The above Ad will no longer appear after you Sign Up for Free!

Loudspeakers Speakers emitting high frequency....

Discussion in 'Sound, Music, and Intercom' started by Thefoxygranpa, Jul 11, 2008.

  1. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    Hello!

    My JBL powered speakers [prx515 and prx518] are making nasty noises. They emit a very high frequency when powered on. I would say above 14kHz. The tone is a steady volume until I run a signal to the speakers, and when that happens that particular frequency is amplified as well. I'm stuck on what it could be.

    I've tried to reset the breaker that they are on, as that solved the problem once before, but only for a short time. I should mention that these speakers are flown...

    Now I think that isn't even near enough info to assess the situation...but let me know what more info you would like and I would gladly tell you, this frequency is bugging me!
     
  2. avare

    avare Active Member

    Messages:
    148
    Likes Received:
    8
    Location:
    Hamilton, ON Canada
    Do they buzz when there is no input cable hooked up to them?

    Andre
     
  3. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    Yes, they do.
     
  4. Eboy87

    Eboy87 Well-Known Member

    Messages:
    1,206
    Likes Received:
    49
    Location:
    Chicago, IL
    So, for reference, you plug in the power cable, power on the speaker, and you get this noise. Is it a ringing or a buzzing noise? If it's a buzz, did you try different outlets? As you said, this only happens when they have no input cable plugged in, which says to me it's either a power issue or an amp issue.

    If it's a problem in the amplifier or speaker itself, send it back to JBL (or Crown, whoever repairs those) and have them look at it.
     
  5. avare

    avare Active Member

    Messages:
    148
    Likes Received:
    8
    Location:
    Hamilton, ON Canada
    As Ian wrote, send them back. There is a problem with them.

    Andre
     
  6. SHARYNF

    SHARYNF Well-Known Member

    Messages:
    1,911
    Likes Received:
    157
    Usually it is a capacitor going bad, definitely get them repaired
    Sharyn
     
  7. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    Just an update to what happened....


    I have found it is only one speaker that is emitting this frequency. I took it down and brought it to another room and plugged it in there....after about five minutes it starts to emit this frequency. Now this is with nothing else but power plugged into the speaker.

    Bad crown amp? I think so...have contacted the guy I bought them from, but the fact that fly points were installed...would that void my warranty?

    [and my apologies, delete this post if my reference to fly points is a no-no!]
     
  8. cjthedj

    cjthedj Member

    Messages:
    11
    Likes Received:
    0
    definately send them in!
     
  9. TimmyP1955

    TimmyP1955 Active Member

    Messages:
    793
    Likes Received:
    55
    Location:
    Indianapolis
    Tis very foolish to install flypoints on a loudspeaker. Should something fail that causes an injury, the whole of the liability will be yours, as you flew a box that was not designed and constructed to be flown. There's more to making a box flyable than just the addition of flypoints.
     
  10. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    For the sake of breaking CB rules I won't discuss the why/how I installed the fly points and safety measures. My main point of this topic was to discuss my malfunctioning speaker, my apologies if this raised any eyebrows....

    As for my speaker it has to be taken to Philadelphia and from my last update the technician couldn't pinpoint the problem:rolleyes: .
     
  11. museav

    museav CBMod CB Mods Departed Member

    Messages:
    4,017
    Likes Received:
    562
    Occupation:
    Acoustical, audio and audiovisual consultant
    Location:
    Marietta, GA
    I think the relevant point is that the speakers were modified in a manner such that they are not being used as intended. I would think JBL would have to refuse any warranty service simply as accepting it could be seen as implicit acceptance of the modifications. In addition, as far as I can tell from what has been posted, it would be difficult to say definitively that the problems being experienced might not be related to the modifications made.

    While you may have accommodated this in your modifications, for others that may not be aware and could take what was said wrong, there is often much more to making a speaker flyable than simply adding fly points.
     
  12. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    Ah yes, the reason I brought my modifications into this topic was to ask opinion on whether they would service this although I did make alterations.

    I just re-read my Warranty paper and it does look that JBL would not cover this under warranty because of what I did. I haven't received an invoice from the repair company yet, so I assume I'll know soon enough if I'll be forking out the cash for the repair.

