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Can i use a cabinet designed for 120 watt heads with a 100 watt head?

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  • Can i use a cabinet designed for 120 watt heads with a 100 watt head?

    I was thinkin of getting a bugera halfstack. a 120 watt head with the matching bugera 4x12. I'd like to find out if u could use the same cabinet for a 100 watt marshall jcm 900 or 800 amp? is there a way of setting the 'ohmage' the amp or cabinet to make a 100 watt head suit the bugera cabinet?

  • #2
    Sure.Go head.
    Originally posted by Unconfigured Static HTML Widget...








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    • #3
      won't it sound muddy? 120 watt amps seem to have more bass than the tighter 100 watt amps.

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      • #4
        Tone and loudness have nothing to do with wattage. Think of wattage like a circuit breaker or fuse. So long as the amperage isn't too high you wont blow a fuse. With a speaker so long as the RMS wattage of a head doesn't exceed the RMS wattage of a speaker you wont blow it into chunks.

        Tone is a matter of the speakers frequency response and cab design. Small cab will have less bottom end compared to a large cab and an open backed can sound different then a closed back. Frequency response is a spec of the speaker.

        The Speakers in Bugera cabs are Bugera Turbosound Speakers TS-12G320A8 made by a company called Turbosound which is a high end PA manufacturer. I did a quick search to find specs but not much came up. Given the fact the cabs are low cost should tell you the speakers are budget speakers. That doesn't mean that sound bad but without the specifications you wont know if they are comparable to the Celestin's a Marshall head is often paired up with.

        They could have the same SPL specs and be just as loud, they could have the same frequency range and similar response curve and the Marshall EQ will work the same as with Celestin's. Unless you have the specs there's no way of knowing besides rolling the dice and trying them, or finding someone who owns one who may have tried it and trusting their opinion.

        Bugera makes nice amps so I don't think they'd use crappy speakers to make their amps sound bad. The question really is can better speakers make their amps sound better. From the looks of them they look to be similar to Eminence speakers but as to the sound I can only guess.

        As far as impedance goes - Amp heads are often adjustable between 4, 8, and 16 ohms. This means the cabs must match one of these three impedances. This is a mathematical issue involving the number of individual speakers and how they are wired.

        You can use an on line calculator for this if you don't know the mathematical formulas for combining speakers.
        Series wiring is simple because you simply add them up for a total. 8+8 =16 4+4 = 8 etc. The total in series must match one of the settings on the amp head.

        Parallel wiring like when you plug two cabs into the same head isn't hard either IF the speakers are the same impedance. You simply reduce the impedance of one in half. 8+8 = 4 16+16 = 8

        Where you run into problems with this short cut is when you don't have matching speakers or cabs. For example a 4+8 = 2.67 ohms which is an oddball impedance too low for most heads. If they were in series you'd have 4+8 = 12 another oddball impedance. A Solid state head may be able to handle it but its a bad thing to run tube heads with mis matched impedances because the power from the tubes isn't being drained away properly and you fry the tubes or starve them.

        You can use this calculator for figuring both series and parallel impedances. http://www.speakerimpedance.co.uk/?a...age=calculator

        One other thing to note. As you can see here where a 4 ohm and 8 ohm are combined - look at the power distribution. In parallel, the 4 ohm speaker receives double the wattage compared to the 8 ohm. Therefore its likely to be much louder then the 8 ohm.



        Look what happens in series. Compare the A & B power used by each. In series its the 8 ohm that sees double the wattage and therefore its likely to be louder then the 4 ohm. (so long as everything else like frequency response and SPL are the same)



        This should tell you that you want to work with matching speaker cab impedances.
        If as you say, you want to use a 4X12 and 2X12 cab together you will have problems if the cabs impedances don't match.

        If the 4X12 has 4X8 ohm speakers, it is likely wired for 8 ohms 8+8 in series = 16 16+16 in parallel = 8 total.

        The 2X12 cab needs to have 2X16 parallel or 2X4 series speakers for a total of 8 ohms

        Then when you plug the two cabs into a head you set the head for a total of 4 ohms. 8+8 in parallel = 4 ohms total

        NOW you have to ask will a 2X12 and a 4X12 sound good together.

        Its safe for the head because the total is 4 ohms and the head set for 4 ohms so you wont blow anything up but lets look at the power distribution.

