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Dave A

La Scala Bass Bin Mid Brace

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I recently decided to try bracing and see if it could produce results perhaps as good as beating off sides and replacing with 25mm Baltic Birch. The other one I did this too had a two piece cabinet and the top section was made large enough for my Large MAHL tweeter with the DE10. What the brace did is a big improvement and I decided that going all the way back was overkill. I had clamped wood to the side of the bass bin in the rectangular section adjacent to the back on the sides and it did not sound like it did anything more than the braces pictured below did.

 

   Cutting five of these, four for use and one for a quick and easy pattern makes me believe these bass bins are pretty consistent as there were no gaps and voids. I cut these a bit short so the narrow end would not go all the way back to that little flat section at the end of the doghouse bevel. This allows one to tap it in place and if needed remove and sand to fit at that time. I drew a centerline on the sides and doghouse where the brace would touch and then a line 1/2" above that for visual on alignment. Drilling two holes through the centerline of the doghouse bevel where I can get to them from the inside with a stubby screwdriver to aid in screwing this brace in.  Glue the two sides of the brace where it will contact the sides and bevel and tap it in place and hold it in place with a clamp while I screw the brace to doghouse bevel.

 

   Dont hammer this brace in as far as you can but do it just enough to be really snug. To far and you will put stress on the sides you will regret later if things split apart.

 I like this brace idea and it really reduces resonance. The DE10 though with the larger MAHL is a whole different animal and I just might try a stand for this to put on the top rather than build a whole new top section just to see how this goes. I am also coming to the conclusion that if you really want your La Scalas to sing you are probably going to have to do some room EQ too. Anyone who comes over to look at these La Scalas I am working on will listen to them with and without room EQ and they can decide what they want to do.

La Scala bass bin braces.JPG

Brace dimensions.JPG

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😀

 

If mine weren't already finished when I discovered their vibrating mouth, .......

 

msg-43-0-95880000-1424364411_thumb.jpg

 

Place them an inch or 2 off center so you do 't just double the original resonance. 

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1 hour ago, JohnA said:

😀

 

If mine weren't already finished when I discovered their vibrating mouth, .......

 

msg-43-0-95880000-1424364411_thumb.jpg

 

Place them an inch or 2 off center so you do 't just double the original resonance. 

OK explain to me why this is better. I figured the center would work best for looks and noise abatement. Hey you need to stop in and hear the S-MWM's

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1 hour ago, Dave A said:

OK explain to me why this is better.

Yes, that was an interesting statement.  I'm curious as well.

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Speculation on my part, but if you put them dead center, you've shifted the frequency x2 from where it once was, and have 4 surfaces where that can happen.  If you offset them slightly, you no longer have an exact harmonic of the fundamental resonance frequency, and you've reduced the area for resonance as well.

 

Am I close?

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Sorry, cant do that. I need symmetry in my life. I don't care how it sounds, it has to look right or it will drive me crazy. Ok, i made the part up about not caring what it sounds like.

Still going to look wrong.

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OK well using the orbital sander research tool the very loudest sound happens at the center front of the sides so I figure that was where to dampen.

2 minutes ago, codewritinfool said:

fundamental resonance frequency

Is beyond my pay scale so you will have to explain all this.

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3 minutes ago, codewritinfool said:

Speculation on my part, but if you put them dead center, you've shifted the frequency x2 from where it once was, and have 4 surfaces where that can happen.  If you offset them slightly, you no longer have an exact harmonic of the fundamental resonance frequency, and you've reduced the area for resonance as well.

 

Am I close?

The whole point is to stop the vibration.  I would think that putting it in the middle would be the best solution for bracing the side.  I never really thought about the smaller sections vibrating.

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Offset bracing is a great idea, just as effective as an offset woofer on the motorboard however i felt the same way about looking at the offset bracing as being sad to look at and chose a center position for my La Scala's and am not unhappy with the results. The coloration is no longer bothersome as it was.

 

Here is a good >link< and lots more on the subject if you take a little time to Google

 

My set for reference.

 

517461874_canon001-1.thumb.jpg.04bf8e57b5e5c25706dddd2e0456bfe5.jpg1695371808_canon004.thumb.JPG.7ee6fc32d21660bd349e2e60c61473e2.JPG

 

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They wouldn't have to be offset so much you could detect it by eye.  Just a tiny bit would serve to avoid making a 2nd harmonic resonance point.

 

Of course, this assumes a few things....

 

1. That I know what I'm talking about.  I don't, necessarily, but it's just physics and seems logical to me.

2. That the resonating point is the side wall.

 

You'll have to wait for someone that knows what they're doing to chime in.

 

BTW, I think I need some of those beautiful braces for my splits!

