Help with frquency and spl readings on Ref 30.

Discussion in 'Archived Threads 2001-2004' started by Steve Morgan, Nov 29, 2001.

  1. Steve Morgan

    Steve Morgan Second Unit

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    I know that there are 3 levels on the tone generator on the Ref 30 what should this be set on? -42, -30, I can't remember the other one.I am taking readings to set up my BFD. My thought is to take the readings of the Servo 15 then another reading of the SVs 20-39cs.Should I do this with the mains and surrounds off?It seems like I should leave these on because they will add to the response of the readings and when you play DVD's or music all channels are driven anyway. Here are my readings at -42dbs.on the Ref 30 Tone generator. I am crossed over at 70hz.

    Servo 15a

    HZ. SPL

    70 63

    68 60.5

    66 63

    64 68

    62 73

    60 78

    58 80.5

    56 82

    54 81.5

    52 75

    50 77

    48 73.5

    46 78.5

    44 82

    42 87

    40 88

    38 85.5

    36 84

    34 82

    32 81

    30 80

    28 79

    26 77

    24 72

    22 68

    20 68

    SVS 20-39cs

    70 67

    68 66

    66 77

    64 54

    62 67

    60 77

    58 80.5

    56 83

    54 84

    52 83

    50 82

    48 80.5

    46 78

    44 69

    42 64

    40 73

    38 75

    36 74

    34 71

    32 73

    30 71.5

    28 69.5

    26 65

    24 64

    22 57

    20 60.5

    Is there something I am not doing right or do these numbers look in the ball park.Should I take readings at -30dbs? Thanks for your help. Steve
     
  2. Steve Morgan

    Steve Morgan Second Unit

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    Come on Guys a little help!

    Steve
     
  3. John Kotches

    John Kotches Cinematographer

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    Steve,

    Sorry, I missed this post earlier today.

    -42dB and -30dB are vs. reference level, so this means (105 - 42) or 63dB and (105 - 30) or 75dB.

    Your numbers aren't that insane (really) and I am betting you have the subwoofer corner loaded based on the spread of the numbers.It looks like you've got a primary resonance at about 40Hz in your room (see how much higher this frequency is than everything else?).

    Also, if you're using the Radio Shack meter, don't forget it's notoriously inaccurate at the bottom end, so make sure you apply the appropriate corrections.

    It would be interesting to see you extend to the octave above the crossover (out to 140Hz as well).

    Regards,
     
  4. John Morris

    John Morris Guest

    Steve: Right or wrong, I do my subwoofer EQ with all the speakers driven. I want to correct what I actually hear during playback and not what each speaker is doing. As for me, I had a nasty hump at around 53Hz. It got much worse when I used dual subwoofers.
     
  5. BruceD

    BruceD Screenwriter

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    Steve,

    If you want to accurately adjust the room contributions of each sub, you should probably measure each sub independantly.

    When you apply Parametric EQ (cut peaks) at a specific frequency it may also influence (cut) higher frequency harmonic peaks. You should start at the lowest frequecy first.

    Measuring and adjusting each sub independantly takes into account their different locations and effects on room nodes.

    This also means it may be easier to identify which frequencies need to be cut with the parametric EQ and how wide (Q) the bandwidth of that cut needs to be.

    As the final measurement, you can measure with all speakers driven to fine tune the EQ adjustment.

