Under the surface cab damage?

[Flatbass]

I've recently bought a QSC PLX1602 poweramp, 1600 watts. It's run in bridge mode at 4 ohms into a 2x12 (500 watts) and 4x10 (400 watts).
I've been kind of hesitant in turning the amp up too much, because of the differences in the power ratings. I let the -10 dB light only blink at peaks.

Yesterday I let another bass player play my amp, and I told him to not turn it up from where I had the volume set, but he did so anyway. He played very aggressively, made the clip light blink occasionally and I saw the speakers moving more than usual. It wasn't as if the speakers were flapping uncontrollably, but you could see them move with every note played.

The QSC had the clip limiter on and a high pass filter on 50Hz.

Today, I played through the 2x12 at a low/medium volume and it sounds fine. There's no visible damage either.
Does this mean that my cab is fine? Or could there be some 'under the surface' damage that will show up later? Any tests I could do to find out?

Thanks a lot.


By the way, I did search for the answer and read a couple of threads on under- and overpowering, but I could find the answer to my question

[billfitzmaurice]

You cab is probably fine, but don't run the amp bridged, the only thing that accomplishes is to double the likelihood of blowing drivers. Run it dual mono, each channel driving a cab, which also allows the independent volume control of each that's a necessity with mis-matched cabs.
If it had been me and another player was abusing my gear I'd have gone right up on stage and turned it down, and told him that if he touched it again I'd turn it off.

[Flatbass]

Thank you very much, Bill Fitzmaurice.

I've noticed your background in professional audio en proceeded to read as much as I could about bridging, voltage swing, power handling and magic smoke.
It sounds like a miracle that my speakers didn't melt.

From what I've read I understand that I should:

-not run bridge mode into both cabs, but parallel mono instead. Even if this will give me 2x300 watts instead of 1600 watts. (The cabs both have an impedance of 8 ohms.)
The bridge mode will be louder, but eventually destroy my cabs.

-run one channel when using only 1 cab.

-if I need to be louder, I need even more cabs, more efficient cabs and/or cabs that will handle the voltage swing of the QSC in bridge mode. (Or possibly a 200 watt tube head?)


Is this correct?

[craig.p]

The fact that you're mixing cabs makes it likely that you're burning more watts (and using more cone excursion) to achieve a given volume level than if you weren't mixing cabs. That's the first point I wanted to make, and it's an overarching concern.

Second, you can launch either of those cabs to Kingdom Come with 300 watts -- or at least get them close enough to it to make them break into a heavy sweat. Think about it: 600 watts into a pair of twelves and a quad of tens. Those cabs would have to be horrendously inefficient in order for that not to be enough. Also see point one above, because this has to be taken in context.

Whenever I use more than one cab on stage, I parallel the channels on my QSC with the proper DIP switch setting. The only possible situation I can see for anyone using bridge mode is at the contractor-sound level where you've got flying bass bins that are super loud but super inefficient, OR you're running a bass rig with one cab but driving it with an undersized power amp and you need to do everything you possibly can to get reasonable volume out of it; some of those 1U power amps come to mind.

Hope this helps.

[billfitzmaurice]

Originally Posted by Flatbass

-if I need to be louder, I need even more cabs, more efficient cabs and/or cabs that will handle the voltage swing of the QSC in bridge mode.

Bridge mode is what you use when you have a high impedance load, generally 16 ohms, and either channel on its own is incapable of adequate voltage swing to drive the cab to full output. The list of cabs that one channel of your QSC isn't capable of driving to full output is a very short one, and I doubt that either of your cabs is on it.

[Flatbass]

Thanks all of you.

They're both decent cabs, SWR WM 4x10 and a Glockenklang 2x12, but nothing extraordinary.

600 watts into both cabs does not produce enough volume for this one heavy rock band. I do play in two other pop/rock bands and in both of them 300 watts into one cab also isn't enough.

Maybe I should focus on playing jazz... I never liked high volumes, anyway...

[billfitzmaurice]

Originally Posted by Flatbass

Thanks all of you.

They're both decent cabs, SWR WM 4x10 and a Glockenklang 2x12, but nothing extraordinary.

600 watts into both cabs does not produce enough volume for this one heavy rock band. I do play in two other pop/rock bands and in both of them 300 watts into one cab also isn't enough.

Maybe I should focus on playing jazz... I never liked high volumes, anyway...

Mismatched cabs doesn't help here, but even so if you can't get enough volume you guys are too damn loud. Let me guess, guitar'd players with stacks, a drummer who uses Louisville Sluggers for sticks, and no PA.
I play in an R&B band, 160w into one cab, never a volume problem. But the guitar players I work with are real musicians, not juvenile ego junkies, and none use more than a 1x12 combo. And they all know that backline amps are only there to drive the stage, the PA drives the room.

[will33]

Originally Posted by billfitzmaurice

Mismatched cabs doesn't help here, but even so if you can't get enough volume you guys are too damn loud. Let me guess, guitar'd players with stacks, a drummer who uses Louisville Sluggers for sticks, and no PA.
I play in an R&B band, 160w into one cab, never a volume problem. But the guitar players I work with are real musicians, not juvenile ego junkies, and none use more than a 1x12 combo. And they all know that backline amps are only there to drive the stage, the PA drives the room.

+1

My guitar player is fairly young and uses a Marshall halfstack but still, it's never over maybe 1-1/2 on the volume, stage volume is always under control and the PA does the heavy lifting. On small little gigs where the backline does carry the room, I've actually had to tell him to turn up a little if you cwn imagine that. The guy likes to hear his vocal and the rest of the band clearly instead of having guitar blast up his ass all night. The guy also can do some pretty good sounding home recordings and knows what a decent mix sounds like, ie: not all guitar, kick and snare.

Just taking a minute to brag on my guitarist here....he really is a musician, not just a player.

[Flatbass]

Will33, great guitar player! I can imagine that you're very happy to play with him. Most guitar players I play with use 2x12 combo's. Tubes or no tubes, all of these amps seem to be capable of drowning out anything or anyone. Although it's mainly drummers who 'decide' how loud the bands going to be.

Most bars over here don't have a PA system, and if they do it's only suitable for vocals. If there is a full range PA, it's great. Anyone who can't hear me well enough can ask for the bass guitar in his/her monitor.

All musicians I play with are actually pretty good. Good ideas about where a song needs to go, good timing, feel, dynamics, everything... but it all has to be loud for some reason. And I'm talking about conservatory level musicians here, not typical wild teenagers or ego-maniacs. I've been trying to tell people to play softer, but always without result. It's always a matter of turning up, constantly being told to turn up or being drowned out.
It doesn't help that I'm usually in the minority when were discussing band volume. Makes me seem overly sensitive...


And oh... I can't express in words how much I like earplugs

[will33]

None of us are what you'd call "conservatory level", just "regular" musicians who've all been playing since we were kids/teens. The drummer and myself are the old guys of the group at 39, the other two are 27-30. And yes, I consider it a blessing, the guy could easily crank up and ruin the sound but he never does. If you're already having trouble finding a good mix, the worst thing you could ever do is turn up.