Subwoofer issue: "Clacketing" sound....

[stephr1]

Hi all,

Happy holidays to everyone!!

I'm not sure if this is the right place to post this, but I thought there might be some knowledgeable people out there who could provide a kind of "2nd Opinion" for me.

Here's the background...

I have a 12-13 year old (bought it new) Klipsch KSW150 subwoofer (10" @ 150W) connected to the LFE output of a Sony STR-DE835 receiver (5.1 @ 100W/ch). About 6-9 months ago I noticed a noise coming from the sub. It wasn't a "scritchy" sound which might indicate voice coil problems and it wasn't a buzzy or fuzzy noise typical of a torn cone or separated edging. It was more of a "clackety" sound, which I thought might be distortion issues. I noticed at that time the noise was obvious only during surround sound (movie, DVR, etc.) and not while a 2 ch. source (CD, tuner) was selected. Also, the sub had to be set at 25% level (volume) or higher for the noise to be heard. As a result, I assumed the receiver's decode circuitry might be the problem.

Just in case, I did do some cursory checking of the sub: pressed the cone a bit to listen for any voice coil rubbing (heard nothing), scanned the speaker for any obvious tears or material separation (nothing obvious). I focused mainly on the receiver. I scoped the output of the LFE at the input of the sub using surround sound, 2-channel and a low freq tone source. I saw no clipping issues and the signal did not appear distorted (at least as much as one can tell on a scope). I concluded I wasn't sure what was causing the noise and decided I would keep the sub level down below 25%.

Fast forward to a couple of weeks ago...I decided I was tired of missing the rich, low end (and rumble) when I could turn up the level of the sub. I flipped the sub over and examined it more closely this time. The "press" test made no noise. In fact, when I reached 1/4"-plus depression on the speaker cone, I felt I might actually poke finger holes in the cone. It felt fairly firm and strong. Visually, other than a bit of dust, there were no tears or separations in the cone or rubberized edging and the speaker looked as if it was brand new.

I also redid my listening test and discovered the problem does exist during 2-ch source material, as well. It turns out the sub needed to be at 50% level or higher to hear the same "clacketing" sound as could be heard on surround sound material at lower levels. While the receiver may not be completely in the clear, it seems the sub may truly be the source of the problem. I plan to check (scope, voltage, etc.) the sub amp and power supply (be nice if I could find a schematic so I knew what normal readings should be and see (actually hoping to find) if there is a clipping issue (bad filter cap, resistor value change, etc.) in the amp circuitry.

This is where I could use some 2nd opinion feedback.....

I decided to reach out to some Klipsch experts so I posted about this problem on the Klipsch forum. I received feedback from an individual who seems to be fairly knowledgeable about this. What I was told is that this problem could be related to age. The material used for the speaker suspension may have weakened over time (something about the fiber structure?) and this could be allowing the speaker to "bottom out". Logically, it would make sense. However, I would think in a good, quality speaker, there would be margin in the design to allow for aging and prevent this kind of thing from happening. Then again, maybe because it is a good, quality speaker, there can be no room for margin.

Anyway, has anyone else experienced this? Is it a fairly common problem? I have Klipsch KG 2.5s for my front speakers. They're about 1-2 years older than the sub and show no signs of any kinds of problems. Then again, I may be trying to compare apples with oranges.

I am interested and appreciate any insight, comments, suggestions in sorting this out.

Thanks in advance and cheers....Steph

[revboden]

check that the tinsel leads are not hitting the cone.

[fastbike1]

Any sub will bottom given the right combination of power, frequency, and tuning.

[stephr1]

I appreciate that and understand how it can happen (I would expect some fairly serious distortion if it got to that point). However, Klipsch speakers are supposed to be good quality and had been doing fine for a long time playing pretty full surround sound material, so I would have expected this to happen a long time before now.

Originally Posted by fastbike1

Any sub will bottom given the right combination of power, frequency, and tuning.

[stephr1]

Thanks for the suggestion. I have not yet pulled the speaker from the box to check for any physical issues and to look at the signal to the speaker, but I'll keep the tinsel leads in mind to check them closely.

Originally Posted by revboden

check that the tinsel leads are not hitting the cone.

[rabbitz]

Also check if the spider is still glued to the basket. Over the years, I've found most of noise issues have come from a loose spider, leads contacting cone or loose dustcap.

[OscarS]

I too would be willing to bet that the spider on this particular model has loosened up dramatically, and combined with playing ultra-low LFE effects from movies, might be encountering a hard physical limit rather quickly in an enclosure that is likely not tuned low enough. Klipsch is good, but if you've ever seen the actual speaker drivers that are used in entry-level systems, makes you wanna slap yourself; very thin spiders, stamped steel frames, cheap terminals (usually spade type connectors).

[DrDyna]

My vote is for either the spider coming unglued from part of the former (which may cause the former to clack in a side to side motion against the pole piece) or that there's a wire or some other object that has ventured too far toward the back of the cone.

[stephr1]

Thanks much for the input and feedback, everyone!

I pulled the driver out of the enclosure to get a better look at it (I'm still amazed at how "new" it appears!). I cannot see anything from the outside that would indicate a physical problem. Cone, spider, etc. all look firmly attached. If the spider has become disconnected from the former, it's not obvious to me. I did gently shake the speaker and heard nothing that I could say was a problem (Not that I'm sure I could hear anything like that anyways). I redid a "press test" and everything still feels firm. I did carefully push the cone in and found that something did bottom out, but that was 3/4"-1" excursion of the cone into the basket/vc area.

However, I may have discovered something of importance. I reinstalled the driver, left the sub upside down and ran some fairly heavy surround sound source material to listen if the sound was coming specifically from the speaker or if there might have been something loose in the cabinet generating the noise. It was the speaker. What I did notice was that during fairly full lo-freq passages, the speaker did just fine. The bass was firm and solid. However, when these low freqs weren't playing and slightly higher freqs were, that's when I noticed the noise (now I'm not so sure it was actually a "clacketing" sound...maybe more "crackling"). Also, absence of any source input, I heard what could be a considered a fairly constant low-level pink or white noise coming from the speaker. The level control had no effect on this noise.

This may be wishful thinking, but I'm now back to wondering if the problem is a leaky cap (bypass, maybe), noisy resistor or marginal transistor (hopefully not a custom IC in the amp circuit (schematic, please I can't remember if I mentioned it, but at one time I had a noise (can't remember if it was the same as this one) that seemed (as in I was never sure) to be related to a dirty level control. I turned the control (and the cross over control) a few times and it appeared to go away. Maybe just coincidence. Also, I've had to resolder a cold connection on one of the ps filter caps).

If I can't find a schematic, I may just bite the bullet and replace any and all caps that could be possible sources of this. I'll get into it with a scope first, of course

In the end, it may still turn out to be the speaker/driver. However, by comparison the amp should be fairly easy (and, hopefully, cheap) to fix.

I'll keep you posted on my progress. Thanks again.

Cheers....Steph

[djmeverett]

What you need to do is use a function generator (sine wave) and do a slow sweep from 20Hz on up. If you don't have a function generator there are free software versions for computers using your sound card from your computer. Not the best but useable for this kind of testing.
You can do that with the speaker in free air (speaker sitting upright on a bench or table out of the box). If you hear the noise, you can start to figure out the cause.
If it sounds good in free air then place it back into the box and run the same test.
If it still sounds good, then start looking at your source material or receiver noise.
Hope that helps