Many questions, more answers

Discussion in 'Amps and Cabs [BG]' started by Hetzer, Mar 30, 2020.

  1. Hetzer


    Sep 5, 2010
    Hi good people of the lower register!

    I have been reading this forum occasionally through the years and I am almost always finding the answers. In the recent weeks some new depths and questions occurred to me and I would dare to directly ask it here.

    Recently I have swapped my Peavey Firebass 700 head for a Genz Benz GBE 750. My old cabs (Marschalls MCB110 and MCB115) still remain but that would have to change soon because I do believe that I could draw a finer sound from my amp with some finer cabs.

    The question 1 is: should I remain at 2 ohms load or should I go to 4 instead?
    According to the amp specs, it gives 750W @ 2 ohms and 625W @ 4 ohms. The difference in the wattage is not really significant but I am not sure how much does it transfer to the sound in a way of the quality. I do believe that the loudness is here more a subject of the speaker configuration than of 125W difference.
    Is a long service with 2 Ohms actually damaging to this amp is what concerns me as well. A am a hobby player and i do not change my equipment often.

    The questions 2 is the optimal configuration of speaker cabs, regardless of impedance. The 410/115 setup was long thought default normal to me, 10's delivering the mids, 15 delivering the lows, tweeter giving the highs... Then I've learned that that is not the loudest setup and scientifically far from the optimal solution. Ii know that it is very much depending on the model and the manufacturer of the cabs but I wonder what would it bring to swap the 115 with some 212 or even 215 and to leave that 410. There are off course the other options of single cabs like 610 or 810 which I never tried.

    The question 3 is the much asked question of the wattage relation between the load cabs can take and the power that the amp pushes through them.
    The most common that I cared of is that the power that goes in the cab should not exceed it's constant load limit because of the danger of blowing the speakers. The new thing that I read is that it is not recommended to push less (or a lot less) power in the cab than it can take because one should then crank up the volume and by doing that the amp takes a lot of strain and distorts and in return the speaker/s get square waves which we do not want as well. Those who warn strongly about that suggest using amps that can push more watts through the cabs that they can take, because we never crank them up all the way. That way they maximize the use and loudness of the cabs and in turn they do not push their amps to hard. To me it looks like that seems fitting only for those who really, really know their equipment good, which is now not the case with me.

    4 would be only a simple recommendations of cabs. Stuff like Messa or Aguillar are just to expensive for my league. Warwicks, Peavey, some used Ampegs, SWR, maybe EBS, Hartke... Ashdown, GK?

    I play mostly in a rehearsal room with a somewhat louder band. When we gig, we often take only amp heads with us. We play mostly death metal, not too technical. My play-style is pick (often a lot of fast, interrupted picking), low action, some frat-buzz and stainless steel stings tuned to flat D (A on 5er)
    My basses are ESP LTD B 2005 with hot EMG's and a Warwick Vampyre SN 5 string with fat MEC's compressed with EBS comp. and dirtied with Boss ODB-3 (that one I intend to swap with some Darkglass drive). The sound that I chase is something like a rolling of metal tracks, rumbling and heavy with distinct metal rattling.

    Thank you very much for your time!
  2. Jim Carr

    Jim Carr Dr. Jim

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    Assuming your Marshall cabinets are each 8 ohms, keep the switch set at 8/4 ohms. If either or both are 4 ohms, set it to 2 ohms.

    No, tone is not affected by the output impedance setting on the back. The operation of the amp at 2 ohms should have no real impact on the amp, as it was designed for such use.

    In general, two identical cabinets, stacked vertically, will outperform mixed cabs, but each case is different. If you really want a full range cabinet, you need to investigate fEARful, Barefaced, Fearless, AudioKinesis, etc. Such "full range/flat" cabs typically have two or three types of drivers with crossovers.

