Sub Cable Problem

Discussion in 'Archived Threads 2001-2004' started by Bryan Acevedo, Oct 3, 2001.

  1. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Hello All!
    I have a Klipsch KSW 12 sub hooked up to a Denon 3802 receiver via the sub out on the receiver.
    I was using Radio Shack Gold Series interconnects, including a 20 foot audio cable for the sub. I recently purchased Acoustic Research Pro Series interconnects all around, including their 25 foot sub calbe.
    First off, these cables are pretty nice, especially for the money. I am really impressed.
    But, I had a problem with the sub cable. It is directional (so they say) and has an arrow pointing in one direction. They say to put this into the input, so I put this on the input of the sub. I guess (by reading on the net) that it has something to do with the way it is grounded. Who knows. Anyway, after using this cable, everytime I turn off my ceiling fan, my sub thumps. I tried everything I could think of to get rid of it. Unplugging the cable from the sub gets rid of it. Even just having the cable plugged in to only the sub gives the thump. No cables plugged in = no thump. RS cable plugged in = no thump. So I reverted back to my RS cable, and now I have no thmp when turning off the ceiling fan. It's like the cable is picking up the RF from the fan turning off and sending it to the sub.
    My question to everyone is, why did this happen? I supposedly got a high quality, shielded, specific for sub cable. Is it a defective cable? Should I exchange it or just return it? I heard no audible difference between my RS and AR cable, but I like the build quality and look of the AR cable, plus the connectors are much easier to work with on the AR cable. I am also anal, and like to have all of my cables be the same. Another note is that the Y-Cable I got is also going back. It seemed to have a short in it. When I would jiggle it, it would cause a loud hum (like a ground loop hum). Very weird.
    I am just wondering why this would happen. The cable is twisted pair, balanced and all that jazz.
    So let me know why it would do this.
    Thanks,
    Bryan
     
  2. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Yeah Sean - I really like the RS cables, but those damn connectors practically ripped the RCA inputs off of the components when unhooking them. I always liked their performance. And now seeing the new cables, I can safely say there is absolutley no performance difference in MY system. Well accept for the sub cable! [​IMG]
    What was funny is that I took the cables back to Radio Shack and told them the problem. I had actually dealt with the manager. It had actually screwed up my sat receiver audio outs. You had to wiggle them to get output out of the left channel. I just returned the cables and used the credit to buy a new sat receiver and moved the other one to the bedroom (to replace a really old one). I only use the coax out to the VCR in there, so I don't care about the RCA cables.
    Well, I went back and talked to the manager again, cause he wanted to buy my old sat receiver, and when I went in, he told me that he was hooking up his Ultimate TV sat receiver with the gold cables and it ripped the RCA connector off of the back! He showed it to me and said - yep, evidence that you are right! He said he mentioned it to the rep - so maybe they will do something about it.
    Bryan
     
  3. dougW

    dougW Stunt Coordinator

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    I had that same thing happen while unplugging an RS cable from an audio video switch box, which I also bought from the shack. Guess what came back to them, not once, but twice!
    Well, I found one solution is to gently take a pair of needle nose pliers inside the pronges, and gradually loosen their death grip. Of course, you do run a risk of breaking a pronge.
    Sounds like that cable has a problem, it shouldn't be the wire itself, but perhaps a weak ground for example, or perhaps it's NOT shielded and the RS cable is.
    As to directional issues, there's little truly directional about standard cabling. Now, were you talking about high priced wire, that goes through special processing, or how it is actually poured, their could be directionality or PERCEIVED directionality. But as far as how it comes off the spool for standard grade wire, there should be no difference, generally.
    But changing direction on the cable will not produce RF or other type noise, that's simply not possible.
    While I don't sell directionality myself, I do believe keeping the electrons flowing in one general direction, is probably not a bad thing for purists.
    Doug
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    Lexman's Theater
     
  4. KenPitzner

    KenPitzner Auditioning

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    Actually, I look for cables with the "death grip". Tighter connections = better connections. Most very high end cables have tight connections. And, come on, how often do you really need to remove cables? The last time I removed cables was the last time I moved, 2 years ago. Now plugging in cables, OTOH, happens whenever I add a new toy to my system [​IMG]
    Ken
     
