Help adjusting sub crossover and volume level??

Discussion in 'Archived Threads 2001-2004' started by John Tyrone, Oct 22, 2001.

  1. John Tyrone

    John Tyrone Agent

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    I'm wondering where do I put my crossover level for the sub? I've got all my speakers set to small. And how about the volume level? Do I need a spl meter to get it to a certain db?
    John
     
  2. Benny G

    Benny G Second Unit

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    Others might disagree, but I think it's best to just experiment and decide what YOU like the most.
     
  3. Edwin-S

    Edwin-S Lead Actor
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    Getting an SPL meter would be a good idea. It would allow you to set the level of all your speakers L,C,R,RR,LR to the same DB level. You can also use it to set the sub; generally at the same level as the rest of your speakers or a couple of DB higher. It would depend on your personal preference. The meter would be a lot easier than trying to set everything by ear. Try reading some of the threads regarding SVS subs there is a lot of information about setting subs and check out the their website. They have a page describing using an SPL meter for setting sub levels. It will be one of the most useful and inexpensive pieces of equipment for calibration that you can buy.
     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    John, seems you're just getting started with subwoofers. Basically you're trying to achieve a flat frequency response in the overall system all the way from the super low frequencies reproduced by the subwoofer to the mid bass frequenceies reproduced by your main speakers.
    It's easiest to conceptualize what you are doing if you thing of the frequency response as a graph with low frequencies on the left and higher frequencies on the right. If you then plot the amount of sound vs frequency you'll end up with a nearly flat curve (no variation in loudness) as frequency changes. Obvously at some point, the system begins to shift sound reproduction responsibility from the mains to the subwoofer. That's the function of the crossover.
    If you want any hope of doing it right, you'll get a sound level meter and a test signal source such as a calibration disc. Those two things working together give you a way of measuring the system response as you make adjustments.
    The three controls you have to work with are crossover frequency, subwoofer phase, and subwoofer volume. I'll take them in turn. I'm sure others will be able to give further hints and details. By no means do I represent this as comprehensive.
    First lets look at crosssover frequency. That's basically the frequency at which a crossover sends half the sound to the subwoofer and the half to the mains. The higher you set the crossover frequency, the higher the frequencies you send to the sub. On most modern receivers, the subwoofer output has already been "crossed over" in the receiver. Typically this is at 80 or 100 Hz. That isn't a brick wall above and below which everything goes to one speaker vs the other, but there is a gradual blending from one to the other. Some receivers let you adjust the crossover frequency. Most don't.
    The thing you typically don't want to see happen is to have two crossovers working in series. Some subwoofers (particularly power ones) have an adjustable crossover frequency. If you set that to its maximal (or out of circuit) setting, you eliminate it and let just he crossover in the receiver do the work. Otherwise, you potentially have the receiver's crossover passing below 80 Hz to the sub, but he sub's crossover set too low (say 40 Hz). That would mean that between 40 and 80 Hz, the sound is going nowhere. The idea is you don't want a hole in coverage.
    In a system with a single adjustable crossover in the receiver, you vary it up and down to find the point which hands off between the mains and subs most smoothly. You can do that by watching the SPL meter reading while playing sweeps, or warbles.
    We'll take a few paragraphs to explain a sweep. A sweep is a signal which varies in frequency. In an ideal system, the measured SPL would remain constant as the freq varies. Conceptually, you'd plot the freq response of the mains alone. The plot the freq response of the sub alone. You'll see that the mains drop off at the lower end of freq and the sub drops off at the higher end of its range. The crossover freq is set so it is at the point at which both mains and sub are about equally adept (where the two curves cross).
    Well we deal non-ideal situations in actual rooms because room modes cause the low freq response to swing up and down widly with frequency. You have to average out those peaks and valleys as the sweeps go by. Another way to look at this is with warbles, a signal which wavers up and down in freq as it goes down in overall freq. The warbles up and down make peaks and valleys appear as SPL swings up and down. Again you try to make the peaks and valleys as small as possible.
    Another way to get around the room caused peaks and valleys distorting measurements is to use test signals with a wider bandwidth. That's what are supplied on calib discs like AVIA for setting subwoofer level. The wider freq content helps hide the peaks and valleys that can confuse your SPL measurements.
    That's getting into more complex explanation than I have time or patience to do. Actually, the most efficient way to do it is with a calibrated mic and the software from www.etfacoustics.com, but that's more than I'd want a newbie to attempt. I'll leave it to others to flesh things out.
    Here's the quick and dirty way. Get AVIA and use the subwoofer test signals. The instruction are on the disc. There are specific tests for setting subwoofer level, phase and crossover frequency on the disc. You'll also want an SPL meter.
    Set your subwoofer crossover to its max freq or out of circuit setting. Let the receiver's crossover do the work.
    Next set the subwoofer phase (I'm assuming you've already set subwoofer distance in your receiver). The phase control is to time align the sub and mains throughout the crossover freq range. Remember that there isn't an abrupt handover from mains to sub. The handover is over a band of frequencies. The usual way to do this is play a signal which spans the crossover range and adjust phase until all those frequencies are well reproduced (both high and low). Have an assistant adjust phase on the sub as you listen at your seating position. Set phase so the subwoofer phase test in AVIA sounds the fullest range in frequency. It should be neither boomy nor high pitch. If you don't have an assistant place the SPL meter at your listening position and carefully watch the needle as you adjust phase. When phase is correct, the sounds of the sub and mains maximally reinforce each other and the SPL meter will read maximally. This works because the AVIA subwoofer phase test signals are "noise" which covers the range at which most systems cross over."
    Finally, you get to set the intensity of the sub so frequecies reproduced by the sub are matched to those in the mains. AVIA provides subwoofer level tests which have a high freq noise (reproduced by the mains) and a low freq noise (reproduced by the sub). Both portions of the noise are recorded to be at the same loudness. The SPL meter is used to measure the reading. You adjust the subwoofer level to make its level match that of the mains. (Actually, that leaves it about 3 dB louder than the mains, but I'll leave those details to someone else as my fingers are getting tired).
    And yes, leave your mains set to "small" There are very very few mains which work as well as the sub for reproducing low bass. Definitely go read the John Kotches article http://www.hometheaterhifi.com/volum...pril-2000.html and you should do some more searches here. There have been a lot of threads on this and related topics.
    ------------------
    Guy Kuo
    www.ovationsw.com
    Ovation Software, the Home of AVIA DVD
     
