Annoying resonant frequency in cabinet, HELP

Sork

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I have a jcm900 1960a 4x12 cabinet that I have some issues with.
There is a ringing frequency around 600-700hz(e4,f4) that feedbacks very easily. When I play certain notes, the cabinet rings like a bell and drowns out whatever notes im playing. Please note that this problem is also present at lower volumes.

Orange rockerverb settings: Gain 6, Vol 4, pretty flat EQ.

I haved tried:
Removing casters
Placing cabinet in different places in the room, away from walls and elevated from the floor.
Moving further away from the amp
Tightening screws in the cabinet aswell as extending the soundpost, even trying without soundpost alltogether.
Tightening handles and removing handles
Replacing a speaker
Trying without cabinet backplate

Also tried:
Different guitars aswell as different pickups(brand new pickups), different pickup heights
Running different tube-amplifiers into the cab: Rockerverb 100 mk2, Jcm800 50watt, Mesa Boogie studio 22

However, when I played through my solid state Laney bass 4x10, the ringing was gone!


Could there be a faulty or micophonic tube?
I have owned these amplifiers for a year or less and havent changed tubes in any of them. It might be time for a tube swap, but again, the problem is with all of my tube-amps. So what are the odds of a faulty tube in every tube-amp that I own?

Is a cabinet supposed to behave this way? Should I just accept this annoying ring?

Thanks for any help or anwser


Sork
 
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jgab

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Speaker cable? I don't see that on your list. They can go bad.

More of a crackle or signal cutout symptom, but you never know.

I would also pull each speaker and reach around the speaker hole to find each of the self catching mounting nuts and make sure those are seated flush with the baffle. Highly unlikely with this issue, but I am just looking for things on your cab you didn't say you checked...
 

Geeze

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Loosen and retighten the screws attaching the speakers. It might be cone cry. I had an issue with a Celestion gold a number of years ago and Dr. Decibel suggested this - fixed it. The frame may have been tweaked and reseating untweaked it.

Russ
 

Sork

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Speaker cable? I don't see that on your list. They can go bad.

More of a crackle or signal cutout symptom, but you never know.

I would also pull each speaker and reach around the speaker hole to find each of the self catching mounting nuts and make sure those are seated flush with the baffle. Highly unlikely with this issue, but I am just looking for things on your cab you didn't say you checked...
Sure, i will try it
 

Sork

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Loosen and retighten the screws attaching the speakers. It might be cone cry. I had an issue with a Celestion gold a number of years ago and Dr. Decibel suggested this - fixed it. The frame may have been tweaked and reseating untweaked it.

Russ
Thanks! I will try that
 

Sork

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Sound clip
 
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jgab

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Thanks! I will try that
Well you said you changed speakers and it didn't help so that's why I didn't suggest speakers. If you haven't checked all four speakers then I would do what Geeze said, but I would also sub out speakers one by one to see if it goes away (in case the re-seating doesn't help).
 

PelliX

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This may be a little 'ghetto', but take the back off the cab and affix something soft to it, covering most of its surface. Old shirt, towel, rubber mat, whatever. Put the panel back on and check. If that mitigated the issue, it's inner resonance in the cab and something similar, but more permanent could present a solution.
 

paul-e-mann

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I have a jcm900 1960a 4x12 cabinet that I have some issues with.
There is a ringing frequency around 600-700hz(e4,f4) that feedbacks very easily. When I play certain notes, the cabinet rings like a bell and drowns out whatever notes im playing. Please note that this problem is also present at lower volumes.

Orange rockerverb settings: Gain 6, Vol 4, pretty flat EQ.

I haved tried:
Removing casters
Placing cabinet in different places in the room, away from walls and elevated from the floor.
Moving further away from the amp
Tightening screws in the cabinet aswell as extending the soundpost, even trying without soundpost alltogether.
Tightening handles and removing handles
Replacing a speaker
Trying without cabinet backplate

Also tried:
Different guitars aswell as different pickups(brand new pickups), different pickup heights
Running different tube-amplifiers into the cab: Rockerverb 100 mk2, Jcm800 50watt, Mesa Boogie studio 22

However, when I played through my solid state Laney bass 4x10, the ringing was gone!


Could there be a faulty or micophonic tube?
I have owned these amplifiers for a year or less and havent changed tubes in any of them. It might be time for a tube swap, but again, the problem is with all of my tube-amps. So what are the odds of a faulty tube in every tube-amp that I own?

Is a cabinet supposed to behave this way? Should I just accept this annoying ring?

