need some sub EQ advice (w/ FR plots)

Discussion in 'Speakers' started by Kevin Eckhardt, Nov 3, 2004.

  1. Kevin Eckhardt

    Kevin Eckhardt Stunt Coordinator

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    After reading a lot of other threads on FR and EQing for subs I thought I would give it a whirl myself. I used the spreadsheet from snapbug.ws as a start for my FR plots and also used the sine wave tones from the same site to make a test CD. Measurements were taken with the receiver set at -25dB in stereo mode, both sub+mains, mains are set to small and crossover is at 80Hz. I used a RS SPL meter attached to a "mini-tripod" and set on top of a box. It was angled slightly forward and ~3ft off the ground. This makes it pretty close to ear level when slouching on the couch and within 6" when sitting up.

    I'm pretty limited in acceptable placement locations. My sub is an SVS 20-39CS w/ ISD and a 250W amp and is currently located along the front wall between the door to the garage and the LF speaker / RPTV. I also took measurements with the sub on either side of the couch.

    Here is a picture of the room layout:
    [​IMG]

    Ceilings are 9ft. Total volume for the LR + kitchen is ~3500cf. The room is open to the dining room which is an additional ~1500cf.

    FR plot for sub in current position:
    [​IMG]

    Things look pretty good from 20-36Hz but then drop off drastically until 80Hz, with the frequency for the bottom of the dip varying with seating position. This was a pretty deep and wide trough so I tried the sub in two other locations:

    FR plot for sub on the left side of the couch:
    [​IMG]

    FR plot for sub on the right side of the couch:
    [​IMG]

    So, any advice on where to go next?

    Kevin
     
  2. Wayne A. Pflughaupt

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    Kevin, all the links are DOA. Can you fix them?
     
  3. Kevin Eckhardt

    Kevin Eckhardt Stunt Coordinator

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    Hmmm, they show up for me on both my powerbook and my sun here at work and did on my PC at home. The images are located at www.kevineckhardt.com/images/ and should be named appropriately if they're not showing up inline for you.
     
  4. Kevin Eckhardt

    Kevin Eckhardt Stunt Coordinator

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    Are the images showing up for anyone? I checked the server logs for my domain and it looks like the images have been served a number of times, but just want to make sure people are actually able to see them since they weren't showing up for Wayne.
     
  5. Wayne A. Pflughaupt

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    Yes, they’re working now. It’s getting pretty late for me - I’ll take a closer look tomorrow and hopefully have something to offer.

    Regards,
    Wayne A. Pflughaupt
     
  6. Wayne A. Pflughaupt

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    Kevin,

    As you can see, moving the sub to the couch locations results in reduced output below 32Hz, as well as rougher response overall, so I’m going to say stay with the front location.

    Working from that chart, what jumps out at me is that your response in the 70-125Hz range is way too high compared to the 32Hz and below range. EQing the sub from those reference points would result in virtually flat response, which seldom sounds right. What you should be shooting for is a house curve, or sloped response, which sounds much more natural to the ear. You get more info on house curves at these links:

    http://www.hometheaterforum.com/htfo...958#post464958
    http://www.hometheaterforum.com/htfo...81#post1975881
    http://www.hometheaterforum.com/htfo...918#post499918

    Here is an example of what a house curve looks like, courtesy of Sonnie Parker’s BFD Comprehensive Set-Up Guide website:


    [​IMG]


    As you can see, response at 100Hz is down about 13dB compared to 22Hz. Every room requires a different house curve, so Sonnie’s slope probably won’t be exactly right for you. The links provided above give instructions on how to determine your own house curve.

    But for the purpose of this discussion let’s go with a 15dB slope between 100Hz and 32Hz. And let’s go with the center-of-couch graph. Ultimately you’re going to have to pick one, and that one seems most logical. So - once you allow for the slope, the trough at 50Hz is only about 15dB deep, not 25dB as it appears on your chart. This shouldn’t be hard to address with equalization.

    A few procedural things: I think the fact that you’re charting with both the sub and mains is exaggerating the high readings in the 70-125Hz range. It’s best to take your readings and accomplish your initial equalizing with just the sub. Then add your left and right mains only and make any needed adjustments. You can expect that there will be some, since things like overlapping frequencies and phase often roughen up response an octave or so above and below the crossover frequency.

    I generally shoot for smooth response and a good blend between the sub and L/R mains only, since that is what’s critical for music. Once that’s accomplished I usually like the sub turned up a little higher with movies compared to music.

    Regards,
    Wayne A. Pflughaupt
     

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