Raspy mids in Khorn

[JonM]

One of my late '70's Khorns has developed (it may have been there all along - I bought them only early in May) a raspy resonance in its midrange. It is volume dependent - it doesn't have to go loud for it to occur, but below a certain level, it doesn't happen. The other Khorn doesn't do it at all.

I really heard it first on the tail end of Diana Krall's "I Don't Stand a Ghost of a Chance with You", where she has some particularly pure notes where you can really hear the raspy distortion (that is not in the recording on headphones or on the other Khorn through either channel of my amp - it's definitely in this one speaker).

I have the alnico K55V midrange and cast aluminum horn, damped with mortite. The crossover is an unmodified AK (3?). I made sure the screws on the horn to the front panel were tight (I couldn't budge them tighter!) and I made sure the driver was snug in the horn (though I did not overtighten it - just snug). No improvement.

What could cause the problem? Do I need a new diaphragm? Do I try reseating the one I have (it works fine except for this distortion)? Can I get a new one from Klipsch?

I am handy with electronics and mechanical things, but the closest to the inside of a K55V I have come is one of Al K's pictures! Any advice is appreciated. I like the speakers a lot - I may like them a lot more if I can get rid of what was probably an insidious distortion that is clearly audible on only certain sounds but there in the background more than I realized.

Thanks!

This message has been edited by JonM on 06-24-2001 at 02:57 PM

[johnnyp]

My good friend had a similar complaint. He unscrewed his K-55V and took it into his Klipsch dealer. The dealer installed it on one of a pair of Khorns in the audition room and played some music. The dealer said he could hear nothing wrong with the driver but my friend insisted he could. A technician at the K dealership ran a frequency sweep test on the driver. Sure enough, there was excessive distortion only at frequencies near 700 Hz. The K dealer apologized and gave my friend a new K-55 V driver -- free.

If your driver has push-on terminals, note the polarization ("+" and "-") of your driver before removing the wires. Terminals on all K-55s are labeled with a small raised "1" or "2". Disassemble your problem driver by removing the 6 screws. Carefully pull or pry the driver apart. Locate the blind hole (about the dia. of a pencil) in the center of the driver half that contains the magnet structure. In the hole, you will find a wad of felt or lint. Sometimes, some of the lint fibers work their way up the hole and begin rubbing on the diaphragm when the driver is operating. You will hear the raspy sound you described when this happens.

Remove only the loose lint fibers or gently push them slightly deeper into the hole. carefully reassemble your driver, tightening screws opposite of each other like you are attaching a wheel to your car. Install your driver and attach the wires to their original polarity. Then test. Your problem may now be corrected. Otherwise, you must order a new diaphragm from Klipsch or send your driver to them for repair.

------------------

John Packard

[djk]

I would take the driver apart and clean the gap.Use masking tape folded back on itself(sticky side out)into triangles.Most likely it is clean.Look at the coil while you have it out.You are looking for scrape marks on either the inside of the former or outside on the wire.If there are scrape marks and the gap was clean you will probably have to buy a replacement diaphragm.Re-assemble the driver and try it again.Try it on the other speaker just to make sure it is not the network.Order a new diaphragm if needed.You only need a screwdriver to clean it.You will need a soldering iron to replace it.

[JonM]

Thanks for the guidance. Over the next week or so I'll take a look inside the driver and see if I can see what's causing the problem, and let you know what I find.

[WMcD]

Whoa, slow down.

I like taking things apart as much as anyone else, and probably more so. But taking the driver apart is a little bit risky without justification.

I'd suggest you switch the drivers between left and right. See if the problem follows the driver.

If so, you'll have more justification for taking them apart, or going to the dealer.

If the problem doesn't follow the driver, you should switch the cross overs. See if the problem follows the crossover.

One good fellow here, some months ago, suggested the loose items in the room could be resonating. So if there is a lamp, picture frame, etc. That could be the cause. Seems like a remote possibility, but worth investigating. Also, check for loose items in the speaker itself like a wire, or the cross over board itself.