  5. Steven Lin

    Steven Lin Extra

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    Actually, some cables are directional. One form uses a twisted pair and an outer, copper shield. One wire is positive, the other ground. The copper shield is also attached to ground at one end. The shield at the other is left unconnected. Clearly, this cable has a direction.
    Personally, I don't believe this type of cable works well. The shield, IMO, would behave like an antenna.
    Bryan, it's possible that your AR cable is constructed this way.
    ------------------
    Steven
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    Thump Issue: When you turn off your ceiling fan, it injects voltage into your electrical wireing. This is called "back-emf" and is a common problem with motor-driven devices.
    Your sub has an amplifier. But what does it amplify? It looks at 2 signals: the electrical ground, and the signal. When it sees a small voltage difference, it amplifies it.
    When you turn off your fan, it injects voltage into your household electrical ground. The amp in the sub detect the difference and ... amplifies it. This gives you your THUD.
    Why does the cable make a difference? (I'm fuzzy on the details but here it the crux):
    With the Radio Shack cable, the outer-shield is tied to electrical ground on both ends. When the fan turns off, the amp "sees" the extra voltage on both it's internal ground, and the outer shield of the cable. Result: it does not detect a difference in voltage so it does not amplify anything (no THUD).
    With the AR cable, the shield on the wire is NOT connected to the destination plug (sub side). This is why you have little arrows to show you the destination.
    (There is some argument that this is a better design for a cable. But it makes some assumptions about how you have your electronics plugged into AC power.)
    Since the sub does not see any ground (0 volts) signal on the AR cable, it looks for a difference between it's own electrical ground, and the center wire on the cable.
    The back-emf from the fan shutting off injects a signal into the electrical ground - this IS a voltage difference - and your sub tries to amplify the difference.
    My best advice is to stick with the RS cable.
    Good Luck.
     
  7. Tor Arne

    Tor Arne Stunt Coordinator

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  8. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Thanks guys for the reply!
    Steven, yes I think it is constructed this way. I thought the reason it was constructed this way was for better sheilding! I guess not! It does seem to act like an antenna!
    Ken, you are right - I don't unplug that often, but enough that I don't want to ruin a $1200 receiver because I didn't want to spend an extra few dollars on a cable. Also, I am moving my rack into a built in unit, and no longer will I be able to stand behind the rack when I am connecting it. I wanted cables that were easier to plug in and unplug when necessary.
    Bob - that is what I figured was happening, but you left me with some questions.
    First, with the AR cable, whether it was plugged in to my receiver or not, or no matter which direction it was plugged in, I got a thump. However, when reversing it, it was a slightly lower thump.
    The RS cable, never got a thump, no matter how I plugged it in or whether or not it was plugged into the receiver. I even moved the sub and plugged it directly into my Power condition (Monster HTS 1000), and with the AR cable still got a thump. This is with all of the other equipment off, and just the sub on.
    So, it sounded like what you are saying is that the power line is injecting the signal, and the cable is just causing it to be a difference between voltages? I don't totally understand because this even happens when the cable is not plugged into anything on the other end. I am using a Y-adapter - so maybe that has something to do with it. Also, why wouldn't the power conditioner filter this out whent he sub and receiver are both plugged in to it?
    Also, all my other cables are like this between the components. Is this bad? They are directional, and I am wondering if they will pick up this noise, too? I haven't noticed anything yet, but I would just rather return them all now (except for the toslink and s-video that aren't designed like this for obvious reasons).
    So it kind of sounds like this is just a design problem. The cables are designed for a different environment or system, and don't seem to work well with mine. Maybe the old design approach of keeping it simple still applies!
    Thanks for the info!
    Bryan
     
  9. Bob McElfresh

    Bob McElfresh Producer

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    I'm almost afraid to ask this, but it's important. On the power cord for your sub, is it a 3-prong plug or are you using a "cheater" plug so that only 2 prongs go into the electrical outlet?
     
