Measuring Frequency in Subs

Discussion in 'Speakers & Subwoofers' started by Bill*L, Aug 5, 2004.

  1. Bill*L

    Bill*L Extra

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    Is there a tool out there that will provide the different frequencies so that I can tell how low my sub is going? I have used the calibration DVD from Sound and Vision to adjust the db levels but am not sure how low my sub will actually go.
     
  2. Rob Kramer

    Rob Kramer Second Unit

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    I know 'DVD Video Essentials' has test tones from 5hz on up. Im sure Avia does too. I am surprised that the S&D disc does not.
     
  3. Bill*L

    Bill*L Extra

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    I do have access to the Video Esentials as well but I did not see anything that told you what frequency was actually being played at that moment. Maybe I just missed it. Does it give some sort of indication what freq is being played or do I need some special sound meter?
     
  4. Wayne A. Pflughaupt

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    I think the BFD Comprehensive Set-Up Guide web page has a link to some test tones you can download. Burn them to a CD and you’re in business.

    Regards,
    Wayne A. Pflughaupt
     
  5. Brad_See

    Brad_See Stunt Coordinator

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    Bill,

    Find some source to play the low tones (someone posted a source for mp3 low frequency sweeps here last week or so...do a search) and use a sound meter to measure at what frequencies the SPL starts to decrease and how much. That will give you an indication of how low your sub goes.

    brad cook
     
  6. Kevin C Brown

    Kevin C Brown Producer

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  7. Bill*L

    Bill*L Extra

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    Thanks everyone for the suggestions.
     
  8. Bill Blank

    Bill Blank Stunt Coordinator

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    I use Rives Audio Test CD2. It has 1/3 octave tones down to 20Hz that are already corrected for the errors in the Radio Shack sound level meter.

    In order to get a true reference of how low your sub is going it'a level must first be matched to that of you mains using pink/white noise. You must then adjust phase correctly and find a reference setting for your receiver/pre-pro volume. Most, including myself, use the 1kHz tone as a reference @ 80dB. The reason for this is that it's about the midway point of the frequency spectrum and the RS meter is dead accurate at this setting.

    After you've done that you're ready to measure your sub's performance.

    Prior to using the Rives disc I used Stereophile's Test CD2. The key is finding a disc with 1/3 octave tones. The nice thing about the Rives disc compared to the Stereophile disc, other than the fact that it's tones are corrected for the RS meter, is that it uses separate tracks for each tone where the Stereophile indexes them and only splits tracks for lows/mids/highs.

    Good Luck!
    Bill
     
  9. Rob Kramer

    Rob Kramer Second Unit

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    The freq being played is clearly displayed on the screen. This is how I calibrate my Spectrum Lab waterfalls.
     
  10. Eric:F

    Eric:F Stunt Coordinator

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    hi bill blank,
    as i understand your post, you use the 1khz tone and play it through the main speakers (left/right) until it reads 80dbs on the rs meter. you then see what volume level your pre/pro is at...
    why is that relevant? as long as all the speakers and sub are balanced, the volume level is what it is.
    can you clarify?
    thanks,
    eric
    also, i too want to use one bfd to eq two subs independently. can someone chime in on the proper bfd set up? the manual is a bit vague.
    thanks,
    e.
     
  11. Bill Blank

    Bill Blank Stunt Coordinator

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    Eric,

    The reason for simply noting the volume setting on your pre/pro is so that you know, should you ever want to come back to testing, immediately what frequency to go to. It also helps if you make changes to your equipment, speaker placement, or listener location to see what a difference if any it might have made. I've tweaked all three in the past few months and where my volume used to be at 53 to get to 80dB @ 1kHz it now only needs to go to 48. It's not absolutely necessary but I find it helpful.

    The reason you must establish a reference is so that you have something to base your results off of when trying to determine how low your sub is playing and how well.

    The decible level you choose for your reference is up to you though most pick 80dB because it's not too loud and is sensitive enough for an accurate reading. I wouldn't recommend using much lower than 70dB though.

    The same goes for the frequency you choose for your reference. You want to pick something in the middle of the frequency range and preferably one where the RS is accurate without corrections. 1khz is the common frequency though Rives cautions that if your speaker's crossover happens to be at that frequency you should pick something slightly higher.

    A reference will give you a point by which all other frequencies are measured. While it may be nice to know your sub plays down to 20Hz, you really don't know much until you find out whether that's +3dB (83dB if using 80dB as your reference) or -25dB (55dB if 80's your reference).

    Bill
     

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