    410, 412, and 415 cabinets all suffer from poor midrange dispersion "off-axis." Simply put, unless you are pretty much directly in front of them, they sound pretty muddy. A vertical array of cabs (two 210s or two 212s stacked vertically) is much better for midrange dispersion than conventional 410 or 412 designs, and thus can provide a more accurate representation of your tone.

    The "dangerous square wave" from amp clipping idea is essentially false. This is the "under-powering myth." It is untrue.

    You can play square waves (from any source) all day through a bass cabinet, and as long as you don't exceed the exceed the mechanical and thermal limits of the speakers, you are fine.

    However, when solid state amplifiers clip, some can produce much more total power than they do before clipping. It is too much power that kills the speakers, not the spectrum of the output. Clean signals or distorted signals that have too much amplitude will both kill speakers. Furthermore, boosting lows or using effects that create sub octaves will also increase stress on speakers.

    About power: Having spare power (which I do) is nice to allow you to avoid any increased distortion due to power amp clipping, but it is also dangerous.

    By having a lot of extra power, accidents can happen. Be really careful if you have an amp that is much more powerful than the rating of your speakers. Furthermore, many speaker cabinet manufacturers' power ratings are not reliable, so use your ears to listen for any distortion, and turn down immediately when you hear it.

    Even that may not save your speakers, especially if you use effects that create a very dirty signal or an "octave below" effect. Sometimes cabs sound great right until they die.

    A high-pass filter, either as a pedal or built into your amp is a good thing for protecting your speakers and making good use of your amp's power.

    Tuning down to a lower pitch also makes speakers much more vulnerable to damage from over-excursion at low frequencies.

    Look for a good pair of identical used cabinets that fit your budget and transportation. Avoid mixing a 410 with a 115. A pair of 410's can be pretty good, despite the limitations of the 410 design. Good luck!
    Last edited: Mar 30, 2020
  3. Bassdirty


    Jul 23, 2010
    Looks like Jim covered the essentials....

    Ill just restate:

    Good Move!! Love me some Genz products. Was it an even swap? Genz hold their value quite well, .. peavey otoh.. (and Im a solid fan of ole used Peavey amps).

    Absolutely. Ditch the Marshalls asap. In fact, you coulda just got better cabs and you'd be surprised how much better the Peavey woulda sounded. I NEVER like Marshalls for bass..period. Great for classic rock sounds on guitar, but not for bass. :( Get some good cabs, and therewss plenty of suggestions if ya do a search on cabs.

    But go with similar cabs, 2x 212a, or 2 410s, or 2x15s.. (if ya need multiple cabs that is.) ;)

    Oldest myth in the book, bass or anywhere. Lots of people believed it.

    4 10's will get way louder, and way lower than 1 15" speaker. (in most normal situations)

    Sounds like your getting things sorted and on the right path now. ;)

    Good luck, and congratulations.
    Hetzer and Jim Carr like this.
  4. Hetzer


    Sep 5, 2010
    I forgot to mention it. They are 4 ohms each, so it is 2 ohms overall load. The switch is, off course on 2 ohms set. The cooler gets pretty warm though. I guess it's normal.

    Those are difficult to find here in Germany. Ampegs, Warwicks, Peaveys, FMCs, Markbass, ... are all over the place. Not that I have anything against that.

    One 810 should be like two 410 topped on each other, right? Would it be wise to get like two diffrent 410 cabs? I don't not see that very often.

    That about SS amps I did not know. I do play with overdrive so I have to be carefull. With allready distorted sound one could easily miss the Distorsion of the amp or the speaker. Luckily we have the LED's. :) I think I will go with the cabs that could take a bit more then risk it. How much more is the question. There is no rule of thumb here? If my amp delivers 375 or 312 watts in a single cab, is it a big diffrenece to have a 500 or 800W cab?

    I thought I should get a device like that but then I read that my amp allredy has something like that built in. According to the specs it clipps everything lower than 23 Hz. Should that be enough or shall I nevertheless
    get something more?

