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Is there a notion of a cab getting "tired" and deteriorating during a 5 hr practice?

Discussion in 'Amps and Cabs [BG]' started by Noshtero, Oct 26, 2013.


  1. Noshtero

    Noshtero Supporting Member

    Dec 2, 2007
    Chicago, IL
    Equipment:
    Carvin B1500
    Glasstone lil'g 212
    Vt-bass deluxe

    I was running the vt-bass into the signal return, using the b1500 as a power amp.

    I had it up quite loud, with the b1500 around 8 volume.

    First off, Though it sounded loud on its own, it was just lost in the mix. In comparison, I ran direct to an Acoustic B200, which isn't anywhere near the power of the carvin/glasstone, yet was substantially louder in the mix.

    So my question: after maybe 3 hours, the Glasstone started sounding horrible. Farty, distorted, low output, etc... I gave up on it and finished practice on the Acoustic B200. Then today I hooked up the carvin/glasstone and it sounded ok.

    So is there a notion of a cab getting tired and deteriorating, only to return to normal after a rest? In my experience, cabs either work or don't. If they wear out, they stay worn out.

    This has me worried because my renown glasstone lil'g seems to be good for a couple hours, but gives out after that. This makes it sort of not reliable, and not feasible for a 3 hour gig with no PA support.

    I wouldn't think I'm pushing the lil'g past it's limits when I hear people using a Crown xls1500, which pushes much more than the B1500 at 4ohm.

    If nothing else, I'll run the same practice next week with my carvin brx10.4neo and see if I get a similar result. If I do, then it's either me or the amp, I.e. My expectations are too high or the amp itself is getting tired.
     
  2. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Nope. The cab works or doesn't. If it doesn't then it won't come back to life after a rest has been my experience.

    More likely something in the signal chain suffers from extended heat...

    5 hour rehearsal... Ear fatigue would set in... Is it really necessary that you rehearse at that volume ? Generally, unless you are on a large stage, lots of volume tends to mask problems as opposed to high lighting them.
     
  3. You were overpowering the cab most likely with lots of lows (mids cut through the mix). The speakers were heating up, cut some bass and boost your mids. You were well into power compression and approaching thermal limits (burn-out).
     
  4. +1.

    That cab, if loaded with 12PR300's or 3012HO's is going to have a realistic power handling of about 600 watts. I suspect you were over heating the drivers and they were loosing their strength due to that heating. With neo speakers it comes back after they cool down.

    IMHO cut the sub bass and lows, boost the low mids. You are not going to get a ton of low end out of that cab anyways. Too much driver in not enough air space.
     
  5. Noshtero

    Noshtero Supporting Member

    Dec 2, 2007
    Chicago, IL
    Then why am I reading all over the Glasstone post of people pumping well past 1000 watts into it?

    I guess maybe I'll go back to my Carvin BRx410 Neo. It's rated to 1200 watts
     
  6. It may be a very nice 2x12, but it's still not a whole lot of speaker for 1000 watts.

    Maybe cut a little of the lowest lows. Also, maybe think about getting a second, identical 2x12, and stack them vertically. This will reduce the load on each individual driver, be louder, and get speakers closer to your ear level.
     
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    This.
     
  8. 1n3

    1n3

    Sep 13, 2007
    USA
    +1. Were you boosting bass?
     
  9. You have to take into account the fact that that 1200W is the thermal rating of the drivers or, when they begin to melt. A typical driver will run out of excursion, the most that the cone can move safely, at about half its thermal rating. I second the isea of getting a second identical cabinet to get to the volume that you need. In every case more speakers beats out more power.
     
  10. Noshtero

    Noshtero Supporting Member

    Dec 2, 2007
    Chicago, IL
    I would love to see the stage volume come down. We have a heavy drummer, and basically have to overcome that. I guess in an absolute pinch I could run the lil'g and the brx410neo. Some don't like mixing like that, but others say it's fine.

    I'll propose we turn it down next week.....on threat that I'll bring my 410 and blow the door off the garage.
     
  11. Mike Arnopol

    Mike Arnopol Supporting Member Commercial User

    Jan 4, 2005
    Chicago
    Owner of MAS Soundworks
    or shoot the drummer
     
  12. Hapa

    Hapa

    Apr 21, 2011
    Tustin, CA
    Buy your drummer an acrylic shield.

    +1 Ear fatigue is likely

    The cabinet is a passive load on the amp that happens to have speakers as the load. The speakers may heat up but they work pretty much the same until they die. If it is not the ears going it is heat effecting the amp, pushing lows for a long time being a class AB a lot of energy is going to heat anyways. As it heats up it looses that performance. If it was the cab it would go bad and stay bad.
     
  13. seamonkey

    seamonkey

    Aug 6, 2004
    Blow a hair dryer into the port for a few minutes then play. See if acts up just because the air warmed up.
    If hot air in the cab changes the tuning enough that the cabinet acts up, then it is truly a suspect design.
     
  14. The only thing absolute Hapa is death and taxes.
     
  15. JdoubleH

    JdoubleH Supporting Member

    Jul 10, 2008
    Ellerslie, Georgia
    Assuming it IS the cab and not the amp...

    I've heard the suggestion that neo magnets in speaker motors might have lower magnetic force if they get hot, but I doubt that's the real culprit here. I have a hard time believing you were heating them beyond the tolerances they were designed for, even if there are two drivers in a fairly small box. Basically, every cab has a max SPL it can produce regardless of how much power you have on tap, or what the thermal rating is (it's determined by cone surface area and excursion). I can't say for certain, but i suspect the total output of your cab is going to be less than the same drivers in a direct radiating cab (the port loaded driver isn't going to produce any mids). I suspect you started near that SPL limit. As ear fatigue sets in, you and the guitar player are likely to reach for the volume knobs trying to hear yourselves more clearly in the mix. But when you hit that SPL limit, your cab won't get any louder. Adding eq or amp gain just creates distortion, which will only make it harder to hear notes and articulation, thus making your sound muddier and less precise in the mix. I don't know what the tuning of the glasstone cab is, but I suspect it is tuned fairly deep, maybe into the 40hz range. I suspect the Acoustic cab rolls off much higher. If it has a peak in the response in the 80-200hz range, that could explain why it was able to sound louder in a loud mix with less power- basically it is more efficient in the range it needed to be in that instance. Lower frequencies take more power and more surface and excursion to produce the same SPL as higher frequencies.
     
  16. JdoubleH

    JdoubleH Supporting Member

    Jul 10, 2008
    Ellerslie, Georgia
    :D

    OR just tell him a real drummer can get more than one gig out of a pair of 7A's
     
  17. Noshtero

    Noshtero Supporting Member

    Dec 2, 2007
    Chicago, IL
    Thanks for the replies all. I'll look into getting the volume down
     
  18. It is not magnet heating, the adhesives would fail before that point. The resistance of the wire increases as heating occurs in the voice coil. Speakers are much better at dissipating amp power as waste heat than sound production.
     
  19. If you are not wearing hearing protection, start NOW. You guys are rehearsing much too loud.
     
  20. Some bands I use a big cab and ear plugs with, some bands I don't.
     

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