Bass 3:1 Guitar, but....

Discussion in 'Amps and Cabs [BG]' started by tresdirnt, Jan 8, 2002.

  1. I've heard it said that for a 50 watt guitar amp you need a 150 watt bass amp. OK. But with this setup, what power do you need for a microphone? I'm guessing more power than the guitar. Thanks.
  2. Depends.. if you want good sound, get high power..

    high power + low volume = high quality

    ( mostly )
  3. It would be more accurate to use the dB sensitivity ratings of the instruments being compared. For example, the 3x rule does not hold close to accurate for a bassist using an Acme instead of an Eden.

    Given: One guitar player with a Fender Hot Rod Deluxe using a single 12" JBL E120 speaker with a sensitivity of SPL 101. This amp is rated at 40 watts, so the guitar player at 40 watts is capable of producing 117 SPL at 1 meter.

    Assume our bassist is using an Acme B-2, SPL=93. The bass amp requires 256 watts to produce 117 SPL at 1 meter.

    Double the guitarists to two players, same amps, and they are putting out 120 SPL combined. The bass rig power requirements jump up to 512 watts to produce 120 SPL. The problem is now, the Acme B-2 won't produce 120 SPL, so the bassist adds another B-2 cabinet, or exchanges his cab for a B-4.

    What this all means is, the bassist now has an SWR Bass 750 and an Acme B-4 to keep up with two guitar players and their little Fender single-12" amps. This situation is exaggerated a bit for purpose of example, as not every Fender amp has a JBL E120 installed, nor does every bassist opt for the worst-case efficiency solution of the Acme cabinets.

    For a high efficiency example, the bassist could opt for an Eden D-410XLT at SPL 106 or D-810XLT at SPL 108 and be able to keep up with a couple of guitar players, watt for watt.

    Bassists lose ground very quickly when up against high power guitar amps with multiple speakers. My personal rule of thumb is 10x more power for the bass. This provides lots of headroom and plenty of reserve on tap.
  4. geshel


    Oct 2, 2001
    Not to mention, 117dB of guitar is bleeding-ears loud (if it's all in the midrange, people will be hurting), while 117dB of bass is just "pretty loud".

    [edit] I don't really mean bleeding ears there. :) Just painfull.
  5. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    100 dB SPL @ 1W1M (-3dB @ 50 Hz and 18KHz) This is an SWR workingman's 4x10.

    Is this efficienct? How much difference is there between say, 96dB SPL and 100 dB SPL? Is it very noticable?
  6. Remember, the 117 dB is at 1 meter and not at audience distance. The one bleeding will be the guitarist who is standing in front of that amp. At 26 feet way, that 117 dB will drop to 99 dB. Our regular Thursday night gig typically runs 100 ~ 105 dB(A) at the audience position, and this is ghastly loud to my ears. I wear earplugs from the time we tune up until tear down time.

    There is a lot of discussion about the audible difference of +3dB, so let's say it is just noticeable. Humans perceive +10dB to be twice as loud.
  7. Matthias


    May 30, 2000
    Vienna, Austria
    While I'm not sure if it is resonable and that simple to calculate and compare SPL-levels on the basis of sensitivity ratings given by the manufacturers, I still ended up with a similiar result as Bruce.

    My approach:

    In our band we had a loud drummer.
    Our guitarist with a 50W tube head and a 112 cab had no problem at all keeping up with the drummer.
    With my old 200W (solid state) head and a 215 cab I had to play close to the limit of my amp - it was easily loud enough but with a lack of low bass and a rather bad sound. Now I have a 400W (ss) amp and a 212 cab (which has more and better defined bottom than the 215) and I feel comfortable :) - with 8 times the power of the guitarist...


