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Why did my speakers blow?

marmadaddy

marmadaddy

Supporting Member
Oct 17, 2005
992
1,054
Rochester, NY
#1
I'm having a hard time understanding this.

I run a MarkBass Little Mark III into two MarkBass NYC 604 cabs.
The head is rated at 500W RMS @ 4 ohms / 300W RMS @ 8 ohms.
The cabs are 8 ohms with a published power handling capacity of 600W RMS each.

Going by the published specs, there's no way this head should have overpowered those speakers.

I played a gig two weeks ago and everything sounded fine right through the end of the night. I didn't turn Input gain or Master volume up any higher than I normally do, actually I've run it hotter. Input was a little shy of 9 o'clock, Master was at 11 o'clock. It was warm in the room but not particularly hot. Stage lights were all LED.

I brought one cab to a worship gig the next Saturday and I get the unmistakable sound of fried speakers.
Later testing showed three of the four speakers have frozen voice coils. The other cab is fine. Speaker cables test fine.

There's no recone kit for these so my only option is buying new ones. It's pricey but I haven't had to replace a speaker for my bass rig in years so I'm not that put out, but I really want to know what could have happened.

How could three of the four speakers in one cab have fried under these conditions? Any ideas?
 
#2
None of the drivers in your cabinets are identical. Manufacturing tolerances make that well neigh impossible.. The weakest one went first followed by the next and so on. The smallest cabinet I’ve ever played through was an 8x8. I didn’t expect much but it sounded pretty good. 8x6 i would question. I thought that just crossed my mind is were both cabinets actually connected. If you stack them vertically and the working one is on top then you might have missed that only one was connected. I’ve done this myself with my pair of 2x10s.
 
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#3
Power handling (voice coil heat dissipation - wattage) rarely is the limit on bass speaker life.

It's almost always Xmax - physically exceeding the ability of the speaker to move, in a relatively narrow low frequency zone. Hammer it against the backplate enough and it stops working.

Grab a copy of WinISD and enter your box and drivers.

Or use fdeck's javascript model. Invalid Link Removed

I could easily blow my 200W speaker with my 130 W amp - actually only takes about 35-40W per modeling, right around 70 Hz.
 
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#4
T_Bone_TL said:
Xmax - physically exceeding the ability of the speaker to move, in a relatively narrow low frequency zone. Hammer it against the backplate enough and it stops working.
Click to expand...
Ah... no. A typical driver has an Xmech of 2x the Xmax. Xmax is merely excursion over which it is linear, Xmech is the excursion at which it hits the back plate or otherwise may be damaged. Achieving Xmech typically takes at least 4x the power of achieving Xmax.
 
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#5
marmadaddy said:
...Later testing showed three of the four speakers have frozen voice coils. The other cab is fine. Speaker cables test fine.

....I really want to know what could have happened. How could three of the four speakers in one cab have fried under these conditions? Any ideas?
Click to expand...

Perhaps only one cabinet was actually connected.
 
#6
RoadRanger said:
Ah... no. A typical driver has an Xmech of 2x the Xmax. Xmax is merely excursion over which it is linear, Xmech is the excursion at which it hits the back plate or otherwise may be damaged. Achieving Xmech typically takes at least 4x the power of achieving Xmax.
Click to expand...

Not a good assumption.

Xmech is the point where mechanical damage occurs. This can be contacting the back plate, or it can be due to non-linear damage to the spider/surround/cone edge, wherever the damage might occur.

IF Xmech is 2x Xmax (not a good assumption, but will use it for this example), it does not take 4x the power to reach this because the voice coil with not be operating under controlled, linear motion but will become free moving (other than suspension compliance) outside the magnetic gap. This could occur with only 1.5x the power required to achieve Xmax depending on the suspension compliance.
 
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#7
First, I am sorry to hear about what happened to you rig.
You didn't happen to mix average or RMS power with peak power ratings? I've seen the same speakers with very different ratings depending on how power is measured. There are different ways to state amp power output and speaker power handling. You don't want to do apples & Oranges.

Now for this...
There are a number of people on TB that claim it is OK to run an amp that is capable of generating significantly MORE power than can be handled by the combination of speakers connected to that amp. These people normally drive me crazy, and well that's my problem.

These guys were pretty adamant that it is OK to run more amp than what your speakers can handle. I'm sure they'll pop up here in droves to explain how this all really works and save you some future grief.
(p.s. if your sarcasm filter isn't on, it should be)
 
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#10
agedhorse said:
Not a good assumption. Xmech is the point where mechanical damage occurs. This can be contacting the back plate, or it can be due to non-linear damage to the spider/surround/cone edge, wherever the damage might occur.
Click to expand...
Yup, that's what I said.
IF Xmech is 2x Xmax (not a good assumption, but will use it for this example),
Click to expand...
Typical bass driver:
[Invalid or Expired Link Removed]
Xmax = 4.7mm, Xlim (AKA Xmech or Xdam) = 9.5mm
It does not take 4x the power to reach this because the voice coil with not be operating under controlled, linear motion but will become free moving (other than suspension compliance) outside the magnetic gap. This could occur with only 1.5x the power required to achieve Xmax depending on the suspension compliance.
Click to expand...
Dunno if bass drivers typically have shorting rings to control that past xmax like many pro audio subwoofer drivers do? In any case I'd love to see that data, I've never come across it in the literature. I'd expect the lower motor force past Xmax to more or less compensate for the increased excursion potential due to loss of control but haven't measured it like you probably have :) .

