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Thread: 2445 condenser

  1. #1
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    2445 condenser

    HI
    Just got my 2445's and I'm using an electronic crossover at 600-1000Hz. A quick listen 600 sounds sweet to me.

    Is it standard practice to use a condenser tuned to 500Hz to protect against misuse? This is for PA use and controls could get moved and buttons pushed by accident. Do JBL cabs always have a condenser in series even when BI-amping or does the switch remove this?

    Cheers

    GCT

  2. #2
    Senior Member Lee in Montreal's Avatar
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    I would use a condenser, but at a much lower frequency and only to cut DC. I am thinking doing it too on my 2445 and 2405, and most likely cutting at 100Hz, well below the drivers' range.

    When I had my Kef 105-2, there were two generations of crossovers. One with 480µF of caps and one with 900µF to protect the woofer, midrange and tweeter from DC. That capacitor was well away from the sound spectrum. Remember it is only to cut DC, not to protect drivers from bad operators...

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    Senior Member Eaulive's Avatar
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    Quote Originally Posted by GCT View Post
    HI
    Just got my 2445's and I'm using an electronic crossover at 600-1000Hz. A quick listen 600 sounds sweet to me.

    Is it standard practice to use a condenser tuned to 500Hz to protect against misuse? This is for PA use and controls could get moved and buttons pushed by accident. Do JBL cabs always have a condenser in series even when BI-amping or does the switch remove this?

    Cheers

    GCT
    I always put a capacitor in series with the compression drivers.
    You can not "tune" a capacitor since it's not a resonant device, it will give you a smooth rolloff and can not be used as a crossover.

    A 100µF will have a 2.65 ohms reactance at 600 Hz, to give you a example.

    In my setup I have 2425Js crossed at 1500Hz and a 47µF in series. This gives me a 2.25 ohms reactance at cutoff.

    http://www.sengpielaudio.com/calculator-RC.htm

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    Quote Originally Posted by Eaulive View Post
    A 100µF will have a 2.65 ohms reactance at 600 Hz, to give you a example.
    In my setup I have 2425Js crossed at 1500Hz and a 47µF in series. This gives me a 2.25 ohms reactance at cutoff.
    I don't want a crossover, I want protection, so I was thinking a 40mF cap should protect aganst DC and give a 12dB/Oct rolloff below 500Hz should anyone connect the horn wrongly - probably me. In the event of wanting to cross over low, it will be with a 24dB/Oct LR type, so I could lift the crossover to higher than 500Hz and all's well.

    Or no?

    GCT

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    Quote Originally Posted by Lee in Montreal View Post
    Remember it is only to cut DC, not to protect drivers from bad operators..
    Mmm... I think I need protection from the latter more than the former, hence I'm thinking 40mF.

    GCT

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    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by GCT View Post
    Mmm... I think I need protection from the latter more than the former, hence I'm thinking 40mF.

    GCT
    The only ways to protect your drivers from a bad operator are twofold.

    1. Lock the active crossovers (all digital crossovers can be protected). Or put the analog crossovers behind a locked panel.
    2. Use fixed passive crossovers.

    There's nothing you can really do against an operator who decides to tweak the system.

    Also, you may still need to protect each driver from DC anyway. Power amps that are used to their limit will induce DC which will destroy your drivers. Amps that don't have a protection circuit may also send DC on start-up.

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    Senior Member Eaulive's Avatar
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    Quote Originally Posted by GCT View Post
    I was thinking a 40mF cap should protect aganst DC and give a 12dB/Oct rolloff
    You were thinking wrong, a single cap in series will give you 6dB/ oct rolloff.

    http://www.electronics-tutorials.ws/.../filter_2.html

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    Right, so 6dB/oct is not much protection. And yes I was thinking of hiding the crossover knobs behind a panel.

    Thanks for the info. Will digest over the next few days.

    Cheers

    GCT

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    Senior Member louped garouv's Avatar
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    Quote Originally Posted by GCT View Post
    ......


    Thanks for the info. Will digest over the next few days.

    Cheers

    GCT
    here's another thread with some more info/links that may be useful...

    http://www.audioheritage.org/vbullet...n-active-setup


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    Senior Señor boputnam's Avatar
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    Quote Originally Posted by Eaulive View Post
    You were thinking wrong, a single cap in series will give you 6dB/ oct rolloff.

    http://www.electronics-tutorials.ws/.../filter_2.html

    This is a great post. I think I'll preserve the Link in the Technical References section, under General Audio Discussion. The question of the phase impact of filters comes up again, and again...
    bo

    "Indeed, not!!"

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    Quote Originally Posted by GCT View Post
    Right, so 6dB/oct is not much protection. And yes I was thinking of hiding the crossover knobs behind a panel.

    Thanks for the info. Will digest over the next few days.

    Cheers

    GCT
    Why would you say 6dB/oct is not much protection? It will still save the CD from a low frequency signal (ie.DC thump!!)


    I have always used single large Caps for 6dB/octave protection with ALL my CDs when testing (I have 15 different CDs sitting around).

    I do have to ask about your post the word "condenser", Im curious about that definition instead of just saying "Compression driver" ??

  12. #12
    Dang. Amateur speakerdave's Avatar
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    Your protection capacitor should be targeted at a frequency an octave or more below the crossover frequency. I think 100 Hz is too low. Its capacitance should be based on the load impedance of the driver. You can find charts for this in various places including the manuals for the UREI crossovers. I'm using 40uf for my nominally 16 ohm drivers crossed at 700Hz.

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    Quote Originally Posted by speakerdave View Post
    Your protection capacitor should be targeted at a frequency an octave or more below the crossover frequency. I think 100 Hz is too low. Its capacitance should be based on the load impedance of the driver. You can find charts for this in various places including the manuals for the UREI crossovers. I'm using 40uf for my nominally 16 ohm drivers crossed at 700Hz.
    For DC protection, as long as the cap is under the response curve of the crossover, ot will be fine. The cap will block DC no matter what the size and in general, anything above 40 or 50 uf will be fine. Some crossovers even use a lamp to soak up excess power.

    Allan.

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    Quote Originally Posted by Bo
    This is a great post. I think I'll preserve the Link in the Technical References section, under General Audio Discussion. The question of the phase impact of filters comes up again, and again...


    And there's the meat of the matter ( nicely illustrating the truth and now bringing me to a pet peeve of mine ) .

    All across the internet, I see this as an ever pervasive misconception ;
    - ( ie Too many incorrectly assume that the most siginificant phase changes, happen within the Pass Band / when in truth, the total phase rotation is fully realized ,,, out there in the "Stop Band" . )

    Eaulive,,, That's a nice website for reference ,,, Thanks !

    <> EarlK

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    Quote Originally Posted by penngray
    I do have to ask about your post the word "condenser", Im curious about that definition instead of just saying "Compression driver" ??
    Condenser is an archaic word ( by North American standards ) for the simple Capacitor .

    Obviously, it's a word that still has meaning to some / I'm pretty sure that my old Land-Rover shop manuals, used the word .

    <. EarlK

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