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La Scala tweaks and hacks? Hit me


jimjimbo
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As you may or may not have seen in another thread, I am in the process of rehabbing a pair of fairly beat up La Scala's.  Right now I have all of the drivers and horns out, the doghouse open, and they are just an empty shell.  While they are in this state, and when I begin to reassemble, I'd like to hear some suggestions from you LS owners and gurus as to the best, cost effective (and relatively easy) tweaks and hacks to make.

 

Some assumptions:

 

1.  I will not be cutting the cabinets or adding bass bins, etc.

2.  I will be using stock parts (except for some crossover parts)

 

OK, so for example....I have the doghouse open.  After re-installing the woofer, does the door need to be sealed with some kind of gasket material, or is the myriad of screws enough?

 

Next - Using a strong adhesive on all of the cabinet joints?  I'm assuming yes.

 

Any damping material to be installed anywhere inside the cabinet?

 

Tennis balls on the side walls????  

 

If there's a link to a previous thread that addresses this and other things, please send it on to me!!  Thanks very much.  

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Jim

 

Do not dampen the bass bin.

 

Seal the woofer enclosure so it does not leak & check the driver screws to make sure they are tight. To check for leaks run a 20-25 Hz tone through the woofer and use a few feet of airhose or vacuum line from your ear around your seal, if its leaking you will hear it better that way.

 

Use a wooden wedge to keep resonances down from the driver enclosure to the outer panels. Tennis ball may help a little but if you're going to do it may as well do it right.

 

Replace your worn crossover caps.

 

Check your gaskets (horn to driver)

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I haven't searched yet, but there has GOT to be a definitive thread on mods for the LS.  Probably a bunch of threads, with everything from full on replacement of parts to quick and easy.

 

Mustang Guy has got 3 pairs of LS on-line at his speaker ranch, and I know he has done extensive restoring of some of the cabs at one time or another.  I bet he has some ideas.

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No, no, no. Not wood glue on the hatch. You'll never get it open again.

I've built several bass horns of the LS type years ago and even K-Horns. And there are others here who have rebuilt units.

You do need some gasket material. One-quarter inch weather stripping will be good. The problem for me was where the ends meet. I tapered them for side by side overlap. An alternative is to cut a continuous gasket out of something like yoga mat or shelf liner.

It is the wisdom of ages that the seams inside the back chamber have to be air tight. Dr. Bruce Edgar (big horn guru) said he used cheap caulking. He said, I'm not sure it works but it lets me sleep at night. I used RTV (room temperature vulcanizing) bathtub caulking.

There is also the place where Klipsch uses some brass machine screws to pass the electrical connection through. I think some RTV on that place might give peace of mind.

As far as mods. There is the notion that the side walls resonate. In the LS II this was addressed by the use of one-inch MDF. But people are, I think wisely, adding a piece of wood from the doghouse to the side wallss.

WMcD

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Tennis ball may help a little but if you're going to do it may as well do it right.

 

Yea, I sort of said that about the tennis balls partly in jest, but I know that we've all seen it....

 

I have to say, this really is quite enjoyable.  I have had lots of speakers in various states of disrepair, but never had to rebuild them quite like this.  I know lots of other guys have done much more extensive work.  Looking forward to many more inputs.  Again, links to other threads are just fine and dandy.

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Don't Use glue on the dog box cover instead use automotive foam weather tape its self adhesive on one side and available in several thickneses

Use new driver gaskets if required

Never use any damping in the dog box

You can use wood glue for joins as required

You can use a clamping device to stop bass driver resonance vibrations

Budget allowing my recommendation is to replace the crossovers with modern alternatives

Brace the side walls with extra Ply or MDF to add thickness OR add external braces but I prefer x 4 per cabinet (2 per side) see link http://www.klipschupgrades.com/lascalabraces.shtml

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Two basic and cost-effective tweaks for La Scalas are new capacitors for the crossovers, and new CT125 tweeters.

