Subwoofer Equalization

Discussion in 'Speakers' started by GregBe, Sep 12, 2003.

  1. GregBe

    GregBe Second Unit

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    I recently upgraded my sub to the Cambridge Soundworks Newton Series P500. The sub has duel 8 inch drivers and goes down to 24Hz. It has a 500 watt amplifier. In addition to the normal crossover, phase and volume settings, the P500 has 2 additional controls: Equalizer Frequency (that goes from 20-60) and Equalizer Level (that goes from -6 to +6).
    According to the manual it briefly states these are used because different rooms have different effects on base response, and then instructs me to adjust them by ear to what sounds best.
    Well thanks to you guys at HTF, I am addicted to tweaking for accuracy (I am not sure if this is a good thing [​IMG] ) using an SPL meter and Video Essentials. I want to do this technically correct.
    The manual states that "the lower you set the equalizer freqency and the higher you set the equalizer level, the more amplifer power you devote to producing the deepest bass. This, in turn, can limit the maximum overall output of your subwoofer. If you want maximum output, setting the equalizer frequency at of above 30 Hz can give it to you." This concerns me because the sub is supposed to go down to 24Hz, so I don't want to limit it to 30, but I also want to be able to set up my system correctly at reference level (even though I never listen to it at this level)
    Any help would be appreciated. Since I have read some posts on equalization and could not follow, a lay man's answer would be great
     
  2. Brian L

    Brian L Cinematographer

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    This reads like you have a one band Parametric EQ with a fixed bandwidth. Sort of a take-off on the Infinity RABOS system.

    FWIW, VE is not going to help you here. You need test tones in 1/3 octave or finer increments.

    You should measure and plot your response, and use the EQ to take down the largest peak.

    While this should help your in room response, I am afraid it will not really do a proper job of matching your sub to your room.

    If you search on the subject of "SUB EQ" you should find a few days worth of reading material.

    BGL
     
  3. Wayne A. Pflughaupt

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    Greg,

    I’ll second Brian’s assessment to limit the on-board EQ’s use to cutting a peak frequency. This will most likely give the best results in your situation.

    Get some sine-wave test tones – at least 1/3-octave, but 1/6 would be even better – and take some readings using a Radio Shack SPL meter. (Be careful of the sine waves – they can damage voice coils. Leave each tone playing only long enough to get a reading – 5-6 seconds should be plenty of time.) Plot your readings on graph paper and connect the dots to see a response chart of your room. You will be able to see which frequency is the peak (i.e., the highest SPL number).

    Next we have to get the on-board equalizer centered on the frequency we want to adjust. I wouldn’t really trust any calibrations on the 20-60Hz frequency knob – they probably aren’t accurate or precise enough to nail down the frequency we want. So we’ll find it by ear.

    First, set the Frequency knob for 20Hz and the Level knob for +6, then play the test tone that you have determined is the hottest frequency. This time, however play it at a reduced volume. Once it’s playing, slowly turn the Frequency knob. As you turn the Frequency knob, at some point the test tone will begin to get louder. Center the frequency knob on the setting that gets the most volume from the test tone. Now you have accurately pinpointed the hot frequency in your response.

    All that’s needed now is to change the Level knob from +6 to its proper counteracting adjustment, which will probably be –6.

    Regards,
    Wayne A. Pflughaupt
     
  4. GregBe

    GregBe Second Unit

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    Thanks Guys. That makes sense. Wayne, in your final adustment you state that I should turn the level knob to it's proper counteracting adjustment (in this case -6). Is it important I know why I am doing this (can this vary?), or should I just do it? Also, where would you recommend that I get the sine-wave test tones?

    Greg
     
  5. Wayne A. Pflughaupt

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    Greg,

    Typically the reading of the frequency with the highest peak is much worse than 6dB (which is way I simply suggested cutting the full 6dB). However, in the unlikely event you find your peak frequency is less than 6dB above the rest, then of course you would not reduce the full 6dB, only as much as isneeded.