  10. Bryan Acevedo

    Bryan Acevedo Second Unit

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    It is a 2 prong plug, one is bigger than the other for correct polarization (or I guess so).
    I don't use cheater plugs, and never would - I would have an electrician come out and fix the problem before I would do a work around like that. It just would bug me too much that I had to use something that wasn't intended to make the system work correctly! Plus that added danger of getting shocked when touching the sub. (especially for my 8 month old son who loves to crawl over to it and see what this big black box is on the ground) [​IMG]
    Even plugging the sub into my Monster power conditioner didn't help, which should filter out all of the noise.
    I did do an experiment last night. I unhooked everything from my receiver (except for the speakers and sub), turned the volume to max, and turned my fan on and off. I got a slight crackle out of my speakers - I am talking slight - I had to have nothing playing, and my volume set to max (which would never happen during listening). So everything in the room will pick it up, but the sub with that AR cable really picked it up and amplified it. I did this to make sure that the other AR cables I had with the same design wouldn't introduce any noise into my system. With the AR cables hooked up, it didn't get any louder. So they passed.
    I think I am going to have them send me another set of the sub and y cables and see if that is any better. I could have just gotten a bad cable. I said earlier that I had a hum when using the Y Cable if I jiggled it just right. So maybe it was the sub cable that was bad. It won't hurt to try another set.
    Bryan
     
  11. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Update:
    I am getting a new set of cables sent to me, and returning the old ones. After talking with the guy I got them from, he says this cable should not do that, and the only thing he can think of is that the cable itself was bad and maybe the shield was lifted on both ends.
    FYI, I got these at www.discounts-n-deals.com - they have been very responsive and helpful. They are paying for my return shipping and shipping out the brand new stuff without any re-stocking fees, etc.
    I highly recommend them for the AR Pro Series cables - they have great prices and great customer service!
    I will post my results when they come in next week.
    Bryan
    [Edited last by Bryan Acevedo on October 05, 2001 at 04:32 PM]
     
  12. Bob McElfresh

    Bob McElfresh Producer

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    Bryan: I hate to be the one to tell you this, but you are already using a "cheater" plug. Any electrical plug without the round ground plug is Un-Grounded.
    Is it safe. Sure. Just dont go playing around with the insides with the power on.
    But this explains your THUMP problem.
    Your sub is tring to amplify a signal. This takes 2 wires. One for 0.0 volts , the other with the signal. Often, the AC electrical ground is the zero-volt reference. (YOU DONT HAVE THIS!) Or, the outer-shield on the coax is the zero-volt reference. (YOU ALSO DONT HAVE THIS).
    I'll bet that new cable does not connect the shield to both plugs, only the source-side.
    Another cable of the same AR model will NOT solve your problem.
    Go back to the Radio Shack cable. This will solve your problem.
     
  13. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Thanks Bob - that makes sense. They are already sending me the cables, so I will check them out, but I do have a feeling that you are correct. So if I got a new sub with a 3 prong connector (do any exist?) would that solve this problem? I notice that my receiver picks up the noise ever so slightly when turned all the way up and nothing is playing. It too has a 2 prong plug. Almost my entire theater has only 2 prongs on the power cord, and I am using the same kind of interconnects. Why don't they pick it up as well?
    I will just have to wait and see what happens.
    Bryan
     
  14. Lee Bailey

    Lee Bailey Second Unit

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    The 'directional arrow' thing is because the cable you have has 2 conductors inside, with a shield wire that goes the entire length of the cable. At the reciever end, the shield is connected to the conductor that is connected to the RCA jack's outer ring. At the Sub's end, the shield is not connected to the RCA jack at all. The reason is to keep any noise picked up by the shield from entering into the sub's circuits.
    There are also many manufacturers of cables that say that there is a 'directionality' to a cable. And, after properly breaking it in(which may take days), that you could hear a difference depending on which direction you connect them to your component. There is even a 'cable-cooker' available for providing the break-in period in a shorter amount of time.
    ------------------
    The Bailey's Web Page and Home Theatre
    The Bailey's DVD Collection
    [Edited last by Lee Bailey on October 05, 2001 at 09:00 PM]
     
