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LS refurb


Marvel

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Been busy over the weekend, but the K400 horns arrived from Mark. These are in beautiful shape. I can understand one of the reasons for changing to the composite material for these horns - they are really heavy!

 

Bruce

Bruce: while you heave these out and open check out the horn throats. Remove the washers and have a look. The throats should be perfectly clean edged and 100% circular. If you see otherwise make them clean and round with some hand files. All of the metal cast K700 I have owned or seen have had from poor to horrible condition throats the result of casting way more parts than the mold was ever designed for.  

   Five to fifteen minutes worth of handy file work to make the throats round and clean edged will result in much cleaner sound. Any discontinuance or non round shape will result in reflections from the throat back to the diaphragm. If you want to do a perfect job measure the ID at the mouth end of your driver and then file the throat of the horn to the exact same ID so the transition will be perfect with no reflection. Any steps smaller from the driver flowing into the horn will cause problem reflections. Opening up the throat of the horn to accommodate a seamless transition between the driver mouth and the horn throat is easy to do. Have fun with the refurbish project.

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Thanks, Moray, I've already been checking them... They are really clean and about as good as it gets. As I mentioned above, these are in beautiful shape. The castings are very, very clean.

Bruce

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A question for anyone... What is the actual exit size on various 1 inch drivers that anyone has? The reason I ask is that the EV drivers I have are 7/8", while the horn throats on the K400s, while very clean and round, are only 3/4".

 

This would mean there is a very real restriction entering the horn. One could consider this to be no different than having the compression slot for the woofer, but everyone who makes/buys the wooden tractrix horn flares, or other commercial horns, a actually getting a 1" entry.

 

Any thoughts?

Bruce

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I have some hardware ordered, #10-32 t-nuts and machine screws, etc, so things moving along. Just a little slower than I would like. (This job hunt thing and stuff going on is time consuming) Here's the K33s, genuine Klipsch, via JWC, to my older son to me. The gasket material on the back of the speaker on the right makes it look like it's all bent out of shape, but it is really fine.


Bruce

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I think I told someone the wrong size machine screw when asked about woofer mounting in LaScalas. I had said 10-32, but I believe they are actually 10-24. If anyone could verify for me that would be great. Mark? Dennis had mentioned 10-32 before, so I ordered these to use. It's ok for the clone cab I have, as they used wood screws for the woofer mount, but the genuine cab is... 10-24 unless someone re-threaded the t-nuts.

 

I got these flange heads, so I will be less likely to slip and poke a screwdriver through the surrounds. A small socket will be easier to handle. The 10-32 will be nice to tighten down evenly and less likely to work loose.

 

Bruce

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  • 2 weeks later...

Since one of the cabinets is a clone, with no t-nuts for mounting the woofer, and the cabs are already together, I made two new baffles from 1/2 inch birch ply, These will mount inside against the original baffles, and keep the t-nuts from falling out. Also using all eight holes instead of the four that Klipsch used. I placed the boards in the cabs and then routed the slot, so they would match correctly.

 

Bruce

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  • 3 weeks later...

Both of the new baffles are done. I removed the back 3 inch strip that goes across the top of the cabinets, as they were both modded to have a 1/4 " phone jack installed. Since I am redoing the way the back is enclosed, I removed them. Dennis has said that Klipsch used ring nails, but the genuine LS just had finishing nails. I cut the board on each side of the nails, removed the small piece of wood and then pulled the nails through the inside, so the tops are still finished.

 

The clone was done with staples. I broke them off and used a Dremel to grind down the ends.

 

Progress is slow, but everything else going on around here, it is still progress.

 

Also, while using my flush cut router bit on part of one, the bearing decided to come apart. Messed up a little, but nothing that can't be fixed.

 

Bruce

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  • 4 weeks later...

Life's been busy...

 

A question for folks with more experience than me: These cabinets are old, and when cutting out some of the top back piece, all that was holding it in were the nails. The glue dried to a point it came right out. So... what can I do to the rest of the cab to make sure it holds together? Could I mix up some epoxy and thin with acetone and soak the interior joints? This would penetrate the wood and hold it together. Thoughts?

 

Or put some glass and epoxy over the joints like Rigma did when he built his Jube clones...

 

Bruce

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I was looking over the K400 horns I have... look great from the outside. When I check the inside of the horns, I found a ridge from the casting, I assume a two piece plug for the inside. It has a ridge on all four sides that I will file down and smooth out.

 

Bruce

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  • 8 months later...

Got the horns mounted on the front of the boxes. I have, for the time being, sealed the tops of the doghouse back as constructed, so I can listen for a while with the bottoms closed up.

 

Bruce

front_mount_horn.jpg

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3 hours ago, The Dude said:

Why to the front?

 

Looks huge, doesn't it? Well, it may sound better. I wiould think so, so there wouldn't be the ripple/deflection as the wave front goes out the opening. I will repaint the horns later, with the screws to match.

 

Bruce

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I did a front mount when I modified my center channel La Scala. Many years ago, a forum member posted his measurements of the improvement frequency response when changing the mid horn from the back side to the front of the La Scala. I don't have that link saved, but I liked the progressive idea.  

