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Thread: JBL L300 / 4333 3 way analog electronic crossover question

  1. #1
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    JBL L300 / 4333 3 way analog electronic crossover question

    There is another active thread on using a JBL L300 with an electronic crossover but I want to confirm a couple of things that are unclear to me.
    I've finally scrounged the parts to build my non-original 4333 with some utility cabs I purchased a while ago.

    I will be using:
    2405
    2311/2441/2445 diaphragms
    2235
    Marchand 3 way XM9 crossover 24db/octave
    DC blocking cap / 20 ohm shunt resistor across 2405 and 2441
    No L-Pads (will control volume in each speaker from either crossover or amplifiers

    Just want to verify before hooking up
    1. All the above drivers have black as their + terminal
    2. The 2441 signal should be inverted compared to the 2405 and 2235 (as shown in the Nelson Pass schematic).

    I appreciate any help.
    Best Regards,
    gwho

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    Administrator Mr. Widget's Avatar
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    Sounds like a cool project!

    Question: What are the 20 ohm resistors for?

    A thought about polarity: Some amps are inverting and others are noninverting. Recently I was helping a friend dial in his tri-amped system and I noticed a massive suck out at one of the crossover frequencies. This was because one of his amps was inverting the phase. Finding this kind of thing as well as balancing your system are best done with some form of measurement system.


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    The original crossover topology in the 4333 was not 24db per octave 4th order filters . The Nelson Pass crossover schematic shows 2nd order for the low and mid and 3rd order for the high. The summing will be substantially different with 4th order filters. You will likely have to determine the best polarity empirically by listening or ideally using test software like Smaart, Foo or REW.



    Quote Originally Posted by gwho View Post
    ...

    Just want to verify before hooking up
    1. All the above drivers have black as their + terminal
    2. The 2441 signal should be inverted compared to the 2405 and 2235 (as shown in the Nelson Pass schematic).

    I appreciate any help.
    Best Regards,
    gwho

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    Riley / Widget,

    Thank you for the responses and encouragement. I will definitely try to take some measurements after putting them together. Just want to get an idea of a starting point.
    I will now assume that I will try it both ways and determine what works best. I've attached a couple pictures of the boxes. They are not perfect but good enough.

    Name:  front_4333.jpg
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    The 20 ohms resistors discussed in one of the threads I read for electronic crossovers where they recommended a DC blocking cap and a shunt resistor across the CD inputs (is this wrong?).

    Regards,
    Gary

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by gwho View Post
    The 20 ohms resistors discussed in one of the threads I read for electronic crossovers where they recommended a DC blocking cap and a shunt resistor across the CD inputs (is this wrong?).
    Not sure why you would need the resistors, I have never used them. I use a very large value cap in series with my compression drivers as protection, but thats it. I am a fan of less is more.

    The cabinets look fine. You can even veneer them at some point if you want.


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    I won't put in the resistors. I agree less is better.

    Regards,
    gwho

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    Senior Member macaroonie's Avatar
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    In my experince it's fairly apparent which way is correct. It might take a little while as you get levels adjusted etc but it only takes a minute or so to switch phase on an amp. you will have a eureka moment.

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by macaroonie View Post
    In my experince it's fairly apparent which way is correct. It might take a little while as you get levels adjusted etc but it only takes a minute or so to switch phase on an amp. you will have a eureka moment.
    Maybe for a trained/experienced listener like yourself. I have heard so many DIY setups that were so very wrong. Basic measurements make it a lot easier to get in the ballpark. Once there, subtle tweaking to taste can be very rewarding.


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    At a minimum I can take a measurement with a DEQ2496 and pink noise to determine what the response of the speaker is. I will likely also try to learn how to use REW if time permits and take some measurements.

    Best Regards,
    gwho

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    REW is a pretty remarkable piece of software particularly for free. I've used measurement software since the original Crown TEF machines and I have SpectraFoo and Smaart licenses and I still use REW for some things. Well worth the time and effort to learn. The RTA in the DEQ ( well any RTA really ) isn't worth much in assessing speaker performance although it is handy for ear training.

    Quote Originally Posted by gwho View Post
    At a minimum I can take a measurement with a DEQ2496 and pink noise to determine what the response of the speaker is. I will likely also try to learn how to use REW if time permits and take some measurements.

    Best Regards,
    gwho

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    Riley,

    I will try to do some reading on REW. Using the Deq2496 relates to my original question about inverting the signal to the mid-horn. The answer was try it both ways. I assume the Deq2496 could show me which connection to the mid-horn provides the flattest response if it was not obvious.

    Regards
    Gary

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    The thing about polarity is that neither could be right. What you want to know is the phase relationship between the drivers. The voice coils in a 4333 are on three different horizontal planes. Something that JBL got 'fairly' close with the phase relationships inherent in the crossover filters they used. Each 6db per octave pole of a crossover filter adds 90 degrees of phase delay to the signal. Your DC blocking caps ( possibly not needed. Depends on how much you trust the output relays in your amps ) each add that same 90 degrees of phase shift. You're using different filters and thus have to come up with a different solution. Perhaps not one available in an analog crossover fixed at 4th order filters. REW will show you the phase ( essentially when the sound arrives at any given frequency ) as well as the frequency response of the speaker system. You can almost certainly get your speakers to sound OK, even pleasant but without time aware measurement it's a crap shoot.

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    Quote Originally Posted by Riley Casey View Post
    The thing about polarity is that neither could be right.
    True.

    Depending on the crossover type, (number of poles and characteristics at the knee) the polarity may make a larger or smaller impact on the overall frequency response. The phase will most certainly be wrong regardless, but we try to make it less wrong.

    Basically, you need to measure, listen, tweak, and listen again until you have the best compromise with the system you are working on. Kind of like making a nice soup. You add a bit of this, you add a bit of that, and with luck it is a masterpiece and not just salty water.


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    Senior Member macaroonie's Avatar
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    Might be an idea to move up a notch in the Behringer stable and get the DCX , then you get the helpful option of delay , parametric EQ and variable filters.
    I understand completely your desire to use the Marchand BTW.

    One other point , my system is very similar and it didn't take long to fathom out that the 2235 is not a happy bunny up at 800Hz.
    I eventually landed on just over 600Hz , I'm using 2380 horn and thats about as low as that goes.
    The mass ring in the 2235 smudges the mids making the sound dark , call it what you will.
    I got a very worthwhile improvement in clarity , defenition and imaging.

    Just my 0.2c

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    Quote Originally Posted by macaroonie View Post
    One other point , my system is very similar and it didn't take long to fathom out that the 2235 is not a happy bunny up at 800Hz.
    I eventually landed on just over 600Hz , I'm using 2380 horn and thats about as low as that goes.
    The mass ring in the 2235 smudges the mids making the sound dark , call it what you will.
    I got a very worthwhile improvement in clarity , defenition and imaging.

    Just my 0.2c
    I agree with your analysis. I would suggest moving to the 2216 woofer. I think it is better than the 2235H in every way. With the 2216, you can keep the 800Hz crossover and stay with the 2312. In an active system, making the swap should be fairly straightforward.

    While the digital crossover has a lot of powerful and beneficial features, I would still stay analog, but then I’m an audio dinosaur.


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