Re: more on fin cutting [message #41264 is a reply to message #41256] |
Thu, 08 May 2003 10:09 |
AstroSonic
Messages: 58 Registered: May 2009
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Baron |
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TDC, I am pretty much convinced that fin cutting will be a part of my 511B ringing control plan. Sam P. (below) also did this and reported good results. He used a sawzall and needed to make several cuts per fin to remove enough material. How did you cut them and what tool(s) did you use? Any hind-site observations greatly appreciated. Good idea using the radial tire matrerial (to damp radial horns!). In as much as I do play some blues and rock on my system, perhaps I should use material from off-road radials. Regards, AstroSonic
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Fin cutting - Just the welds! [message #41266 is a reply to message #41265] |
Thu, 08 May 2003 11:12 |
AstroSonic
Messages: 58 Registered: May 2009
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Baron |
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TDC, Just to clarify: I am considering cutting out only the welds and/or enough material to leave an open (damped) gap in each fin. That is what Sam P. did as well. In searching the archives here I did run into a post by someone who had cut out the fins entirely and reported no improvement beyond that obtained from just cutting out the welds and leaving a (damped) gap.I had not considered a cutting wheel for cutting out the welds. I imagine that the working room was pretty tight? The hand drill I have would probably not allow a square cut with a cutting wheel - it would have to be angled in. Were you able to get reasonably straight, clean cuts? How would you describe the resulting improvements in sound quality? Regards, AstroSonic
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Re: Just say no to dope [message #41267 is a reply to message #41243] |
Thu, 08 May 2003 12:14 |
bmar
Messages: 346 Registered: May 2009
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Grand Master |
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First I had the little brother 811B horns. I did not cut the fins because I was happy after damping them. I don't think cutting the fins on a 811 or 511 is an issue. The horns are not so rare that it will decrease the value. If they cut with a good saw, water, laser, plasma arc. You wont even hardly see the kerf.I build boxes that went up to the rear flange. I wanted the ability to change the driver conveniently. If your going to use the same driver you could box the whole rear portion. On the front side the sides of the box came up to the flange but the top and bottom extended past the flange. I would consider this a matter of taste in decorating only. You could damp the lips if the cabinet covered them too. I pretty much always multi amp this stuff. Almost all compression drivers need compensation when used in a 2way or 3way, and I wouldn't cross a 511 any lower than 750 - 1000 hz IMO Bill
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Re: Just slice them [message #41268 is a reply to message #41262] |
Thu, 08 May 2003 12:18 |
bmar
Messages: 346 Registered: May 2009
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Grand Master |
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I dont know anyone who has ever cut the fins out. You just slice the fin right in the middle at the welded joint. If you want to get tricky you can fill the kerf with an elastomer like SikaFlex and repaint the horn. The metal will still be seperated and stress relieved yet invisable as a cut.Bill
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Breakup modes and crossover points [message #41270 is a reply to message #41255] |
Thu, 08 May 2003 12:59 |
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Wayne Parham
Messages: 18791 Registered: January 2001
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Illuminati (33rd Degree) |
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About crossover points, I want to point out that all speakers using cones or domes (including compression drivers) are operated through much of their range in a mode that introduces cone flex. This has been called breakup mode operation, and no speakers are immune. While most designers attempt to suppress this mode of operation, many have designed features that take this behavior into consideration, some taking advantage of it to extend response. An example is whizzer cones, which are designed to move independently of the rest of the cone at high frequencies. The fact is that it is difficult - bordering on the impossible - to create a speaker using current technologies that doesn't enter this mode of operation. Over the years, I've crossed large-format midwoofers a variety of crossover points from 100Hz to 3kHz. Usually in a three-way system, I'm using the LF driver as a woofer and crossing between 200Hz and 500Hz. That tends to keep the woofer in its pistonic range, or within an octave of it. I tend to expect 250Hz is pistonic range and 500Hz is the first breakup mode. In a two-way system, I'm usually crossing over much higher, in the octave where midwoofer DI and compression horn DI match - between 800Hz and 1.6kHz. In this regard, my designs are much like JBL's two-way monitor speakers that are almost always crossed over above 1kHz. The JBL 68881 is a 1.5kHz passive two-way crossover and it is a good example, being used with a 15" midwoofer and a 1" exit compression horn tweeter on a radial horn flare. But whether a person uses two-way or three-way configurations, the drivers are going to be used in their breakup modes over a large part of the audio band. I think its important to consider all things, and drivers that are designed to be used at high frequencies usually have well-behaved cone flex patterns and don't become excessively anomalous. Lots of high-efficiency drivers are made this way, especially compression drivers and high-efficiency large format cone midrange and midwoofer drivers. I find that a well-designed midwoofer operates pretty well in the vocal range, provided its breakup modes are well damped, which is something that is easy to determine from its response graph.
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