  5. Karim Nogas

    Karim Nogas Stunt Coordinator

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    Thanks for taking the time to share your knowledge Guy. That was a very helpful response.
     
  6. Gerard Martin

    Gerard Martin Second Unit

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    Guy
    I have to second that, your
    response should be required
    reading for anyone wishing to set
    up a sub correctly. Thanks again.
    ------------------
    Jerry
     
  7. John Tyrone

    John Tyrone Agent

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    Thank You Guy, that has been very informative. I have turned my crossover all the way up. I just got Avia and need to head to Radio Shack to get the spl meter. My phase has two settings: normal and reverse, it's on normal for now, and the volume is about 1/3 up.
    The strange thing is my living room has hardwood floors and is also built on a crawlspace, so while playing Jurrasic Park during the t-rex scene you can really feel the bass in your stomach and I'm wondering if the room structure is a good thing or bad thing??
    John
     
  8. Guy Kuo

    Guy Kuo Supporting Actor

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    I'm happy it was helpful despite being riddled with tons of late night typos and low cohesion.
     
  9. Sean Conklin

    Sean Conklin Screenwriter

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    Guy, your the MAN, you have some of the most informative and thorough post's I've ever read! [​IMG]
    ------------------
    Sean
    "I was thinking of the immortal words of Socrates who said.......I drank what?"
     
  10. Wayne A. Pflughaupt

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    Yes, great post, Guy.
    It should be noted, however, that the ultimate goal is not flat response. Flat room response sounds "thin" and is not pleasing to the ear. Manufacturers or high-quality equalizers, like AudioControl and Ashly, recommend that the EQ target is 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.
    Regards,
    Wayne A. Pflughaupt
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    My Equipment List
     

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