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for all the speaker guys, my 18 farts

Discussion in 'Amps and Cabs [BG]' started by SRSiegel, Nov 4, 2001.


  1. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    ive got this cab i built for myself. it has an eminence omega pro 18 woofer, the 4 ohm version. its rated at 600 watts rms. just recently ive really been cranking my R600 at band practice, as we just got a PA, and so everythign can be louder. (but the PA isnt good enough to handle bass yet) anyways, im running it biamped. the 250 watts i get to my 210's are enough for the high end, but the 18 just doenst cut it. it farts a lot. i know its not blown. it sounds kinda "loose" could it be that the box i built for it is too big? would any kind of damping material inside the box help this out? or do i really need more power? im looking for a cheaper solution to buying a 1000 watt poweramp... thanks
     
  2. CrawlingEye

    CrawlingEye Member

    Mar 20, 2001
    Easton, Pennsylvania
    You're probably clipping the power amp if it "farts."

    Answer? Stop doing it before you blow your speaker.
     
  3. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks, but im sure im not clipping it, as the volume isnt even that loud, and the clip led's on my R600 arent coming on. if i turn it up more, they will, but not at my current setting. my amp isnt turned all the way up, only to about half, as high as i can get it before it clips. any other possibiltiies?
     
  4. CrawlingEye

    CrawlingEye Member

    Mar 20, 2001
    Easton, Pennsylvania
    Bad chords going from your head to cab?
    Your 18 might be blown?
    Make sure your 18 IS a bass speaker.
     
  5. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    yeah its a bass speaker. its advertised on the eminence website as a bass guitar/sound reinforcement speaker. its got a 109 oz. magnet. i sure as hell hope thats for bass... i havent thought of the cords, ill hafta look at that next time we have practice.

    i also know its not hitting the speaker grill, i did think of that, as it throws out quite a bit. it has the same muffled sound when the grill is removed. ive been told that i just need to put about 4 times the power into it, about 1000 watts, in order to get a better sound. im trying to see if theres a cheaper way. im a poor college student. thanks.
     
  6. MikeyD

    MikeyD

    Sep 9, 2000
    That's a decent woofer. Since you say the amp isn't clipping, it sounds like you are driving the system with too much low bass and the woofer is bottoming out. My guess is the tuning of the box is too high and you are pounding out too much signal below its tuning frequency (e.g., maybe a low B at 31 Hz.). This is an example of doing mechanical damage to a speaker that is rated for much higher power handling than the amp can deliver. You may have already done some mechanical (not thermal) damage to it, but the first thing to do is make sure the box tuning is right for the driver. There are many earlier threads and good resources on this subject in this forum. Do a search for "cabinet building 101" and that kind of thing.

    And if you aren't driving your amp into clipping, even when slapping, a bigger power amp isn't going to help this situation particularly.
    - Mike
     
  7. Dolan

    Dolan

    May 23, 2000
    Vienna Md
    And if it start's smelling......you burnt it up.
     
  8. The Omega Pro 18" is optimum in 3.12 cubic feet tuned to 42 Hz. It can be run in a 1.63 cubic foot sealed enclosure but the bass will roll off from middle E (80 Hz) and down. But... the driver cone will be fully loaded and receive the maximum protection the cabinet can offer. However, the bass response will really suck.

    If you are playing a 4 string bass, the ported tuning above is ideal for you. It will offer the maximum port loading at low E which means you will have almost no cone movement.

    I suspect your homebuilt cab is not tuned correctly. Hook the cab to an amplifier driven by a computer sound card. Put a 100 ohm resistor in series with the cabinet. Use a digital volt meter and measure across the cabinet connectors. Get a free sound generator from my site in my signature below. Sweep the signal down and read the DVOM in A/C mode. The point of lowest voltage is the tuning frequency of your cabinet. It will coincide with the least amount of cone movement. If not, your cab has air leaks.

    If your cab is tuned too high, it will unload the speaker at notes lower than the tuning which is very unhealthy for the speaker and you will trash it. The more it farts, the more damage is done to it.
     
  9. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks a lot bgavin, i can now see why my cab sounds like **** when i turn it up (still sounds good at low volumes tho) the only problem is that both my basses are 5 string. so im guessing the low B probably isnt too good for my speaker in its current situation. do you have any reccomendations for protecting it (settings on my R600's onboard compressor/preamp/limiter) until i can build a properly tuned cab? when i rebuild it, should i stick with the 3.12 cubic foot box tuned to 42 Hz, or should i try to get a lower frequency response out of it for the benefit of the B string? protecting my investment at this point is more important that a completely honest open B string. thanks again for all your help.

    btw it may sound stupid compared to the ideals, but the guy at the speaker shop i bought this from said it would be fine in a 7.5 cubic foot box tuned to 36 Hz. thats where it is now.:mad:
     
  10. This is an oversized extended bass shelf tuning. An EBS alignment is 125% to 175% larger than optimum, but yours is larger than this. This alignment extends low bass response at the expense of reduced power handling and degraded transient response below the tuning frequency. This alignment should never operate below the tuning frequency due to the very high cone unloading.

    Since you are a 5 string player, my suggestion is to accurately tune this box to 31 Hz using a digital VOM. This will provide maximum cone loading and protection at low B, where you need it the most. The cone will hardly move at all at low B (no farting) and all the sound will come from the port. You will have to make the port duct longer to lower the tuning.

    To solve you farting problem experiment with running both the Omega Pro and the 2x10 in full range mode. If I remember right, the RC210 bi-amp crossover point is at 200 Hz, which is G string, 12th fret. This means the 18" is generating the entire fundamental and the 2x10 are loafing and not carrying any of the load except harmonics.
     
  11. SRSiegel

    SRSiegel Guest

    Sep 17, 2001
    Ann Arbor, Michigan
    thanks for your help man! what can i say, this place is great for the "im an idiot, someone help!" kinda stuff. next time i can get the PVC i need i will extend the port further into the cab and tune it correctly. i can alter the port length sometime this week and put it in, and i can paobably tune it with the VOM this weekend. i know i may be killing this thread, but i have a couple more questions...

    a) do you know of a good place to get a crossover unit, so that i can send a full range signal to the 210, and then cut the highs to the 18? ive heard that this would further protect the 18.

    b) you said an EBS is 125-175% larger than ideal. so the new cabinet i build for it should be something between 3.9 and 5.46 cubic feet. where in that range, from personal experience and vast knowledge, do you feel the best saftey/performance ratio would be?

    i have looked through past threads here on talkbass, and they have been particularly helpful. thanks again.
     
  12. MikeyD

    MikeyD

    Sep 9, 2000
    With the amp you're using, I wouldn't worry about overpowering the 18" - so no need to cut the highs. I would do just the opposite: cut the lows to the two 10s, if anything, to protect them from overexcursion. Yes, the lowest bi-amp frequency on the Carvin head is (unfortunately) 200 Hz. Poor choice on Carvin's part. I run my rig full-range into both channels (one feeding my Carvin 2x10 and the other feeding either an Eden 2x15 or Carvin 1x18), except I insert a simple high-pass filter (capacitor) into the preamp/amp loop on my 2x10 channel to attenuate the lows.
    - Mike