    I am now thinking either 2x410 or 410 +212 or one 810.
  5. Hetzer


    Sep 5, 2010
    Sorry for the poor choise of words, I'm not native in English.
    I swapped like in my ussage. I bought the Genz and I still have the Peavey. :)

    The Peavey cabs are quite affordabe and could be found here used as well, mostly with Sheffield Speakers I believe.

    Slowly I'm getting the hang of it.
  6. Jim Carr

    Jim Carr Dr. Jim

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    Two identical 410's would be more flexible than a single 810, but probably more expensive.
    Have you considered building a cabinet?

    LED's on an amp that show "clipping" usually only warn about preamp clipping. That is of little use in avoiding damaging your speakers. The only real protection is to listen for distortion in clean signals that are sent from a well-controlled amplifier.

    Better cabs are always better, lol. Have as much power handling as you can afford in your cabinets.

    23 Hz is pretty low, and it doesn't clip it off like a pair of scissors, it sort of rounds it off like a sander, lol. An adjustable HPF should cover 30-120 Hz or so. I like Fdeck v.3.

    I'd avoid a 410+212 rig. A matching pair or a single big cabinet is usually better, IMHO.
  7. Wasnex


    Dec 25, 2011
    The dB difference between 625W and 750W is only 0.8dB; which is not really significant. It will be even less significant when the power is split evenly between two speakers. There may also be some slight differences in the amp's damping factor at 4 and 2 ohms. Damping factor relates to how well the amp controls the motion of the speakers. Although the amp is designed to run at 2 ohms, and I do believe running at lower impedance is a bit harder on the amp. The current will be higher so there will be more heat generated. I doubt this is significant unless you really run the amp hard.

    It's really impossble to answer the question without considering the specific speakers you plan to run. I would recommend finding a speaker you like and then getting two of them.

    An important spec to keep in mind is the sensitivity rating, which is the SPL the speaker will make with one watt applied. With each doubling off power, it is assumed the speaker will make three more dB. If you have two identical speakers the power will be split evenly between them. To determine how loud your rig will play, figure out how much power the amp can make with the total load, divide the power by two, and then calculate the SPL one speaker makes off the result. Now add +6dB for acoustic summing between the two speakers, and you have approximately how loud your rig will play.

    For example if you have two 4 ohm speakers with a 95dB 1w/1m sensitivity rating, the total load is 2 ohms and the amp will make a maximum of 750W. This will be split evenly between the two speakers so each will see 375W. Here is the doubling of power sequence: 1,2,4,8,16,32,64,128,256,512. As you can see the power can can be doubled 8 times to 256W, and there is a little more left over. Multiply 8 by the 3dB change for each complete doubling of power 8x3=24dB. If you use a watt to dBm convert you can actually see the dB difference for 1 to 375W is actually 25.74dB. Add this number to the sensitivity rating 95+25.74= 120.74dB. This is how loud the speaker will play with 375W (I.E max SPL). Since you have two speakers that are getting the same power, so you will get near perfect acoustic coupling in the frequency range where the drivers are within about 1/4 wavelength. This will result in approximately +6dB in the low end. 120.74+6=126.74. This is the estimated max SPL of both speakers run off the amp.

    You can use the power rating of the amp and the specs of whatever speakers you are interested in to get a better idea whether it is better to run the amp at 2 or 4 ohms.

    If you want to use the watt to dBm converter it's here: Watts to dBm conversion calculator

    1W comes out to 30dBm
    375W comes out to 55.74dBm
    312.5W comes out to 54.95

    To get the decibel difference just subtract one power level from the other and drop the "m" from the units. For example 55.74-30=25.74dB, which is the number I mentioned above.
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    A few important things to consider:

    1. Your current speakers are a poor choice because each speaker is horrible overpowered unless you are super careful. Over 300 watts into any 110 is too much IMO, your speaker is at the lower end of 110 cabinets.

    2. Your GBE-750 already has an effective high pass filter built in.

    3. 410's don't in general suffer from midrange dispersion issues to anywhere near the extent in practice that the rule of thumb might suggest.

