Squishy sound? What am I hearing?

[frankie5string]

Are you using the same speaker cable on both cabinets?

Or does the "good" cabinet have a different cable? I've seen instances where a dodgy speaker cable caused weird things like this. Also, something wrong with the jacks on the speaker cabinet could cause this odd sound, too. I've certainly seen abused/dodgy NL2/NL4 jacks before, especially if moisture somehow got in them. They are self-cleaning to a degree - so twisting them on and off can usually brush off any crud, but sometimes it doesn't.

 

[AlexanderB]

I am not familiar with your setup, but when speakers are driven hard, and the temperature rises, the impedance (or inductance...) will increase. Depending on the amp, the higher impedance might reduce the amplifier output notably.

 

[jimmyjames77]

Probably mentioned already at this point, but sounds like your bass preamp battery is going dead. Good luck.

 

[mikeswals]

Are you using the same speaker cable on both cabinets?

Or does the "good" cabinet have a different cable? I've seen instances where a dodgy speaker cable caused weird things like this. Also, something wrong with the jacks on the speaker cabinet could cause this odd sound, too. I've certainly seen abused/dodgy NL2/NL4 jacks before, especially if moisture somehow got in them.

Yes I used the same speaker cable for both events.

This morning another Mesa owner says he has two PH era cabs that he found bad input jacks on and he replaced them. Never heard of that, but I'm going to tear into this cab this afternoon and try looking at everything.

Probably mentioned already at this point, but sounds like your bass preamp battery is going dead. Good luck.

Thanks. I did check that. I gig with two identical basses and the noise happened with both.

 

[Ric5]

Kinda has me baffled. For equipment background, I have two Mesa PH210's and two PH212 cabs. Been using a Mesa Prodigy since mid summer.

I mainly gig with my two 210 cabs, all's been fine, casino work, amp is on for 4-5 hours usually. The 212 cabs mainly stay at home and rarely only come out only a couple times a year. A week ago decided to bring just one 212 and the mentioned Prodigy. First couple of hours the rig sounded fine. After hour 3 the attack started sounding squishy and by hour 4 it was hitting distortion pretty easy. I didn't hear any of these noises two weeks prior with the Prodigy and both 210 cabs.
So I figured the power tubes being original and over six years old are probably done, but I still didn't touch them yet.
Yesterday hit a thrown together jam with some new players. I brought the Prodigy and only one of my PH210 cabs. We were playing loudy and for 3 hours...and I didn't get any squish or distortion, so that tells me the amp and its tubes are fine.

Ok, so seems the drivers in that PH212 are doing whatever I was hearing. But never heard that before and why did it take 3 hours before doing it? Casino work is not loud at all-they keep low stage volumes, the amp volume is only at 9'o-clock and the bass knob setting is actually cut from center.
I suppose I need to take the grill off and check for any rubbing.

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the squishy sound comes from the gray text

 

[mikeswals]

 

[agedhorse]

Respectfully, IME the temperature of the magnet argument with drivers being powered as they are in the OP's situation is a non-starter with me. Especially the arguments that Neo drivers suffer from this because IF this were true, we wouldn't be using Neo drivers so successfully (AND almost exclusively) in pro audio (subs and tops) at similar (and much higher) power levels. The temperature rise of the magnetic structure is simply nowhere near high enough to be an issue. The curie temperature (the temperature where the material loses its magentic properties) of Neo magnetics used in a speaker is over 600 degrees F, and the magnetic slug is (generally) buried within the pole piece so the pole piece would have to transfer this heat from the voice coil through the air to the pole piece and return plate, and then to the magnetic slug. The same applies to both ceramic and Neo ring magnet motors, where the magnetic material is sandwiched between the back plate that's part of the pole and the top plate that's part of the return circuit.

In order to get the magnetic material to even 200 degrees F, that voice coil would be MUCH hotter than this, but the insulation and adhesives are limited to maybe 300-350 deg F. Ultimately, the voice coil will fail long before the magnet loses strength. This is ignoring the major loss of heat transfer due to air moving within the gap and structure. A couple of thermocouples and scientific testing will make this crystal clear.

Now there is SOME power compression with the rising temperature of the VC, it may not be as dramatic as it appears because there is also power compression due to non-linear losses in the motor under high power, high excursion operation. These losses, IME, end up being about 50%-50% (depending greatly on the electromagnetic and electro-mechanical design)

 

[bcbassman]

When a single cabinet causes problems that disappear when you switch cabs, I suspect you may have an impedance problem with the troubled cabinet. What impedance is the cab and what impedance does your amp ant to see?

I had a problem with and amp when a ran 4 ohm and 8 ohm cabinets together. Bad idea. My amp shut down mid -gig until I disconnected one of the cabinets. I would suspect that maybe one of the speakers in one or both of the 12" cabs was replaced with an incorrect impedance speaker. A wacky Ohm rating can really mess up an amp. This is just a guess.

