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...So I creased my speakers...

Discussion in 'Amps and Cabs [BG]' started by Davidoc, Nov 22, 2003.


  1. I just checked out my speakers (700 watts my ass...) and they have that circular mark thing around both of them near the edge. (the shape is really irregular)

    Anyhow, from the description's I've heard, this is definitely a crease.

    The cab sounds alright, but I have nothing to compare it to. Should I be worried?
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Worried...depends on how you feel about having to have your speakers reconed...

    Once they're creased, they're permanently damaged and you'll have to get them reconed eventually.
     
  3. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    You can crease your speakers with less than their rated power if you crank the lows excessively and drive them past their excursion limit. Creasing is usually a result of user error.
     
  4. T. Brookins

    T. Brookins Supporting Member

    What I have done with some old overdriven speakers has worked! I applied about two coats of Tung oil to the cones. The crease is less likely to flex. The tung oil penetrates and hardens the cones- voila! Instant resin impregnation.
     
  5. T. Brookins

    T. Brookins Supporting Member

    Applying tung oil to speaker cones does not seem to alter their acoustic properties. Do it with discretion. I did it on an expendable speaker on its "last leg". Don't apply too much (20 coats) You know why. It makes the speaker stronger, look new, and protects it from moisture. Dont apply it to the surrounds.
     
  6. T. Brookins

    T. Brookins Supporting Member

    That was an exaggeration! ONE to THREE coats is all that is honestly needed. It is just a few grams and does not seem greater than the miniscule difference between two identical drivers. I know this. I do not want to drastically change the piston's weight as to shock the surround and spider thusly off-cencering the voce coil. 20 coats was what was NOT to apply. Sorry.
    I don't thnk the fact that I saved a speaker would even let me worry about reducing cone breakup that gives the driver its highs. I wouldn't think that the sound difference would be noticeable.
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Agreed.

    Have a look at this graph. It shows speaker cone excursion for a cab that's tuned to 75Hz. By the time we hit 60Hz, this speaker is near the red line which indicates the Xmax of the speaker. Look how rapidly the excursion increases below 60Hz.

    Your cab is probably tuned lower than 75Hz. I just used this graph because I had it handy. But the same principle applies.

    What sort of cab is it? And I'm guessing you play more than 4 strings?
     
  8. Thanks for the information guys. I may just look into the tung oil if it becomes a major problem.

    Hmm, I guess overexcursion probably had its way with my cab. I was just always hearing about how clipping is the real evil, and you don't have to worry about speaker damage unless you're clipping.

    The cabinet is an Avatar b210, and while I play a 5 string bass, a don't use the B string often.
     
  9. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Pete,

    What program did that graph come from?

    Knowing that a speaker's impedance increases dramatically below the resonant frequency, thereby reducing the power that an amplifier will provide to it, I'm having a hard time understanding why enclosures tuned above 30 Hz would be a problem for 5 string.

    I guess if the user is cranking up the EQ to force low end response, I can see it. But beyond that it doesn't seem logical to me...

    Can you help set me straight?
     
  10. The Avatar B210 is advertised with a tuning frequency of 63 Hz. The driver unloads very rapidly below the tuning frequency, and is essentially hanging out in the open air. (no loading). This is where drivers become damaged from over excursion.

    The Delta 10 used in the Avatar has a 0.74" mechanical excursion limit before it becomes damaged. Since your problem is creasing, and not a dislocated voice coil, over excursion is not the cause of failure. I suspect your problem came from applying too much crank at a much higher frequency:

    63 Hz.

    The reason is the cone having maximum acoustic loading at the tuning frequency. The cabinet resonance opposes cone movement by applying a strong air load against the cone. Watch the cone at the tuning frequency, and it comes to a virtual stand-still. All the radiation comes from the vent at this time, but the cone is what is exciting the cabinet. The voice coil is driving in the opposite direction from the air load... a crease occurs when sufficient power causes the cone to buckle.

    In a vented box, impedance is at the lowest point (highest power transfer) at the tuning frequency.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Billy, that graph came from a program I found while surfing the net. It's free and it's called Unibox. It's basically a smarter than average Excel spreadsheet that lets you save graphs in .gif format. To be honest I haven't used it much because it's a bit confusing difficult to navigate, but it seems to work.

    The new version of WinISD does excursion graphs. That's probably a better option.

    Bruce, 63Hz is close enough to being the first harmonic of the low B. So is it possible that hitting that low B at high power will crease the speakers, even if't not a regular occurance?
     
  12. IMO, all it takes is too much crank at 63 Hz, no matter how it is generated.
     
  13. hmm, it seems to be working fine anyhow. A new set of fatbeams seemed to fix the lack of definition that I blamed on the crease.

    I guess there's no problem!