    Re test tones, I think you can download some somewhere on this site.
    Comprehensive BFD Set Up Guide

    Regards,
    Wayne A. Pflughaupt
     
  6. GregBe

    GregBe Second Unit

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    I have been playing with this, and I want to make sure that I am achieving the most I can from my sub. In the manual it states that "For recordings with deep bass content, setting the Equalizer Frequency control below 30 HZ will produce highly accurate and room-shaking results as it reveals near-infrasonic signals. There are only two main reasons to set this control above 20 Hz - the very deep bass bothers people in adjoining rooms or the overall output level isn't as strong as you would like. If you have a large room, or desire very high sound pressure levels, setting the equalizer frequency control at 30 Hz or higher will still provide good deep bass, but will allow greater overall output."
    Do you think that if I want the deepest bass response possible I should set the frequency as low as it goes and up the levels, or should stick with what has been suggested and lower my peak?
    Sorry if I am coming across as asking the same question again and again, but equalization is very new to me.
    Thanks
    Greg
     
  7. Brian L

    Brian L Cinematographer

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    I think I would ignore the directions.....

    The overall goal is to have flat response across the bass region. Once that is achieved (or you get closer, since truly flat bass is pretty hard to come by, and darn near impossible with a single band of adjustment), you can then adjust the overall sub level for the most pleasing balance relative to the main channels.

    So, back to business. Take your readings, and plot then on graph paper. Although you will need to do some interpretation, you should be able to see that there are peaks and valleys. Try to determine what frequency has the highest peak, and use the adjustments on your sub to to bring it down.

    If there are a group of adjacent frequencies that create a broad peak, set the adjustment in the middle of the range.

    The Infinity RABOS uses a very similar approach. The theory is that, by taking down the worst peak(s), you can run the sub louder without having that peak overly emphasized, which can make the sound appear boomy.

    BGL
     
  8. GregBe

    GregBe Second Unit

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    Thanks Brian,

    That is what I will do. So in the process of calibrating my sub, which order should I do each step. Should I set the crossover first, match the spl to my other speakers second, set the phase third and equalize after that. If so will the equalization effect the other settings.

    Also once this setting is in place should I not touch the equalizer freqency and equalizer level regardless of what I am listening to.

    Finally, do any of the other test discs have the sine waves that will help me. I am thinking about upgrading from VE to DVE.

    Thanks so much. You guys are Awesome!
     
  9. MikeLi

    MikeLi Supporting Actor

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    I get so confused with this mapping stuff. I have a Rat shack meter. Anyone in the Portland, OR area want to make a few bucks and come on over and calibrate this PB2+ for me. I have no complaints its working great... just would like to know its doing its best.
     
  10. LanceJ

    LanceJ Producer

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    I seem to be in the minority with this, but here goes anyway.....

    GregBe: Setting your sub using "reference" levels (insanely loud to me) I think will cause unneccesary problems because human hearing is less sensitive to bass frequencies as volume goes down. And this effect is logarithmic (i.e. both don't change at the same rate) so things can get messy fast when trying to calibrate a system.

    If you want more info on this subject do a search on the "Fletcher/Munson curve". This curve is why most receivers (until the late 90s when they practically disappeared for some odd & irritating reason) included loudness controls to boost the highs & lows at conversational listening levels.

    Personally speaking I would calibrate your system at the level you normally listen to your HT with. Otherwise I think when you turn down your system from reference level and use it to watch a movie or listen to music you will be disappointed in the sound. And it definitely won't be accurate.

    LJ
     
  11. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Wayne and Brian L have given excellent advice. As they have explained, using that feature in your sub to attenuate your worst in room peak is the best thing you can do with it. The stuff you quoted from the manual is mumbo jumbo.

    Meanwhile, do not "set" your sub's crossover frequency. Assuming you are feeding your sub a "sub out" or "LFE" signal from an HT receiver, your sub's crossover is superfluous and destructive. Get it out of the picture by setting it as high as possible or defeating it entirely if that is supported.

    First step is to get your 2 equalizer settings done exactly as Wayne has described. Do not touch these again unless you move the sub (in which case the process will have to be repeated). The second step is to calibrate the overall level. Then your done. Unless you want to take this process to its glorious anal extreme and get a BFD to make a perfect deep bass response. The BFD gives you not just one filter to tweak but 24, and the frequencies can be set exactly, and the width of the filter is adjustable too.
     
