The LMII's Low-Mid is centered at 360Hz

Discussion in 'Amps [BG]' started by Youngspanion, Feb 2, 2013.


  1. Youngspanion

    Youngspanion

    Joined:
    Jun 16, 2003
    Messages:
    2,072
    Location:
    Staten Island, NY
    I've read this in a post and I'm not sure what it means.

    If a "Tone Knob" is set for a certain frequency, like the Low-Mid knob on the LMII, does the knob actually increase or decrease the volume of that particular frequency?
     
  2. joelb79

    joelb79 Supporting Member

    Joined:
    Mar 22, 2006
    Messages:
    4,328
    Location:
    Lansing, Michigan
    IN the case of the LMII, then yes. However some EQ's mention a center point but the EQ seems to effect more than just the center point adding to the confusion. Depends on the EQ. But in the case of the LMII, the numbers are accurate. The frequency most boosted or cut is 360hz with that knob. This is above the "low mids" that people typically put as being around 200-250hz. Most of us who used the LMII have found that the best sound comes from having the knobs south of noon/flat.

    I personally liked to roll off the lows and use the VLE a little bit to accentuate the lower mids. YMMV.
     
  3. christw

    christw Get low!

    Joined:
    May 11, 2008
    Messages:
    6,055
    Location:
    Dayton OH
    Disclosures:
    Endorsing: J Worrell Bass
    It boosts or cuts around a certain frequency by a predetermined amount. In the case of your low mid knob it's centered at 360 Hz which means it might boost between 120 and 800 Hz or so with the maximum boost being around 360 Hz. I'm just guessing on the high/low frequency cutoffs though. I like my low mids to be centered at 120-160 Hz personally. I shoot for an old school "punch" as much as I can and that delivers it with my particular styles and bands. :smug:
     
  4. Codger

    Codger Supporting Member

    Joined:
    Apr 13, 2008
    Messages:
    975
    Stock LM2 low mid control is centered around 350 Hz. Someone comfortable with surface mount could change a couple of resistors, move it down to 150 Hz or so.
     

    Attached Files:

  5. Register to disable this ad
  6. MuthaFunk

    MuthaFunk

    Joined:
    May 8, 2007
    Messages:
    2,012
    Location:
    GTA Ontario Canada
    It'd be nice to get a schematic to find out where the 350Hz network is! Anyone know where to get a schematic for the LMII.
     
  7. dincz

    dincz

    Joined:
    Sep 25, 2010
    Messages:
    991
    Location:
    Czech Republic
  8. Youngspanion

    Youngspanion

    Joined:
    Jun 16, 2003
    Messages:
    2,072
    Location:
    Staten Island, NY
    Codger. I cant understand the graph. I don't understand the graphs on the last page of the LMII manual either.
    Can anyone explain it?
     
  9. dincz

    dincz

    Joined:
    Sep 25, 2010
    Messages:
    991
    Location:
    Czech Republic
    The green line is maximum boost. Orange is maximum cut. The two graphs show the effect of two different center frequencies.
     
  10. Youngspanion

    Youngspanion

    Joined:
    Jun 16, 2003
    Messages:
    2,072
    Location:
    Staten Island, NY
    And we are dealing with just the volume of the specific frequency range that the control? I see on the right side of each graph a dB sign with a number with nothing or a number with a negative sign ( -). with 0 being the 'Center'. Is this right?
     
  11. Jack

    Jack

    Joined:
    Sep 6, 2003
    Messages:
    1,752
    Location:
    Newcastle, UK
    Yup, there's no point showing actual gain because that depends on the level of the gain controls, eq just boosts or cuts and you can see on the x axis what frequencies are being boosted or cut at what amount on the y axis.
     
    Codger likes this.
  12. steve_rolfeca

    steve_rolfeca Gold Supporting Member

    Joined:
    Nov 21, 2006
    Messages:
    4,430
    Location:
    London, Ontario, Canada
    It's not just the center frequency that affects the sound of a given tone control, it's the "Q" or width of the filter.

    A really narrow, sharp slope is used for something like a feedback buster, because you want to surgically cut out just the feedback frequency, and leave the rest of the spectrum alone.

    On a bass amp, wider filters are used. So when you boost at 360Hz, you'll actually affect a broad band of frequencies, starting to ramp up an octave or more below, and tapering off again an octave or more above the center frequency. The wider the filters are, the more the bass, mid and treble controls will overlap and interact with each other.

    Markbass deliberately chose a higher than average center frequency, presumably to stop the low end from sounding too tubby when the mid control is pushed. Depending on your cabs, your basses and your taste, you might hear that as a having a nice "tight" low end, or you might hear it as lacking "punch".

    This is why variable midrange controls have become so popular, because you get to hone in on the exact frequency range you want to affect.
     
  13. figuredbass

    figuredbass Supporting Member

    Joined:
    Jul 11, 2007
    Messages:
    607
    Location:
    NYC vicinity
    Well, I can't give you a schematic but I can tell you which caps to change to re-voice the control!:hyper:
    The capacitors that voice the Lo-Mid frequency are:

    C18: 47nf
    C48: 3.3nf + C49:15nf in PARALLEL = 18.3nf

    The parallel combination of C48 and C49 act as a single composite capacitor of 18.3nf (probably done to save the cost of an additional 18nf cap rather than tweaking the frequency, since it's only a 1.7% difference - far closer than the actual real world tolerance of the caps themselves). The cap size is inversely proportional to the frequency. So if, for example, you changed C18 to 56nf and the parallel combination of C48 and C49 to 22nf, the frequency would move down from 360Hz to about 300Hz. This is what I did to mine and I greatly prefer it over the stock values. A single cap can be used for C48 OR C49, but if this is done the other cap should be removed entirely. Both C18 and C48||C49 have to be changed together in order to retain the original bandwidth and properly calculate the new frequency using this inverse proportion.

    The Hi-Mid values can be tweaked too, though I've left them stock on my amp. Here are the values:

    C24: 6.8nf
    C50: 470pf + C51: 2.2nf in PARALLEL = 2.67nf (2.7nf)
     

Share This Page