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Distorted sound

Discussion in 'Amps and Cabs [BG]' started by peterboy1968, Jan 6, 2018.

  1. peterboy1968


    Dec 20, 2011
    Can anyone tell me what might cause a distorted sound / Speakers working backwards. My set up is Ampeg SVT 3 Pro with two Markbass 104 HF / 4 Ohm cabinets. I'm playing Epiphone T-bird pro. Problem occur when I hit low notes on E string. Time to time coils pull back hard. Signal is clear when I use my back up amp (EBS 250W head).
  2. Speakers farting out due to too much power or excessive low end EQ?
    Aqualung60 and agedhorse like this.
  3. Paulabass

    Paulabass Supporting Member

    Sep 18, 2017
    I'm a little baffled by your question 'working backward', but if a speaker ever moves forward, or backwards ONCE, your amp is leaking D.C. and that is very, very bad. The chances are if your amp produces any D.C. your speakers would have fried right away, so...I'm baffled.
  4. People keep saying DC voltages are bad for speakers.
    So how much harm comes from doing the battery test?

    Does anyone here honestly beleive that hooking a battery (with appropriate current limiting to avoid coil heating and maximum excursion) to a speaker and leaving it connected until the battery is fully discharged, will damage the speaker?
    This inquiring mind would like to know the science behind DC being bad for speakers.
  5. Paulabass

    Paulabass Supporting Member

    Sep 18, 2017
    Wow, that's quite the question- A battery test for a second or two is fine. A nine volt battery will burn a voicecoil if left connected (It's called a space heater). Also, big power amps use insulated binding posts or speakons because they will produce enough current to kill you at the output, when they go D.C. it is instantly catostophic. No amount of D.C. to a speaker is safe or good. If your amp produces ANY, it has to go to the shop immediately.
    Lets ignore science for a second. If you take apart a speaker coil you will notice it's pretty fine wire, enough that it will turn red hot in a second connected to a battery. No amount of ferro fluid will cool that, and once the insulation burns, the speaker is TOAST.
    FunkHead likes this.
  6. anderbass


    Dec 20, 2005
    Phoenix. Az.
  7. Jaco who?

    Jaco who?

    May 20, 2008
    May or may not have anything to do with it, but you should probably stop running a 2Ω load. Unless I'm even more dense than I thought, I believe the SVT3 pro specs show a minimum load of 4Ω.
    Bim1959 and Aqualung60 like this.
  8. I don't dispute what you say about a DC voltage source being able the exceed the current rating of VC wires for a long enough time to cause damage. But you can apply the equivilant average current from an AC source to cause damage as well. It is all about how much energy is available over time. The wires in the VC do not care if the current is DC or AC. They care about the average current over time causing heating and whether or not the resulting heat is sufficient to break down the insulation, glues, or turn the VC wire into a fuse that burns open.

    My challenge to everyone was based on the blanket statement "DC voltage is very bad for speakers." That statement, in and of itself is false. Please note that my challenge also included the condition of current limited DC voltage. People who just say "DC voltage is bad for speakers" without qualifying that statement, only serve to spread misinformation among those who do not understand how this stuff works.
    Kro likes this.
  9. If a speaker cone moves and stays there after you switch your amp on, then the amp needs to go to a tech. Continued use will damage your speakers.
    agedhorse likes this.
  10. Jaco who?

    Jaco who?

    May 20, 2008
    AND if you've been running the poor thing at 2Ω, it should probably go to a tech anyway. HELLO? IS THERE ANYBODY OUT THERE?
    Bim1959 and Aqualung60 like this.
  11. Shush please, I'm taking a nap. :sleep:
    agedhorse and BassmanPaul like this.
  12. [QUOTE="My set up is Ampeg SVT 3 Pro with two Markbass 104 HF / 4 Ohm cabinets." The SVT3 pro cannot run a 2 ohm load.
  13. Wasnex


    Dec 25, 2011
    Not true in absolute terms, but in practical terms this a useful "over generalization."