  12. LanceJ

    LanceJ Producer

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    I think what the subwoofer's designers are saying is that because their sub only has so much amplifier power and woofer cone ability to work with, if you don't think you will be listening to material with frequencies lower than 30Hz, using the crossover to eliminate them will allow the sub to reproduce the frequencies you DO want to hear at louder levels AND with less distortion. The extremely low bass being discussed requires butt-loads of power and long woofer cone excursion rates, so why bother stressing everything out just for the isolated movie or CD that contains such wacky bass? So for me, tossing the sub-30Hz bass to gain cleaner bass everywhere else is a sensible compromise.

    I'm all for accuracy (read my recent posts on the receiver forum), but not at any cost. And really, how many movies & music actually contain that sub-30Hz stuff? Is there a site somewhere that lists the dvd's or CDs that do? I asked about this before and no one answered.

    LJ
     
  13. Brian L

    Brian L Cinematographer

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    Brian F has given you the correct sequence to follow.

    And I agree with what LanceJ is saying about Fletcher/Munson, and loudness, and all that, but that really speaks more to the overall topic of "reference level" and all that. And believe me, the concept of reference level is a separate subject for debate.

    I think in your case, you want to simply try your best to take down the worst peak that your sub is producing in your room. And FWIW, you can set the sub to any reasonable volume to do that.

    Once you have that part addressed, then you can move on to getting the relative channel levels right, which is where Lance's comment comes in to play.

    True reference level for Dolby Digital sources is 85 dB on each channel with test tones that are calibrated to be -20 dB relative to full scale. That equates to peaks of 105 dB with actual sound tracks.

    I am a guy that likes things loud, but listening to a movies at true reference in most normal rooms is insane.

    The most important thing to do is just make sure that the main channels are all equal. As Lance said, you should make the adjustments at a volume that is comfortable for you, your family, your room. etc.

    As for the sub, while you should start out having it match the mains, most users find that they will tweak the sub by ear to suit their personal preference, the particular sound track, etc.

    I promise that if you do this, no one will arrest you, and you will be much happier with the sound!

    BGL
     
  14. GregBe

    GregBe Second Unit

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    Thanks for the Help
     
  15. LanceJ

    LanceJ Producer

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    I think if a sub manufacturer came out with a model that included a system similar to Pioneer's MCACC, it would be a very popular seller.

    And why don't more subs have remote controls?

    The accurate calibration thing is the biggest reason I have avoided buying a subwoofer, but since a proper dvd-audio surround system requires one I have had to think about those brooding cubical boxes a lot more lately.

    LJ
     
  16. GregBe

    GregBe Second Unit

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    For what its worth Lance, the Cambridge Soundworks Sub that I have, has a control box that controls everything, and is seperate from the sub so you can place it with the rest of your components so you don't have to reach down to the sub to make adjustments. It also comes with a remote control for the volume function that I moved to my universal remote. I am very pleased.
     
  17. Brian L

    Brian L Cinematographer

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  18. LanceJ

    LanceJ Producer

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    Brian:

    Back in the 80s I realized I had come to the point that WAS all I was doing (fussing over numbers, equipment,etc) and my previously-fun audio hobby was no longer enjoyable because it had become filled with too many worries over inconsequential (to me) things.

    So I stopped the mental hand-wringing, and listening to music and watching movies became fun again, though I'll freely admit sometimes I still repeat a section of a CD track to hear how well a cymbal sounds or if the imaging sounds real. It still amazes me that a bunch of wires, silicon, magnets and plastic can put Geddy Lee and others practically in my living room. COOL!!!

    LJ
     
  19. LanceJ

    LanceJ Producer

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    Greg: Sounds like a neat piece of equipment. That's why I like things designed with Henry Kloss' influence--they always seem to have funky but useful features & don't cost an arm and a leg.

    BTW: did you ever get to hear that BassCube 12S subwoofer?

    LJ
     
  20. GregBe

    GregBe Second Unit

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    Lance,
    I never did listen to the basscube 12s because of its size. I am sort of restricted in my living room by size. I did own the 8S and auditioned the 10S as well. To my ears, the Newton series was leagues above the basscube stuff. The p500 that I wound up upgrading to sounded terrific, and the size was real small. It is about 13" in each direction, and has two 8" side firing woofers That coupled with control unit and the ability to do very limited equalization sold me on the unit. It lists for $800, but I was able to pick up an unused open box (customer returned it without plugging it in, because the finish was mahogony and the box say slate) for only $399. It may not be an SVS, but I am real happy.

    Greg
     

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