Off-Axis Live Tone Phenomenon: Insight/Solutions?

Discussion in 'Live Sound [BG]' started by CharlieFla, Aug 1, 2021.

  1. CharlieFla


    Nov 3, 2017
    We played an outdoor show last night. Full PA support. Used an Ampeg SVT212AV. Stage volume was high, but not extreme. Problem: When standing directly in front of the cab, the tone was harsh, clanky, and wholly unpleasant. When standing next to the cab, or even 45 degrees or so to one side or the other of the cab, the tone became much more tame and pleasant, though somewhat diminished in volume.

    What is causing this? Any solutions or suggestions?

    I was DI’d to FOH, and I certainly hope that the crowd only heard the pleasant tones. If not, I must retreat to the caves at the edge of town and live amongst the forest creatures to repent for the shameful bass sounds I imposed upon the nice people at the concert.
    Zbysek likes this.
  2. WayneP

    WayneP Supporting Member

    Oct 11, 2004
    Corpus Christi, Texas
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  3. MattZilla


    Jun 26, 2013
    six more speakers.
    CharlieFla likes this.
  4. The fact that HF sound and the HF driver are more directional could be the cause? EQ for position in front of the cab as a possible solution.
  5. Wasnex


    Dec 25, 2011
    Cone drivers become directional as frequency increases.

    These image polar plots are for a 15" driver:

    Here is the text that explains the images:

    Off axis cancellation effects are often illustrated through polar response graphs which show the dB level at various angles from 0 to 90 degrees. In the diagram the dimensionless number ka refers to circumference* divided by wavelength. *circumference can be easily calculated as pi or 3.141 multiplied by the diameter.
    For example a 15″ piston has a circumference of around 4ft, so ka is around 250Hz. Above ka = 1 the piston starts to become directional. Relatively smooth off axis response is maintained to ka = 2 (500Hz for the 15″ piston) but by ka = 5 (1250Hz for the 15″) the piston is beaming with notable response lobing.
    A 10' driver would develop similar dispersion patterns, although at a higher frequency.

    The interaction between two drivers also has an impact. If you have the speaker oriented horizontal, it actually narrows horizontal dispersion. Likewise if you orient the drivers vertically, the vertical dispersion is narrowed.

    I suggest aligning the drivers vertically and aiming it at your heard. Then adjust the amp to taste.

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  6. Zbysek


    Mar 23, 2017
    Czech Republic
    One possible solution is to stand in front of your cab and change your EQ settings (decrease highs)...
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  7. Jack


    Sep 6, 2003
    Northumberland, UK
    Neither your on-axis nor your off-axis cab sounds will sound the same as the di, but I bet you the on-axis is closer.
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  8. Pat Harris

    Pat Harris

    Nov 17, 2006
    Brighton, MI
    On an outside gig, even with PA support, there are no walls and no coupling to help "beef up" your stage rig. A 2x12 can sound thin outdoors from the player's perspective simply because all of the actual low end is likely blowing right past you and more prominent about 20 feet out front.
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  9. Ender_rpm


    Apr 18, 2004
    St. Louis MO
    IIRC, the 212AV speakers are on a diagonal, possibly the worst overall configuration for this sort of filtering. Try to tilt it up next time and stay in the front cone. If the sound there is too harsh, thats the sound the house is hearing. Fix it :)
    CharlieFla likes this.