cuts actually went further than a smooth ball. Kind of off topic, but even when porting a cylinder head, the port and bowl are left slightly rough, with carbide cutter marks. This also has a side benefit of keeping fuel in suspension, and from condensing on the walls of the port. Quote Link to comment Share on other sites More sharing options...
Mick Bell Posted January 15, 2005 Author Share Posted January 15, 2005 On further examination of the horns, they don't seem to have been manufactured with much concern about the surfaces. Which to me says the shape is more important than the texture of the surface. The cast aluminium is smooth but not slick and in fact in some places (welds) quite rough (particularly in the vertical fins). It doesn't seem to me that a good coat of black paint -- to cover the original green -- could do much harm. Mick Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 15, 2005 Share Posted January 15, 2005 double post sorry Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 15, 2005 Share Posted January 15, 2005 Actually I watched a creative tv show that showed the basis of why golf balls have dimples. Actually it was about this bomb the allies had in WWII that skipped off the surface of the water to hit dams and break them. The dimples actually cause turbulance on the surface of the the ball. Why would you want turbulance? because turbulance doesn't allow the air to stick on the surface of the ball. They showed it by using a smooth golf ball and not. It was proven that the golf ball with dimples went further because it reduces hooking (where the ball would drift one way or other) and thus further increased distance. Since golf balls usually do not carry a spin unless specifically hit to create a backspin, golfballs move with little movement. Bullets stay in a straight projectory due to the rifling spin. But golf balls do not gain lift by the dimples I believe. Bernoulli's effect says low pressure creates lift but since all the ball is created symmetrically (unless you buy those directionaly and partly illegal golf balls that cost 20 bucks each) it should not create any lift. That is why airplanes wings have more surface area on the top then the bottom. makes the air travel further to get to the other side or makes it high pressure on the top. simples and cool experiment. get a piece of paper and put the edge next to your lips. but blow air only above the top part, if you blow hard enough the papaer should get lift. I believe michael was touching on the turbulence effect with the car port head. edit: I just found a website to give the explanation a bit more. http://www.howstuffworks.com/question37.htm Quote Link to comment Share on other sites More sharing options...
JJkizak Posted January 15, 2005 Share Posted January 15, 2005 Actually bullets are spun and usually precess to the right, but the same amount each time so once you sight the gun in it's the same every bullet. If the bullet does not spin it acts like a knuckle ball, that means you don't know where it will end up. This is the same for big guns like 12" on battleships. JJK Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 15, 2005 Share Posted January 15, 2005 ---------------- On 1/15/2005 12:13:12 PM JJKIZAK wrote: Actually bullets are spun and usually precess to the right, but the same amount each time so once you sight the gun in it's the same every bullet. If the bullet does not spin it acts like a knuckle ball, that means you don't know where it will end up. This is the same for big guns like 12" on battleships. JJK ---------------- Since golf balls usually do not carry a spin unless specifically hit to create a backspin, golfballs move with little movement. Bullets stay in a straight projectory due to the rifling spin. as per above Quote Link to comment Share on other sites More sharing options...
Mick Bell Posted January 15, 2005 Author Share Posted January 15, 2005 Since sound travels roughly 700 mph at sea level and it's going to travel over the surface of this horn for a maximum of 14 inches, I don't believe it's going to be affected very darn much whether it travels over the rough cast aluminum or over a smoother painted surface. Mick Quote Link to comment Share on other sites More sharing options...
michael hurd Posted January 15, 2005 Share Posted January 15, 2005 If you are wanting to refinsh them, and they are origianlly green, then have them soda or glass bead blasted. Then you can spray on a coat of a durable epoxy primer sealer, followed by a low-sheen satin black finish. Unless you are willing to spend hours grinding to smooth all the welds, a satin finish is about your best bet. Quote Link to comment Share on other sites More sharing options...
Jim E Posted January 16, 2005 Share Posted January 16, 2005 Mick, In the past I have taken 511 and 811 horns to the local powder coating shop. They can produce any type of finish you could want from flat to high gloss. Even hammertone. The process is very durable and looks fantastic. I'm sure the type of finish does'nt effect the sound much. Altec painted these flat green, hammertone green and semi-flat black. I would choose what looks best for your app. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 16, 2005 Share Posted January 16, 2005 Just a thought would it not be best to make the material as dense as possible? like adding material to make it sturdier? how about some clay on the other side to make it less prone to vibrate? just a thought. Quote Link to comment Share on other sites More sharing options...
Mick Bell Posted January 16, 2005 Author Share Posted January 16, 2005 Thanks, Jim. I appreciate the response. Mick Quote Link to comment Share on other sites More sharing options...
Marvel Posted January 16, 2005 Share Posted January 16, 2005 The wavelength for 20kHz is 0.678 inches. If you are talking about an 811, the lower end 800Hz is over 16 inches (16,95). Going on up to 5kHz you are still pretty long at 2.712 inches. It isn't going to make much of a difference. Marvel Quote Link to comment Share on other sites More sharing options...
sunnysal Posted January 17, 2005 Share Posted January 17, 2005 btw yaffstone, the latest swim suits (like those used in the olympics) are textured with dimples, etc. to reduce friction in the water. the same systems are beginning to be used on airplane wings (the top surface) the idea is to break the laminar flow from the surface...golf balls, airplane wings, swimsuits and horn interiors...regards, tony Quote Link to comment Share on other sites More sharing options...
WMcD Posted January 18, 2005 Share Posted January 18, 2005 When this started, I thought it was a foolish question. Now I think it is a rather profound question. Additional profound questions have come up. I do think the notion that an airplane wing works because the air travels a farther distance over the top than the bottom is a great old wives tale . . . and should be challenged. Look at a sail boat sail or a hang glider wing. The "wing" is just a thin piece of curved cloth. There is no difference in path length to speak of. Yet each produced an overall force perpendicular to the relative air flow. So when there is no path difference, there is still lift. The same can be said of our little balsa wing toy gliders. There is the same sort of curve and the balsa wing is very thin. No path length difference. In a typical airplane wing the top camber is indeed longer. Yet there are diagrams of the measured air pressure at each point along the surfaces. They are very messy. At some points on the top there is relative positive pressure. It all just averages out to a lift. Of course we should be suspicious at any explanation that assumes the little air molecules have two synapses to rub together. It is as if the guys on the top surface "know" they have to go faster to catch up with their brothers at the bottom surface. How do they know there is a bottom surface in any case? Smile, Gil Quote Link to comment Share on other sites More sharing options...
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