And in any case sure would be interesting to autopsy one of these and see if the former is mashed, suspension FUBAR, or VC cooked?
 
#12
Downunderwonder said:
I am liking this but not sure if you can blow 3/4 of one cab without noticing at the time. I have never been accused of blowing anyone's speaker.
Click to expand...

My guess is the remaining "unblown" driver no longer has all nine of its lives left. ;)
 
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#13
RoadRanger said:
Yup, that's what I said.Typical bass driver:
[Invalid or Expired Link Removed]
Xmax = 4.7mm, Xlim (AKA Xmech or Xdam) = 9.5mmDunno if bass drivers typically have shorting rings to control that past xmax like many pro audio subwoofer drivers do? In any case I'd love to see that data, I've never come across it in the literature. I'd expect the lower motor force past Xmax to more or less compensate for the increased excursion potential due to loss of control but haven't measured it like you probably have :) .

And in any case sure would be interesting to autopsy one of these and see if the former is mashed, suspension FUBAR, or VC cooked?
Click to expand...

While you showed one driver commonly used for bass, typical doesn't really apply here because the variables are really all over the place depending on the driver's design.

Most bass drivers do not use a shorting ring, and a shorting ring does little to control the cone outside of Xmax, but does lineraize the inductance which improves linearity (reduce distortions) at higher frequencies (which is why it is used).
 
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#14
Hmm... Looks like the MarkBass Little Mark III is "old school" HPFless tech - blech. If you had the amp's bass EQ up past noon it's possible that it did overexcursion the cab - especially if only one was actually plugged in. Personally I'd not run an amp rated at more that 1/4 the rating of a ported cab without a HPF, especially if using an OD either separate or built into the amp. OTOH 300w of amp with a decent HPF into a well designed 600w cab shouldn't be a problem...
 
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#16
Old Garage-Bander said:
First, I am sorry to hear about what happened to you rig.
You didn't happen to mix average or RMS power with peak power ratings? I've seen the same speakers with very different ratings depending on how power is measured. There are different ways to state amp power output and speaker power handling. You don't want to do apples & Oranges.

Now for this...
There are a number of people on TB that claim it is OK to run an amp that is capable of generating significantly MORE power than can be handled by the combination of speakers connected to that amp. These people normally drive me crazy, and well that's my problem.

These guys were pretty adamant that it is OK to run more amp than what your speakers can handle. I'm sure they'll pop up here in droves to explain how this all really works and save you some future grief.
(p.s. if your sarcasm filter isn't on, it should be)
Click to expand...
I routinely run an amp rated at more power than the rating of the cab. I have never blown or even creased a speaker. The way it works is you don't crank the amp past what the cabs can handle. Once the cabs start complaining, you have to turn it down.

Now getting down to the OP's predicament, I would bet the EQ was set bass heavy. Those little 6-inch speakers can't begin to handle the amp's full output if it has a lot of bass content. Correct me if I'm wrong about the EQ.
 
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#19
If you didn't notice your bottom cab was NOT connected you are doing something essential wrong, may be soundwise, may be somewhat else was the reason, as it isn't a mixing rig it could be somewhat else ...

My initial thinking what may cause broken speakers:
too much of bass EQ
very low tuning like F#
OD and/or compressor
very "percussive" damping technique of "personal" playing style
"noisy" music genre like punk

a cab loaded with smallish drivers but rather highish cab tuning,
the missing of an effective HPF or a HPF that isn't properly aligned to cab tuning.

Too much of amp power, but that's relative due to the listet "individual" possible boundary conditions.

The more of these factors do apply alltogether then the more is potential to smash drivers.
 
#20
Being a veteran speaker wrecker, I can't comment on the technical side of "how" BUT, I can offer:

Parts Express

You'll want the exact model number and specs from the cabinet & speakers originally installed to replace correctly.

I DO use the direct box and have the PA help move the bass around (you may too). In many situations, unless you want to bring extra cabinets, you'll need PA support because the guitars & keys & vocals (oh yeah, the drums) all travel a lot easier through the atmosphere than bass does...and your bass tone needs a certain amount of fidelity to give it ooomph, tone and presence.

I have a spare set of 2 x 10's ready to go having replaced drivers a few times now inspite of my best efforts to 'control' the situation.

P.S. IF you're bass is active, be v e r y mindful of you overall volume.
 
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