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"Smoothing" inside of metal mid-horns?


davemac

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08/07/2017

 

Hi Folks,


I'm just finishing a project with some '84 and '85 Cornwalls. I swapped out the factory tweeters and B-3 crossovers for Bob Crites' B-3s and T-120 tweeters then decided to try the smoother A-55-G mid driver that he sells. (The resin K-601 horn that came with the speakers has a bolt-on driver and the A-55 driver is threaded so I needed the older threaded K-600 horns. Managed to find 4 of them on Ebay.) I mentioned the horn-swap to Bob and he said he understood Klipsch changed to the B-3 crossover because they went with the resin horns. He didn't know for sure but he thought the newer crossover should be OK with the older '55/600 horn assembly so I'll just have to let my ears decide. If for some reason it doesn't sound right I'll have to get some plain vanilla "B" crossovers. So, I have the tweeter and mid horn lenses wrapped in rope caulk, I added 1/16" rubber gaskets to the horn mounting flanges, and made a drill template for the new/old mid horns. (Of course the replacement horns have different holes!) So that's where I am now.

 

OK, to the actual subject --

 

Looking over the metal horns I noticed that one in particular has a very rough internal surface finish compared to the other 3. The newer resin horns are definitely a bit smoother feeling than the metal ones. Maybe one reason for the crossover change? Would there be any practical benefit to smoothing or even polishing the interior surface texture of the metal mid horns? Maybe a better match to the crossovers? Or would it adversely affect the way the sound waves bounce around inside the horn -- the horn's inherent "sonic signature?"

 

I'm not necessarily dying to try it. There is a limit to amateur "If it ain't broke, fix it anyway. It might sound better." I haven't installed the horns yet so I thought I'd toss this out there.

 

Any thoughts?

 

Dave

 

 

 

Edited by davemac
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I see no need to grind down the ridge inside the horn. look how the horn mounts to the back side of the motorboard, the horn sides are about 45* angle but hit the motor board cutout which is now a 90* angle. I would think that has more potential to interfere with the soundwave than the tiny ridge from assembling the horn

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Hi edmjm,

 

I wasn't referring to what sounds like the weld "seam" running along the inside sides. I meant that the overall surface texture of the inside of one of the 4 horns feels like a cinder block where the other 3 feel more like semi smooth concrete. It's like the mold wasn't clean or something. That make sense? It seems like a pretty dramatic difference and I wondered if I could/should sand or file it so it's closer to the other 3. In fact, the throat where the driver screws in has a nasty looking rough spot right in front of the driver that looks like it would have some effect on the sound entering the horn. I think I should file that down so it at least looks round. Then I thought about what if I sanded or even polished all 4 nice and smooth? Would that drastically change the sound for better or "badder?" And would the crossover then need changes?

 

I've actually thought about your other comment too. I've sometimes wondered if there was a benefit to routing those right angle opening edges to a 45 degree. My brother suggested a 5/8 or 3/4 radius would be better. Tweeter, mid, woofer, and what about the bottom bass ports?

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I am still filing down the casting marks on a pair of k-400 horns. Roy said the mold was probably wearing out and it wouldn't hurt to smooth them out.

 

You can use a spray primer/filler from Autozone/O'Reilly, etc. Easier to smooth out than bondo.

 

Bruce

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This is my speculation but it would seem to me that the inside surface finish would have some kind of effect on the sound output, maybe a rough surface having less negative effects. This after reading on this forum where the placement of a small protrusion would have a major effect.

JJK

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the rough spot down the throat I would sand down but I'm not sure if there would be any gain in sound quality from smoothing the inner surface of the horn; that being said, if there is something to be gained then make sure to put the same finish on all the horns to avoid an imbalance. there's no need to make any changes to the crossovers cause you're not actually changing anything. you probably would have to make a change if you were switching from cast metal to plastic horns or vice versa

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4 hours ago, Marvel said:

I am still filing down the casting marks on a pair of k-400 horns. Roy said the mold was probably wearing out and it wouldn't hurt to smooth them out.

You can use a spray 0rimer/filler from Autozone/O'Reilly, etc. Easier to smooth out than bondo.

Bruce

 

Good tip. Thanks Bruce. Sounds like that would be good for filling in pits and such without being too heavy. I wouldn't want to build up the inside of the horn and actually change its dimensions.

 

 

2 hours ago, JJkizak said:

This is my speculation but it would seem to me that the inside surface finish would have some kind of effect on the sound output, maybe a rough surface having less negative effects. This after reading on this forum where the placement of a small protrusion would have a major effect.

