EQ Expert advice needed, here is my data, now what?

Discussion in 'Archived Threads 2001-2004' started by Dave N., Mar 19, 2001.

  1. Dave N.

    Dave N. Stunt Coordinator

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    I was using a Paradigm X-30 to set the xover for my pair of SVS 25-31 but it crapped out. I ended up springing for an Audio Control Richter Scale III.
    I have been having some trouble getting a flat response from my room. I was wondering if I gave you the measurements in settings if you can give me an idea as to whether a flat response is possible in my room. As you will see from the table, my sliders are pegged at certain frequencies and I cannot obtain a 0 db response. Is this due to having the equalizer set at a 50 hertz crossover point?
    Freq. SliderMeter w/o EQMeter with EQ
    125 12- 50
    90 - 400
    63 + 920
    45 -12+ 103
    31.5 -12pegged~+8
    22.5 + 4+ 8- 0.5
    Obviously I'm getting much better response using the equalizer. Do you think that I should be concerned about the hump at 31.5 Hz? Is this a function of the crossover point chosen? When I make these measurements I have all five of my speakers plus the two S. V. 25 -- 31 CS subs driven.
    Thanks,
    Dave
     
  2. Wayne A. Pflughaupt

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    Dave,
    I have many years of experience with equalizers and adjusting EQs for flat response in cars, home theaters and public auditoriums.
    However, Dave, your numbers are bizzare and meaningless. That is why no one has responded. 90-400? 63+920? I have no idea what this is. You have the 63Hz slider on your EQ boosted an amazing 920dB??? Your SPL meter is reading -400dB at 90Hz???????
    What you need to do is get some filtered pink noise test tones and post dB readings for each frequency that you have a band your EQ can adjust.
    For instance:
    125Hz-83dB
    90HZ-87dB
    63dB-86dB
    And so on. Then it will be easy for someone to help you adjust your EQ.
    Regards,
    Wayne
     
  3. Richard Greene

    Richard Greene Stunt Coordinator

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    I've had the original Richter Scale since the early 1980's.
    Its 1/2 octave bands are usually too wide for effectively reducing output at room mode frequencies.
    It's better than nothing, of course, if a slider's center frequency happens to match (or is close to) the room mode frequency. A 30 band 1/3 octave equalizer is better if it has a control(s) that matches your worst mode(s) -- a parametric equalizer capable of narrower than 1/3 octave
    equalization is best for taming room modes.
    "Taming" room modes is what I assume you want to do.
    I can't figure out your post either -- sometimes the
    formatting changes radically when you post -- so I'll just provide general advice on the use of an equalizer to reduce output at room mode frequencies:
    The other poster is not correct when he advises the use of pink noise for your purpose. Pink noise consists of random sounds that do not last long enough to excite room modes, so you'll be fooled into believing your room has a much better frequency response than your ears actually hear (axial room modes are quite easy to hear when excited by musical content).
    In my own listening room, for example, the equalized frequency response measured at my listening position with pink noise is about +/-5dB from 20Hz. on up. and my loud floor-to-ceiling axial bass resonance measures a lot better than it sounds! But with a slow sine wave sweep, the frequency response is barely within +/-10dB
    (that's actually very good for a home listening room)
    and that bass resonance now measures as loud as it sounds!
    If you want to work on your room modes you must use
    sine wave tones or a slow sine wave sweep. The warble
    tones from the Richter Scale's warble tone generator
    change frequency too rapidly to excite room modes much.
    Pink noise is too random to excite room modes very much.
    I highly recommend the Stryke BassZone test CD
    with it's very slow (5 minute) 1Hz to 100Hz sine wave
    frequency sweep to measure your overall frequency response
    variations and help you find the many rattles that most rooms have when a loud subwoofer is added -- these
    "home noises" add a very obnoxious form of distortion to subwoofers -- much worse than harmonic distortion.
    Below 20Hz. you may find walls and floors begin to resonate loudly if a subwoofer is placed close to them
    The many sine wave test tones on the BassZone CD will help you locate the approximate frequencies of your room modes
    (a signal generator would work better but then the CD is only $10).
    If you have a rectangular room, the formula 566/room dimension in feet will approximate one axial mode frequency
    in Hertz. Use the length, width and height dimensions to estimate your three axial room modes. If two or more modes overlap, or are within 5Hz. of each other, you're in trouble! If any room surfaces are cement, you're in more trouble! The actual modes are likely to measure a few Hz. lower or higher than your estimates.
    Good luck
     
  4. Wayne A. Pflughaupt

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    Great Post, Richard. Sounds like you’ve been around the EQ block a few times yourself!
    I know what you mean about pink noise being random. At lower frequencies you can’t get a steady dB reading. However, I have had success by taking the highest number that appears for each filtered tone (the RS digital meter also has an averaging function, which is very useful). Or, you could use the lowest number—the main thing is to be consistent.
    Of course, the ultimate test is the ears. It took several attempts modifying the EQ curve (1/3 octave in my case), but I was able to achieve balanced response from my subs. My reference “test track” features a bass guitar that runs the neck from top to bottom, and each note has the same volume as the next.
    Someone at another thread posted a link for the Stryke Bass Zone CD. I’m going to be sure and pick up one for my “arsenal.” I noticed is has individual sine-wave test tones. I’m interested to see how those compare to filtered pink noise tones.
    Regards,
    Wayne Pflughaupt
     
  5. Dave N.

    Dave N. Stunt Coordinator

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    Wayne,
    I attempted to post the data as you suggested. Unfortunately when tables or imported onto this board the table format is all screwed up. My data was presented in four columns. Column 1 is the frequency. Column 2 is the position of the adjustment slider on the equalizer. The third column is the dB level on the meter without equalization. The fourth column is the dB level on the meter with equalization. I couldn't figure out how to go back in an edit the table, sorry.
    These measurements were made using the internal warble tone. Is it possible to infer anything from this data or must I use a test cd? Where can I purchase the BassZone cd?
    Dave
     
  6. Wayne A. Pflughaupt

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    Dave,
    All we need is dB readings (with EQ set to flat) for each frequency that you have a band your EQ can adjust. Obviously you’ll have to enter the data into a new format. The examples above I did in Word and just pasted into the post.
    Richard is correct that the *best* way to do this is with a 1/3 octave EQ, or even better, a parametric EQ. However, in most cases just about any EQ can make improvements, even if less that optimal. If you don’t think the EQ settings give improved bass response, or solve some problems but create others, you always have to option to use no EQ.
    The site to order the BassZone CD is http://basszone.stryke.com/testcd.html
    Regards,
    Wayne
     
  7. Jones_Rush

    Jones_Rush Stunt Coordinator

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  8. Wayne A. Pflughaupt

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    Jones,
    Daves's equalizer is a half-octave model. For instance, it has two bands per octave. A more sophisticated 1/3 octave EQ would have 3 bands per octave. In both cases, the bands (center frequency) on the EQ are fixed, as is the affected bandwidth, although a 1/3 model is more flexible. Parametric EQs are the most flexible, as they can dial in virtually any frequency or bandwidth.
    So lets take Dave's EQ as an example how adjustment might solve one problem but create another. Among other, he has bands centered at 125Hz, 90Hz, and 63Hz, etc.
    First you will need to know a little "EQ theory." Namely, anytime you move a slider, you affect not only the designated frequency (i.e., the one indicated on the slider) but frequencies on either side of center. They are automatically pulled up or down as well, albeit to a lesser degree. Frequencies are measurably boosted or cut as far 2 or even 3 octaves to either side of the adjusted slider.
    For instance, if you boost the 90Hz band by 10dB, you have also boosted 125Hz and 63dB by at least 6dB, even if you didn't touch those sliders at all. Frequencies further away, say at 200Hz and 30Hz would also show measurable increases of at least a dB or two, maybe more.
    So let's say Dave took SPL readings that showed a 6dB hump at 100Hz and a 4dB dip at 75Hz. The 100Hz hump as closer to the 90Hz slider than it is to the 125Hz slider. However, the 75Hz dip is about dead-centered between the 90Hz and 63Hz sliders. If you cut the 90Hz slider by 6dB you are reducing the 100Hz hump, but you are also at the same time increasing the dip at 75Hz, which has gone from -4dB to about -8dB. You could help that problem by boosting the 63Hz band, but then you have created a new hump at 63Hz! As you can see, this is a no-win situation.
    Of course, this is all theoretical, but it does happen. Dave might get lucky and find his room problems are close enough to the bands on his EQ to make a significant improvement. But you never know how a room will measure. If your EQ can fix your problems, that's great, and you'll be happy with the results. If it won't, you'll either have to live with the compromise, use no EQ, or get one that will address the situation.
    Hope this helps,
    Wayne
     
  9. Jones_Rush

    Jones_Rush Stunt Coordinator

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  10. Wayne A. Pflughaupt

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    Jones,
    A parametric would address just about any sub EQ situation—as long as you don’t have more problems than the EQ has bands. But this is almost never the case.
    No need to worry about equalizer-induced phase changes. Phase shift is a fact of life with any electronic filter, including electronic crossovers. Fortunately, changes in phase are very difficult to detect in the mid and high frequencies. In the low frequencies it’s a non-issue.
    Regards,
    Wayne
     

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