 

58db995ce9e30_DSCF0298-Copy21.jpg.c13327d64079042f81bce095d6607879.jpg

 

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Looks very good to me, and I don't doubt the improvement.  Nonetheless, I heard PWK utter with his own lips, "Not a dime's worth of difference."  As a good engineer., he engineered for a cost of production target, not perfection.  Implied in his remark is that there was a difference, but not enough to justify the increased cost of production.  Mounting the K77/T35 horizontally was also a compromise for cost savings.  EV designed it to be mounted in the vertical orientation.

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Here is what I personally recommend if using a new (replacement) woofer motorboard in a La Scala bass bin:

 

Do all of the layout for the woofer mounting holes PRIOR TO cutting (routing) out the compression slot in the motorboard, then....

Prior to drilling the T-nut holes and installing the T-nuts, Chuck up a Forstner drill bit whose OD is just proud of the OD of the T-nut flange and set the depth stop on the drill press so that you are boring into the T-nut flange SIDE of the motorboard about 1/16" DEEPER than the thickness of the T-nut flange for ALL the woofer mounting holes.  The tip of the forstner bit will give you a guide to drilling for the shank of the T-nuts so that they can be mounted centered-to the forstner bit "counterbore" and already be aligned.

 

PRIOR TO installing the T-nuts, coat the MOUNTING BOLTS' threads with a release wax agent...or paste wax, and screw the bolts all the way into the T-nuts from the FLANGE END of the T-nuts.  Once you have done this to ALL THE T-nuts you intend to use, then mix up some bondo and hardener...it won't take much, so avoid mixing up TOO much.

 

Slather the needed amount onto the shank and the flange of the T-nuts on the side of the flange with the Spike things on it...then take a block of wood and a mallet and drive the T-nuts into the CORRECT SIDE of the motorboard (its rear side!) as far as they will go. and wipe away any bondo squeeze-out from the T-nut flange side of the motorboard.

 

Now you SHOULD have a T-nuts that have their flanges JUST BELOW the PLANE of the rear side of the motorboard with bondo ONLY between the flange (and around its edges!)and the bottom of the hole you counter-bored into the rear of the motorboard...the rest of the bondo SHOULD BE GONE.

 

Let that bondo set up overnight.  The next day, take the motorboard and a small drill bit (for whatever screws you intend to use) and drill THROUGH the flange so that you can install the screws THOUGH the tiny holes and into the wood on the "spike" side of the t-nut flanges (it only takes two screws opposite of each other per flange!).  BE SURE to use wood screws which will help KEEP THE T-nuts from EVER backing out of those holes, but whose screw-HEADS will NOT be "proud" of the rear SURFACE of the motorboard itself, nor wil the LENGTH of those screws cause them to go ALL THE WAY THROUGH the motorboard, itself.

 

Now...remove the woofer MOUNTING BOLTS from the T-nuts, take some MORE release agent wax and coat the threads of the bolts AGAIN...then screw them into the T-nuts from the WOOFER SIDE of the motorboard and screw them into the WOOFER side of the motorboard.

 

Now mix up some MORE BONDO and spread it around the bolts sticking out from the FLANGE SIDE (rear) of the motorboard, and let that set up overnight.

The next day, back the woofer mounting bolts OUT of the T-nuts.  then SAND THE BONDO FLUSH with the rear of the motorboard.

 

Now you have T-nuts that are NOT gonna go ANYWHERE!.....PLUS you have perfectly SMOOTH first Bass Horn flare plane on the rear of the motorboard.  THEN you can mount the woofer to the CORRECT SIDE of the motorboard, and use a permanent marker to mark the mounting bolts so that you can GRIND THEM TO LENGTH which will keep the tips of them from PROTRUDING into the soundpathway of the first flare of the Bass Horn Lens.

 

You have PERMANENTLY mounted the T-nuts, and have also created a smoother soundpathway for the first flare of the bass horn.  It may not SEEM like a big deal, but you will HEAR the difference.  After you install the WING units, and the LaScala bass bin REAR PANEL, but PRIOR TO installing the bass bin sides...you apply a urethane finish to aid in the sealing of that SMOOTH soundpathway for the first flare of the bass horn lens.

 

I hope I explained this well enough!  And yes...you CAN HEAR the difference.  It is labor and materiel cost-prohibitive to do this for factory-production builds, but not for the DIY folks.

 

DaddyDee confirmed the difference CAN BE HEARD!  It simply REDUCES DRAG...why do you think they use flush riveting on fighter aircraft?  If you reduce drag you eliminate MORE AIR TURBULANCE to the surfaces...and AIR turbulence is akin to distortion of soundwaves.  I am almost AFRAID to say this "isn't exactly ROCKET SCIENCE!" ;)

 

Stiffening up the joints of the rear-to-side panels of the bass bin, will also improve the sound...you can use rabbet joints for this...and this pic will give you some idea of what I am talking about...look to the side panels as you view them from the rear in the HF rear opening...and you can see how the rear of the bass bin, itself  was rabbeted to the side panels.

 

LaScala rear showing assembly details and guardcat option.jpg

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