JJK

 

1 hour ago, edmjm said:

the rough spot down the throat I would sand down but I'm not sure if there would be any gain in sound quality from smoothing the inner surface of the horn; that being said, if there is something to be gained then make sure to put the same finish on all the horns to avoid an imbalance. there's no need to make any changes to the crossovers cause you're not actually changing anything. you probably would have to make a change if you were switching from cast metal to plastic horns or vice versa

 

Hi JJK and "ed." Hi again, "moray."

 

Yeah, the more I consider it the more I think a really smooth/mirror type polished finish wouldn't be a good thing. I mean, Klipsch would have already done it, right? The 3 "normal" metal 600s I call rough only to compare them to the slightly smoother resin 601s. Even they aren't slick smooth like an ABS plastic.

 

That ragged looking spot in the one throat I think definitely should be smoothed down. The same for the really bad casting marks. (Thanks, that's the term I was trying to think of. These days the neurons don't always connect right away!) Then a light hit with some paint to pretty 'em back up.

 

Today I'm going to put 1 pair together and fire 'em up. Got the horns wrapped in rope caulk and 1/16" gaskets on the mounting flanges. I have to install the mid horns so I can finish screwing on the new drivers. Got several turns left and I can't do it one-handed.

 

Gotta get Mom up and get her fed. I'm not sure which will take more effort, that or putting all those screws back into the Corns. At least I can use a drill on the Corns. Don't think I should try that with Mom.

 

Many thanks for all the helpful comments! Oh, any thoughts on radius-ing the outer corners of the motorboard openings?

 

Dave

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On 8/8/2017 at 10:49 AM, davemac said:

Yeah, the more I consider it the more I think a really smooth/mirror type polished finish wouldn't be a good thing. I mean, Klipsch would have already done it, right?

 

Smoothing them out is a labor/time intensive task that means more money spent. I would think they probably wouldn't do it unless really bad and then they might just return them to be melted down and cast again.

 

Here's a pic of the inside of one of my K-400 horns.

 

Bruce

K-400.jpg

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1 hour ago, Marvel said:

I would think they probably wouldn't do it unless really bad and then they might just return them to be melted down and cast again.

 

PWK's oft repeated statement, "Doesn't make a dime's worth of difference" comes to mind.  That's how he responded to my question about mounting the tweeter and squawker horns to the back of 3/4" plywood.  He wasn't suggesting that an improvement wasn't possible, just confirming that, in his engineering opinion, any benefit was not justified by the expense.

 

As a DIY person, I would smooth the inside of the horn before flush mounting it to the front of the motorboard.  The priorities are much different to the hobbyist than to a commercial production process.

 

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This discussion reminds me of a story regarding Rolls Royce and it's use of GM automatic transmissions, which I believe to be fundamentally accurate.  RR purchased it's first automatic transmissions from GM.  Being RR, they immediately disassembled one and "improved" upon the crude Yank contraption by polishing every component.  When the now jewel-like components were reassembled, it did not function.  RR contacted GM, which informed them that some of the components were intentionally designed and manufactured with a rough surface, and that polishing those components to a mirror finish would prevent the transmission from functioning properly.  RR stopped trying to "improve" the transmissions.

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23 hours ago, Billzumwalt said:

Just a note about the B3 crossover . My 83' cornwalls had the B3 with a metal threaded horn throat . So I doubt the B3 had anything to do with the change to the plastic horn. 

 

 

Very Interesting, thanks for letting me know that. I've since listened to my '84s where I swapped the horns (another post -- "Crites tweeter/midrange upgrades") and didn't notice any issues with the B3 crossover. I wonder what the change was and why? Well, no matter. My only remaining issue is whether or not to keep or remove the rope caulk I wrapped the horns with.

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5 hours ago, DizRotus said:

This discussion reminds me of a story regarding Rolls Royce and it's use of GM automatic transmissions, which I believe to be fundamentally accurate.  RR purchased it's first automatic transmissions from GM.  Being RR, they immediately disassembled one and "improved" upon the crude Yank contraption by polishing every component.  When the now jewel-like components were reassembled, it did not function.  RR contacted GM, which informed them that some of the components were intentionally designed and manufactured with a rough surface, and that polishing those components to a mirror finish would prevent the transmission from functioning properly.  RR stopped trying to "improve" the transmissions.