        In this example A and B and are two different cabs. One contains two speakers and the other four. The 200W power is split between the two cabs each receiving 100 watts in this case. A & B are you 2X12 and 4X12 cabs totaling 8 ohms each.



        The problem is, each speaker in the 2X12 cab will see 50W each,



        In the 4X12 cab each speaker will see 25W each.




        If you stack the 2X12 on top of the 4X12 your ears will be blasted from the 2X12 compared to the 4X12.

        This is exactly why you see full stacks on stage containing two 4X12 cabs.

        Each speaker would see 25W and you wont have any hot spots blowing you away.

        Getting 6 speakers to match in power and impedance to the head requires using oddball speaker impedances. I have a 6X12 Sunn Cab which uses six 12 ohm speakers. Pairs are wired in series 2X12 = 24. Then three pairs are wired in parallel 24+24+24 = 8 ohms

        If I use standard speakers you get oddball totals like 5 or 10 ohms which are fine for some SS heads but not correct for tube heads that have fixed impedances.

        Play with that on line calculator. Try and match impedance and power of each speaker. You'll then know why the industry uses specific matches of speakers vs cabs. Again the issues with loudness between a 2X12 and 4X12 can be balances out to some extent by using different SPL speakers but getting their gain curves to match up at different wattage levels is nearly impossible so I don't advise going that route.

        You'll have no problem running each cab separately however so if that's your intension go for it.





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        • #5
          Originally posted by WRGKMC View Post
          If you stack the 2X12 on top of the 4X12 your ears will be blasted from the 2X12 compared to the 4X12.
          Why would that be? Each cabinet is receiveing 100 Watts.

          The first time I played through a Fender Super Reverb it did not seem like four individual speakers but as a single array
          "Isn't it a pity, isn't it a shame,
          how we break each other's hearts
          and cause each other pain"

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          • #6
            The power rating for a speaker cabinet is the maximum 'safe' allowable power. So your 120 watt speaker cab should be fine with any amp that's 120 watts OR LESS. The power ratings don't have to match. The impedance (OHMS) of the amp and cab DO NEED to match, or you'll risk overheating your speaker transformer.

            By the way, you could still 'blow' or damage a speaker cabinet even when connected to an amp with rated power or less. For example, trying to push too much bass frequencies in a guitar cab can damage the speakers.
            This space left intentionally blank.

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            • #7
              Originally posted by mbengs1 View Post
              won't it sound muddy? 120 watt amps seem to have more bass than the tighter 100 watt amps.
              The amp's wattage will have zero influence on the tonal / frequency response of an amp. Not all 100W amps sound the same. Same with 120W amps.

              You need to worry about two main things when picking a speaker cabinet. The first is that the cabinet's impedance matches the output impedance of the amp. If the amp has an 8 ohm speaker output, then you need a cabinet with an 8 ohm rating.

              Second is power handling capability. The cab's power rating needs to at least match the amp's rated output, or be higher. IOW, you can use a 8 ohm speaker (or cabinet) rated to handle 200W with a amp that has an 8 ohm output with 100W of power, but you shouldn't use a 8 ohm speaker rated at 50W with your 100W amp, and you shouldn't use a 4 ohm speaker (or cab) with your 8 ohm amp.

              The third thing to be concerned about is how the speaker actually sounds - that's the subjective part, and there are a lot of different options available.

              Also note that it's possible to wire multiple speakers in various configurations (series, parallel, series/parallel) and that can affect the total load and power handling capability of the cabinet. For more on that, check out this article on speaker cabinet wiring.
              **********

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              • #8
                Originally posted by mbengs1 View Post
                I was thinkin of getting a bugera halfstack. a 120 watt head with the matching bugera 4x12. I'd like to find out if u could use the same cabinet for a 100 watt marshall jcm 900 or 800 amp? is there a way of setting the 'ohmage' the amp or cabinet to make a 100 watt head suit the bugera cabinet?
                Does it have an ohmage knob or a Speaker adjust valve? That's where I'd start.

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                • #9
                  What about the differences of capacitive and inductive reactance when mixing different speakers?
                  Originally posted by MrKnobs
                  God, that's beautiful man! And they say romance is dead!

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                  • #10
                    Originally posted by Grant Harding View Post

                    Does it have an ohmage knob or a Speaker adjust valve? That's where I'd start.
                    no

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