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Thread: 4311B woofer constantly "flapping"

  1. #1
    Junior Member nee's Avatar
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    4311B woofer constantly "flapping"

    When my 4311Bs are connected to the amp and the amp is on, both woofers are moving when no signal is applied and the volume is down - maybe 10-12 cycles per second. One of the woofers moves so much I would call it flapping - really quite a large excursion.

    If I plug the ports then the flapping stops.

    If I swap channels it's the same speaker that flaps. I know I need to try them with a different amp, but has anyone come across this kind of thing?

    IanG

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    Senior Member 1audiohack's Avatar
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    I have seen a couple of "unstable" amps do that. I have a GTI1800 that has the suspension absolutely socked out from that. Don't wait for it to kill something, get it out of your system and repair or replace it.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Senior Member jcrobso's Avatar
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    Unhappy NOT a good thing.

    Quote Originally Posted by nee View Post
    When my 4311Bs are connected to the amp and the amp is on, both woofers are moving when no signal is applied and the volume is down - maybe 10-12 cycles per second. One of the woofers moves so much I would call it flapping - really quite a large excursion.

    If I plug the ports then the flapping stops.

    If I swap channels it's the same speaker that flaps. I know I need to try them with a different amp, but has anyone come across this kind of thing?

    IanG
    The amp is oscillating with the speaker load, this is a dangerous thing, lots of power is going to the woofers, get a different amp ASAP!!

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    Senior Member Beowulf57's Avatar
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    Heed the warnings...this used to be called "motorboating" as in a low frequency oscillation/instability in an amplifier circuit: "Putt, putt, putt, putt."

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    Motorboating

    You can try connecting a 20 Ohm 10 Watt resistor across the speaker terminals, if the oscillation stops,leave the resistor in place. Reflex systems can exhibit a large impedance peak at a very low frequency, plugging the port removes the lower peak. This was very common in Fisher Amps of the late 1960's. Best to replace the amp if possible.

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    Senior Member pyonc's Avatar
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    Smile Mine, too

    Quote Originally Posted by nee View Post
    When my 4311Bs are connected to the amp and the amp is on, both woofers are moving when no signal is applied and the volume is down - maybe 10-12 cycles per second. One of the woofers moves so much I would call it flapping - really quite a large excursion.

    If I plug the ports then the flapping stops.

    If I swap channels it's the same speaker that flaps. I know I need to try them with a different amp, but has anyone come across this kind of thing?

    IanG
    Hi,

    I have the 4311B, too.
    When I play CD, there is no "flapping" on the woofers even at noon volumn, but when I play LP, the woofers start to flap from 11 o'clock volume. I've no idea why. I play 4311B with a Marantz receiver.

  7. #7
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by pyonc View Post
    I have the 4311B, too.
    When I play CD, there is no "flapping" on the woofers even at noon volumn, but when I play LP, the woofers start to flap from 11 o'clock volume. I've no idea why.
    Turntable rumble? :dont-know
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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    Senior Member herki the cat's Avatar
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    Quote Originally Posted by nee View Post
    & [pyonc ] & [IanG ] =My 4311B's connected to the amp, with no signal, & volume controis down = One woofers moves maybe 10-12 cycles per second - really quite a large excursion. If I plug the ports the flapping stops. nee283769, pyonc & IanG.
    [quote=BMWCCA;285188]Turntable rumble? :dont-know[/quote]

    Quote Originally Posted by Loren42 View Post
    & this circuit should be just about perfect for you. It is tuned for 17 Hz to provide a rumble filter, but you can change it easily if you need to.Loren42
    Member nee; It was mentioned in this thread, "cone flapping does not occur playing CD's" which confirms BMWCCA suggestion "turntable rumble" __read: "a Turntable rumble filter is in order". To that end. Member Loren42;283351 is fixing his cone "flapping" & "slamming" with an excellent high pass filter at his power amplifier input, to wit: >Click this button= < This circuit should be just about perfect for you.

    Also with due respect for the other excellent posts regarding amplifier instability & susceptibility to "speaker enclosure Ports , amplifier motor boating, & speaker low frequency impedance aberrations", and other instabilities primed to flare up etc suggesting the need for a better, more stable power amplifier before ALHBL="all hell breaks loose." = very cogent advice.

    Bonne Chance, herki the cat
    Last edited by herki the cat; 04-09-2010 at 01:35 AM. Reason: Natha

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    Senior Member pyonc's Avatar
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    Quote Originally Posted by BMWCCA View Post
    Turntable rumble? :dont-know
    Nope! Turntable stands tight on a wood stand.
    When I push the 'Loudness' button on the Marantz receiver, though,
    I see the woofers starting to flap from around 11 o'clock volumn when I play LPs. But, I don't see that happen at all when I play CD.

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    Administrator Robh3606's Avatar
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    It's not rumble at all it's acoustic feedback from the bass boost of the loudness switch. Either move the turtable or lay off the loudness switch. You should only be using it at low voulme. All you are doing is wasting all your amps headroom and that could be part of the reason why you are have issues with how the 4343 sound in your other thread.