    4. In general match the RMS or continuous power of the speakers to the RMS power of the amp.

    5. Get 8 ohm 112's, 115's, 210 cabinet, and a 4 ohm 212, 215 or 410. These will better power match to your amp.
  9. Hetzer


    Sep 5, 2010
    Since I moved to Germany, I do not have conditions to do that. There is however a company called FMC which makes custom cabs, but for that money one could get a new SVT Ampeg cab or equivalent.

    Is 120 Hz to high? Wouldn't we be needing those frequencies?
  10. Hetzer


    Sep 5, 2010
    I hoped for something like this as well. I know the numbers are not everything but t kind of helps me sort things out.
    Wasnex likes this.
  11. Jim Carr

    Jim Carr Dr. Jim

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    I understand. Looking for used gear is probably your best route.

    Yes. But don't forget, the frequencies are not removed with a knife, they are rolled-off on a slope. Some such slopes are steep, some are gradual. It is surprising how little fundamental you need for the lowest notes.
    Last edited: Apr 3, 2020
  12. Hetzer


    Sep 5, 2010
    It looks like I made a typo and I can't edit it know. It is 410 MCB cab, sorry. 110 would be totally wrong.

    Is that like not too hard to the amp, to power two cabs of different impedance values? I should then get like 2,6 ohms of total load and the cab with lower impedance gets 2/3 of the power, the other one gets 1/3, right?
  13. Hetzer


    Sep 5, 2010
    That is the most probable solution. The good thing is that I am not in a hurry.

    I know, it gets a sort of curve, a bend.
    Well I have a Boss GEB-7 EQ pedal, a bass pot an my basses and an EQ an the amp. Maybe I should experiment with those. I already noticed that I like the lows from the tube channel that the ones from SS channel.
    Jim Carr likes this.
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    If the amp is rated to drive a 2.67 or 2 ohm load, there's no problem for the amp to drive this load.

    Correct on the power distribution, which is exactly why I recommended the impedance versus driver configurations that I did.
  15. Hetzer


    Sep 5, 2010
    I guess I should then set the switch on back of the amp on 2 Ohms?

    What does this distribution bring to the tone? I mean the cabs that are already louder get in this case more power and the quieter get less.
    With 4 ohms 410 / 8 ohms 210 I see the sense of it.
    With 4 ohms 410 / 8 ohms 115 I don't get it, except to spare the 15' speaker a bit.
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Yes, you must use the 2 ohm position on your amp, otherwise it's possible to damage the amp.

    This is covered in the owner's manual for the amp. If you do not have it, PM me and I will forward a copy.
  17. Jim Carr

    Jim Carr Dr. Jim

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    At 2 ohms or 2.67 ohms, an amp will not change its tone, as I stated earlier.

    However, if you present a 2.67 ohm load and the amplifier is set for 8 or 4 ohms, catastrophe awaits.

    Your amp will soon over-heat, and if you are lucky it will go into thermal shutdown. If you are not so lucky, the amp will go into the repair shop, or perhaps a trash can.

    Running any amp with an impedance load less than that for which it is configured and designed, can destroy it. Your choice.
  18. Hetzer


    Sep 5, 2010
    Thanks. I have it already somewhere as.pdf but I probably did not read it completely. :angel:
    agedhorse likes this.
  19. Hetzer


    Sep 5, 2010
    OK so at 2,67 I turn on the 2 ohms switch. I do not want to risk anything.

    I believe I will just use the flexibility of the amp and not limit my self to just 4 or 2 ohms load. In this way I have more choice.
    agedhorse likes this.
  20. Hetzer


    Sep 5, 2010
    I report that I have made my call and got these two used FMC cabs, 410 CL, 600W and 2128 CL 500W, each 4 Ohms and they are great. I turn up the volume to 1/3 and the sound is already as big as a house and it doesn't peak on A tuned H string. Plenty of low end, plenty of power in reserve. I am pretty satisfied now. :hyper:

    Attached Files:

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