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Thread: 4435 choke values

  1. #1
    Senior Member Guido's Avatar
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    4435 choke values

    In my 4435 xover DIY I use chokes with significantly better DCR ratings.

    The 2,6mH choke will have appr. 0,17 Ohm instead the original ?0,45 Ohm?

    The 18mH choke will have appr. 0,5 Ohm instead the original 1,41 Ohm

    Do I need some port retuning?
    What improvements are to expect with these chokes?

    Thanks!

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    Re: 4435 choke values

    Use your BB6P to model the effects of the low pass filters. There is a place for you to input DCR values along with all the other component values of the filters.

    Keep in mind that many of the larger JBL systems are meant to be bi-amped which, of course, removes any inductor DCR from the low pass signal path. Usually LF response is "flatter" when in bi-amp mode unless the system was designed and tuned for specific inductors. That is one reason why some systems never intended to be bi-amped sound unbalanced in the LF when bi-amped. Reducing the DCR in your 18 mH inductor so dramatically should have an audible effect although not quite as dramatic as bi-amping.

    The really nice thing about the 4430 and 4435 is that you can biamp them and use a 6 dB/octave passive line level high pass instead of the 6 dB/octave active high pass in a 5234 or 5235. You can fine tune it with precision resistors if needed. It will work in conjunction with the series 20.0 uF capacitor (which should also be of the highest quality) to provide the necessary 12 dB/octave attenuation.

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    Senior Member Guido's Avatar
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    Re: Re: 4435 choke values

    Thanks for answer Giskard.

    What i found out with BB6 is that the lower DCR gives me the possibility to tune the 4435 a little bit lower.
    I came to a duct of 180 to 200mm (instead of 133mm)
    This yield in a tuning frequency of appr. 24 Hz and 3 dB more output below 20 Hz. I should try this when the cabs are finished.

    What do you think?


    Originally posted by Giskard
    The really nice thing about the 4430 and 4435 is that you can biamp them and use a 6 dB/octave passive line level high pass instead of the 6 dB/octave active high pass in a 5234 or 5235. You can fine tune it with precision resistors if needed. It will work in conjunction with the series 20.0 uF capacitor (which should also be of the highest quality) to provide the necessary 12 dB/octave attenuation.
    This I do not understand. What do you mean with "6 dB/octave passive line level high pass instead of the 6 dB/octave active high pass in a 5234 or 5235"?

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    Re: Re: Re: 4435 choke values

    Originally posted by Guido
    This I do not understand. What do you mean with "6 dB/octave passive line level high pass instead of the 6 dB/octave active high pass in a 5234 or 5235"?
    The 52-5130 card for the 5234/5235 and 4430/4435 has a 6 dB/octave active high pass. One can use a line level passive high pass instead. They are considerably "cleaner". Decide what amplifier you are going to use for the high pass and then figure out the capacitor value to place between the preamp and power amp to obtain the same voltage drive as the stock 52-5130 high pass. The input impedance of the high pass amplifier can be augmented with a parallel precision resistor. Just keep the value of the precision resistor as high as possible to minimize insertion loss.

    Look at a BX63A schematic to see the simplest way to make your own 6 dB/octave passive line level high pass. I think it makes the 4430/4435 sound as good as it possibly can in bi-amp mode, especially if you also replace the 20.0 uF series capacitor (and 2.0 or 2.5 uF EQ capacitor) in the stock network with something like a Hovland.

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    Senior Member Guido's Avatar
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    After a closer look at the schematic I saw that the 18mH inductor is always in line with the low 2234. Even in biamp mode.

    So this should improve the 4435 even in biamped mode.

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    "After a closer look at the schematic I saw that the 18mH inductor is always in line with the low 2234. Even in biamp mode."

    Yes, the second LF driver always has the 18 mH inductor and resistors in line. In theory the situation isn't ideal. In practice it appears to work well enough. Just for grins you may want to see if you can hear the difference between the stock 18 mH inductor and a very low DCR type. You should be able to.

