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Dave A

La Scala Bass Bin Mid Brace

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1 hour ago, DizRotus said:

Notice they are not vertically centered.

 

I’m not so sure of that.... not the best picture for that determination since the chair arm is blocking the view of one brace and it could be a visual illusion caused from that and the camera angle.

 

miketn

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  I dream over the top. How about two braces per side? Maybe closer together than thirds, say gaps of 35-30-35% of height to better contain the mid panel deflection and spread the resonance frequency?

  I have a giant roll of automotive double sided “tape” used to attach trim to cars. Sticks to paint and varnished surfaces. Grey rubber looking stuff.

  Do not laugh, used it to mount some LED lights under kitchen cabinets. A friend laughed when they saw my project. But they have been there over 16 years now. Never drooped or fell. Yet.

  I am sure it would work great to temporarily mount these braces. Plus not damage the finish of the LS ii. 

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5 hours ago, DizRotus said:

Notice they are not vertically centered.

 

How can you tell with the bottom hidden? If it is off it is not as much as John's was.

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13 hours ago, DizRotus said:

EDIT 9/7/19 @ 08:47 EDT

 

I see this photo was posted earlier.  It’s comforting to see hat PWK’s lab was no neater than my workspace.

 

 

@pzannucci noticed the braces in the attached photo @HDBRbuilder posted in the thread about the new H4.  Clearly PWK was aware of the sidewall resonance issue and braces as a possible solution.  Notice they are not vertically centered.

 

49BD074E-51C6-429D-BD4E-4862C0C78971.jpeg

The braces ARE vertically-centered to the bass bin portion of the speaker...which is where they are needed...the HF portion is a non-issue.  BTW, there are numerous ways to brace (AKA STIFFEN) the bass bin side panels...from the inside OR the outside of the bass bin.  For instance, one could apply a vertically attached solid-wood just to the mouth of the bass bin sides...such as taking a solid dowel...and running a rabbet along it so that it could be mounted where its curvature began at the forward inside edge of the bass bin side panel, with no interference with the with the inside edge of the mouth of the inside edge of the side panels...make sense?  I would opt for at least a 1" diameter dowel...preferably 1.5" diameter...in birch or oak.  That would be sufficient to eliminate the resonance, since the bass bin side panels area already stiffened along the top and bottom and rear of the bass bin construction.  Make sense? Not only that, but for aesthetics-sake, one could run the dowels all around the perimeter of the entire cabinet, using miters at each corner!

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Not sure how much good it did, but these are glued and nailed 3/4" square cherry.  I still would add braces, an inch off center, if I were to do another pair.  I hate it, but I think Cy retired. 

 

post-2142-13819247217712_thumb.jpg

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I have been told twice this week that there should be a radius on the wood at the mouth of the horn and preferably 1/2" at least. I did that with the set I rebuilt into 25mm Baltic Birch as a two piece in the bass bin mouth. It was clearly better than this set is. Now there was more than one variable between the two sets I still wonder what effect the rounding had and if it is worthwhile pursuing from now on. A question I am taking to Roy next month for sure.

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2 hours ago, Dave A said:

I have been told twice this week that there should be a radius on the wood at the mouth of the horn and preferably 1/2" at least. I did that with the set I rebuilt into 25mm Baltic Birch as a two piece in the bass bin mouth. It was clearly better than this set is. Now there was more than one variable between the two sets I still wonder what effect the rounding had and if it is worthwhile pursuing from now on. A question I am taking to Roy next month for sure.

a stiffer mouth will have a significant impact upon low end performance, you have to have a large radius to improve diffraction.

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7 hours ago, HDBRbuilder said:

The braces ARE vertically-centered to the bass bin portion of the speaker...

 

Cant disagree with you Andy, you were there.  Upon closer inspection, I was starting to agree the braces could be centered, now you eliminate any doubt.

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2 hours ago, Dave A said:

I have been told twice this week that there should be a radius on the wood at the mouth of the horn and preferably 1/2" at least. I did that with the set I rebuilt into 25mm Baltic Birch as a two piece in the bass bin mouth. It was clearly better than this set is. Now there was more than one variable between the two sets I still wonder what effect the rounding had and if it is worthwhile pursuing from now on. A question I am taking to Roy next month for sure.

Then running a rabbeted 1.5" dowel up vertically would ALSO provide that radius, wouldn't it?  EXCEPT that instead of REMOVING any of the wood from the inside, you would merely be adding the radius to the front edge....the rabbet I am talking about would, if you saw it from the end of the 1.5" diameter dowel, look like 90 degrees of the wood is missing in a "removed pie slice"...make sense?  It would have a total FRONTAL width of 1.5", seeming to "wrap around the outside of the bass bin side panels...this would stiffen up the front edge of the side panels, which are already stiffened up everywhere else...eliminating any flex possible due to resonances at the mouth of the horn lens.  I sure wish I had a modeling program to play with, because a picture is worth a thousand words.

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