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13 minutes ago, codewritinfool said:

They wouldn't have to be offset so much you could detect it by eye.  Just a tiny bit would serve to avoid making a 2nd harmonic resonance point.

 

Of course, this assumes a few things....

 

1. That I know what I'm talking about.  I don't, necessarily, but it's just physics and seems logical to me.

2. That the resonating point is the side wall.

 

You'll have to wait for someone that knows what they're doing to chime in.

 

BTW, I think I need some of those beautiful braces for my splits!

 

Every cabinet is off just enough to make each brace different unfortunately, you will need to fine tune each brace as you install.

 

Yes, hope somebody with some experience will give some details. :rolleyes:

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I agree with the notion of off-center.  I remember as a kid playing with an acoustic guitar, a clamp-on-the-edge-of-the-hole pickup, amplification, and speakers.  Could get a string swinging with just the right amount of feedback, then briefly touch it in the middle and the middle stays motionless while the two halves switch right into swinging back and forth in opposite directions.

 

Placing the bottom edge of the stiffener on the centerline instead of the center on the centerline may be enough offset to prevent that.

 

Being a tad off-center vertically might appear as being centered when viewing from above or below center anyway, what with "perspective" and all.  I remember reading back in the day how Rolls-Royce made the vertical bars in the grille slightly bowed (opposite) sideways so they'd appear parallel, which they didn't when straight due to the front-to-back bow of the grille when viewing from above.  (Going for that extra 4% in resolving power? Hahaha)

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Well, first, look at the Pic.  What did Mr. Paul do? 

 

What happens to a guitar string when you fret it at the 12th fret (mid span)?  You get the same note and octave higher (2f).  If the side walls want to ring at 140 Hz, what will stop them from ringing at 280 Hz (unbraced, it already does)?  Only the internal damping of the plywood and the ratio of the sidewall's new stiffness to the energy applied.  If you offset the braces, you now have 2 different resonant frequencies (2 different unbraced lengths) that are no longer integer multiples of each other and thus are less likely to reinforce each other even if they do resonate a little. 

 

If you strike one tine of a tuning fork, does the other one vibrate? 

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Well, first, look at the Pic.  What did Mr. Paul do? 
 
What happens to a guitar string when you fret it at the 12th fret (mid span)?  You get the same note and octave higher (2f).  If the side walls want to ring at 140 Hz, what will stop them from ringing at 280 Hz (unbraced, it already does)?  Only the internal damping of the plywood and the ratio of the sidewall's new stiffness to the energy applied.  If you offset the braces, you now have 2 different resonant frequencies (2 different unbraced lengths) that are no longer integer multiples of each other and thus are less likely to reinforce each other even if they do resonate a little. 
 
If you strike one tine of a tuning fork, does the other one vibrate? 


Yes! This is what I was trying to say.

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When the band director first complained about what were confirmed to be resonance problems at the sidewalls, the quick diagnostic “solution” was to wedge short dowels between the sidewalls and the doghouse where the doghouse roofline is closest to the sidewalls.  The improvement was immediate and dramatic.

 

Eventually, I fashioned the braces shown below.  Did I measure precisely on this pro bono project?  I did not.  Were the speakers plagued by new resonances at higher frequencies?  They were not.

 

Unless we want JDM to weigh in, IMO, you might as well argue about fairies on a pinhead.  Braces are good; no braces is bad.  Exact position doesn’t matter.

 

YMMV

 

 

post-6832-0-52040000-1442844835_thumb.jpg

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2 minutes ago, CECAA850 said:

EDIT

 

Now you’ve really piqued my curiosity.

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3 hours ago, jason str said:

Offset bracing is a great idea, just as effective as an offset woofer on the motorboard however i felt the same way about looking at the offset bracing as being sad to look at and chose a center position for my La Scala's and am not unhappy with the results. The coloration is no longer bothersome as it was.

 

Here is a good >link< and lots more on the subject if you take a little time to Google

 

My set for reference.

 

517461874_canon001-1.thumb.jpg.04bf8e57b5e5c25706dddd2e0456bfe5.jpg1695371808_canon004.thumb.JPG.7ee6fc32d21660bd349e2e60c61473e2.JPG

 

 

Want to-make a few bucks and make me a few?

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3 hours ago, jason str said:

Offset bracing is a great idea, just as effective as an offset woofer on the motorboard however i felt the same way about looking at the offset bracing as being sad to look at and chose a center position for my La Scala's and am not unhappy with the results. The coloration is no longer bothersome as it was.

 

Here is a good >link< and lots more on the subject if you take a little time to Google

 

My set for reference.

 

517461874_canon001-1.thumb.jpg.04bf8e57b5e5c25706dddd2e0456bfe5.jpg1695371808_canon004.thumb.JPG.7ee6fc32d21660bd349e2e60c61473e2.JPG

 

Those look great 👍

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