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Simple 4x12 Cab Mod?

Discussion in 'Recording' started by BarilkoLives, Mar 24, 2003.

  1. BarilkoLives

    BarilkoLives Guest

    Hey everyone! :) Just thought I'd ask for a few informal pro opinions on a guitar cabinet mod I've been thinking about. Here's what I've got: Fender Stage 100 head and Crate GX412S Cabinet. The Fender sends either 100 Watts @ 8 Ohms (mono) or 160 Watts @ 4 Ohms (dual/stereo). :eek: The cab speakers are 16 Ohms each and wired in series/parallel to give the following switchable input options: 16 Ohms Mono (S/P) ; 4 Ohms Mono (P) ; 8 Ohms L-R Stereo (P). The power rating for the cab is 100 Watts RMS (50 Watts/side).

    My goal is to have an on/off switch for each speaker in the cabinet, or at a minimum to have a switch that could cut the bottom two drivers in the cab, transforming the 4x12 into a more proper 2x12. Now for the questions:

    Is it generally safe to send "Lo" Ohm power into Hi" Ohm drivers? What are the ramifications of this for the gear? Also, could you talk about the reverse (Hi Ohms to Lo Ohms) and exactly how dangerous that could be?

    The switchable speaker/Ohmage configs are courtesy of a small electronic circuit board. Could I simply alter the wiring at that point or do I need to maintain the current S/P config for this whole thing to work?

    Are there any other pertinent questions that I should be asking?

    If I follow up with a basic schematic of the cab's wiring, could I get some input on where the switches could and should go?

    :w: Thank you kindly in advance for your time and effort. :p:
  2. AudioBond

    AudioBond Guest


    If you want to turn it into a 2x12 cab, you could simply flip the cabinet switch to "stero" which you said is 8 ohms per side (16ohm spkrs in parallel) and plug the amp 100W 8 ohm "mono" output into only one side of the cab which would use only 2 speakers, thus eliminating the need for aditional switches.

    As far as your question about impedance matching... The amp's impedance rating (ohms) refers to how low of an ohm load the amp can handle. Hooking up a higher impedance speaker to that output (for instance a 16 ohm speaker to an 8 ohm capable amp) won't really hurt anything, but is far from ideal as you won't get the full potential of the amp. However, doing the reverse (hooking up a 4 ohm speaker to an 8 ohm capable amp) is trouble. It may seem ok at first, but the amp will heat up and burn out. Not good.

    I personally see no need to modify the wiring in the cab as the solution I mentioned above works fine (I do it on my cab sometimes) and if you were to just put a switch on the wire going to each speaker, you would start creating different ohm loads. For instance if you were running the cab in mono 4 ohm mode, and turned off one speaker, the impedance would rise to 5.333 ohms. Turn another off and now your up to 8 ohms. Again, going back to matching the impedance of the speaker/cabinet to the amp output is key to getting the most out of your amp.

    Hope this helps!


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