    Rob

    http://en.wikipedia.org/wiki/Loudness
    "I could be arguing in my spare time"

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    Senior Member pyonc's Avatar
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    Quote Originally Posted by Robh3606 View Post
    It's not rumble at all it's acoustic feedback from the bass boost of the loudness switch. Either move the turtable or lay off the loudness switch. You should only be using it at low voulme. All you are doing is wasting all your amps headroom and that could be part of the reason why you are have issues with how the 4343 sound in your other thread.

    Rob

    http://en.wikipedia.org/wiki/Loudness
    Thanks. Actually I don't turn on the Loudness button when I play CD or LP because of this issue...

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    Junior Member nee's Avatar
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    Thanks for all the excellent suggestions, but this one has got me really stumped. Here's a run-down:

    1. With amp volume on zero, one of the JBL 4311Bs flaps a lot, the other flaps a little. i.e. it's not turntable or other rumble (I have no turntable) so a high pass filter at the input would make no difference. Indeed, if I disconnect the preamps the flapping continues.

    2. No matter which channel the speakers are connected to, the speaker that flaps a lot continues to flap a lot! So it's not one amp channel "flapping" or motorboating more than the other, it's one speaker "flapping" more than the other.

    3. Plugging the 4311B's port stops the flapping

    4. Changed out the 2 x 2200uf power supply capacitors - no difference.

    5. No other speakers hooked up to the amp show the least signs of motorboating or flapping.

    It just must be the way that that particular 4311B interacts with the amp. I'm gonna try webmonkey's idea of the 20Ohm/10Watt resistor - his/her explanation of an impedance peak at low frequencies sounds most likely.

  13. #13
    Senior Member herki the cat's Avatar
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    amplifier flaping the speaker

    Quote Originally Posted by nee View Post
    Thanks for all the excellent suggestions, but this one has got me really stumped. Here's a run-down:

    1. With amp volume on zero, one of the JBL 4311Bs flaps a lot, the other flaps a little. i.e. it's not turntable or other rumble (I have no turntable) so a high pass filter at the input would make no difference. Indeed, if I disconnect the preamps the flapping continues.

    2. No matter which channel the speakers are connected to, the speaker that flaps a lot continues to flap a lot! So it's not one amp channel "flapping" or motorboating more than the other, it's one speaker "flapping" more than the other.

    3. Plugging the 4311B's port stops the flapping

    4. Changed out the 2 x 2200uf power supply capacitors - no difference.

    5. No other speakers hooked up to the amp show the least signs of motorboating or flapping.

    It just must be the way that that particular 4311B interacts with the amp. I'm gonna try webmonkey's idea of the 20Ohm/10Watt resistor - his/her explanation of an impedance peak at low frequencies sounds most likely.
    BTW, What amplifier are you using. It may be intersting to run the woofer straight fromthe amplifier to isolate the cross over network from the profile. see if that makes any diference. The problem stays with the particular speaker in either channel. Do you have impedance data in the subsonic spectrum to read the frequency where flap occurs which i would expect to find coincides with the open port resonant frequency. Also try a slow frequency sweep in the spectrum of the flapping. Put a 50 0hm resistor in series with the voice coil and read the voltage profile vs frequency to look for a voltage peak developed across the voice coil at the the flap frequency

    Do the same test on the good speaker also for comparison. Save the data for us to see and compare speakers.

    herki the cat

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    Senior Member jcrobso's Avatar
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    I still think it is amp oscillation with the JBL.

    Quote Originally Posted by nee View Post
    Thanks for all the excellent suggestions, but this one has got me really stumped. Here's a run-down:

    1. With amp volume on zero, one of the JBL 4311Bs flaps a lot, the other flaps a little. i.e. it's not turntable or other rumble (I have no turntable) so a high pass filter at the input would make no difference. Indeed, if I disconnect the preamps the flapping continues.

    2. No matter which channel the speakers are connected to, the speaker that flaps a lot continues to flap a lot! So it's not one amp channel "flapping" or motorboating more than the other, it's one speaker "flapping" more than the other.

    3. Plugging the 4311B's port stops the flapping

    4. Changed out the 2 x 2200uf power supply capacitors - no difference.

    5. No other speakers hooked up to the amp show the least signs of motorboating or flapping.

    It just must be the way that that particular 4311B interacts with the amp. I'm gonna try webmonkey's idea of the 20Ohm/10Watt resistor - his/her explanation of an impedance peak at low frequencies sounds most likely.
    Many years ago I had an amp that oscillated with my JBL D140Fs, I did put a 20 ohm resistor in parallel with the speaker and this did dampen the oscillation, but did not stop it. You could try a Zobel network!
    http://www.trueaudio.com/st_zobel.htm
    The cure is a different amp!

  15. #15
    Junior Member nee's Avatar
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    I should have mentioned earlier that I have no idea what make this amp is. It's certainly not a high-end one. I got it at a yard sale, saw that the 4 rectifier diodes were blown, replaced them, and it worked. Replaced the 2 x 2200uf power supply caps, and tried adding a third cap also. There's nothing else in the power supply, and everything else in the amp is stereo - and as I mentioned if I disconnect the preamps from the power amps with no result.

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