Help me with Qtc...

Discussion in 'Home Theater Projects' started by Gianluca, Jun 29, 2003.

  1. Gianluca

    Gianluca Agent

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    Hi everybody,

    I am thinking about building my own sealed subwoofer and would like to use a SHIVA as a driver and AVA250 as an amplifier.

    I have some doubts about Qtc...

    What is the difference in sound between 0.6 and 0.707 ?

    I will be using my sub mostly for music, do you think that I will get good results with this setup?

    Thanks
     
  2. Jay_Garcia

    Jay_Garcia Extra

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    I just completed my 54L (Q=.707) sealed shiva sonosub. Check out the thread - "Sonotube Questions"

    I honestly haven't gotten to watch alot of movies yet (I just finished it yesteday), but have watched several scenes - Black Hawk Down, when they are beginning the intial raid and Terminator 2, the chase after the mall arcade scene. I have listened to music also, mainly Billy Joel, and some other stuff. I can honestly say, it rocks! It does pretty well for both HT and music. To be honest, I haven't even cranked it up loud yet. For my first (notice, I said first - meaning there WILL be more!! [​IMG] ) sonosub, I had size constraints (a.k.a. the wife [​IMG] ) and also wanted to start off easy. The next one I do will be vented and bigger. Either way, this one is going to be around along time!
     
  3. TimForman

    TimForman Supporting Actor

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    As a general rule you want a lower Q for music. My sealed Tempest has a Q of .707 and I've found it a very good compromise for music and HT. I don't think I would want anything higher for music. If your main interest is tight bass for music (I don't mean techno,hip-hop or other pop type stuff) and not HT go for the lower Q. But, if you say "mostly music" and you're talking about the genre's above go for the .707 Q.
     
  4. Frank Grimes

    Frank Grimes Second Unit

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    Basically once you reach a Qtc of .707, going lower is a tradeoff of F3 and the slope at which the sub will roll off. Higher alignments, let's say .9, will have a high F3 and a steep rolloff, but also an SPL peak that isn't present with lower Q setups. I wouldn't consider this ideal for any type of listening, but would probably be regarded highly by a kid that likes a boomy sound while he blares his new Jay Z album in his car keeping people up at night.

    As you approach a Qtc of .707, F3 drops and the rolloff becomes less steep. Once you go below .707, the rolloff continues to improve, but F3 rises. This somewhat explains why drivers with a high Qts are more at place in freeair applications than low Q drivers. When placed freeair, the "Qtc" of the speaker is very close to the Qts of the speaker. (Notice the quotation marks, as it's not really the accurate term in this case, though close enough.) Using a low Q driver freeair could result in the driver's F3 being well higher than desired.
     
  5. Patrick Sun

    Patrick Sun Studio Mogul

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    Q also describes the damping of a speaker enclosure in concert with the driver(s).

    A high Q near 1 is described as being underdamped, and you'll get less damping action on the drivers, it might give off the impression that the driver is a bit out of control, i.e. the transient response for the driver is sloppier, looser.

    A low Q near 0.5 is described as being overdamped, and you get more damping action on the drivers, it might give more control over the driver, and that results in better transient response, i.e. a tighter snap to the driver's output. Properly sized sealed enclosures are usually in this range for the Q, and it lends itself to a "punchier" feel to the mid/high bass frequencies, but at the expense of low end extension to its frequency response.

    A Q around 0.707 is described as being critically damped, and is a compromise between overdamped and underdamped, and is mainly desirable for low end extension with enough transient response not to feel sloppy. Properly vented enclosures will usually have a Q near this value (but there are other alignments as well).
     

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