 

 

I've been a self-taught amateur gunsmith for many years and back in the day when I first started "tinkering" I'd been reading in old and new gun mags (no InterNet yet!) about polishing certain mating parts to improve function and accuracy. Before you know it I had out my needle files and Dremel and polished every nook and cranny of a hammer/trigger assembly to a beautiful mirror finish. And not long after that I was sending my prized .357 to Ruger for them to fix what I "improved."

 

 

On 8/8/2017 at 9:42 AM, edmjm said:

the rough spot down the throat I would sand down but I'm not sure if there would be any gain in sound quality from smoothing the inner surface of the horn; that being said, if there is something to be gained then make sure to put the same finish on all the horns to avoid an imbalance.

 

 

My goal in all this "smoothing" business is to make sure the four horns I bought are reasonably matched to each other by filing down and/or filling in obvious nasty casting marks, not to smooth the complete interiors of all the horns. I get where that would be counter to Klipsch's intended and tested design. One horn had a really rough area at the opening of the throat just beyond the driver threads and other areas in the "flats" that looked and felt like the surface of a cinder block. Another, while still a 600, seems to be a different version with a V-groove molded into the inside surface that I filled to match the others. Yet another was welded slightly off-center so the weld seams were actually small ledges.

 

 

5990b611116e8_Differenthorns.thumb.jpg.93dd8289ade6ae5bd09f74b119e530ef.jpg

5990b627bbd78_Differentfills.thumb.jpg.9af0ad8818c014950a7b6414eeefa532.jpg

 

 

I'm not necessarily trying to improve the sound, that's what the replacement drivers are for, I just want the four speakers to sound the same when done.

 

But regarding "improvenment," I asked earlier whether it would be beneficial to round-over or radius the the horn and woofer openings (including the bass ports?) on the outer face of the motorboard to "improve" dispersion. Or is that a solution in need of a problem?

 

"Oh Sir, just one more thing. If you don't mind."

Why do I keep "timing-out" and have to keep signing back in? It's hard using words and sometimes it takes a while to get them right!

 

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On 8/13/2017 at 2:11 PM, davemac said:

 

But regarding "improvenment," I asked earlier whether it would be beneficial to round-over or radius the the horn and woofer openings (including the bass ports?) on the outer face of the motorboard to "improve" dispersion. Or is that a solution in need of a problem?

 

 

2 hours ago, edmjm said:

instead of radiusing the openings on the motor board have you considered routering a small countersink to flushmount the speakers to the front of the motherboard? 

 

 

Actually, I was just exploring your comment from last week about the sound waves coming through the curved horns and being somehow affected by funneling through the straight motorboard openings. I honestly don't know if rounding over those openings would have any real practical effect. It seems reasonable and logical to me that it would have some effect. I contemplated some time ago whether routing the openings to 45 degrees to essentially match the horn contours would be beneficial for soundstage and such and my Little Brother suggested rounding instead. If my speakers were in my dream room (which probably won't happen for at least a few more years) and more appropriately positioned than they are now in my too small room then it would be a more immediate issue. Right now I'm hoping this august body (that's you guys) can help me brainstorm ideas for the future that maybe I can get out of the way now. (One way or the other.)

 

I don't want to do "CornScalas" and if I do anything more I would rather consider re-contouring the edges of the openings than countersinking them and remounting everything. Besides, I don't think countersinking would work with the tweeter where rounding or "45-ing" could be done with all three.

 

So the question remains, with proper positioning in a good sized room would re-contouring the tweeter, mid, and woofer opening edges (and the bottom bass ports) have any practical beneficial effect on the sound? Or, again, is that a solution in search of a problem?

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On 8/13/2017 at 4:00 AM, ricktate said:

post-7905-1381971187178_thumb.jpgpost-7905-13819711878824_thumb.jpgpost-7905-1381971281781_thumb.jpg

 

I smoothed my lascala and Khorns down by sanding. The throat I did with emery cloth and dowel rods on a drill. Then I painted them inside and out with rustoleum black enamel. Not a good picture but they do look a lot better than before.

 

 

Very nice. Do they sound any different with the smoother finish?

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7 hours ago, davemac said:

 

 

Very nice. Do they sound any different with the smoother finish?

I could not say....I did them both together. I have no testing equipment to verify. I have never seen anyone test a smoothed horn against a stock rough one. But pretty sure smooth has to be better. I do think the enamel paint on inside and out helped the ringing part. I painted one and held it up and hit it with a piece of wood it sounded different than the one not painted. post-7905-13819791346262_thumb.jpg I also put dampening material on the center outside of the horn hard to see in pic though. 

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