recommend calibration tools besides spl meter?

Discussion in 'Home Theater Projects' started by JohnnyN, Feb 9, 2004.

  1. JohnnyN

    JohnnyN Stunt Coordinator

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    Anybody here use anything besides a calibration disc and an SPL meter? For the cost of some of these measuring and calibration devices, I know I'd be much better off just hiring a professional to make my room acoustically and sonically great, but I'm just curious what the tweakers and diyers do besides using the SPL meter?
     
  2. Garrett Lundy

    Garrett Lundy Producer

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    measuring tape, string, protractor, & compass. Can't have speakers too perfectly placed.[​IMG]

    I actually know someone who uses Feng Shui to promote better energy for his HT. This is probably optional however.
     
  3. PaulT

    PaulT Supporting Actor

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    Cheap laser pointer to place on top of (or tape to the side of at tweeter level) the speakers to angle them towards the listening area.
     
  4. Ted Lee

    Ted Lee Lead Actor

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    how expensive do you think this stuff is? the spl is about 40 bucks, another 40 for the calibration dvd ... and you're 75-percent there.

    heck, i haven't even used a laser pointer...that's just excessive... [​IMG]
     
  5. PaulT

    PaulT Supporting Actor

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    I'm no good with string......[​IMG]
     
  6. Bob McElfresh

    Bob McElfresh Producer

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    Actually, a cheap laser pointer is very nice. You can even get laser-levels that work better for about $30.

    Try one on your speakers that you think are toed-in the correct amount. You may be suprised at how far off you are doing it without some sort of measuring tool.

    Calibration Tools:

    A setup DVD is fine for level-adjusting your speakers. But do you have a external subwoofer?

    A number of people use NCH Test Tone generator to create a CD with 16 hz, 24 hz, 32 hz,... to about 104 hz. Just a few seconds of each. Then they use their SPL meter to chart how loud each sound is. It is suprising how your room reflects/enhances some sounds and absorbs others.

    The "Stryker Bass" test CD also works if you dont want to bother burning your own CD.

    Check the Speakers and Subwoofer fourm for "House Curve" for lots of posts from people who have done this.
     
  7. Dave Pobuda

    Dave Pobuda Stunt Coordinator

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    I have been looking for a good subwoofer calibration disc myself. I did a search in the speakers forum for house curve but this is the only thread that showed up. I also tried a google search for Stryker Bass but had no luck there either. Any ideas where I can find this C ?

    TIA

    Dave
     
  8. Brian L

    Brian L Cinematographer

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    In addition to Stryker, I might also suggest the Bass Mekanix CD (I think the one I have is BM IV?). Its has discrete tones from 20 hz to 99 hz in 1/2 hertz increments.

    It can be had at Amazon and I think Parts Express.

    BGL
     
  9. Cameron Yee

    Cameron Yee Executive Producer
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    I just bought one off eBay for a paltry 2.30!
     
  10. Ted Lee

    Ted Lee Lead Actor

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    re: subwoofer calibration

    i think i have an older cd somewhere with tone-sweeps. not sure about frequency stops, duration, etc...but i remember it goes pretty low. low enough that you get that sickly feeling.

    would that work in the same manner as the stryker cd's?

    also, how exactly do you use something like that. what should i be listening for?
     
  11. BruceD

    BruceD Screenwriter

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    Depends on how much you want to know about acoustics.

    A good place to start (you can try the sw for free) is the ETF website. There is also lots of tutorial info about room acoustics on that site.

    It allows you to use your RS SPL meter and a PC to measure your speaker/room response (no test CD needed).
     
  12. Bob McElfresh

    Bob McElfresh Producer

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    What you are doing is a "Poor Man's Real Time Analyzer"

    You create a plot of frequency and volume like this:

    16 hz 50 db
    24 hz 45 db
    32 hz 55 db
    40 hz 60 db
    48 ha 68 db


    This is why you need to know what frequency is being played. A "Sweep" of sound does not let you know what frequency produces what volume.

    Here is the trick: all the sounds on the CD are at the exact same volume. But the sound your SPL meter picks up is different for each wavelength!

    This is because your speakers and your room do funny things to the different frequencies. It absorb's some, and reflects/enhances others.


    Once you have this data you have some choices:

    - Notice that things are fairly level - perfect
    - Notice some peaks. You might try moving your subwoofer along the wall to tame some of them
    - When all else fails, you might consider an equalizer for the subwoofer cable. A very popular unit is a "Behring Feedback Destroyer". This unit lets you program something like:

    - Take sound from 53-57 hz and reduce it by 4 db
    - Take sound from 60-61hz and reduce it by 1 db
    - etc

    So it acts/is really a parametric equalizer.

    Try searching for "BFD" in the speakers fourm. (There was a lot of plotting and discussion about house-curves/room responses about 2 years ago so these threads may be archived off by now).
     
  13. SteveL

    SteveL Agent

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    I knew a guy who spent soo much time calibrating and aiming, he did not want to listen unless everything was perfect, but because he couldn't get everything perfect, he never listened. Any of you guy's actually listen to the system or do you just measure and calibrate.....heh....heh.
    From another measurebator.........
    Steve L.
     
  14. Ted Lee

    Ted Lee Lead Actor

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    thx bob ... that kinda sounds like fun. i may have to look into it. [​IMG]
     
  15. BruceD

    BruceD Screenwriter

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    The key to optimizing sound quality is not simply a stroke of luck or magic. [​IMG]

    It's clear that measurement sessions can increase and expand your knowledge of speaker/room acoustics while helping you optimize your sound quality, never a bad thing, IMO. [​IMG]
     
  16. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    Make sure you get correction values for the SPL Meter. There's a table somewhere online, but I don't remember where. The meter is suprisingly in-accurate over the frequency spectrum, especially w/ lower frequencies.
     
  17. Bob McElfresh

    Bob McElfresh Producer

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    Here is a thread about House Curves and BFD that you may find interesting.

    Here is a short correction table for the Radio Shack SPL meter:
    Here is the compensation chart from SVS on the Radio Shack SPL meter.

    12Hz add 16.5dB
    16Hz add 11.5dB
    20Hz add 7.5dB
    25Hz add 5dB
    31.5Hz add 3dB
    40Hz add 2.5dB
    50Hz add 1.5dB
    63Hz add 1.5dB
    80Hz add 1.5dB
    100Hz add 2dB
    125Hz add .5dB


    Here is a link to a web site with more SPL Correction Values
     

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