Loud "crack" from subwoofer at relatively low volumes (SVS PB12 Plus)

Discussion in 'Subwoofers' started by mistermann, Nov 28, 2010.

  1. mistermann

    mistermann
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    Have been having an issue with my SVS PB12-Plus subwoofer (ported box enclosure, 12" driver, 525 watt amplifier).

    When I first got the sub, it worked flawlessly, never had to run at high volumes, but a few times just for fun turned it up to likely about 75% gain and let er rip. Peformed without a hitch and absolutely shook my apartment building.

    Shortly thereafter, I moved to a new house. I moved the sub myself and was extremely careful, no bumps or anything. In the new house, my theatre room is probably about 50% louder than my previous room, with vaulted ceilings. So performance will obviously be different.

    But at my new place, I am getting very frequent cases where either a very loud "crack" sound, or sounds like distortion (blown speaker) are coming from the sub when it hits hard bass sounds (explosion in a movie, for example). Now, this is *not* running the sub at really high volumes. This problem occurs with the amp at or below reference volume, and the gain on the sub at 50%. I have tried moving the sub to different parts of the room.

    I should note, this is a very old house, and the wiring is pretty substandard, so one thing that makes me wonder is if insufficient current might cause this problem?

    I've owned this sub for probably a 3-4 years now, and the problem started happening about a year in. Having a kid cuts down on my home theatre time.

    Could anyone offer some advice on what they think the problem could be?
    Any suggestions on things to try so I might be able to get a pretty firm idea on what the actual problem is?

    Thanks!
     
  2. drummerjohn

    drummerjohn
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    Are you using eq ie Audysey?

    Can you see the cone move when this happens? Does iit look like the excursion is close to maxing out?
     
  3. mistermann

    mistermann
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    Yes, my amp is an Onkyo TX-SR705 which has Audyssey:
    Onkyo TX-SR705 - THX

    I unscrewed the base of the sub after posting this yesterday. The speaker looks undamaged. I ran through an offending movie clip several times (the scene in Iron Man 1 where they are first attacked in the Humvee and a "bomb" explodes right beside him on the ground). I don't know how to tell when a speaker is close to "maxing out" but I can confirm that it was moving a great distance.

    I made a few changes to the settings on the sub:
    1. I changed the subsonic filter from 20Hz to 25 Hz (has a total range of 12 to 25 Hz; when using 12Hz you are supposed to have 2 of the 3 ports plugged)
    2. Raised the crossover (on the sub) to 120Hz (although this may be largely irrelevant as the amp will have set its own value according to the Audyssey run).
    3. I added one port plug (despite having the subsonic filter at 25Hz; 20Hz and above does not require a plug) - the thinking behind this is that it will impede the travel of the speaker, so if it is maxing out, this should mitigate that somewhat. (This is a guess on my part).

    After these changes, running at the exact same volume, and it seemed better. If running at the exact same volume on both the amp and the gain on the sub I don't think #2 would have any effect. #1 and #3 I can see. #3 to provide physical resistance to the sub maxing out, and #1, if I understand what subsonic filtering is, basically limits the power below the specified level.

    So this tuning seems to have had some success. That being said, the mid range bass just does not seem loud at all on this sub (based on my past experience with it, and the fact that it is maxing out somehow).

    Is it theoretically possible that an electronic problem in the subwoofer amp could somehow be causing an incorrect (excessive) amount of power to the low end relative to the mid end....so, my 50% gain is properly affecting the mid range, but the low end is effectively receiving 50%++ gain?

    If I took it to a speaker shop and they hooked it up, would this fact jump out at them? Or, if I borrowed a sound meter and test CD from someone, should this be immediately obvious?

    Anyone have any other ideas??
     
  4. drummerjohn

    drummerjohn
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    Turn off Audysey and retest. Not a fan of it for ported subs unless you run your sub at low levels.

    Certainly turning up the subsonic filter to 25Hz will help but you can still get a hell of cone movement at 30Hz it's just not so violent.
     
  5. AngelEyes

    AngelEyes
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    Sounds like you may be suffering from a room null and perhaps Audyssey is compensating for that and your sub is having to work too hard, causing the distortion/bottoming out.

    The solution is likely a change in the subwoofers position relative to your listening position and hope you pick a spot with better response. Ideally you should use something like Room EQ Wizard to measure the room response at various positions and place your sub in the best. This will give Audyssey much less to do and hopefully give you your performance back.

    Adam :)
     

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