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View Full Version : 4311B woofer constantly "flapping"



nee
03-25-2010, 09:39 PM
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

1audiohack
03-25-2010, 09:55 PM
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.

jcrobso
03-26-2010, 10:45 AM
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!! :biting:

Beowulf57
03-27-2010, 06:34 AM
Heed the warnings...this used to be called "motorboating" as in a low frequency oscillation/instability in an amplifier circuit: "Putt, putt, putt, putt."

webmonkey
04-08-2010, 02:39 PM
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.

pyonc
04-08-2010, 08:30 PM
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.:barf:

BMWCCA
04-08-2010, 10:24 PM
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

herki the cat
04-09-2010, 12:58 AM
& [pyonc http://www.audioheritage.org/vbulletin/images/buttons/viewpost.gif (http://www.audioheritage.org/vbulletin/showthread.php?p=285179#post285179)] & =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.


Turntable rumble? :dont-know


& this circuit (http://sound.westhost.com/project99.htm) 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" [I]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 (http://sound.westhost.com/project99.htm) 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

pyonc
04-09-2010, 08:11 AM
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.;)

Robh3606
04-09-2010, 08:26 AM
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

pyonc
04-11-2010, 07:57 PM
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...;)

nee
04-11-2010, 08:14 PM
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.

herki the cat
04-12-2010, 06:46 AM
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

jcrobso
04-12-2010, 09:28 AM
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!

nee
04-13-2010, 08:46 PM
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.

BMWCCA
04-13-2010, 09:29 PM
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.

Do mean no "change in the result"?

Gee, I'm not real smart but maybe it's time to try another amplifier known to produce a clean output before you condemn your 4311Bs??? :banghead:

nee
04-13-2010, 10:02 PM
Do mean no "change in the result"?

Yes, no change in the result.


Gee, I'm not real smart but maybe it's time to try another amplifier known to produce a clean output before you condemn your 4311Bs??? :banghead:

Oh yes - this is not my main amp at all, just one I picked up along the way. My original post was just a general throwing out of curious symptoms in case anyone had a cure. My 4311Bs are fine everywhere else.

herki the cat
04-13-2010, 11:46 PM
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!


I agree with member jcrobso, after reading all the posts related to this amp, it is time take it to the Good Will Store.

herki

nee
04-14-2010, 12:20 AM
I agree with member jcrobso, after reading all the posts related to this amp, it is time take it to the Good Will Store.

herki

But that's where I got it from!:D

herki the cat
04-14-2010, 02:12 AM
The cure is a different amp! :cool:,
It is time to take yours to the Good Will Store!:crying:

But that's where I got it from!:D
Well, at least you are having fun, new member, nee:applaud:Welcome to our museum! & BTW, do you have a cat?:)...& Maybe a motorcycle?;)

herki

jcrobso
04-14-2010, 09:07 AM
After all of this I'm curious what it looks like!;)

SMKSoundPro
04-14-2010, 02:24 PM
I am too! Please post pics of the offending amp, and it's internals if possible. It may be a simple fix, or it just may be trash! Let us help you decide.

Scotty.

herki the cat
04-14-2010, 10:10 PM
I am too! Please post pics of the offending amp, and it's internals if possible. It may be a simple fix, or it just may be trash! Let us help you decide.Scotty.

Me too! and while you are at it, please trace out a schematic so we can have look at the forward gain/phase shift topology in terms of the negative feed back stability margin which probably would benefit from the Zobel Net Work recommended by jcrobso. He has been around the block a few times, Scotty also.

herki

nee
04-15-2010, 12:11 AM
Yep, certainly having fun!

I have a cat, but no motorcycle.

I started tracing out the schematic but then gave up after a confusing half an hour - the amp cost me nothing, I fixed it with 4 diodes, it sounds fine, I won't use it with the 4311Bs and if I do I'll plug the ports. I'll try and get a photo of the guts though.

herki the cat
04-15-2010, 02:45 AM
Yep, certainly having fun!
I have a cat, but no motorcycle.I started tracing out the schematic but then gave up after a confusing half an hour - the amp cost me nothing, I fixed it with 4 diodes, it sounds fine, I won't use it with the 4311Bs and if I do I'll plug the ports. I'll try and get a photo of the guts though.

Great, nevermind the schematic, but please do send the pictures of amplifier inside & outside. We will be looking for them.

Thanks very much, herki

Mike Caldwell
04-15-2010, 04:24 PM
Thanks. Actually I don't turn on the Loudness button when I play CD or LP because of this issue...;)


Irregularities in record vinyl can cause sub low frequency output. A good high pass filter when using LP's is always a good idea. Play the silent sections at the beginning and end of a LP and watch the cone motions. It may not be flapping around but i bet it will be at least quivering/fluttering. with music playing you may not be able to directly see it but it will still be in the background.

JBL 4645
04-15-2010, 11:51 PM
Maybe a video would help us see what is happening.

