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Anyone Notice Big Frequency Dips/Peaks After Re-Tuning A SVS PC+ ?

Discussion in 'Speakers' started by James Edward, Apr 20, 2003.

  1. James Edward

    James Edward Well-Known Member

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    I'm wondering if my results are typical...

    After adding a port-blocker, changing my 25Hz tune to 20Hz, several things occurred:

    A 6db peak around 20Hz. I would not have expected this.

    A 5db peak at 50Hz and a 4db peak at 63hz

    I did not measure any change at the often mentioned 30hz mark where the lower tuned sub is supposed to fall off somewhat.

    Prior to the 25hz-20hz retune, EQ'd response was flat to +-1.5db

    My readings were adjusted using the SPL meter correction values.
     
  2. Jeremy Anderson

    Jeremy Anderson Well-Known Member

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    Re-tuning can do some funny things to the response curve because of the acoustics of the room. On my 20-39CS+, I had too large a peak at 50Hz to even back it off with my EQ... but when I re-tuned to 16Hz, the 50Hz peak dropped to 6dB and I was able to flatten it out. You really just have to measure both ways and see what works best. In my case, it was worth losing a little bit of maximum output to have a flatter response before EQ'ing.
     
  3. MingL

    MingL Well-Known Member

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    From my measurements, there was never a hint of such change.

    A change of tune in my 16-46PC+ to 12hz did not register any significant change in freq response, other than deeper extension to 12 hz........
     
  4. Doug BW

    Doug BW Well-Known Member

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    James, were your measurements for the 25 hz tune done immediately prior to retuning? That is, did you measure your 25-hz-tune FR, then plug a port, then remeasure with the SPL meter left untouched on a tripod in between?

    If not, you can't really compare your results. Moving the SPL meter (or the sub) a small amount can affect the FR considerably.

    In any case, why didn't you expect the FR at 20 hz to go up? Wasn't that the whole point of retuning?
     
  5. James Edward

    James Edward Well-Known Member

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    Doug- I guess that is a good point- I had not plotted my FR for several weeks, so I'm sure that sound meter position, etc. did affect my results.

    But... What I meant about the 20hz peak was that the 20 Hz region was now 6db higher than the 25hz signal. I would have expected it to be at about the same level.
     
  6. Doug BW

    Doug BW Well-Known Member

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    Oh, okay. I thought you meant 6 dB higher compared to the previous 20 hz measurement.

    I've found that it's a real pain to accurately do before-and-after comparisons. Not only do you have to lock in the meter and sub position, but things like a door to the room being open, closed, or ajar at different angles can make a difference. Open/closed windows makes a huge difference. Body position with respect to the SPL meter can also have an effect. I suppose moving furniture around the room can matter. (Things like air temperature, humidity and barometric pressure also affect things, but I'm not sure to what extent their effects would be observable.)
     
  7. Edward J M

    Edward J M Well-Known Member

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    James:

    Tuning my 20-39PC+ to 16 Hz (i.e., plugging one port) flattened a 6 dB hump at 25 Hz, but left the higher regions of the curve completely unaffected.

    Of course, tuning to 16 Hz also filled out the sub-20 Hz region considerably. In fact if I set the SS filter to 12 Hz just for testing purposes, the FR stays essentially flat to 11 Hz with just one port plugged.

    Here's a graph - a picture is worth a thousand words.

    Regards,

    Ed
    [​IMG]
     
  8. Edward J M

    Edward J M Well-Known Member

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    James:

    I had a chance to throw both graphs on the same chart for you to see the difference. Sorry I was not able to do it earlier today. Hope this helps.

    Regards,

    Ed

    [​IMG]
     
  9. James Edward

    James Edward Well-Known Member

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    Thanks for the replies. I redid everything AGAIN, and my numbers remained fairly close. BUT, I decided to put the meter on a tripod, and at a fixed spot at the listening position. This will make future testing more accurate and results repeatable. Even small movements had an effect on the meter response. Not to mention they drove me crazy.

    Now I like the 20Hz re-tune. Prior to having an EQ(ART355), the re-tuned sub always sounded 'slow' and muddy. That would have been due to the large peaks at certain frequencies. I'm happy now. But I should have gotten the 16-46 or 20-39 in the first place. Oh well.
     

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