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Thread: Strange object found inside a Harmon Citation 7.4 sub

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    Member clwinbe's Avatar
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    Strange object found inside a Harmon Citation 7.4 sub

    I was working a bit on the internal dampening material in two passive subs. I was surprised to find what looks like crossover inside. It had a bit of a strange configuration. Not sure what all of those resistors are forÖmaybe trying to head something off when the resistance rises in the upper frequencies.

    Iíve have very high quality sub amps so I removed this from the cabinets. Possibly the Harmon Cardon amps used to power these were not dedicated sub amps.

    itís a head scratcher.
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    Heather [Senorita member] hjames's Avatar
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    Other than Harmon Cardon actually being Harman Kardon,
    looks like probably a simple low pass filter for the subs ...
    Can't hurt to keep the high freqs off the woofers anyway.
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    Administrator Robh3606's Avatar
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    Quote Originally Posted by hjames View Post
    Other than Harmon Cardon actually being Harman Kardon,
    looks like probably a simple low pass filter for the subs ...
    Can't hurt to keep the high freqs off the woofers anyway.
    I agree but it looks odd. Where is the black wire connected?? Almost looks like a jumper has been cut out. What are the "green" things? Wonder what the back looks like?

    Rob
    "I could be arguing in my spare time"

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    Junior Member speakermaker's Avatar
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    Are the resistors for higher Q ts ?

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    Photo of the other side of this would be helpful

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    Member clwinbe's Avatar
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    Quote Originally Posted by short_circutz2 View Post
    Photo of the other side of this would be helpful
    Photo Name:  F7053F1F-E5E9-4500-9550-91853D0C7C12.jpg
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    Member clwinbe's Avatar
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    Quote Originally Posted by Robh3606 View Post
    I agree but it looks odd. Where is the black wire connected?? Almost looks like a jumper has been cut out. What are the "green" things? Wonder what the back looks like?

    Rob
    Name:  8A021690-9B10-4F67-BAA1-E9A582E9E056.jpeg
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    you can see where the speaker connections are in this pic. I clipped the wires to reuse. The red and black attached to terminal cup.

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    Senior Member HCSGuy's Avatar
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    As I mentioned in your other thread about this and your subs, this looks like a filter meant to make the load easier on the amplifier. RL circuits (resistance in parallel with inductance) are used in a circuit to counter reactance, which related to back emf from the voicecoil, which is at its maximum in a woofer at its resonance frequency. This makes current lag voltage, and a lot of this can be tough for an amplifier not designed for it. Since your speaker (A passive subwoofer) is designed for most of its use in a very narrow frequency band that is near its range of maximum reactance, since the woofer used has a huge voicecoil and magnet, and since the amplifier to be used was unknown to the speaker designer, they may have thought it prudent to tame the speaker's reactance. I do not know if they did this to limit their liability, or just to be careful.

    To limit my liability, I am disclosing that I am not a crossover expert, and am only posting because none of the guys that design passive crossovers have chimed in. If they do, and contradict everything I say, I will deny I said it, accuse foreign actors of hacking my LH account, and say I was never here. I will count on you guys to back me up on this
    That the internet contains a blog documenting your life does not constitute proof that your existence is valid. Sorry.

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    Hi,

    if these neg- and Pos+ markings in your last pic mean that the driver was connected there, it's just an inductor of unknown inductance in parallel with four 10 ohms resistors, which equal a total resistance of 2.5 ohms. This combo is in series with said driver. Inductors in parallel with resistors are widely common in transistorized power amplifiers to isolate capacitors in crossover networks, hence improving the amp's stability.

    Anyway, you said it's a subwoofer. So no capacitors to be expected there. Or is there any that isn't on this board? If not, I'd say this is a simple LPF with much less than 6 dB/oct.

    Best regards!

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    Member clwinbe's Avatar
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    Finally have an answer

    Quote Originally Posted by clwinbe View Post
    I was working a bit on the internal dampening material in two passive subs. I was surprised to find what looks like crossover inside. It had a bit of a strange configuration. Not sure what all of those resistors are forÖmaybe trying to head something off when the resistance rises in the upper frequencies.

    Iíve have very high quality sub amps so I removed this from the cabinets. Possibly the Harmon Cardon amps used to power these were not dedicated sub amps.

    itís a head scratcher.
    After spending some quality time with RBH Sound engineering chief Rich, he believes this sub was part of a specifically tuned system. This crossover actually tunes the sub back a bit so it doesnít overpower the rest of the system so heck yes, yank it out.

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