What is flat EQ?

Discussion in 'Amps [BG]' started by the low one, Oct 10, 2009.


  1. the low one

    the low one

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    I always try to start with a flat EQ on my amp and then adjust from there for the room but what is flat EQ? My amp has a mid shift button which changes mids from 400 hz and 1 khz, so if I leave all my EQ’s at 12:00 and just engage or disengage the mid shift it radically changes the tone.

    So, is my EQ set flat with or without the mid shift?
     
  2. bassforce

    bassforce Guest

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    You EQ is never flat in "12:00 position". Every amp has unique voicing, and "set flat" does not give a flat response.
     
  3. spencer

    spencer Guest

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    from the sound of it no, the midshift button shouldn't change the tone if the mid was set flat.. Try playing with the mid knob while switching the midshift button to get them to both sound the same and that will be flat.
     
  4. MIJ-VI

    MIJ-VI Banned

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    Which amp?

    Details are helpful...
     
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  6. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    If your EQ is boost only, then flat is all EQ controls turned all the way down. If your mid gain is set at 0 dB, pushing the mid shift will do nothing, so 12 o'clock isn't flat for your amp. For example, 12 0'clock is "flat" for the EQ on the Eden WT-800. With the mid gain in that position, the mid frequency control has no effect.

    As bassforce said, every amp will have its own character when its EQ is set flat.
     
  7. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    OK, the Trace Elliot Commando 15 has separate mid knob and button. I'd say it's likely the button works pretty much independently of the knob and colors the tone with a mid shift regardless of the position of the knob. Just a guess.
     
  8. PBass101

    PBass101

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    An amplifier's EQ is difficult to set "flat" because they are typically voiced to have a distintive sound - hence we buy certain brand's amplifiers over another's. You buy what you like to hear.

    "Flat EQ" in a more scientific sense is difficult to imagine with an integrated bass guitar amplifier + cabinet.

    Smarter people than me on this forum will explain in further detail.
     
  9. the low one

    the low one

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    Sorry, forgot to mention that it is a Trace Elliot Commando 15 combo. The manual says it has passive eq. With the mid eq at 12:00 engaging the mid shift button make a big difference to the tone.
     
  10. billfitzmaurice

    billfitzmaurice

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    Neither. When set flat EQ has no effect, so shifting the frequency would not have an audible result.
     
  11. the low one

    the low one

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    It must be a feature of the Commando combo because with the EQ at 12:00 engaging the mid shift has a very audible result. It really seems to move the voicing of the mids. Does the fact that the EQ on the Commando is passive make any difference?

    I know what you mean. I have tested on a Laney combo which has bass, middle and treble controls along with a mids frequency rotary knob. On the Laney with the EQ set at 12:00 rotating the mids frequency has no effect on the sound, only when you cut or boost the mids does the frequency selected become audible.
     
  12. fretlessrock

    fretlessrock Supporting Member

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    There is "flat", meaning all tone controls at neutral, with no cut or boost. Then there is "flat", meaning that you sweep the input with an audio source and the output response matches the input response = the preamp/amp is not enhancing or attenuating any range of frequencies more than any other. Some amps, and the Fender/Alembic tone stacks come to mind, have flat settings that are not 12:00, 0, or 10.

    Probably not a great/appropriate answer when talking about a specific piece of gear, or a generalist inquiry, but it is one way to look at the "flat" question.
     
  13. JimmyM

    JimmyM Supporting Member

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    Actually, I just saw that it has 3 tone controls, bass, mid shift and treble, correct? To me it sounds like the mid shift moves the center freq and does it audibly, and if it has a passive tone stack, it's entirely possible that it's the reason you can hear it. I think everyone else is confusing it with the mid controls on some amps where you have a knob to control the center frequency AND a knob to control how loud your mids are.
     
  14. R Baer

    R Baer Supporting Member

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    Actually a good explanation. There are very few amps out there with a truly flat response. Check out the amp reviews in Bass Gear Magazine and it's easy to see just how far from a flat frequency response some amps are. Is this bad thing? Not if you can plug in your bass and get a great sound. You either like an amps tone, or you don't. Even if your amp has a ruler flat response from 20Hz-20kHz, you then are putting that signal through a cabinet that has its own tonal signature. Now start adding in the sonic nightmare that the room your playing in is adding to your sound and you can see how far from flat the sound reaching your ears truly is. No matter what the 'flat" frequency response of the amp is, that amp is going to sound quite different with each player, instrument, cabinet, room, etc...

    That's why we put Eq controls on amps. Feel free to use them as needed and please don't panic if the sound you like best doesn't end up with all the controls at noon!
     
  15. billfitzmaurice

    billfitzmaurice

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    Flat EQ is the same as no EQ, so if you hear a change with the shift the EQ is working and therefore it's not flat. The 12:00 position may be flat in either an active or passive, and then again, it may not, it depends on the circuitry.
     
  16. Red Planet

    Red Planet

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    Flat is not flat by the time you plug into a cab.
     
  17. fdeck

    fdeck Supporting Member

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    Technically speaking, "flat" means constant gain across the frequency spectrum that you are interested in. PA amps are typically flat, and mixers tend to be when their EQ controls are centered.

    Many (most?) bass amps are designed to have something other than flat response when their tone controls are centered. I don't know if there is an official term for this, but I call it "voicing." The reason for voiced amps is that they sound good, or at least, the designer of the amp wants it to sound good when you try it out with the knobs centered.

    You can measure the voicing curve if you care what it looks like, using a real time analyzer (RTA). Going further, you can try to dial the EQ knobs on a voice amp until the curve is reasonably flat, as I have done as an academic exercise on one of my amps.

    A few bass amps are known to be flat -- these tend to be favored by upright players.
     
  18. JimmyM

    JimmyM Supporting Member

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    The only reason I panic if the tone controls aren't at noon is because I don't like overhyped tones. A little boost is fine, but if I'm moving knobs more than a quarter turn, I don't like it. I don't like the extra noise and the peaky sounds that can result from it.
     
  19. MIJ-VI

    MIJ-VI Banned

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    Like those made by Acoustic Image?
     
  20. the low one

    the low one

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    No, that's not correct. It has 3 tone controls, bass, middle and treble, and then a mid shift button to move the frequency of the mids from either 400hz or 1 Khz.
     
  21. JimmyM

    JimmyM Supporting Member

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    Well then theoretically you shouldn't hear a change at all when you set mid volume to noon and sweep the mid sweep knob.
     

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