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La Scala resonance problem


Dave A

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1 minute ago, mikebse2a3 said:

How does the splitter size compare to the one in the La Scala AL5...?

 

 

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BAF10127-6633-4BB0-A65C-5B7C33EEF71A.jpeg.d129a78016e858bf7d95c9c6bc5ce00f.jpeg

 

Smaller and that one looks smaller than the ones I have seen in the La Scalas from the 80's and 70's. It looks more like a true equal leg triangle.

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This is an oddball possibility, now that I understand the problem is more of a howling sound (orbital sander ....). If the signal was not "going through" the series inductor on the lowpass crossover, could this be harmonic distortion coming from the K-43? Again, I assuming this "noise" was not present prior to swapping the old crossover with the "new" AA one.

 

It is an odd possibility, but it  might explain what you are hearing. Easy enough to track down with a volt meter and a tone generator (even a crappy one on the internet).

Good Luck,

-Tom

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57 minutes ago, PrestonTom said:

This is an oddball possibility, now that I understand the problem is more of a howling sound (orbital sander ....). If the signal was not "going through" the series inductor on the lowpass crossover, could this be harmonic distortion coming from the K-43? Again, I assuming this "noise" was not present prior to swapping the old crossover with the "new" AA one.

 

It is an odd possibility, but it  might explain what you are hearing. Easy enough to track down with a volt meter and a tone generator (even a crappy one on the internet).

Good Luck,

-Tom

I don't think that is such an Odd idea

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1 hour ago, PrestonTom said:

could this be harmonic distortion coming from the K-43?

As I replied to John I have also used a brand new Kappa 15c and same thing. I will be back on this thread when I have an answer as we are all guessing and there will be an answer. I can't rule out something simple I am overlooking but what it is is not apparent yet. I do appreciate some of the tips which I have tried or will soon try.

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The Kappa will still be going through a series inductor as part of a low pass. So the problem could still exist. I will admit that the possibility of a the inductor being "shorted" or something is remote.

 

Although this is not the fundamental problem, will the crossover be re-worked now that the Kappa is installed?

 

Yes, you are correct that we are all guessing about a problem that is not in front of us.

 

Good luck,

-Tom

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I'd like to offer any encouragement which will give Dave the "OK" to experiment on his splitter.  

The smaller than expected splitter could be a "test-bed" for the smoothness of a modified example.

The shaky jpg mouse activated example below, is itching for a 3-D rendering, but it's meant to be a 3 sided triangle (the width of the woofer port) and cut with a triangular notch in the top and bottom, to slide in from the back side (sans the rear panel)

 

 

Splitter Mod idea.pdf

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Well when I re-veneered mine I put a few screws in the side panels and then veneered. Before I could move side walls very easily with just my hands. Where now I can put my knee on one side and both hands on the other and cant even budge it.

So if he added material on top of the old panels and the underlayment ones were not tight it would vibrate would it not? 

Another idea I think it could be is the mid range horn is loose have you tightened up all screws? Also the woofer access panel could be leaking making noise also.

Also have you tried a new woofer inductor such as this one ? https://www.parts-express.com/erse-super-q-25mh-16-awg-500w-inductor-crossover-coil--266-908

I replaced mine on my K-horns cause they were from 1972. 

Its hard diagnose a sound with out actually hearing it but I cant think of any others that weren't already mentioned. 

 

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OK here is my stupid speaker guy story. Turns out that when you put a nice shiny new set of those great MAHL tweeters in a La Scala that you ought to remember to tighten the clamp plate to the lens body. Finger tight does not work real well and when the start loosening it gets real interesting. As I hang my head in shame and slink off tonight thinking you just never know the limit to bone headed things that can be done.

  The flip side to the story is that braces work and I will post pictures of quick and easy later this week.

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9 hours ago, ricktate said:

Also have you tried a new woofer inductor such as this one

OK the old OEM coil measure very close so is there an advantage to replacing it with a new one? I figure these are not like caps that go bad.

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17 minutes ago, Dave A said:

OK here is my stupid speaker guy story. Turns out that when you put a nice shiny new set of those great MAHL tweeters in a La Scala that you ought to remember to tighten the clamp plate to the lens body. Finger tight does not work real well and when the start loosening it gets real interesting. As I hang my head in shame and slink off tonight thinking you just never know the limit to bone headed things that can be done.

  The flip side to the story is that braces work and I will post pictures of quick and easy later this week.

Glad you got it solved.  Would have drove me insane racking my brain trying to figure it out. 

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9 hours ago, glens said:

So did you make it sing steadily while you poked/prodded around or did you start at the bottom and work your way up checking every fastener, finally stumbling onto the pea under the mattress?

I took a rubber mallet and started tapping to see where the sound might come from. By ear it was hard to see where and I will buy a stethascope if this happens again before trying to find the rattle. The howl from this was most prominent from the bass bin while being played but the top section had the rattle when tapped on. Eventually I put my hand on the tweeter by accident and there they were loose. New tweeters were not in consideration at all but you can bet I will double check from now on.

 

2 hours ago, PrestonTom said:

I like a story with a happy ending. 

Me too even if it is a bit embarrassing.

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12 hours ago, Dave A said:

OK here is my stupid speaker guy story. Turns out that when you put a nice shiny new set of those great MAHL tweeters in a La Scala that you ought to remember to tighten the clamp plate to the lens body. Finger tight does not work real well and when the start loosening it gets real interesting. As I hang my head in shame and slink off tonight thinking you just never know the limit to bone headed things that can be done.

  The flip side to the story is that braces work and I will post pictures of quick and easy later this week.

Sounds like something I'd do.  Those kind of issues drive me crazy till I figure it out.  Glad you found it.

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11 hours ago, windashine said:

... o O ( after 15 year's )

 

thinking that we need to see sawdust, and a 4" horizontal splitter screwed in there, along with a woofer motorboard reinforced with 1/2" steel angle iron....

 

.... o O (just because) 

I do have an idea for the back side of a La Scala but not quite that large. Wonder what a 1/2" aluminum plate La Scala would be like?

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This story brings up a point I have never had occasion to share.

 

I have removed tweeters to replace diaphragms only to find the bolts holding the lenses on were loose enough to be spun off with one finger.

 

Certainly something to keep in mind when giving a used set of speakers the once over.

 

Great to hear the successful resolution of this.

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