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Thread: Infinite baffle "cabinet"

  1. #1
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    Infinite baffle "cabinet"

    How large would a speaker enclosure have to be for it to function as an infinite baffle? And does this eliminate the need for enclosure tuning? As a reference; horn HF, horn MID, 18" cone LF.

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    Senior Member spkrman57's Avatar
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    My best gestimation is....

    When the cabinet size approaches the Vas of the LF driver the alignment is considered a "infinite-baffle" design.

    This would be a "sealed" cabinet the way I'm looking at it.

    Let's see if anyone else chimes in on this topic.

    Regards, Ron
    Last edited by spkrman57; 05-25-2009 at 09:47 AM. Reason: added info
    JBL Pro for home use!

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    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by midlife View Post
    How large would a speaker enclosure have to be for it to function as an infinite baffle?
    As Ron said, fairly big.

    But what is your intention? With a real open baffle you can get loose of enclosure resonances. But with a maintained enclosure you will miss this advantage. And you will presumably have an early bass roll off which must be compensated.

    Which 18 inch speaker do you have in mind?
    ____________
    Peter

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    Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle.

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    Quote Originally Posted by 4313B View Post
    Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle.
    A formula, I may be able to figure that one out...what is Qtc?

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    Qt of a closed box

    Here's a handy gadget to measure such things in real life:

    http://www.woofertester.com/wt2product.htm

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    Senior Member Loren42's Avatar
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    Quote Originally Posted by midlife View Post
    How large would a speaker enclosure have to be for it to function as an infinite baffle? And does this eliminate the need for enclosure tuning? As a reference; horn HF, horn MID, 18" cone LF.
    Once the volume of air inside a cabinet is so large that the air's compliance is greater than the compliance of the woofer's suspension, then the box is considered an infinite baffle.

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    Senior Member Loren42's Avatar
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    Quote Originally Posted by 4313B View Post
    Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle.

    Um, I thought a Qtc < .5 tended toward a vented enclosure.

    I am not aware of a guideline for infinite baffle, but I will look that up.

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    Quote Originally Posted by Loren42 View Post
    I am not aware of a guideline for infinite baffle, but I will look that up.
    I just posted it above.

    Basically it is when the sealed enclosure volume loses the ability to offer any kind of restoring force.

    Qtc relates to sealed volumes. Qtc < 0.5 tends towards infinite baffle.


    Just go with #2, #3, #7 above, it's easier to understand.

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    Quote Originally Posted by Loren42 View Post
    Um, I thought a Qtc < .5 tended toward a vented enclosure.

    I am not aware of a guideline for infinite baffle, but I will look that up.
    Cabinet large (>=Vas) is a pretty good guideline. Qts and Qtc are different. Qts is the driver in free air, the Q of the combined electrical and mechanical components of the driver at Fs (Qes and Qms). This determines (largely) what sort of box you want to use. Higher tends to need less help from a port, hence the preference for sealed. Lower tends towards vented, and very low belongs in a horn (for bass anyway).

    Qtc is the Qts with the influence of the enclosure. When this is close to Qts, it's an infinite baffle enclosure.

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    Senior Member Loren42's Avatar
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    Quote Originally Posted by badman View Post
    Cabinet large (>=Vas) is a pretty good guideline. Qts and Qtc are different. Qts is the driver in free air, the Q of the combined electrical and mechanical components of the driver at Fs (Qes and Qms). This determines (largely) what sort of box you want to use. Higher tends to need less help from a port, hence the preference for sealed. Lower tends towards vented, and very low belongs in a horn (for bass anyway).

    Qtc is the Qts with the influence of the enclosure. When this is close to Qts, it's an infinite baffle enclosure.

    Thanks! I was confusing my Qtc with Qts.

    What happens when you put a low Qts driver (i.e., .28) into a sealed enclosure of small volume?

    I have a specific reason for asking the question.

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    Quote Originally Posted by badman View Post
    and very low belongs in a horn (for bass anyway).
    Well... that might be some generallity found somewhere but I'm not real sure I'd want a 124/2203 or 136/2231 in a horn.
    Quote Originally Posted by Loren42 View Post
    What happens when you put a low Qts driver (i.e., .28) into a sealed enclosure of small volume?
    Note that JBL puts low Qts midbass drivers in small sealed boxes.


    The problem with these kinds of forum discussions is that they probably shouldn't exist (especially since they all go to Google now). Read the AES papers and myriad books instead. They do the subject a hell of a lot more justice than anything you'll find on some Internet forum. We went over this with Zilch early on and he dove right in as suggested.

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    Senior Member Hoerninger's Avatar
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    More than the definition and relationship of speaker parameters by Claus Futtrup (former Dynaudio employee):

    http://home1.stofanet.dk/cfuttrup/dpc/dpc.htm
    ____________
    Peter

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