If the caps are more than fifteen years old, they're well past their prime. Installing new and more modern types will improve the clarity of the sound.

The stock K-77 tweeters start to peter out above 14KHz, plus older ones will likely no longer have exactly the same output, meaning your stereo image is compromised. The CT125 tweeters go straight in, although you may need to relieve the cabinet lid a little if the driver touches it. They also improve the clarity of the sound.

I fitted new caps and tweeters to my La Scalas a few months after I got them. I did the caps first and the tweeters a few days later, so it would be possible to see what each change did. It was well worth it. I was much happier with the sound.

One more tweak is cheap and easy, but a bit controversial. My La Scalas had rough-looking K400 horns. The insides were lumpy and the paint was blotchy. As well, the sound was kind of "shouty".

To fix both problems, I bought some stretchy black grille cloth and stapled it to the inside of the front of the cabinet, which both hid the mid horn and smoothed out the sound. After some experimenting with different thicknesses of cloth, I settled on three layers as sounding best to my ears. Your ears may decide that one or two layers is enough. Don't cover the tweeters, as the cloth will have a greater effect on them, and will cause the sound to sound a bit muffled.

If you'd really like to take the sound to the next league, and don't mind spending quite a bit of money, look into the JubScala conversion. That means replacing the squawker and tweeter with a Jubilee tweeter, which is a K-69 driver and K510 (large) or K402 (huge) horn. This makes the 3-way La Scala into a 2-way JubScala, eliminating one crossover point.

Then there are the electronics. JubScalas are bi-amped, with an active electronic crossover. That means you need two matching 2-channel amps and a pro audio processor. The Electro-Voice Dx38 or DC-One are recommended.

The power amps should be high quality, because this conversion will really improve the sound, so it's not worth going to all that trouble and expense, only to cheap out and not get the full result that is possible.

So there are two options for your consideration.

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"Never use any damping in the dog box"

 

 1 inch thick layer poly foam added to the inside of the doghouse and some measurements. The poly foam used is the same stuff that is in your couch bumm cushions. Below are results with a 2 foot by 2 foot sheet of 1 inch foam added to the legacy sealed cabinet. The notch at 200Hz is all but gone and the one at 575Hz is substantially reduced. And notice the new gain above 700Hz in the red circle.

* LEGACY CABINET UNPADDED *

6405d01f_DIRAC_LEGACY_01.jpeg

* LEGACY CABINET PADDED *

81772e3f_DIRAC_LEGACY_PADDED_02.jpeg

Thanks to Carl Huff for all the work.
 

Edited by djk
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Horn loaded bass bins & subwoofers do not suffer from above bandwidth harmonic distortion like a direct radiating type would so there is little to no benefit padding the chamber.

 

The downside is padding reduces sensitivity and my guess is this is why PWK decided not to use it in his design.

 

The notch @ 575 Hz & gain above 700 Hz in the above chart is moot as the woofer is crossed over before ever reaching those frequencies.

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I used O-Rings on my mid driver just put very small amount of Vaseline on the ring to help with seating . I also got better terminals from PE for the woofer wire going into the dog house. If they sit on hard wood floor install what they use to call grippers for furniture it keeps speaker hooked to floor without transferring vibrations. Then I put metal plate under the veneer I put on so I could put small round magnets in the grill surround trim so I could remove them or not. Base shoe molding is what you use for the grill frame regular 1/4  moldings looks wrong. I got pics some where on the forum...lol.  Rick

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Horn loaded bass bins & subwoofers do not suffer from above bandwidth harmonic distortion like a direct radiating type would so there is little to no benefit padding the chamber.

 

The downside is padding reduces sensitivity and my guess is this is why PWK decided not to use it in his design.

 

The notch @ 575 Hz & gain above 700 Hz in the above chart is moot as the woofer is crossed over before ever reaching those frequencies.

 

Disclaimer:  I am not a chart and graph guy, so some explanation is helpful, my ears are open.

