Subwoofer calibration

Discussion in 'Speakers' started by TonyWright, Sep 30, 2004.

  1. TonyWright

    TonyWright Second Unit

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    I am trying to calibrate an SVS PB2-ISD. This is the first sub I have ever had so I am struggling with the calibration.

    I have the Avia disc, and I calibrated it to 80db at reference taking into account the required adjestment for a Radio Shack SPL meter.

    I guess I just expected to get slammed in the chest.

    Don't get me wrong, the sub is awesome, but I am wondering if I have misconfigured it.


    I have it set to 20Hz with one port plug in. For movies I have it running 2db hot. The gain is set at about 1/3.


    One thing I noticed in using the Avia disc was during test that starts at about 200Hz (or something of the like). The sub seemed to roll of at around 40Hz. I made some crossover adjustments and then was able to hear it down to about 28Hz. The volume seemed to really drop off below 30Hz. I kind of expected to feel it all the way down to 20Hz and below.


    Does anyone have any suggestions?


    I would really appreciate any help.

    Thanks in advance.


    Tony
     
  2. Kevin C Brown

    Kevin C Brown Producer

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    Tony- You got it! [​IMG]

    You have your sub in a corner? C weighting, slow response for the meter? Also, are you using the set of Avia test tones that toggle between left front speaker then sub, center then sub, etc? Not the sweeps. (I always use left front to sub, because my sub is in that corner of the room.)

    How is the BM setup in your receiver or pre/pro? (All small, sub on, is a good place to start.)

    Be aware, that with a properly calibrated sub, you aren't really supposed to "hear it". It more "supports" what's coming out of the rest of your speakers. I.e., after you do have it calibrated, pop in a bass test movie like Matrix II or III, U-571, any LOTR, Underworld, etc. *Then* see if you don't get kicked in the chest. [​IMG]

    You probably know that the accuracy of the Radio SHack meter really drops off by when you get to 20 Hz...

    Shoot, I think I remember that Ed JM has a good sub setup troubleshooting guide he posted a while back.
     
  3. TonyWright

    TonyWright Second Unit

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    Kevin,

    Yeah it finally showed up. I have the following settings configured for my sub:

    phase is at 0
    gain is at 1/3
    runs at 2db hot

    The sub is no currently in a corner. WAF issue there. I may be able to try it out in a corner tomorrow. I'll hopefully gain a bit more there.

    The receiver is crossed over at 100Hz for the mains the center and the surrounds. My receiver allows me to set crossover points for all of my speaker groups.

    I tried calibrating using all of the Avia tests. Maybe that was my problem. I'll try again with just the tests you mentioned.



    I'll do a search for that post you mentioned about Edward J M's sub setup guide.


    Thanks!

    Tony
     
  4. Michael Hedman

    Michael Hedman Auditioning

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    Tony,

    It could be that you're having acoustic issues with your room. It's pretty common to have dips and peaks in certain frequency ranges. Of course this would show as a sudden drop in SPL on your meter. If that is the case try moving the sub around. If that doesn't help you probably need to get a parametric equalizer like the Behringer feedback destroyer.
     
  5. Ryan Tsang

    Ryan Tsang Second Unit

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    The Behringer is a great piece of equipment (I have one)but it should be used to tame peaks. Don't get the idea that you can add +10db to a null cuz you won't do a thing (other than adding distortion/overload).

    Tony: When your prettier half is gone, try putting the sub in the listening spot and crawl around to different places in your room to be aware of nulls/peaks in your room. (you are simply swapping places between sub and you) Serves two purposes: 1) you can ID if your listening spot is in a null or not 2) find potential sub placements
     
  6. Edward J M

    Edward J M Cinematographer

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    There are common set-up errors that could be causing some problems. Double check all of these things before you try to recalibrate:

    In the AVR:

    1) All speakers set to small.
    2) Crossover set to 80 Hz.
    3) Sub set to on/yes.
    4) Subwoofer Remix or LFE + Mains set to off/no.
    5) Dolby Dynamic Range Compression Circuit set to off/no.
    6) LFE (0.1) channel level set to maximum (i.e., unattenuated) value (if the AVR has the capability).
    7) THX (or any other) bass limiter circuits set to off/no.
    8) Subwoofer channel level to -5.

    In the DVD player:

    1) Output set to bitstream (digital output via the digital coax).
    2) Dolby Dynamic Range Compression Circuit set to off/no.