Thanks for any help or anwser


Sork
Take the back off the cab and see if it goes away. If it goes away put some insulation inside the back of the cab. Another thing to try is remove one speaker at a time to isolate if one of your speakers is bad. Also check that the cab is wired correctly and not out of phase.
 
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Michael Roe

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Has the speaker cab been in a high humidity/ wet area? Maybe not played for a while?
The voice coil on a speaker could be stuck from corrosion caused by water. This will definitely cause feedback.
I have seen this happen once to a friend. It took us a while to find out that was the problem.
 

Gene Ballzz

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My guess is that it's related to how you set your tone/EQ settings and the sound you are shooting to achieve! That 600hZ to 700hZ range sits right in the center of where many of us attempt to "thicken up" the mids a little bit!
Just Thinkin'
Gene
 

Sork

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My guess is that it's related to how you set your tone/EQ settings and the sound you are shooting to achieve! That 600hZ to 700hZ range sits right in the center of where many of us attempt to "thicken up" the mids a little bit!
Just Thinkin'
Gene
I agree with you, however this is more of an uncontrolled spike.
 

Sork

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Has the speaker cab been in a high humidity/ wet area? Maybe not played for a while?
The voice coil on a speaker could be stuck from corrosion caused by water. This will definitely cause feedback.
I have seen this happen once to a friend. It took us a while to find out that was the problem.
That is interesting, altough I cannot recall that the cab has been sitting in an damp area. Can I tell from just looking at the speaker? I suspect that the voice coil is encased inside the speaker, am I right?

And is there an easy fix for that? Or is the speaker to be replaced entirely?
 

Sork

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Take the back off the cab and see if it goes away. If it goes away put some insulation inside the back of the cab. Another thing to try is remove one speaker at a time to isolate if one of your speakers is bad. Also check that the cab is wired correctly and not out of phase.
Yea, tried with insulation inside the cabinet and also without backplate... still ringing. The wiring is standard marshall 1960 with two jacks, seems correct comparing to other images online.

Now, if I am going to remove one speaker at a time, do I have to change the wiring in that case?
What is the easiest way of doing this without damaging anything?

Or are you simply suggesting to unscrew the speaker without unplugging it?

They are each 16 Ohm, 75 watt

Thanks
 

Sork

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Well you said you changed speakers and it didn't help so that's why I didn't suggest speakers. If you haven't checked all four speakers then I would do what Geeze said, but I would also sub out speakers one by one to see if it goes away (in case the re-seating doesn't help).
Right. I only changed one speaker, maybe i will have to change a few more for it to have an effect...What is the easiest way of sub-ing out speakers one by one?

Thanks
 

paul-e-mann

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Yea, tried with insulation inside the cabinet and also without backplate... still ringing. The wiring is standard marshall 1960 with two jacks, seems correct comparing to other images online.

Now, if I am going to remove one speaker at a time, do I have to change the wiring in that case?
What is the easiest way of doing this without damaging anything?

Or are you simply suggesting to unscrew the speaker without unplugging it?

They are each 16 Ohm, 75 watt

Thanks
Do you have an extra speaker, any speaker of the same ohms and close to the watts? The easiest would be substitute one speaker at a time with the extra speaker, see if you can isolate which speaker is making the noise. Otherwise you'd have to monkey with the wiring which I dont suggest you do.
 

Sork

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Do you have an extra speaker, any speaker of the same ohms and close to the watts? The easiest would be substitute one speaker at a time with the extra speaker, see if you can isolate which speaker is making the noise. Otherwise you'd have to monkey with the wiring which I dont suggest you do.
Yea i do! Thanks! I will try it.
 

Sork

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Update:

Looking at the speaker gasket I realised the speakers has been rather overtightened for a while... I believe this probably had an impact on the ringing. How does cone cry sound? Is it mostly buzzing or could it sound like feedback?

I want to eliminate the possibility of it being a damaged speaker, how do I check if a speaker is blown/damaged? I have heard some people discourage using 9v batteries to test speakers.

IMG_3500.jpg
The speaker gasket is compressed around the screw-holes from overtightening, however the frame seems to be alright.
 

Gene Ballzz

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Is that gasket made of cork, paper/carboard or foam rubber? FWIW, that clip sounds like simply too much gain and is quite heavy in the frequency range you are fighting with. Are there any foot/pedal/stomp/thingies involved?

I would suggest re-installing the speakers, just gently, but firmly snugged, tightening them in small steps in a cross patern. The only other thing I might suggest (to compensate for the unevenly crushed gasket) would be to get some of the peel and stick foam rubber gaskets and apply them to the cabinet baffle. Again, tighten as described above!

Best To Ya,
Gene
 


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