Subwoofer levels..expert advice please !!

Discussion in 'Archived Threads 2001-2004' started by Jon Slater, Aug 7, 2002.

  1. Jon Slater

    Jon Slater Extra

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    I am always striving for the best most 'correct' sound from my equipment.
    I ran a few test tones from 22hz to 160khz using amp in dolby surround mode,sub crossover set at 80hz, frounts set to small.
    Below is the graph of my results
    [​IMG]
    Can an expert comment about the graph and give any advice where neccesary ?
    I understand that a flat frequency response from 20hz to 160khz is 'ideal'
    But how can i achieve that ?
    I understand i can get a behringer feedback destroyer to lower some of the levels on the peaks and boost levels at the dips.
    If i did this would i really hear a better sound ?
    cheers
     
  2. Ned

    Ned Supporting Actor

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    Rather lumpy response. Could you make a simple room diagram and show the sub's placement?

    You can tame the peaks with the BFD but you cannot push up the dips. Doing so is basically sending power to an unquenchable blackhole.

    Placement will help a lot more than an EQ. If you can fix the dips but still have some peaks, you can then consider getting the BFD.
     
  3. Jon Slater

    Jon Slater Extra

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    Hi ned..heres a diagram of my room
    the sub is behind the left speaker and the driver is facing towards the listning area.
    [​IMG]
     
  4. jeff lam

    jeff lam Screenwriter

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    A BFD would help a lot. I had a similar peek at 40Hz just like you, mine was huge at almost 15dB. The BFD helped a great deal in getting an even response. I highly recommend it if your system is up to the challenge(if you have a sub worthy of the expense).
     
  5. JohnDG

    JohnDG Stunt Coordinator

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    I've worked with the PDR-10, and I've found something interesting: turning down the cross-over on the sub really allows you to boost the low-end, and flattens out the frequency repsonse curve (FR).
    I found this info at http://www.audio-ideas.com/reviews/h...gm-stylus.html . The FR chart shows that, by moving the sub's cross-over down to 90Hz (I use 100Hz), that you can turn up the sub, and thus the low ranges, without adding to the 40-100Hz range. I've checked this out on my sub, and the FR results are very flat, less a room induced lull at 45Hz that I would need an equalizer to remove.
    jdg
     
  6. Ned

    Ned Supporting Actor

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    The bottom left corner is probably the best location as long as you don't have localization problems.
     
  7. John Kotches

    John Kotches Cinematographer

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    Ned,

    This is not necessarily so. The corner will give you the highest overall output, but at the expense of an FR curve that is fairly jagged.

    There's a room induced peak in the 40Hz range, and a room induced null in the 56Hz range. To get a more accurate gadge of what's going on use 1/12th octave as a minimum. There are missing peaks / nulls for two of the other room dimensions in this graph that would likely be uncovered with a smaller spacing of tone intervals.

    If it isn't a terrible effort I would suggest halfway down the front, side or back wall to see what the results look like.

    Maximum SPL will be compromised, but I'm pretty sure the frequency response will be better than the +/-10dB range we're seeing. I know that was the case in my room.

    Regards,


    Regards,
     
  8. KeithBR

    KeithBR Agent

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    What programs do those graphs?
     
  9. Jon Slater

    Jon Slater Extra

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    Thanks for all the replys guys...I shall try turning the crossover down from full to 90 as you sugested John.

    KeithBR, I can email you the chart if you like, its in an exel document and also adjusts the radio shack spl meter readings to 'true' levels.

    just post your email here and i'll send it.

    cheers
     
  10. Jon Slater

    Jon Slater Extra

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    just a thought JohnDG, My pioneer amp is set to output bass below 80hz via subwoofer, surely setting the subs crossover at 90 will not make any difference ?

    I was told to turn it fully clockwise to 120hz so that the crossover on the sub wasnt used..and just rely on the amp to output the 80hz and below bass to sub..

    Is this not the correct way to do it ?

    cheers
     
  11. Doug_B

    Doug_B Screenwriter

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    Is it true that even an equalizer (such as the BFD) cannot do much with a severe dip? I'm currently in the process of fooling around with a BFD and have a large dip around 50 Hz at my sitting position. I did do measurements with the sub in a different corner a few months back and discovered that position may be better off overall, but I'm putting off "permanent" position changes of equipment while I decide on some new gear. I guess I'll try fooling around with the filters to see what happens. I don't listen near reference level, and my primary concern is music. At this point, my BFD exercises are simply to prove value of having the BFD.

    Doug
     
  12. John Kotches

    John Kotches Cinematographer

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    Doug,

    Basically yes. There's one way to get rid of a null, move either the subwoofer or the listening position. You can throw all the power you want at a null and end up barely effecting it.

    Regards,
     
  13. JohnDG

    JohnDG Stunt Coordinator

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  14. JohnDG

    JohnDG Stunt Coordinator

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  15. John Kotches

    John Kotches Cinematographer

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    JohnDG,

    Yes and no. After you drop the output levels to match the null, you're now going to use more power up getting a particular output level.

    Moving the subwoofer a matter of 1/2 to 1 foot will impact the severity and frequency location of a null.

    Regards,
     
  16. Doug_B

    Doug_B Screenwriter

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  17. Wayne A. Pflughaupt

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  18. John Kotches

    John Kotches Cinematographer

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    Wayne,
    Have you read Floyd Toole's recent paper on loudspeaker placements in room?
    I'd suggest giving it a read when you have the time. Here's a link to the paper on subwoofer placement.
    This is a distillation of some work presented at the AES on loudspeaker placement for multi-channel systems.
    Regards,
     
  19. Wayne A. Pflughaupt

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    I have the highest respect for Mr. Toole, John. Thanks for the link to the excellent article.

    Was there something specific in it that you thought was relevant to this discussion?

    Regards,
    Wayne A. Pflughaupt
     
  20. John Kotches

    John Kotches Cinematographer

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    Wayne,
    Professinally speaking it's Dr. Toole for him [​IMG]
    My specific point was to discuss corner placement vs. non-corner placement.
    My goal is flattest unequalized response, not maximum output. Start with a smoother response curve, and you have less work for the equalizer to do!
    Personal experience shows that (at least in my room) placement at 1/2 down the front wall gives the smoothest response unequalized. Once I've purchased my new processor, it'll be time to get serious about smoothing out my problem frequencies [​IMG]
    By the way, all of the speaker placement articles were presented to the AES, almost certainly at a much more technical level.
    Regards,
     

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