    On the subwoofer:

    1) PB2 to all ports open (we can try 20 Hz tune later).
    2) Tune switch to 25 Hz.
    3) Crossover switch to off.
    4) Set the phase to 0 degrees initially unless you have the capability to evaluate the FR of the system.

    Avia is true Dolby Digital and uses the speaker channels for sub calibration and therefore allows the speaker channel in question to contribute bass to the subwoofer tone.

    I have found that the amount of bass each speaker contributes to the sub tone is highly dependent on its room location, its inherent bass capabilities, its proximity to the subwoofer, and the xo you have selected.

    For example, the left main channel in my system is several dB higher than any other channel on the subwoofer tone. If I selected the left main channel for sub calibration, it would result in undercalibration of the sub.

    The best way is to run the Avia sub test tone for each speaker channel and note the results. Pick the one that seems most representative of the average and go with it for final sub calibration.

    Also, a good way to evalaute the effect of the phase control when using Avia is to run the sub calibration tone for the speaker closest to the subwoofer and try the phase at 0 and then at 180. Observes what happens on the SPL meter. Usually one setting will be considerably higher than the other, indicating the subwoofer and the nearest speaker are the most "in phase" at that phase setting. This may not be completely desireable from a smooth FR standpoint, but it can help you understand the effect of the phase control, since Avia does rely on redirected bass.

    Keep your sub level in the pre/pro around -5 to minimize pre-out distortion levels, and adjust the sub volume at the PB2.

    While bass tastes will vary, most prefer the sub 2-3 dB hot for HT, and flat for music. Because it is C-weighted, the RS sound meter reads about 2 dB LOW on the typical subwoofer rumble tone.

    So an average reading of 85-86 dB on the meter is about 87-88 dB in reality - or 2-3 dB "hot". This would be a good starting point for HT. If it's not "hot enough", crank it up another 2-3 dB; the PB2 can take it.

    An average reading of 83-84 dB on the meter is about 85-86 dB in reality - or about "flat". This would be a good starting point for music.

    The above assumes you are using 85 dB with Avia to calibrate to Reference Level. You can use a lower level of course (like 80 dB as you stated above). I just find using 85 dB and Master Volume to 0.0 easiest.

    If you retune the PB2 to 20 Hz, bump the sub level in the pre/pro 2-3 dB (over the 25 Hz tune) to compensate for the loss in sensitivity.

    Regards,

    Ed
     
  7. Jeff Gatie

    Jeff Gatie Lead Actor

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    All advice given above is golden. I'd like to add that when upgrading to a quality sub such as an SVS, some may find it lacks the "punch" or "slam" they are used to. I do not know what you had for a sub before, but some lesser subs try to make up for a lack of frequency response by boosting output in the 40-50Hz spectrum. This is what we hear as "boom" and it sounds great to an uninitiated ear. It is also inaccurate bass. The FR of the SVS is wide and flat, with no boost to any one part of the spectrum. Although a boosted "boom-boom" every time a 40-50Hz sound comes across can make it seem like the bass is slamming you in the chest, it is nothing compared to a true 20Hz tone played at or near reference. Like Kevin said, a properly calibrated sub should not overpower your system, it should play when it is called for and what is called for, nothing else. Give your sub a chance, listen for a few weeks and I guarantee you'll start hearing things the way they should be and never go back to "booming" bass.
     
  8. TonyWright

    TonyWright Second Unit

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    Thanks to all for the replies! This is my first sub ever, so I guess I am just not yet used to what a sub should sound like.



    Edward,

    I use a H/K AVR630. I wonder if you might be familiar with this receiver.

    It allows me to set individual crossover settings for each of 4 speaker groups including the mains, center, surround and rear surrounds. Then it also has a setting where you are to match the sub with one of those groups. The manual recommends mathcing it with the group that is set closest to 120 Hz.

    Could this be one of the settings you recommended be disabled in your previous post?

    Incidentally I believe I have all of my speakers crossed over at 100Hz. I will change that to 80Hz this evening.


    Sheesh, I never knew setting a sub up could be this complicated. Not to worry though, I love a good challenge. [​IMG]

    Tony
     
  9. TonyWright

    TonyWright Second Unit

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    By the way Edward, your list of settings to check is outstanding. Thanks a bunch for taking the time to list all of those for me.

    Tony
     
  10. Aaron_Mum

    Aaron_Mum Stunt Coordinator

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    Hey Tony:

    I am a relative sub rookie as well and I find that the "calibrated" level for the sub is a lot quieter than I would have expected.