  15. Bryan Acevedo

    Bryan Acevedo Second Unit

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    So Lee - does it sound like my cable had a short in it -maybe the other end of the cable was connected? Or both ends were unconnected?
    Bob, if it was what you say, why would it not thump without that cable plugged in? There is then no reference to ground anywhere. Just curious as to why plugging in only one end of the cable would introduce the noise - I don't see how this could be a grounding of the sub problem.
    Thanks,
    Bryan
     
  16. Bob McElfresh

    Bob McElfresh Producer

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    The problem is you have 2 amps in your system: the receiver and the subwoofer amp. Having a second amp is what tends to make you prone to ground-loop hum and other issues.
    My guess is that the rest of your system works fine because you have 1 device that is grounded (hopefully your receiver) and everything else is not. These other devices do not do power amplification so the receiver ground becomes the 0 volt reference for everything. This happens through the outer-shield on the interconnect wires.
    Often, people with external subs have to use a "cheater" plug so that 2 different amps dont try and fight over the ground. Even a few milivolts difference in the ground causes a loud subwoofer humm. Your sub manufacturer solved this problem for you by NOT including a 3-prong plug.
    Your case, you dont have the electrical ground in the power cord, and that new cable does not provide a ground on the shield.
    Without the cable plugged in: there is no signal wire. And the sub is trying to amplify ANY TINY VOLTAGE difference between the signal and ground. No cable = no voltage difference = no THUD.
     
  17. Lee Bailey

    Lee Bailey Second Unit

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    Bryan,
    Do you have all your equipment plugged into the same outlet, using a power strip? If not, they should be, so the ground is at the same potential for everything.
    It may be that the new cable is actually sending a better signal to your sub, and you are now hearing the thump. To see if the shield is actually connected at both ends, you would have to open up the RCA jack on the end that connects to the sub, and take a look. You are obviously getting a transient sent through your equipment from that fan switch, hopefully it is not on the same circuit breaker as your equipment.
    ------------------
    The Bailey's Web Page and Home Theatre
    The Bailey's DVD Collection
     
  18. Bryan Acevedo

    Bryan Acevedo Second Unit

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    Thanks guys. Here is the deal.
    I have all of my equipment, except for the sub, plugged in to a Monster HTS 1000 Power Strip. It is a power conditioner and filter.
    I can't plug the sub in to it because it is 25 feet away (well where the cable would have to run). So I have it on a different switch.
    But, Lee, I get the thump even when the cable is not plugged into the receiver, and only plugged into the sub. So the end that would normally go to the sub pre-out, is left unplugged - and I still get the thump. If I do this with any other cable, it doesn't happen. I thought that most sub cables (including the Monster) were made this way, where one end doesn't have the shield attached. So would I then get this noise with every cable made like this? If so, why would they make the sub cables like this, knowing this is the kind of environment they are going to be in. Yes, the fan is on the same circuit, not really any way of changing it now. The Monster Power strip should filter it out from the other equipment, which seems to be doing its job.
    I will see what happens when I get the new cables, but I am not too hopeful. I am just trying to understand what is going on.
    Bryan
     
  19. Lee Bailey

    Lee Bailey Second Unit

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    Bryan, I really can't tell you why you are hearing the thump with just that cable installed. It sure doesn't make sense to me. But, you have answered the question about the fan switch being on the same circuit. Go back to the original cable. It would sound like your new cable is picking up the transient and putting it directly into your sub's amp, just like an antenna.
    ------------------
    The Bailey's Web Page and Home Theatre
    The Bailey's DVD Collection
     
  20. Geoff L

    Geoff L Screenwriter

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    Bryan,
    I, like you, useing a 10.00 over the counter 25ft cable & Y feeding my subs. The basic setup, was nearly identical to yours. Bought the best I could afford, 150.00 sub cable (which will remain nameless) and experienced the same BS you are, along with intermitent humming. I am anal about my cableing to, this bugged the shit out of me.
    I tried everything suggested here and more. After countless hours, experiments, and suggestions, I sucummend to the 10.00 cable and have never looked back!!!!
    Im not a electric gooroo, but nosie is nosie. And no noise is no noise! I took 150.00 bucks and put it into DVD's..
    My 02cents
    Geoff
     

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