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Sub "resonance" ??

Discussion in 'Audio & Video' started by Lurkin, Nov 15, 2010.

  1. Nov 15, 2010 at 12:34 PM
    #1
    Lurkin

    Lurkin [OP] Well-Known Member

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    I'm having a bit of a problem, I think, with my new sub setup. I was using an 8" L7 that hit pretty well, but I wanted to upgrade to a 10" round since that was what I had before the L7 and was happy with that.

    The amp is the same, it's a Rockford T-400, with the back channels bridged to the sub (200 rms rated, 276 rms from build sheet).

    I installed a Arc Audio ARC10 sub into one side of a SoundOffAudio sub box (.75 cuft sealed box). At normal listening levels all sounds good, but when I want to shake it a bit and turn up the bass, it begins to sound like it has a resonance. My eardrum tends to feel like it's reverberating.

    I don't think it's due to vibration damping, as I have some cheapo dynomat on the backwall and doors, but also when I kicked up the L7 I never had this effect and it could definitely shake the mirror without this resonation.

    Could this be the box? If so, what can I do to test that? Or is it easier to add stuffing or damping to the box, assuming stuffing or damping would help? What else might this be? Not even sure if it's just me.

    Was considering taking it to a local shop or two just to hear what they heard and had to say, but haven't done so yet.
     
  2. Nov 16, 2010 at 6:36 AM
    #2
    Lurkin

    Lurkin [OP] Well-Known Member

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    No comments, advice?
     
  3. Nov 16, 2010 at 8:50 AM
    #3
    ItalynStylion

    ItalynStylion Sounds Gooooood

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    Could you describe the problem a bit more? I'm having trouble understanding what exactly is happening.
     
  4. Nov 16, 2010 at 10:46 AM
    #4
    Lurkin

    Lurkin [OP] Well-Known Member

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    Yeah, that's the tough part, putting words to an sound :) And not being a qualified audiophile, not sure of the right terms to use.

    Not sure how else to explain it though. At normal bass levels (flat to 1-2db boost) bass sounds SQ good even at high volume levels. When I up the bass boost to 5-6db and kick up the volume, the bass sounds like it's resonating. Best anology I can think of is that the bass feels a bit like a resonating exhaust, just at a deeper note.

    Again, only when I feel the need to "feel the investment". SQ is good (at least to me) at normal bass boost, but when I feel like pushing a bit of SPL with the bass end, I get the resonating, or what I call eardrum flapping.

    Didn't happen with my 8" L7 with a small truck box (.35cuft), but just appeared with the 10" Arc and new box/amp board.
     
  5. Nov 16, 2010 at 11:04 AM
    #5
    ChompsterTacoma

    ChompsterTacoma Well-Known Member

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    It's always the enclosure. Make sure the woofer box is within spec with sub. Some subs sound better ported and vice versa. I know what you are trying to explain. Check your amp main level and is it centered? Is the woofer wired correctly?
     
  6. Nov 16, 2010 at 11:44 AM
    #6
    Lurkin

    Lurkin [OP] Well-Known Member

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    The Arc's optimum sealed enclosure spec is .65 cuft, vs. .75 for the enclosure, and is sold as being optimized for a smaller sealed enclosure, so should be good.

    As for the input levels, for the sub it's actaully a bit higher at about 70% or so, but I have had it down at around 55% before with no difference. The sub is wired to present a 4ohm load (DVC 2ohm wired in series).

    I've also tried setting the HP and LP crossovers higher and lower to see if this is something that can be tuned out, but no difference.

    Tell me more about your statement "It's always the enclosure". What am I looking at for the enclosure? Sub box flexing (how would I verify this?), needs some Polyfill, etc.?

    Still looking for some reasons behind this resonance that I hear.
     
  7. Nov 16, 2010 at 11:48 AM
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    ItalynStylion

    ItalynStylion Sounds Gooooood

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    Set your LP crossover to about 80hz. Leave it there.
    Turn your bass boost down all the way. If you want more bass, turn up the gain.
     
  8. Nov 16, 2010 at 11:52 AM
    #8
    especk

    especk Nothin' Special

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    I've had a 12" kicker in mine for a few weeks and just started adjusting the settings on the amp - increased bass, increased sensitivity, and decreased minimum Hz response.

    I noticed if I had the sensitivity turned up so it was really sensitive I got a noise like you mention. It was louder but didnt sound as good. It picked up everything and constantly slumped and rattled even when it wasnt "supposed to". It didnt sound as good and was annoying so I decreased the sensitivity slightly to find a happy medium.

    If you have a sensitivity adjustment on your amp, try to decrease it and see what happens. On my kenwood amp, this adjustment knob is actually called 'sensitivity'.

    I'm not an expert at all on this kinda stuff, I just like loud quality bass.
     
  9. Nov 16, 2010 at 12:01 PM
    #9
    Lurkin

    Lurkin [OP] Well-Known Member

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    LP was, and is now, at 80Hz, I played with setting the HP-LP's from 50-120. Just as a test.

    Amp bass boost is at 0, when I mention adding bass db's, it is at the HU using either the bass or the built in equalization settings.
     
  10. Nov 16, 2010 at 12:06 PM
    #10
    Lurkin

    Lurkin [OP] Well-Known Member

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    I'm not sure if this is the same thing. I've had a setup where the amp was clipping the outputs before (using a 2 ohm load to an amp that was not 2 ohm stable). The thumps and sub "noises" are different than what I have now. What I hear now is much more subtle than when it's clipping. The bass sound and response is still there, there is just a resonance on top of it.
     
  11. Nov 16, 2010 at 12:24 PM
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    especk

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    oohhh. Well good luck figuring in out. I hate when little things like that just bug the shit outta me
     
  12. Nov 16, 2010 at 12:29 PM
    #12
    Lurkin

    Lurkin [OP] Well-Known Member

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    Thanks, that's just it, if I just leave it alone and don't try to rattle the yard apes in the back seat, then all is good. It definitely is bugging me though.
     
  13. Nov 17, 2010 at 11:53 AM
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    BeerHat

    BeerHat Got Beer?

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    This can cause your "resonance". When you increase the bass levels on your headunit it is usually at a specific frequency(generally around 40 hz, though some units allow flexability). As mentioned before, open up (increase) your gain settings on your amp to increase output at various volume levels. The gain is across all frequencies.

     
  14. Nov 22, 2010 at 9:31 AM
    #14
    Lurkin

    Lurkin [OP] Well-Known Member

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    Ding ding ding,,, we have a winner. Dropping the gain down to a bit less than 50% on my amp cleared it up entirely. Thanks for the leads.

    After this I might have to actually learn a bit about how to tune the amp. Up till now, never had a problem with doing it by ear, but apparently my ear ain't dat good, and this is the first time I've run into this situation. Usually they start clipping when the gain is too high and it's blatantly obvious, even to me.
     
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