 

[mikeswals]

What impedance is the cab and what impedance does your amp ant to see?

The PH212 is 8ohm. (Both of my cabs are 8ohm). I also checked today and the impedance hasnt changed even after over two hours of playing: still both read out at 7.1ohm sitting static with my multimeter.

The Prodigy is a tube amp has both 8 and 4 ohm jacks.

 

[mikeswals]

I guess I'm going to have to chalk this up to bad power in the wall outlet at the casino.
Even though I only took one cab that day, I just ripped open both of my 212 cabs, checked all speakers for rubbing, checked impedence, made sure all connections are tight and solid. I pulled the player network control panels off the back and inspected all solder joints, cleaned all the jacks with contact cleaner, and again used my multimeter and checked for any faulty circuts by tugging and wiggling anything.
I can't find anything wrong here! Had the amp on for a few hours now and it sounds great as ever.

 

[frankie5string]

Can the casino provide you with a set of quads off of a few independent breakers? If they can, you might have to change your rider to ask for it.

Usually when I play conventions or casinos, they provide a 3-phase drop for the band with its own breaker panel and quads that come right from the floor transformer and aren't daisy chained off of anything else.

They do it not to protect us, but to isolate the current draw of the band from the rest of the building, which comes from its own power feed. Thinking that high-power draw music amplifiers could damage other things if we were to use a regular 120v socket on the wall.

 

[Wasnex]

I guess I'm going to have to chalk this up to bad power in the wall outlet at the casino.
Even though I only took one cab that day, I just ripped open both of my 212 cabs, checked all speakers for rubbing, checked impedence, made sure all connections are tight and solid. I pulled the player network control panels off the back and inspected all solder joints, cleaned all the jacks with contact cleaner, and again used my multimeter and checked for any faulty circuts by tugging and wiggling anything.
I can't find anything wrong here! Had the amp on for a few hours now and it sounds great as ever.

Bad power (low voltage) would definitely produce the symptom. Also the thermal runaway issue I mentioned could possibly takes hours to manifest. If the problem returns late during long gigs, check to see if the amp is unusually hot.

I would suggest checking the bias on your amp. Set it in the proper range and then let the amp run for a while. Then check the bias again to make sure the tube current is not drifting higher over time.

 

[mikeswals]

Can the casino provide you with a set of quads off of a few independent breakers? If they can, you might have to change your rider to ask for it.

Usually when I play conventions or casinos, they provide a 3-phase drop for the band with its own breaker panel and quads that come right from the floor transformer and aren't daisy chained off of anything else.

I'll find out before next time. We're back there in a month.

 

[mikeswals]

Bad power (low voltage) would definitely produce the symptom. Also the thermal runaway issue I mentioned could possibly takes hours to manifest. If the problem returns late during long gigs, check to see if the amp is unusually hot.

I would suggest checking the bias on your amp. Set it in the proper range and then let the amp run for a while. Then check the bias again to make sure the tube current is not drifting higher over time.

You know, last time we played there was in August, and I took my Strategy, and now I'm remembering it was hotter than what seemed normal! So definitely a power problem.
However, the Prodigy wasnt hotter than any other time. But the Strategy would no doubt be more power hungry.

 

[agedhorse]

Wait a minute, lower line voltage isn't going to make the amp run hotter, so it can't be said that it's definitely a power problem as this would be a false conclusion.

There MAY have been a power problem, it also could have been ear fatigue for example or even just a perception.

Also, a speaker can fail or be defective without rubbing. Something as simple as shorted turns on the vc as the vc heats up can and does happen (though it's not very common.

 

[Wasnex]

Wait a minute, lower line voltage isn't going to make the amp run hotter, so it can't be said that it's definitely a power problem as this would be a false conclusion.

There MAY have been a power problem, it also could have been ear fatigue for example or even just a perception.

Also, a speaker can fail or be defective without rubbing. Something as simple as shorted turns on the vc as the vc heats up can and does happen (though it's not very common.

Low voltage can sap the power of an amp, but I agree it should not cause the amp to run hotter than normal.

The excess heat would come if the tubes are going into thermal runway after being on for an extended period of time. Say the tubes slowly pick up current over time, so by the third set the amp is red plating. If the amp has a single bias supply, one gassy tube can cause this. The bad tube will pull the bias down across the entire grid network.

Ear fatigue combined with volume crepe can definitely give you the impression something is wrong. The Prodigy makes a nice bit of power, but if the band has a super loud stage presence 250W is not going to cut it.

I have definitely used a few speakers that had intermittent problems. I could conceivably see where a driver might develop a partial short after it heats up that cause it to lose sensitivity. I have also had speakers that would sometimes open up and go silent. If half of the drivers in a cab stop working midway through the show, the volume will go down. With a tube amp, you also have to deal with the resultant impedance mismatch decreasing the amp's ability to make power, so the SPL change would be even more noticeable.