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Goliath III Wiring and Impedance

Discussion in 'Amps and Cabs [BG]' started by Korey, Jan 16, 2004.


  1. Korey

    Korey

    Oct 29, 2003
    Lexington, KY
    Hi. I just bought a used SWR gloiath III cab along side a Hartke HA 3500. When I got the rig home and started to push it, it seemed to 'fart out' on almost any note below E (the cab is rated to 40Hz and E is about 41Hz is the the problem?). I started looking into the cab the see is i could find any problems and found something a little interesting. The Goliath III was stamped 8 ohms on the backplate. I pulled all four speakers to look for and defects and found none. I threw a meter across the speakers to have a look at the voice coils and all four speakers read 4Ohms individually (is this normal for the goliath III). The horn in the cab is stamped 8 ohms and reads 8 ohms on the meter. When I reinstalled all four speakers and the horn I used the exact wiring that scheme it had before. The problem persists. I did a little more testing and found that the entire cab tests at 4 ohms, not 8 like it says on the backplate. I also checked for an out of phase speaker with a good ole 9 volt battery, and found one. These two findings (the cab reading 4 ohms, and the out of phase speaker) leads me to think that the previous owner has tweaked with the wiring. Does anyone know where i can come by a correct wiring schematic to run this thing at 8 ohms.

    Another question:
    I'm pushing the cab with the hartke 3500 that I bought with it. I know the head will run perfectly fine at 4 ohms, but it seems that all of the literature surrounding the amp suggests that you are best off with 2 8 ohm cabs to get to 4 ohms. Is this true, or can I wire the goliath to run at 4 ohms, and get the most out of the amp (or does it matter at all).

    I really appreciate any help with this. There is nothing more disheartening than dropping all of your savings into a rig that your not happy with. I think the rig gets a great tone if I stay away from the b string, but that is not what I had in mind. I am well within the return/exchange period of the dealer, but I'd like to just sort it out and keep the equipment.

    Thanks!
     
  2. kmacleish

    kmacleish

    Nov 19, 2003
    Atlanta, GA
    There are a few things to consider, here.

    The first thing is that speaker impedance is not a DC measurement, which is what you are getting from the meter. The meter is measuring DC resistance. It is possible that the speakers are, in fact, 8 ohm drivers. But in most cases, the DC measurement is at least close to the actual rated impedance (say, 6.75 ohms DC for an 8 ohm driver). So if you are getting 4 ohms as a DC resistance reading, they may actually be 4 ohm drivers, and if they are wired in the usual series/parallel arrangement, then you have a 4 ohm cabinet. SWR's Web site says that the Goliath III is available both in 4 and 8 ohm versions, so it may have endured a complete driver replacement at some point in its earlier history.

    The other thing: you may be running out of power.

    I'm guessing from your post that you are playing a 5-string, which goes down to about 31 Hz for the low B. If you are boosting the bass control, the 30 Hz slider on the graphic EQ, or (worst of all) both together, you might be piling on more than 30 dB of boost at the lowest frquencies. This could mean that your amp, which is rated at 240 watts into 8 ohms and 350 into 4 ohms, might be facing a demand of ONE THOUSAND TIMES as much power at 30 Hz than it is at higher frequencies. The result could well be the dreaded "farting", which would be tha amp running out of clean power and clipping hard.

    The cabinet is rated as being 3 dB down at 40 Hz, so it is reasonable to assume that it simply won't do a satisfying job on the bottom string, no matter what power is thrown at it.

    Hope this helps.
     
  3. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    If it's stamped 8 ohm on the backplate and you're reading a 4 ohm cab I'd suspect more than a funky speaker. Are you sure that the drivers are original SWR issue? The type of wiring and impedance problems you've encountered would make me suspect the seller.

    IME, A Goliath III can handle a low B, within reasonable eq parameters.

    Also, the amp doesn't care if the 4 ohm load is a result of connecting 1 cab, 2 cabs or 3 or more cabs. The difference is that using more speakers to achieve a certain load results in more volume, therefore you don't have to turn up as much and the amp will run cooler.
     
  4. Korey

    Korey

    Oct 29, 2003
    Lexington, KY
    seems like a few things to keep in mind. I think I am running out of power. I'll jack with the eq and see whats up. does anyone know how i can identify the speakers in my cab? from the front they look like any other swr cab's speakers. there are no identifiable markings on the back. the terminals for the speaker wire are the spring loaded type that you push in and insert the wire into the whole in the side. thanks again TBers.
     
  5. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    look around the edge of the magnet, sometimes serial numbers are stenciled there. Is the speaker cast frame (thick metal) or stamped (thin)?
     
  6. www.pas-toc.com

    PAS .pdf link This shows one of their 10" drivers (MB 1080C), this may not be _exactly_ like the drivers that SWR uses but you can see some of their visual characteristics. You can see the cone, frame, front and back plate, and magnet.

    I’d send an email to SWR and report your findings, asking them how to ensure your drivers are wired as intended. BTW – if you go to the Avatar speakers website, they show a basic four-driver series / parallel wiring schematic that may help to make sense of how multiple drivers give the resulting cabinet impedance.

    Same here. It won’t fill a medium to large club with gut churning bass like a PA with 2000 to 3000 watts and 2 to 4 eighteen inch subs, though.

    SWR has used PAS brand tens for years and years, as far as I know, they still do. My older generation GIII has PAS drivers, and they have a cast frame (black in color) with a ceramic magnet, and silver front/backplates on the magnet (as in the photo on the .pdf above). I don’t recall any identifying marks on them.
     
  7. Korey

    Korey

    Oct 29, 2003
    Lexington, KY
    It looks like it has the mb-1080 c's in it. Will the four ohm speakers with the 8 ohm horn give me any problems?