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    It looks like the Erse 18 mH coil available from Parts Express has a DCR value of ~ 0.5 ohms.

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    RIP 2011 Zilch's Avatar
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    Giskard:

    Why are the resistors there? Is it merely attenuation?

    This came up when Figge wanted a cheap-and-dirty low-pass for 2235....
    Last edited by Zilch; 09-20-2004 at 10:05 AM.

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    The resistors help flatten the impedance curve of the 2234H.
    They also, unfortunately, have an effect on overall sensitivity.

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    Passive Line Level; Yep, a whole lot cleaner .

    Hi Guido / Giskard

    One can use a line level passive high pass instead. They are considerably "cleaner".


    I can sure vouch for what Giskard stated above regarding "Passive Line Level HiPasses". Early this winter I moved the hipass for my biamped setup to a "balanced" passive inline line-level hipass . I don't use any "load" resistors in this circuit - just two surplus polystyrene capacitors per channel ( or actually, 4 once I DC-biased the network ) . This is certainly the fastest ( and cheapest ) way to uncover and draw upon the "resolution well" . My circuit , being inherently "sloppy" doesn't achieve a 6 db slope until octaves down into the "stop-band". The slope is really more like 4 db an octave below the choosen point. This "first" pole of my 2-pole approach is also set to be about an octave below the desired Fc .

    My circuits second pole ( inline with the horn driver ) is from a "shunted" inductor that's @ 1/2 the book value ( or about an octave above the desired Fc . This combo actually represents a "flipped" approach to obtaining a 2-pole LR transform . This inductor is "hidden" from what the amp "sees" by the 8 ohm resistor within the RC network ( for 8 ohm drivers ) . This "very necessary" and critical resistor prevents the amplifier from seeing a frequency dependant short-circuit .

    The sharp "eyed" will notice that this portion of the circuit lacks "DC" blocking caps between the amplifier and horn drivers . This is true. And, therefore, this approach is a dangerous setup for those with amplifiers of marginal stability ( or a full comprehension of all the ramifications ) .

    The net results, sound really , really good .

    <. Earl K

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    Re: Passive Line Level; Yep, a whole lot cleaner .

    Sounds cool Earl!

    Biased eh?

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    Re: Giskard:

    Originally posted by Zilch
    Why are the resistors there? Is it merely attenuation?

    This came up when Figge wanted a cheap-and-dirty low-pass for 2235....
    Ok, I ran some impedance curves on a trashed 2234H (complete with the usual aftermarket refoam job - note the excessive Fs). The red curve is just the driver. The green curve is the driver with the four 62 ohm resistors in parallel. The blue curve is the driver with the 30 mfd + 5.1 ohm conjugate (zobel) filter in parallel.

    The 18.0 mH choke on the secondary 2234H likes the green impedance curve.

    Notice how the conjugate (blue curve) affects the impedance from ~ 500 Hz to 2,000 Hz on the primary 2234H. A bit of fine tuning of the low pass is occurring there.
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    BB6?

    Please pardon me for digging out this ancient thread !

    As I've also found inductors of different DC resistances that might be suitable for my upcoming 4430 project, may I ask what »BB6« means?

    And what would happen if I replace the 2235H's 2.6 mH LP inductor by a nowadays stock 2.7 mH one?

    Best regards!

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    Quote Originally Posted by Kay Pirinha View Post
    Please pardon me for digging out this ancient thread !

    As I've also found inductors of different DC resistances that might be suitable for my upcoming 4430 project, may I ask what »BB6« means?

    And what would happen if I replace the 2235H's 2.6 mH LP inductor by a nowadays stock 2.7 mH one?

    Best regards!
    BB6 = Bass Box Pro 6

    Stick with the quoted values seen in the schematic.

    Buy a multimeter that can measure inductance, then unwrap a couple of turns ( from your 2.7mH coil ) to arrive at the 2.6mH value.


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    Thanks, EarlK!

    I see BB6Pro is from Harris Software, as is Eminence Designer. I own the latter one. Are there significant differences between both?

    Best regards!

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