It is worth checking all input and output connections at the amp. Usually this shows up as distortion at low levels which clears up at high levels, when it is hit with higher voltage. None the less, it is worthwhile to check.

Best regards,

Gil

[m1garand]

Gentlemen,

I have a similar problem with one of my K-55s on my LaScalla. It only appears (noticibly) on piano music. When I place my head behind the speaker, I can hear the metalic ringing/buzzing from the midrange driver. No doubt that it is coming from there!!! A few years back I took it apart and (very gently) went over what looked to be like a small rough spot on the coil with an emory board. It appeared to clear up, but I noticed it again last night. I'll follow the steps above, but can anyone tell me how to order a replacement driver or diaphragm from Klipsch? I couldn't find any info on their web site. Also, how tight is "too tight" to screw the driver back on. I'm certain that I didn't go overboard putting it back on, but I noticed that the decal on the back was not clocked in the up-down position like on the other speaker (I figure the factory is proud of this) which leads me to believe that it may be on tighter than the factory assembly. Any help will be appreciated.

JJJ

[Pete C]

m1garand,

1-800-Klipsch

There was a link to a list of replacement parts on this site, but then the site was improved (read: web designers prolonged their jobs.)

The ringing may be from the metal horn, if you have one. Search this BB for dynamat, unless you have already done this.

[Pete C]

m1garand,

I should have searched before telling you to. Here is a thread that tosses around many ideas for the ringing...

http://216.37.9.58/ubb/Forum2/HTML/000110.html

[JonM]

Well, it was easier than I thought. I tipped my Khorn over face down on the carpet. Removed the six screws, and carefully pulled off the back of the driver. (It's easy in this position - the horn holds it real steady, and you don't need to desolder anything!) The felt damper had started to creep into the cavity right by the diaphragm, so I gently reinstalled it about a millimeter below the bottom inner edge of the cavity it's in (where it's close to the diaphagm but not so close as to risk touching it). I noticed that the diaphragm was dated May 1981 - the serial number on the speakers has a P, making them vintage 1977 or 78. A replacement diaphragm? Could it be an "M" diaphragm in a "P" driver? Anyway, I also noticed two pieces of scotch tape on the flat surface of the magnet, right up against the gap. I removed them and their residual adhesive. I thought maybe the coil was rubbing against the edge of this tape. I cleaned out the gap with tape and a small paint brush, and checked the coil for debris (I removed some small stuff) and scraping (saw none). Carefully reinstalled the back (the guide pins make that easy), reinstalled and carefully tightened the 6 screws, tipped the speaker back up on its feet, and - apparent success! The resonant raspiness is so reduced as to make me wonder if it's there at all (before it was really obvious). There is so little difference between the two midranges now (being fed the same signal by the same channel of my amp) that I am not sure than any differences aren't my imagination or other effects (resonances elsewhere, etc).

So thanks for all your help. I really would have had zero idea what to do without you guys.

JonM

[JonM]

Just a quick update - a frequency sweep still found some resonant raspiness somewhere around 800 Hz (not really clearly audible on music). Again, only above a certain level (not that loud - 70 dB or so in my room).

So I tipped the Khorn over again, removed the back of the squawker, and again, more carefully than the first time, cleaned the gap. Some cardboard was just the right thickness to run around the inside of the gap and loosen any small stuff in there. Followed by scotch tape to grab anything still lurking. (I may have seen a couple of very small things that looked like very fine metal pieces - got them completely out.)

I put it all together again, watching carefully from the side as I reinstalled the back, to make sure the voice coil was going inside the gap, reinstalled the screws, and tipped her back up in the corner. Now the frequency sweep was completely clean - no raspiness or roughness. Thanks, guys!

It is weird the way you can hear the tones start in the woofer and gradually move into the midrange, with phasing effects making the tones sound like they are moving closer and farther away as the frequency goes up. Some designers of direct radiator speakers spend a lot of time on phase/time coherence of their speakers. I don't see that issue discussed with horn speakers - much more emphasis on pure frequency response. How would you make a Khorn "time aligned"?