    When you run that baby for the first time you want to know it can flex the walls of your house bringing tears of joy to your eyes. The calibrated level is much lower, blending better with everything. Just turn up the gain when you want to get kicked in the chest! If turning up the gain doesn't help then you know it is a problem with your room accoustics.

    Thanks Edward for taking the time to post all that info. It helps us out tons!
     
  11. Edward J M

    Edward J M Cinematographer

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    Normally, if a speaker channel is set to small, the high pass frequency for the speaker, and the low pass frequency for the subwoofer (for the redirected bass), is the same. Ideally, the filter slopes would be the same too (but often they are not).

    So if you set your center channel xo to say 100 Hz, then the pre/pro should automatically redirect any center channel bass below 100 Hz to the subwoofer. And so forth for all the other speaker channels.

    You can certainly experiment with setting a different xo for each speaker according to its inherent bass capabilities, but it's not necessary for good performance. On the contrary, it might actually create more problems than it solves.

    Some pre/pros even allow the user to vary the low pass frequency for the LFE channel.

    What speakers are you running in each channel, and what is the rated extension of each (the -3 dB bass extension rating), and are they vented or acoustic suspension?
     
  12. TonyWright

    TonyWright Second Unit

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    I am running Swan 6.1 for my mains. They are advertised to roll off at around 35Hz. The Swan C3 is my center and it rolls off at around 65Hz. The I use the Swan R3's as my surrounds. They roll off at 65Hz as well.

    I am not sure what you mean by -3db bass extension rating. Where could I locate this information?


    I also have a question about tone. I have a setting for tone with my receiver that allows me to adjust treble and bass from a -10 to +10 value each. I currently have them both set to 0. I think the tone setting is still active though and could be adding information to the signal path. Should I totally diable the tone setting?


    Thanks again for all of your help.


    Tony
     
  13. TonyWright

    TonyWright Second Unit

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    What is a reasonably acceptable gain level for a PB2-ISD? I realize this will change from room to room, but are there people out there that have to run these with the gain cranked way up?

    Currently I have mine set to 1/3.


    Tony
     
  14. Mort Corey

    Mort Corey Supporting Actor

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    All great advice Tony [​IMG] I just replaced a ten year old Klipsch SW10 with a PC Ultra and was unimpressed at first. It wasn't the slam/boom I was familiar with so it seemed weak.....this was of course by doing exactly what you're NOT supposed to do...just plugging it in and cranking it up without calibration (hey, sometimes you get excited) After calibrating, first with the receiver test tones then with Avia, it still seemed weak. I plopped in a Master and Commander DVD and the lights finally went on...AHA, so that's what everybody talks about [​IMG] I still want to fine tune things a tad, but I think I'm really close.

    At present, I've got some older, large, floor standing Klipsch mains that go down into the 30hz range and I'm not sure whether I like them large or small best. At present I'm leaning towards large with my Denon 3805 set to LFE + Main. Playing the Avia tones that span the frequency I can almost see the tone running across the room from the main to the sub and there is not hump or cut out, just a smooth progression of sound....guess I'll just have to keep playing with stuff.

    Anyway, once you get close I can guaranty you'll know it...

    Mort
     
  15. TonyWright

    TonyWright Second Unit

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    Thanks Mort,

    I'm sure it's just a bad calibration. I just need to get every thing set properly.


    Tony
     
  16. TonyWright

    TonyWright Second Unit

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    Edward,

    Sorry I forgot to mention before, the mains are ported in the front, but the center and the surrounds are sealed cabinet designs.


    Sorry about that...


    Tony
     
  17. paul clipsel

    paul clipsel Stunt Coordinator

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    That is what I found when I sold off my old CHT15. I was so used to hearing that boom I thought my new Hsu was not working properly. I just had to get used to flatter frequency response, I would say this could be what your hearing. A good sub makes a lot of difference.

    PC
     
  18. Edward J M

    Edward J M Cinematographer

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    Some pre/pros disable the EQ circuit for DD and DTS playback; check that. Regardless, I have never found the need to EQ any DD or DTS source. If you are going to use EQ for music, you might want to look into a multi band unit instead of the basic bass/treble tone controls.
     
  19. TonyWright

    TonyWright Second Unit

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    Many thanks Edward!

    I have my work cut out for me tonight. The good part is that I have as much fun setting everything up as I do listening to it.


    I'll post my results as soon as I have re-calibrated.


    Thanks again!

    Tony
     
  20. TonyWright

    TonyWright Second Unit

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    Thanks to all who have replied here. As usual, this community comes through when someone needs a little direction.


    Tony
     

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