SVS subwoofer FR measurment / calibration question

Discussion in 'Archived Threads 2001-2004' started by Troy_K, Feb 13, 2002.

  1. Troy_K

    Troy_K Stunt Coordinator

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    I'm trying to determine the FR of my subwoofer's output to see if some EQing would be beneficial for me. I am confused on a couple issues, though.

    First, does anybody know of a Doby Digital or DTS formated test cd/dvd that may be available. I have a stereo bass mechanics test disc.

    Should I measure sub FR in stereo mode or pro-logic? It seems I get much different sub response between these modes. I run all my speakers small, and my Denon has low pass at 80 hz. My svs is powered by a Kenwood 175 wpc amp.

    My other question is to how loud should I take my measurements. My CD has a female voice that tells the FR in 5 hz increments (actually quite helpful). But if I have the volume up high to measure my sub, the voice is very loud!!! It's painful.

    Should I run in stereo, and turn speaker A off (then I get sub only)? I'm not sure if there is a change to output to sub when I do this though. There might be.

    Thanks for your thoughtful answers. I think something sounds a bit missing from my SVS experience, and I wanted to make sure I am measuring FR correctly before looking into EQing.
     
  2. Wayne A. Pflughaupt

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    Troy,

    You don’t need a DTS or DD disc to test for sub response. Your test disc will be fine, as long as it has frequencies from at least 20Hz to 100Hz.

    As you have seen, thing’s just aren’t right when you use Dolby Pro-Logic for this. DPL is designed to decode a two-channel matrixed signal. Since frequency test tones are mono, use standard two-channel mode.

    Take readings first with the sub only. After EQing, then turn on the L/R mains, to check how they blend with the sub.

    As for level, just make sure your lowest readings are at least 65dB. If levels get much lower than that you risk having ambient room noise corrupt your readings.

    Regards,

    Wayne A. Pflughaupt
     
  3. Doug Drake

    Doug Drake Stunt Coordinator

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    I might also suggest you run your Denon in Direct mode, which will bypass ANY possible eq affects from Stereo...
    Doug
     
  4. Troy_K

    Troy_K Stunt Coordinator

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    Thanks Wayne.

    I took some measurements via that method...unfortunate results. Everything was going great until I got to 50 hz, and things then quickly went up, and then down, down, down until I bottomed out at 70 hz. Take a look..

    corrected values:

    16hz - 81db

    20-89

    25-87

    31.5-90

    35-86

    40-86.5

    45-88.5

    50-92.5

    55-93.5***

    60-92

    63-89.5

    65-85

    70-76****

    75-81

    80-86

    85-87

    90-83

    95-85

    As you can see a peak of 93.5 and a valley of 76 seem very unacceptable. I'm not sure the greatest of EQs can fix this. What do you all think? I'm not very satisfied with my mid bass performance during music, and I guess this helps explain why. Could it be the crossover in my Denon's bass management, or do I have to get a new Sub amp and EQ?

    Oh yea, this is a 20-39+

    Thanks,

    Troy
     
  5. Troy_K

    Troy_K Stunt Coordinator

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    I think I will try the following. Let me know if this is a good idea:

    Since my main speakers are spec rated to 30 hz, I was thinking of turning off the sub completely, and taking some spl measurements with the same bass tones between 45-80 hz and plot them agains the FR of my subwoofer. IF I get the same DIP it should be safe to assume the problem is in my room. If it is flat, the problem may be in the sub crossover, sub, or sub amp. Is this correct thinking? Of course, this is all assuming my Mains have a flat FR in this area.

    Troy
     
  6. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    The problem is the room, and the solution is the BFD.
     
  7. Greg_R

    Greg_R Screenwriter

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    In addition to the EQ, I would experiment with alternative sub placement options. To fix the loud voice issue, turn up your sub volume and decrease overall system volume (you can readjust the levels when you're done EQing the sub).
     
  8. Ranga

    Ranga Stunt Coordinator

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    Troy

    I have a similar problem.. bass peaks at 100HZ and 50Hz. My speakers go down to 55Hz and I use an SVS 25-31PC. What I found was that my left speaker (with and without sub) had even readings, but my right speaker had peaks at 100Hz and 50Hz contributing to the system's bass peaks. My right speaker is close to the side wall while the left has no wall.

    I am not sure if a EQ can be used to fix this. I may have to use some room treatment on the right.

    Ranga
     
  9. Troy_K

    Troy_K Stunt Coordinator

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    I turned off the sub, and tested as I mentioned above. Interestingly, I found that I had a relatively flat FR (+/- 3 db), especially in the trouble regions that I had with just the sub. What does this mean?

    My sub is placed in the corner just behind my right front tower. I really have no other place to put it. I could put it behind the Left tower, but then it won't be corner loaded anymore, which will result in overall depressed DBs, right?

    Thanks,

    Troy
     

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