    IMHO, if your amp is putting out significant DC voltage it should be taken to the shop, and some speakers may indeed be damaged if left connected to a 9V battery for an extended period of time. Would a 9V battery pose a risk to a woofer with an 800 watt voice coil?...to be honest I am not sure this is important as I can't think of a valid reason to hookup a battery to a speaker long term. YMMV

    FYI, I checked the service manual for an old Crown PB1 and and DC offset is spec'ed at <10mv.
  14. Paulabass

    Paulabass Supporting Member

    Sep 18, 2017
    ^Which brings up the second question- If EVERYONE agrees D.C. Has no place in a amplifiers output, why go to such trouble to prove it's not harmful? By this crazy notion- Small amounts of arsenic are not lethal, so why not put some in your food?
    I own over forty power amps- Every single time one goes into protect it goes to the tech, who, among other things, immediately checks for D.C. Why? Because of the five or six reasons an amp will go into protect, only D.C. Will take out speakers on it's way south.
    If the poster feels a strong desire to feed his speakers D.C. For whatever reason- they are his speakers.
  15. Please read what I said. There was nothing in my discussion about an AMPLIFIER putting out DC, because the claim I was refuting was simply that... DC was very bad for speakers. Nothing more, nothing less than just that phrase. You may have inferred a faulty amplifier, but I certainly did not imply one. I set the conditions of the DC voltage to be current limited. The point being that if you properly limit the DC current that you apply to the speaker, you can avoid damaging it and therefore prove that the blanket statement about DC being bad, just because it is DC, is false.

    The whole point of this is that people are making claims while leaving out important information that would qualify that claim. This is how poorly qualified statements end up becoming widespread misinformation.

    Of course if your amp is pumping out enough DC to do damage, it will do damage. But the qualifier in that statement is that it has to be *enough to do damage.* That applies to both DC and AC. If the Voice Coil can safely dissipate the heat generated by the voltage source, it won't be damaged. If it can't it doesn't matter if it's AC or DC.

    The unqualified claim was... DC is very bad for speakers. Period.

    The fact that the voltage is DC, *IN AND OF ITSELF* does not contribute to speaker damage.

    If you are going to tell me that my statement is false, do so based on the conditions of my statement. Please do not add or subtract factors that change what I said and then tell me I am wrong.

    Thank you.
  16. Paulabass

    Paulabass Supporting Member

    Sep 18, 2017
    And my point is- if D.C. Is not going to improve your tone, or make you a rock star, why are we aguing this?
    All my QSC amps shut down at .75vdc........to protect speakers.
  17. bikeplate

    bikeplate Supporting Member

    Jun 7, 2001
    Upstate NY
    Is your amp rated for 2 ohm? Id start there
  18. Of course you are correct that DC is not going to improve your tone or make you a rock star and I totally agree with you.

    Of course I may just be tilting at windmills in my effort to try to get people to stop making unqualified statements that lead to misunderstanding. But it's my windmill, and I'm pretty well tilted from the start anyway.

    I do wish to thank you and Wasnex for including in your posts that some DC voltage is acceptable.
  19. Wasnex


    Dec 25, 2011
    Rather than discounting what you wrote (which I read before posting), I attempted to explain why the statement is a useful "over generalization." I don't think I wrote anything that would infer the statement is an absolute truth or that your example is wrong.

    You wrote, "If the Voice Coil can safely dissipate the heat generated by the voltage source, it won't be damaged. If it can't it doesn't matter if it's AC or DC."

    Isn't there some difference in the duty cycle between AC and DC? DC is at 100% all the time. AC varies from off to on continuously. There is less heating when the voltage is between the peak to peak values, and the coil even has an instant to cool when the wave form crosses 0V. (I should qualify here that to my understanding, voltage and current are not perfectly in phase).

    Additionally in some designs, the cooling effect achieved by voice coil motion would likely result in a need to rate the coil differently for AC and DC. If this were not true, why would engineers go to the trouble of venting voice coils. Do you really think JBLs VGC technology is all marketing hype? https://www.jblpro.com/ProductAttachments/tn_v1n22.pdf

    Additionally you have to consider the excursion limits of the driver in addition to its thermal limits...I would not use a 9V battery to check a 20 watt compression driver, even though the 5 ohm nominal resistance of the driver should limit the power dissipated by the voice coil to about 16 watts.
    Last edited: Jan 7, 2018
    Paulabass likes this.
  20. in context of a discussion about amplifiers DC to the speaker needs no qualification, it's bad news.
    Paulabass likes this.

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