Equalization for a subwoofer

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  • Joe
    Junior Member
    • Jan 2003
    • 2

    Equalization for a subwoofer

    Is equalization generally needed on a subwoofer? I have a DIY ported box with a BP1203 that sounds pretty good but I have never measured the FR. With a test CD and my ear, it goes to about 25 Hz.
    Anyone in Si valley, Palo Alto area, care to do a measurement for me and show me how it is done? I'll supply the drinks.
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    The BP1203 will need something to drop the FR hump that's a function of the relatively high voice coil inductance.

    Here's a link that should be helpful


    IB subwoofer FAQ page

    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson


    • Hank
      Super Senior Member
      • Jul 2002
      • 1345

      Thomas, thanks for the link. I see he recommends several programs for room measurement:

      There are many good software programs for predicting/evaluating/measuring loudspeaker performance. CARA, ETF 5.0, and RPG Acoustics Room Optimizer look at loudspeaker placement and the interactions in with room.
      Has anyone actually used/compared these programs?

      I've just about decided to buy the Behringer mic and their DSP110 to power it, so I'll need a good program.

      He also put in a couple of compliments for TruRTA.


      • Pat
        Super Senior Member
        • Aug 2000
        • 1637

        Hank, the link was to a page on the "AudioWorx" site...Thomas and Jon's site.

        Pat's Page
        Pat's Page


        • Hank
          Super Senior Member
          • Jul 2002
          • 1345

          Pat, I don't understand your point. When I click on the link, here's what comes up ("audioworx" is in the URL):
          "Electronic room treatment and loudspeaker correction

          Passive room treatments work well, and are the preferred method of room correction. However, there are circumstances where passive treatment simply is ineffective or impractical. The solution is then to use active controls.

          The most effective form of active control is to utilize a parametric equalization. Parametric EQ is preferred over 1/3rd octave because of it's greater flexibility and control. Parametric equalizers range in price from $135-$5,000+ depending on their sophistication, accuracy, and sonic signature.

          In order to use active equalization it's mandatory to have a basis for adjusting the controls. This is usually created by measuring the frequency response of the room. Near-field (3" or less), 1 meter, or GP (ground plane), are measurement distances. The least expensive and most simple method of measuring loudspeaker performance in a room; is by using a device like the Radio Shack SPL meter, while sending sine waves through the loudspeakers. The resulting meter readings can be plotted in Excel, and the FR (frequency response) of the loudspeaker's performance in the room can be easily seen.

          If one has the ability to send a computer generated signal into their audio system, the NCH Tone Generator by Swift sound is a great freeware program. For those that can't use their computer to send the signals, many CDs are available with test tones burned on them.

          One of the better investments for those needing help to EQ lower frequencies, is the Behringer DSP1100P/1124P. Available for as little as $135, this device offers 12 bands of stereo parametric EQ. It is a very flexible and powerful tool. But the supplied instructions leave something to be desired. Also, it should be noted that the Behringer unit is fine for subwoofer frequencies. Since it digitizes the signal it's not recommended for use with full-range audio signals

          Here are links to 2 websites that describe in great detail how to use the RS meter and adjust the Behringer DSP1100P/1124P for optimal performance of subwoofers. The Brinkster Site uses the program ETF 5.0 and the RS SPL meter for making the measurements of the speakers performance. Sonnie Parker's BugSnap Website goes into great detail on the set up and use of the Behringer DSP1100P/1124P.

          For those using the Behringer DSP1100P/1124P, Anthony Gomez has created a need little program to program the equalizer. The program can be downloaded HERE

          There are many good software programs for predicting/evaluating/measuring loudspeaker performance. CARA, ETF 5.0, and RPG Acoustics Room Optimizer look at loudspeaker placement and the interactions in with room.

          TrueAudio's TrueRTA is an excellent program. The 1 octave freeware version will give the user a good idea of the program's abilities. The 1/24 octave version is an amazing tool when married to a proper microphone. The latest version has a .cal file for use with the Behringer ECM 8000 mic (see discussion below..."


          • Brandon B
            Super Senior Member
            • Jun 2001
            • 2193

            I think his point was, you asked if anyone had used these. Since Thomas sent you a link to his own page, it's safe to say he has used the stuff.



            • Pat
              Super Senior Member
              • Aug 2000
              • 1637

              Brandon, you are correct.

              Hank, sorry if I was too vague :?
              I use a Behringer 1124 to eq my sub.

              Here are 2 of the links you mentioned but forgot to include. (I don't have Anthony Gomez' site in my bookmarks)

              Joe, I don't know if EQ is generally needed or not...I'd say it depends on how picky you are about flat response. I'd guess that most people don't even know why you would EQ a sub.
              If you do EQ for a flat response be prepared to be underwhelmed...especially if you are used to a peaky/boomy sub.

              Pat's Page
              Pat's Page


              • JonMarsh
                Mad Max Moderator
                • Aug 2000
                • 15213

                I'll put in my 0.02 and say that our experience is that the best subjective (and measured) results have been achieved when we've first EQ'd the subwoofer for flat near field response through at least a half octave above the nominal crossover frequency just measuring the sub alone, without active crossover. Then, when the active crossover is added into the equation, the acoustic transfer function follows closely the electrical one in the crossover, and the matching between sub and mains is fairly optimized.

                If instead you choose to equalize at a listening position, you run the risk of things being fairly OK at that position, and not even close most other places- especially if the listening position you choses is subject to room peaks or worse, nulls. It's best to spend more time on optimum positioning of the sub and the listening positions to avoid eigenmodes. Use the search engine for more discussion on this topic. Acoustic solutions to acoustic problems.

                This EQ most often involves more work in the area above 75 Hz than you'd think- as well as some trimming of the response in the region below 40 Hz down to the system Fs.

                Note: NEVER use EQ to attempt to increase the output of a ported system below the port tuning! Most folks understand this, but in case you don't, below the port tuning, the woofer unloads, and the port output and woofer output are out of phase, resulting in weak output and low power handling. Generally it's a reasonable idea if possible to have a high pass (rumble) filter to cut out the infrasonic bass below the system tuning if your sub is ported.

                Sealed is a bit different; more LF output is possible, but it is still limited by the driver excursion and swept area. Hence, the desirability of systems like ThomasW's 12 Shiva's Dancing. No substitute for cubic inches! :B

                Best regards,


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