need help with SPL chart for my new sub

Discussion in 'Archived Threads 2001-2004' started by Ryan T, Mar 24, 2002.

  1. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    My church lowned me there Radio Shack Digital SPL meter today. I set it up about two feet off the floor on the edge of a table about two foot from where I sit. I have my receiver hooked up to my computer so I used the winISD signal generator. I did test tones from 12 Hz to 90 Hz. here are my results.

    Hz--------DB

    12--------52

    14--------57

    18--------59

    20--------60

    24--------60

    28--------61

    30--------63

    32--------62

    34--------63

    38--------63

    40--------63

    42--------63

    44--------63

    46--------63

    48--------63

    50--------63

    52--------63

    54--------63

    56--------62

    58--------62

    60--------60

    62--------60

    64--------60

    68--------63

    70--------64

    72--------64

    74--------64

    78--------63

    80--------63

    82--------63

    84--------64

    86--------64

    88--------64

    90--------64

    I thought the readings would be all over the place but they seem really flat, did I do something wrong? By the way the SPL meter was set to c weighting and fast response. The sub is a 230 L sealed tempest. The meter was 7 ft. away from the sub and I sit about 9 ft away from it.

    Ryan
     
  2. Patrick Sun

    Patrick Sun Studio Mogul

    Joined:
    Jun 30, 1999
    Messages:
    38,777
    Likes Received:
    492
    Trophy Points:
    9,110
    Usually you should use c-weighted, slow response. Did you already apply the correction values for the low end frequency readings?
     
  3. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    Why is the slow response better than fast?

     
  4. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    1
    Trophy Points:
    0
    That curve is outstanding. I would run it again louder though- in the 80 to 90 dB range.
     
  5. Patrick Sun

    Patrick Sun Studio Mogul

    Joined:
    Jun 30, 1999
    Messages:
    38,777
    Likes Received:
    492
    Trophy Points:
    9,110
    Are you using sine waves for that tone generator?

    The Radio Shack microphone isn't as sensitive down really low, so usually people apply correction values to the measured response.

    Slow response is used for this type of SPL measurement. I forget the specifics, but it is the preferable way of measuring SPL from speakers/subwoofers.

    Also, you might want to up the overall volume so that you are measuring roughly 75dB across the board. SPL readings in the 60's is too close to the bottom end of the SPL meter's range.
     
  6. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    I will run it agian at 70 to 80 db range tomorrow. I did not wan't to play it loud today because my sister was slepping. I'm not sure if the signal was a sine wave or not. I just went into winISD's signal generator and pulled up my sub project then selected the get frequincy from cusor option. my room is really small (14' x 10') so I think that might be why the bass is boosted so much in the lower range.

    Ryan
     
  7. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    I redid the SPL test today with my receiver at -40 db. The results seem much more like what I expected the first time.

    Corrected. All the ones with ? i'm not sure on. I did not see any correction values on the web page. So i just left them at what the SPL meter said.

    Hz db

    12--------70

    14--------64 ?

    16--------74

    18--------65 ?

    20--------79

    22--------65 ?

    24--------64 ?

    26--------70 ?

    28--------73 ?

    30--------84

    32--------81

    34--------82

    36--------82

    38--------81

    40--------83

    42--------81

    44--------81

    46--------83

    48--------85

    50--------86

    52--------84

    54--------83

    56--------83

    58--------74

    60--------72

    62--------73

    64--------73

    66--------75

    68--------81

    70--------82

    72--------83

    74--------84

    76--------83

    78--------82

    80--------84

    82--------82

    84--------83

    86--------83

    88--------82

    90--------81

    92--------81

    94--------81

    96--------80

    98--------80

    100-------76

    I just new the my first test numbers where to good to be true. the crossover starts at 100 Hz I think thats why there is a sudden drop then. There is a nasty drop from 86 Hz to 56 Hz. looks like I will be getting a BFD after all. I guess the F3 is between 30 and 28 Hz does that sound right? I do have the sub corner loaded. Later today I might check for max output, I'm just wondering where I should check at. I think maybe 29 Hz because that is close to the F3. I did not apply the correction values, could someone tell me how much I need to correct?
     
  8. Patrick Sun

    Patrick Sun Studio Mogul

    Joined:
    Jun 30, 1999
    Messages:
    38,777
    Likes Received:
    492
    Trophy Points:
    9,110
    Go to this page and use the correction values (interpolate if you have to since the list is for 1/3 octave tones).
     
  9. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    Thanks Patrick. I edited the other post because i did not want to retype all those numbers. Is there any values that need to get changed on all the ? readings or is the Radio Shack SPL meter accurate there?

    Ryan
     
  10. Patrick Sun

    Patrick Sun Studio Mogul

    Joined:
    Jun 30, 1999
    Messages:
    38,777
    Likes Received:
    492
    Trophy Points:
    9,110
    Interpolate the values.

    For 22Hz, +6.5

    For 24Hz, +5.5

    For 26Hz, +4.5

    For 28Hz, +4

    For 30Hz, +3.5
     
  11. Manuel Delaflor

    Manuel Delaflor Supporting Actor

    Joined:
    May 25, 2001
    Messages:
    657
    Likes Received:
    0
    Trophy Points:
    0
    Ryan

    Those look like normal results. Most people are unaware that the most difficult element to control in audio is the bass response. Those "valleys" should be room effects, if you can, play with the position of your sub until you get the flattest response.

    Now, regarding this, I doubt that the SPL meter is appropiate to measure below 30Hz. I know about the "correction values", but everybody seems to just take them as proven facts, which I highly doubt.
     
  12. Ryan T

    Ryan T Second Unit

    Joined:
    Sep 10, 2001
    Messages:
    406
    Likes Received:
    0
    Trophy Points:
    0
    Okey-Dokey. I just pasted the chart here with all the corrected values(I hope). Thanks for your help Patrick.

    Hz db

    12--------70

    14--------70

    16--------74

    18--------69

    20--------79

    22--------71

    24--------69

    26--------74

    28--------77

    30--------84

    32--------81

    34--------82

    36--------82

    38--------81

    40--------83

    42--------81

    44--------81

    46--------83

    48--------85

    50--------86

    52--------84

    54--------83

    56--------83

    58--------74

    60--------72

    62--------73

    64--------73

    66--------75

    68--------81

    70--------82

    72--------83

    74--------84

    76--------83

    78--------82

    80--------84

    82--------82

    84--------83

    86--------83

    88--------82

    90--------81

    92--------81

    94--------81

    96--------80

    98--------80

    100-------76

    Ryan
     
  13. brucek

    brucek Second Unit

    Joined:
    Dec 29, 1998
    Messages:
    335
    Likes Received:
    0
    Trophy Points:
    0
    Ryan,
    Generally, when you want to do a frequency response of a subwoofer, you will record readings from your listening position using 1/6 octave tones and a level around 85dBSPL.
    I have included a site URL below that you can download an Excel graph from that allows you to enter your raw 1/6 octave readings and it will automatically apply the appropriate Radio Shack meter correction values and produce a proper graph that will be logarithmic in scaling which is representative of the way humans hear sound.
    Scroll down on the site and click on Microsoft Excel workbook. Enter your 1/6 octave values into the RAW SPL column.
    http://www.snapbug.ws/bfd.htm
    brucek
     

Share This Page