    PS regarding sensitivity ratings:
    In a recent thread someone reported that an Ampeg 410 (rated 97dB/1W/1m) sounded as loud (if not louder) as a SWR Goliath (410, rated 105dB/1W/1m) in an A/B-test....
  8. geshel


    Oct 2, 2001
    105? I have a hard time believing that number from SWR. (not believing you, I see it on their webpage, believing them. :) )

    I guess Eden rates theirs at 106, with the 8x10 at 108. SWR doesn't list the sensitivity for the Sr., and oddly the Megoliath is rated at 100.
  9. Matthias


    May 30, 2000
    Vienna, Austria
    back to the original questions:
    If you really need it depends on wether the guitarist uses his full power (a 50W guitar amp can get really loud!)
    More critical is the drummer. I haven't seen one with a volume control yet :D

    I don't really know, but I guess the same wattage as the guitar should be sufficient. A powered mixer with 4 to 8 channels is the cheapest solution here.

    As an example, in Germany the company Nobels sells a complete 'mini-PA' (60W powered mixer w/ 4 channels, 2-way cabs equipped with a 10" speaker, rated 60W each, cab-stands, cables and bag(!)) for only ~430 US$. With regard to different reviews this is sufficient for many rehearsals and small gigs if you use it for vocals only.

    The smallest PA that I ever used was the Spirit Folio Powerpad (4 channels, 2x30W) which was ok for rehearsals with a not too loud band - we have never tried how loud this little thingy can actually get though.

  10. You are correct. My technique of using sensitivity SPL comparisions is simply better than a SWAG.

    The input sensitivity 1s/1m is a "small signal" measurement, and cannot simply be multiplied by the power rating to accurately determine full power SPL. Other factors come into play, such as Xmax and thermal limitations. The large signal calculations can be made if one has all the T/S data for the drivers in question.

    My educated guess technique is still an "apples to apples" comparision if confined to small signal measurements. For the Fender example above, at 1 watt / 1 meter, the bass amp with Acme B-2 would need about 8 watts to produce 101 SPL at the same distance.

    My real world experience gives me a 10:1 power ratio of bass:guitar for the bass to keep up. Watts are cheap... buy as much as you can afford.
  11. ok guys,

    call this strange, but i seem to be the exception to the rule here: at the moment, i use a 300 watt peavey mark iv head with 2 4x10's. my guitarist uses a marshall jcm 900, that's a 100 watt, all tube head. that's not that weird, cos we play in a punk rock band. here's the real weird thing: he(my guitarist, damo) runs his head at about 3/4 of full power, i guess it wouldn't be warmed up before we start really, we don't take the time we should, but anyway... and i only ever run my head at half way. can anyone tell me WHY THE HELL i'm keeping up with him?!?

    i have thought about it and i think maybe it's because, being in a punk band, the bass has lots of mids going through it, but still...

    stranger things have happened i guess.

  12. Matthias


    May 30, 2000
    Vienna, Austria
    different things come into play:

    large speaker surface area (as you have with 8 tens) makes up for quite a few watts.

    the settings of the volume knobs do not tell you how much power you actually utilize.

    if your guitarist uses a lot of bass this will 'eat up' his amp power - meaning that he uses much of his power to produce low frequencies on the expense of volume.

    of cause boosting the mids will help you to get 'more volume per wattage' as you said.

    and finally you've got 3 times of the power of your guitarist anyway which is rather close to the rule of thumb of having 4 to 10 times the power (btw doubling the power equals an increase in volume of 3dB, which is not much more than a just audible difference)

    Now if you said that you can keep up with a 50W practice amp, THAT would be strange ;)

  13. granchulo82

    granchulo82 Guest

    May 13, 2001
    Severn, MD
    this is making me see how much i really need a new amp, i have to compete with two fender roc pros, 100w tubes, both with 4x12 cabs and the guitarists attached to them who compete to be louder, the drummer isn't a problem i can keep up with him easily, but my poor fender bxr 100 hasn't got a shot against the roc pros. if i weren't for my bass driver and bass compactor (thanks tech 21) giving me a volume boost i'd never hear myself

    with that said i'm thinking about getting the landmark 600, also from tech 21 with two 4x10 cabs, one next to each guitar cab, will give me enough juice to keep up? any info or opinions would be appreacitated.