    Thanks!
     
  13. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    Yarg!

    So my speaker comes back yesterday, I take a look at the invoice and it says "Can not get it to reproduce sound you described. Check your XLR cables and AC power if the problem persists"

    Now this had to go to philly to get repaired, and it turns out they did nothing!

    My question now is where do I go from here? I got the speaker back, put it in my office and powered it on. I had the gain all the way down, and after 30 minutes[amps warm to touch], it started to produce this frequency again!

    What would someone suggest! I'm at a loss as to what I should do, and even tempted to send this speaker straight to JBL if they do repairs.

    Thanks CB!
     
  14. waynehoskins

    waynehoskins Active Member

    Messages:
    782
    Likes Received:
    49
    Location:
    Arlington, TX
    The first thing that comes to mind is perhaps a switching power supply going unstable or losing regulation with heat and time. It may require going back to the guys who made it, or some time in the service manual at least performing tests. Just my guess, though, and I could be totally wrong.
     
  15. RichMoore

    RichMoore Member

    Messages:
    75
    Likes Received:
    4
    Location:
    Corpus Christi, Texas
    Are you powering the speakers from regular wall outlets? If so, that could be your problem.

    You might want to investigate "power conditioners", which 'clean' the ac power.

    Most likely, the shop where you sent the speaker to be checked out was using 'clean' power at the work bench and noticed no problem, which could be an indicator that your power is 'dirty'.
     
  16. Thefoxygranpa

    Thefoxygranpa Active Member

    Messages:
    137
    Likes Received:
    5
    Location:
    Delawhere?
    I should mention that both the speakers are running off of the same power line, however one makes the noise and the other does not.
     
  17. SHARYNF

    SHARYNF Well-Known Member

    Messages:
    1,911
    Likes Received:
    157
    this may sound crazy but take the speaker to another location say your home and try it there, it is possible that you have something in that speaker/amp that is sensitive to a high frequency signal that it is picking up, could be another electronic item near where you have been testing it
    Just a thought
    Sharyn
     
  18. FMEng

    FMEng Well-Known Member Fight Leukemia

    Messages:
    1,870
    Likes Received:
    695
    Location:
    Tacoma, WA
    The problem is clearly internal to the speaker. Someone did a poor job of evaluating it. That has to be frustrating. Basically they just plugged it in, ran it for a few minutes, and gave up when they did not hear the problem. Had they let it run for awhile, they would have caught the problem.

    Your problem is typical of a thermal intermittent, which is a fairly common way for electronics to act up, particularly in things that run rather warm, like amps. When it warms up, some section starts oscillating. It could either be in a power supply regulator or an audio stage.

    Send it in again with a more detailed description of the problem. The important points are that the noise occurs with no audio cable connected, with the volume turned down, and AFTER it has been powered up for some time. Given that info, any good technician should be able to reproduce the problem, then fix it. Make sure to tape a type written note directly to the speaker, to make sure the bench tech sees it.

    I would also instruct them not to return the speaker un-repaired without calling you first. If they can't fix it again, and call you, then I would tell them to replace all of the electrolytic capacitors in the power supply, especially those located next to hot things. If the quantity is reasonable, do them all. Electrolytics are a very common failure item in hot blooded equipment, and they are not usually expensive parts or time consuming to do. Just replacing a bunch of parts like that is a gamble, but one based on an educated guess. I would take that gamble since shipping a heavy speaker around is expensive.
     
  19. jkowtko

    jkowtko Active Member

    Messages:
    807
    Likes Received:
    51
    Location:
    Redwood City, CA
    When my Mackie SRM450 had a problem, Mackie allowed me to remove the amp from the back of the speaker cabinet, and replace just the amp. They shipped me a new amp, I swapped them out and returned the broken one. You might want to check with JBL to see if they will do this -- a much easier way to get the speaker repaired, and you won't have to worry about cabinet modification issues.
     
  20. waynehoskins

    waynehoskins Active Member

    Messages:
    782
    Likes Received:
    49
    Location:
    Arlington, TX
    By the way, since it's on your desk, you might open the back up and see if there are any of the standard signs of catastrophic failure on the power supply or PA sections.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice