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Bass Frequency Response, Measurement, and EQ

Discussion in 'Archived Threads 2001-2004' started by Brian L, Aug 2, 2001.

  1. Brian L

    Brian L Cinematographer

    Jul 8, 1998
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    What is the general consensus regarding room response, particularly in the bass region; is flat response the goal, or is in some amount of boost in the low end normally desirable? Is truly flat response across the whole spectrum really something that is pleasing to listen to, or is it merely a starting point?
    I have gone through a fair amount of trial and error in order to arrive at room bass response that, in my room and with my ears, sounds authoritative when true low bass is present (read; I can feel it in the couch!), yet does not normally sound boomy (some content does require some level adjustment of the sub). That said, it is NOT flat, but rises gradually from about 80 Hz and below, peaking at about +10dB at 25 to 30Hz relative to frequencies above 80 Hz.
    Now, to be clear, I don’t consider that there is any problem per se, in that the system sounds great to me, but I am curious if there are those that do run their systems set for flat response, or if the consensus is that some amount of low end boost is usually needed.
    I use an Audio Control Bijou (1/6th Octave control below 80Hz), and have taken measurements with various test devices including SpectraPlus software with a Sure SM57 mic (using a compensation curve for this mic), the venerable Radio Shack SPL, and now with the Infinity RABOS SPL meter (which BTW, is quite nice for measuring and graphing low bass response, even without Infinity RABOS speakers).
    The room response was tweaked to be reasonably flat in the bass region (
  2. Wayne A. Pflughaupt


    Aug 5, 1999
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    Corpus Christi, TX
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    As you have discovered, flat room response is not pleasing to the ear. Manufacturers or high-quality equalizers, like AudioControl and Ashly, recommend that the EQ target is not flat response, but a so-called “house curve,” a gradual rise in response from the highs to the lows.
    The amount of deviation on the slope is room dependent. Smaller rooms require more low frequency boost, but fortunately they supply it naturally—the so-called “room” or “cabin” gain factor.
    Larger rooms require less of a rise in response. For example, my listening area is a very large 6200 cubic ft. When I finally dialed in my EQs where things sounded best, response is 16dB higher below 63Hz than it is at 20kHz. However, that half of the rise in response is in the sub region below 100Hz.
    My system sounded best with a 8dB rise between 100Hz and 63Hz. Response flattens out below 63Hz; I found that further increases in response below that point made most program sources display an annoying and unnatural “rumble.”
    The trick is finding out the proper house curve for your room. If your room is smaller than mine, you will probably need greater than an 8dB increase below 100Hz. If it is significantly larger, then you might need less than an 8dB low-end boost.
    The room size will also determine at what point you want to level off the response curve. You may need to shift my 63Hz figure up or down until you get the best sound.
    Wayne A. Pflughaupt

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