+++

 

If there is no benefit to padding the chamber, then why do the numbers in the graph change for (I presume) the better?  The fact that the woofer crosses over at a lower point seems irrelevant if padding changes make a positive sonic difference.

 

Thanks!  -Dave

Edited by wvu80
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The woofer crosses to the mid at 400Hz. I could definitely see adding to get rid of the notch at 200Hz.

 

While the boxes are apart, your could use a router to open up the doghouse into the top chamber, enclose the back of the top section and put in two 7 inch long ports, 4 inches in diameter. This will give you a bit deeper bass. It's reversible, by simply covering the opened doghouse.

 

If you would like to try it another way, you can build a box the same size and leave off the bottom hatch cover.

 

Bruce

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No, no, no. Not wood glue on the hatch. You'll never get it open again.

 

I can see where my comment would have been interpreted that way.  I was answering 2 questions but only quoted one,  Glue on the joints and weather stripping on the removable covers.

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Horn loaded bass bins & subwoofers do not suffer from above bandwidth harmonic distortion like a direct radiating type would so there is little to no benefit padding the chamber.

 

The downside is padding reduces sensitivity and my guess is this is why PWK decided not to use it in his design.

 

The notch @ 575 Hz & gain above 700 Hz in the above chart is moot as the woofer is crossed over before ever reaching those frequencies.

 

Disclaimer:  I am not a chart and graph guy, so some explanation is helpful, my ears are open.

+++

 

If there is no benefit to padding the chamber, then why do the numbers in the graph change for (I presume) the better?  The fact that the woofer crosses over at a lower point seems irrelevant if padding changes make a positive sonic difference.

 

Thanks!  -Dave

 

According to the posted chart the notch at 200 Hz seems better but gets funky around 250-350 Hz but its hard to tell without overlapping the two charts for comparison.

 

If it helped why would Klipsch not use a little padding in one of their higher model designs, more than likely the tradeoff in efficiency. Just my guess anyways.

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According to the posted chart the notch at 200 Hz seems better but gets funky around 250-350 Hz but its hard to tell without overlapping the two charts for comparison.

 

 

If it helped why would Klipsch not use a little padding in one of their higher model designs, more than likely the tradeoff in efficiency. Just my guess anyways.

 

 

Maybe this is where I am unclear; is the chart of the woofer only, or is the chart showing the entire working speaker, woofer-->mid-->tweeter?  I am assuming this is the entire frequency range of the enclosure through all drivers.

 

"If it helped why would Klipsch not use a little padding in one of their higher model designs, more than likely the tradeoff in efficiency. Just my guess anyways."

 

Yeah, I know what you mean.  On my CF-4's to get 1.5 inch thick foam Klipsch just kinda put two 3/4" sheets together folded them and put them in loosely behind the drivers in 3 separate sections and called it a day.  There was no cutting, gluing, fitting, or anything else like you or I might do.

 

But like you said, Klipsch ought to have a pretty good idea what they were trying to accomplish, so what do I know?  :P

Edited by wvu80
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According to the posted chart the notch at 200 Hz seems better but gets funky around 250-350 Hz but its hard to tell without overlapping the two charts for comparison.

 

 

If it helped why would Klipsch not use a little padding in one of their higher model designs, more than likely the tradeoff in efficiency. Just my guess anyways.

 

 

Maybe this is where I am unclear; is the chart of the woofer only, or is the chart showing the entire working speaker, woofer-->mid-->tweeter?  I am assuming this is the entire frequency range of the enclosure through all drivers.

 

"If it helped why would Klipsch not use a little padding in one of their higher model designs, more than likely the tradeoff in efficiency. Just my guess anyways."

 

Yeah, I know what you mean.  On my CF-4's to get 1.5 inch thick foam Klipsch just kinda put two 3/4" sheets together folded them and put them in loosely behind the drivers in 3 separate sections and called it a day.  There was no cutting, gluing, fitting, or anything else like you or I might do.