    BruceD
     
  6. Wayne A. Pflughaupt

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    John, you know I love you, but I have to part ways with you on this one. [​IMG] Steve only has a sub EQ. Running the mains for the test and you might end up EQing the subs in the crossover range to compensate for deficiencies in the mains have in that area. Not the best of ideas. Not to mention cancellation at specific distance-related frequencies. Did you notice that huge, narrow hole the SVS has at 54hz? [​IMG]
    Steve,
    I trust you took these readings independently?
    I’ve been telling you that non-matching subs is a bad idea, and non-matching subs in two locations is even worse. Now you have the numbers to prove it. Consider the following:
    • At 70Hz the SVS is 4dB higher than the Servo 15.
    • At 62Hz the Servo is 6dB higher.
    • At 50Hz the SVS is 5dB higher.
    • At 40hz the Servo is 15dB higher.
    And so on. Neither sub is consistently higher than the other; they see-saw back and forth above 46Hz. Not good.
    The goal of EQing is to get sooth response from both subs and get them so that frequency by frequency, there is no more than 1-2dB variation between the two. (In other words, the numbers you now have for 58, 56 and 60Hz are ideal.) It should be clear, Steve, that EQing both these subs, especially the way you have them placed, is going to be very difficult.
    I also recommended putting both subs in the corner for the best performance (maximum output and lowest extension). Again, now you have the numbers to prove it:
    • From the readings, I can tell that the Servo is the sub in the corner. Notice the SVS (the one not in the corner) peaks at a relatively high 54Hz. The reading at 27Hz (one octave down) shows that response from 54Hz is falling at a rate of 14dB/octave.
    • Notice the Servo peaks almost half an octave lower, at 40Hz. However, response at 20Hz (one octave down) shows that response from 40hz is falling at a steep 20dB/octave. This is a function of your very large room. It will be difficult to get much below 30Hz with these subs in this room.
    • Notice that the sub in the corner (the Servo) has at its peak reading (at 40hz) 4dB more SPL than the SVS at its peak (54Hz).
    • The readings show that the sub in the corner (the Servo) has greater output at 19 of 26 (or about 66%) selected frequencies.
    • At 46hz and below, the Servo’s average output is 10dB higher than the SVS (79dB vs. 69dB).
    I suggest putting the Servo in the corner and taking new readings. Since its peak was only 4dB down from the Servo in the corner, and its response falls slower, that tells me it might be the better performer of the two (provided there was no discrepancy with the gain settings, that is). You definitely want the stronger sub in the corner.
    The good news is, response is overall very smooth for both subs. I’m not seeing the ragged peaks and dips that some rooms exhibit. With only a few specific places, response gradually rises from 70Hz to peak and smoothly falls below that point.
    Regards,
    Wayne A. Pflughaupt
     
  7. Steve Morgan

    Steve Morgan Second Unit

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    Wayne, The servo is about 2/3's along the back wall, the SVS is in the corner.The Servo is about 2 feet from my listening position.I will try and put both in the corner and see what this does.When I do this should I take the readings of the subs independently or together? As they are positioned now here are the readings when they are both playing:

    HZ SPL

    70 75.5

    68 78

    66 78.5

    64 80

    62 82

    60 85

    58 87

    56 87

    54 86

    52 83

    50 80

    48 77

    46 69

    44 69

    42 79

    40 79

    38 80

    36 77

    34 71

    32 73

    30 74

    28 72

    26 66

    24 64

    22 56

    20 67

    I am ordering the ETF software and hopefully this will help in placing the subs but I still have the SAF to consider.If I corner laod what is the best corner?The corner where the longest walls meet?Thanks Guys.This is going to be one hell of a job but with your help I think it can be done.Do I need to add another sub? One for the center and surrounds,one for the mains and one for LFE.
     
  8. John Morris

    John Morris Guest

    Wayne: Now you have me thinking that maybe I am doing it wrong too? I have a single subwoofer (SVS Ultra) that sits in the corner behind and slightly to the left of my left front speaker. I run my front three channels full range and my rear four speakers as small. The pre/pro allows me to set the fronts as large and also to send sub 60Hz frequencies to my Subwoofer. Since my fronts extend spec wise down to 30Hz, I have some overlap in the frequencies between 40-60Hz. That is why I have been EQing(only my subwoofer) for those frequency bumps that I can find when driving all my speakers.

    Should I do it some other way?

    Then again, a big brown truck just dropped off a new ICBM for me to play with. I guess that's gonna change everything.?
     
  9. Steve Morgan

    Steve Morgan Second Unit

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    Want to make clear these numbers are without corrections for the RS spl meter.

    Steve
     
  10. Steve Morgan

    Steve Morgan Second Unit

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    bump
     
  11. Wayne A. Pflughaupt

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