Flapping :dont-know

I want to see the video without excuses no later than today 6pm UK time.;) So chop, chop get to it and may the flapping be with you.:D

you now have "flipping" 28 minutes till 6:00pm UK time that's 18:00 hours for all those who can't tell time.:D

herki the cat
04-18-2010, 01:51 AM
Irregularities in record vinyl can cause sub low frequency output... A good high pass filter is always a good idea. You can Play the silent sections at the beginning and end of an LP & see the cone quivering & fluttering which is still evident in the music play back.
Mike, the text of my two cents here certainly is old hat, :dont-know but it may nudge some creative person to come up with a few ideas to improve turntable technology simplicity that doesn't need to cost $10,000 to $125,000.

BTW... BMWCCA, where did you find this lovable :dont-know icon.

The "Well Tempered Arm Turntable" system iS a good example of very simple, clever, reliable, well designed system in all respects. To see the "Amadeus GT model," visit this link= http://www.welltemperedlab.net/welltemperedlab/

This problem of floppy records as you know is further aggravated by reinforced woofer feed-back energy coming up through the turntable plinth to the LP record. The usual fix consists of adding 50 to 75 pounds to the turntable platter and extremely complicate bearings plus another identical mass to the turntable plinth supported by a "highly damped spring" isolator system all of which collectively forms a low-pass filter tuned some where well below five Hz. This filtering is obviously necessary. Simplying product design always goes a long way.

Also, damping is required to manage the lateral and vertical resonance occurring some where in the spectrum of 6 to 12 Hz which is formed by the pickup stylus armature compliance and the pickup arm & cartridge mass reflected to the stylus point.

Record Master flatness requirements are addressed in the lacquer master cutting industry by use of a complicated " turntable platter-to-master disc" vacuum clamping system. The first mature Professional Quality Home LP Turntable Clamping System surfaced in the early 1980's in the "Canadian "Oracle Turntable Company" product featuring a slightly concaved platter top surface and a screw-down three-inch diameter record clamp machined out of Teflon to sort of squash the LP Record completely flat & locked down to the platter. This system is extremely effective.

There is an other interesting item regarding the sub-frequency spectrum of LP mastering where the mastering engineer struggles to achieve a minimum 17 minutes of program material on each side of the LP; this has to do with groove spacing and groove modulation amplitude of the cutting which becomes quite gruesome in the last half of the recording space because the groove diameter is reducing very fast towards the center of the record and the cutting wave front is fast becoming very steep.

The mastering engineer salvages stereo LP groove area by recording the spectrum below 100 Hz in monoral format there by sacrificing the vertical components of the bass spectrum in the stereo 45/45 two channel LP stereo recordings. This has always been the practice from day one in stereo LP recording which has misled nearly everyone to believe the myth :bs:saying there is no perceptable "natural stereo imaging" in the low frequency spectrum, which of course is what happens "man-made" in LP stereo recordings below 100 Hz to conserve LP groove area as described here.

This problem does not exist in digital CD recordings and sub bass stereo imaging does come in your CD's. :applaud:

herki

BMWCCA
04-18-2010, 06:46 AM
BTW... BMWCCA, where did you find this lovable :dont-know icon.

Apparently this list's owners knew there would be those (like me!) who would offer opinions based on their own experience without the technical training to back them up. I use it with full knowledge of my own limitations. It also comes in handy when a question is posed without giving enough information, as well. And it seems more gentile than the ubiquitous "WTF".

Now, if your question was literal rather than rhetorical, click on the "More" button in the "Smilies" window during a reply and open up a whole new world of emoticon expression. No substitute for human-to-human interface but it can help with some problems of electronic communication that strip emotion and nuance from the message.

http://www.mye28.com/images/smiles/popcorn.gif

jcrobso
04-19-2010, 08:51 AM
http://www.youtube.com/watch?v=2L0nGWDPt6A&feature=related
This test at the low frequencies 5~10Hz reminds of what my D140F looked like on that one amp. The cone would just move back and fort at a very low frequency. Look at the motion about 20sec into the video.:blink:

eso
04-19-2010, 09:59 AM
http://www.youtube.com/watch?v=2L0nGWDPt6A&feature=related
This test at the low frequencies 5~10Hz reminds of what my D140F looked like on that one amp. The cone would just move back and fort at a very low frequency. Look at the motion about 20sec into the video.:blink:

That's a cool video.

When I first powered up my bass horns I borrowed a disc "Bass Mechanics" from an auto sound guy I knew. It does a slow sweep from 0-100Hz or something like that. Car guys use it to locate rattles. I had to reseal my windows and secure a few things after doing that sweep a few times, but the room is quiet now...

Some serious over excursion on that woofer in the video.

eso

Rolf
04-19-2010, 02:04 PM
I had a similar problem with the 2231A woofer some years ago. When the Alnico magnets was re-charged, the problem was gone.


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.