 

But like you said, Klipsch ought to have a pretty good idea what they were trying to accomplish, so what do I know?  :P

 

 

 

 

I’ll give it a shot in explaining what I have understood about stuffing a sealed box/chamber vs. lining the walls of a ported box for which the concepts would apply when stuffing the sealed back chamber in a sealed back chamber transducer/driver combination of a front loaded horn.  There again, once the horn experts/engineers read the post, they can tweak and correct certain aspects that I may not be clear on.

 

Any sealed cabinet or sealed chamber can potentially benefit from “stuffing” (or potentially made worse in certain instances) as opposed to simply lining the walls, while a vented cabinet does not really have the same benefit.

 

I believe that the primary reason for “lining” the box walls with some type of padding may be to break up standing waves or prevent the midrange sound waves from reflecting back to the cone.  

 

In a sealed box, the “theory” was that stuffing a sealed box would make the box “seem” acoustically larger to the transducer/driver.  Essentially, I believe that current thinking about this physics may be that this stuffing really increases the resistive impedance within the sealed box, thus lowering “box Q,” which typically results in a “taming” effect to a response peak that can initially be caused by a sealed box that is too small. 

 

While the flatter response appears to emulate the response that could be obtained with a larger box, the “fb” and overall sensitivity really remain the same.  There again, you get no free lunch as the overall effect is not the same as using a larger sealed box.

 

With "front loaded" horn speakers that have a “sealed back chamber” you have a calculation for the back chamber volume size that is called the “reactance annulling” point and here is an area where “stuffing the back chamber” could make the horn worse or could make the horn much better in overall response, such as the improvements in the response in the example measurements that djk has shown. 

 

I suspect that when the La Scala was originally designed, these equations may not have been as specifically known as they are now; however, I believe that we all realize that PWK seemed to do a damn good job of designing his horns with the tools he had to work with at that time and got overall good match ups with the back chamber volume and the K33 drivers he used.  This aspect of specific back chamber volume that works in relation to the K33 and the overall horn is one of the reasons that not many 15 inch drivers can be substituted for the K33 with success that results in improvement of sound.

 

I believe that determining the appropriate reactance annulling point given certain "back chamber" volume/size differences for each specific 15 inch transducer modeled may have been what ClaudeJ was doing when he was modeling the different sizes of the back chamber for specific drivers his Quarter-Pies (the ClaudeJ Q-Pies) would need in the Horn Resp program. 

 

Both Horn Resp and Akabak are proficient at calculating the actual back chamber volume needed for a specific transducer/driver to achieve the appropriate reactance annulling point for a sealed back chamber front loaded horn design.  I do not believe that Horn Resp has the function to calculate the "emulated" chamber size from “stuffing the back chamber;” however, while I’m not 100 percent sure, I believe that Akabak might have that function.  Since I have not use Akabak, I may have misunderstood that point though.

 

Another way to think about reactance annulling, is that you can gain “extra bass” near the cut-off point of the horn by aligning the reactive part of the drivers "load" below resonance with the air mass reactance in the throat of the horn.   It almost seems like we have found a way to get that “free lunch” or “free bass” in this instance.

 

What we are really describing is that a horn can achieve a higher efficiency at Fc (cut-off) if the overall “system resonance” is close to the Fc.  When the system resonance is below Fc a person can “push” the resonance up to a higher point by making the compression chamber smaller.

 

When the compression chamber may be slightly on the small side from perfect reactance annulling volume, “stuffing” the compression chamber will potentially "increase" the size by increasing the resistive impedance within the chamber making it seem “acoustically larger” and help move the resonance close to the Fc of the horn.  

 

With a sealed chamber front loading horn, this is a reason why the Fs of the transducer/driver is not necessarily as important as other T/S measurements since the sealed back chamber size in combination with a specific transducer/driver is critical to get system resonance close to the Fc of the horn.

 

I suspect that in the folded horn subs that Jason typically deals with, this type of horn will tend to filter certain harmonics out in the bends of the horn and the stuffing or padding may not have that great of impact.

Edited by Fjd
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