[djk]

"How would you make a Khorn "time aligned"? Add an external 400hz low pass filter to this http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1443365169

[Steve Phillips]

I have a K-55-V in my modified Heresy center channel that's doing the same thing.Took it apart and found nothing unusual.Sounded no better after so I took one off one of my K-Horns and swapped them.

Driver replacement time!

At least my center sounds better,but music took a dump.

Dang a new one from Klipsch is $120,might look into a JBL driver or something like that.I have the adapter.

O Well

[JohnA]

Steve,

Just have somebody OH that -V. You shouldn't need a new driver at all.

John

[Steve Phillips]

Thanks John,still working on the old one.

www.speakersupply.com

They have some complete Atlas drivers for $69.Sorry Klipsch,but if they are the correct ones,they are more affordable than $120 or so.And the old style.I'm waiting to hear back from them.I have dealt with them in the past with good results.

I might take the magnet structure out again and use my air compressor(carefuly)and blow it out(not the felt)

JonM,reread the frist post and remembered what you said about Diana Krall and she is the one that pointed out my problem.I thought it was there and She verified it with some of her guitar players notes on Love Scenes and her voice on some cuts.

This message has been edited by Steve P on 07-07-2001 at 10:00 AM

[Steve Phillips]

Well guys,took it back apart and used a bit more care at cleaning out the gap the coil goes into.Sounds much better,but still think I'll look into getting a complete driver just to make sure.Kinda like getting that ugly noise out of you car engine,not feeling safe about taking any long trips.Know what I mean?

[JonM]

Just a thought here, something I mentioned to Steve P in an off-line email. I wonder if part of the fix I got was due to realigning the voice coil in the gap. The K55V has a rubber grommet between the front and back halves of the driver. That grommet compresses somewhat when you tighten the 6 case screws, and I'd imagine that if the compression isn't even, you could get the voice coil at an angle in the gap and maybe even get some rubbing, especially if there's already debris in the gap.

One thing I noticed after I got my squawker fixed was that the speaker's volume seemed higher. I had noticed before that the speaker with the rasp seemed lower in volume than the other one - the sound stage seemed to shift toward the speaker that was working properly. But once the raspiness was fixed, so was the soundstage shift.

So I think the coil was actually being held up from moving somehow in the gap, which turned to raspiness when the volume was high enough to force it to move against whatever it was touching; prior to that level, the diaphragm was vibrating but not all of the voice coil was, hence the lower output.

That's my current theory/guess. I wonder if it's worth it for Steve P to experiment a little with different tightness on those 6 screws, or working to get them all as close to the same tightness as he can. Seems to me that if the driver is working properly, there's zero reason to buy a new one.

[Steve Phillips]

Well I seemed to have fixed it too.This time apart I took a thick piece of paper and ran it around in the gap.A piece of masking tape is actually the preferred"thingy"to get all the whatever out of the gap.

Diana is now back to herself.

[JonM]

Steve -

Congrats!

Jon

[WMcD]

I don't doubt what is being written.

However, how do these voice coils get out of alignment to create a rubbing problem. Also, what is the source of foreign matter in the gap?

Just wondering.

Gil

[JonM]

My guess (and I emphasize "guess") has to do with the rubber gasket/grommet between the two halves of the driver. The diaphagm and voice coil are adhered to the front half, the magnet assembly and gap _are_ the back half. If the gasket is compressed asymmetrically, I could imagine rubbing could occur.

As for debris in the gap, what I saw were just a couple of very small pieces of what looked like metal flakes (I meant really small). Shavings from the manufacturing process? I was able to dislodge them with a thick piece of cardboard run around inside the gap, followed by tape folded over on itself. I can't say if these were the issue or not. Could have been completely benign.

These drivers are almost 25 years old. While I wonder how these problems arose in the first place, I'm thrilled I could fix them myself, in my case for free.