Home » Sponsored » Pi Speakers » Damping 511B ringing: Whats your experience?
Re: more on fin cutting [message #41264 is a reply to message #41256] Thu, 08 May 2003 10:09 Go to previous messageGo to next message
AstroSonic is currently offline  AstroSonic
Messages: 58
Registered: May 2009
Baron
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

Re: more on fin cutting [message #41265 is a reply to message #41264] Thu, 08 May 2003 10:27 Go to previous messageGo to next message
tdc is currently offline  tdc
Messages: 34
Registered: May 2009
Baron
Since I only cut the welds I used a cuttng wheel on a drill. If you want to remove the whole fin you would need something more. I don't know what you would gain by removing the fins. The idea is to release the pressure on the bell part of the horn which contibutes to the ringing. At least thats what Altec told me. tdc
Fin cutting - Just the welds! [message #41266 is a reply to message #41265] Thu, 08 May 2003 11:12 Go to previous messageGo to next message
AstroSonic is currently offline  AstroSonic
Messages: 58
Registered: May 2009
Baron
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

Re: Just say no to dope [message #41267 is a reply to message #41243] Thu, 08 May 2003 12:14 Go to previous messageGo to next message
bmar is currently offline  bmar
Messages: 346
Registered: May 2009
Grand Master

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

Re: Just slice them [message #41268 is a reply to message #41262] Thu, 08 May 2003 12:18 Go to previous messageGo to next message
bmar is currently offline  bmar
Messages: 346
Registered: May 2009
Grand Master

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

Re: Fin cutting - Just the welds! [message #41269 is a reply to message #41266] Thu, 08 May 2003 12:38 Go to previous messageGo to next message
tdc is currently offline  tdc
Messages: 34
Registered: May 2009
Baron
I did all the steps more or less at once. I did not conduct extensive listing test with each step progress. There is some improvement but its not like going from a bad crossover to a perfect one. When you strike the horn after all the above is done there is a dull lower thud and you know its dampened. You could also use the horn to make a cast and then pour the cast with depleated uranium from surplus operation Iraqi Freedom shells. Now that would be dead. tdc
Breakup modes and crossover points [message #41270 is a reply to message #41255] Thu, 08 May 2003 12:59 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18791
Registered: January 2001
Illuminati (33rd Degree)
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.

Depleted uranium and radial tire rubber [message #41271 is a reply to message #41269] Thu, 08 May 2003 13:02 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18791
Registered: January 2001
Illuminati (33rd Degree)
Depleted uranium and radial tire rubber! Only dampen radial horns with rubber from radial tires! [grin]
Re: Depleted uranium and radial tire rubber [message #41272 is a reply to message #41271] Thu, 08 May 2003 13:36 Go to previous messageGo to next message
tdc is currently offline  tdc
Messages: 34
Registered: May 2009
Baron
Hi Wayne. On cone break up. The comment pertains to the over 50 year old Altec 416a which I use with the 811b in the A-7 set up. It seems to work well up to about 800-1200 but not at 1600hz. I have 4x 4648a boxes with 2226 woofers. One pair is used with the Pi crossover at 1600 hz ( pseudo Butterworth) to the JBL 2426-2370. I hear no break up or any problem with this woofer in your design. I love it. The old Altec system is used with triodes and vinyl. Its warm and wonderful but maybe a bit fat. Goes well with Merlot, Cabs and Zinfandel. I use your system with s.s. amps (Crown and Apt) for everything else. tdc
Re: Depleted uranium and radial tire rubber [message #41273 is a reply to message #41272] Thu, 08 May 2003 13:50 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18791
Registered: January 2001
Illuminati (33rd Degree)

Gotcha on the 416. I suspected that you might be talking about a part that didn't like going up so high. There's lots of 'em that are great parts but that get a little edgy up top. I just wanted to mention the breakup thing 'cause there lots of midwoofers that get way up there smoothly.

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