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Thread: Passive Monitor Thread

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    Administrator Robh3606's Avatar
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    Passive Monitor Thread

    I started setting up to build a new system. I was lucky to be able to purchase a pair of 476Mg's and was gifted a pair of 2216Nd's by my friend 4313B. I am going to use my favorite waveguide PTH1010. It has certain advantages similar to the 2344 because it is very short and has a rapid flare compared to the other PT Waveguides and is 100x100 which works very well in my room. I started taking some preliminary measurements on a temporary baffle of the raw drivers on the PTH1010.


    It actually measures very well and has a distinct advantage over the 435Be in this application. It has a rising high frequency response which makes it much easier to set-up with systems using higher sensitivity woofers. With the 435Be on this waveguide you have to trade woofer sensitivity to get a usable last octave response. Attached are plots for the 476Be no network and 435Be with nework and raw.

    Rob
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    Administrator Robh3606's Avatar
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    After the raw measurements I looked for a suitable network and chose the 9900 which uses the 476Mg. I simplified the crossover from a Charge Coupled Network and put that into LEAP. Then I copied it and added switches so I could take out the 3 notch filters to see what each did. First is the Schematic then the network response with all the notches in place.

    Rob
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    Administrator Robh3606's Avatar
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    Here is what the response changes are as you take out the notches one by one. The first is Notch 1, then Notch 2, then the Sereis Notch /HP The Blue curve shows the changes from the original circuit.

    Rob
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    Administrator Robh3606's Avatar
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    The next 2 attachements show all the changes and the last is with notches 1 and 2 removed. This became the baseline for a modified crossover.

    Rob
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    Administrator Robh3606's Avatar
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    New schematic which shows the final network for now until I can take actual baffle measurements. As you can see from the previous post the response with both notches 1 and 2 removed was not bad. What I ended up doing was changing the values of the inductor and capacitor in the series HP filter and adding a low Q 1.5 notch filter centered at 1.6K. The notch took out the bump around 2 K and the changes in the HP smoothed out the response in the upper octaves.

    Attached are the results after the changes. So far they look good. I need to build up a network to see what the actual measurements look like.

    Rob
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    Senior Member JuniorJBL's Avatar
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    Looks very good Rob!!
    Always fun learning more.......

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    Senior Member grumpy's Avatar
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    Nice work.

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    Senior Member pos's Avatar
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    Impressive job and great result so far!
    What crossover frequency and slope are you considering?

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    Administrator Robh3606's Avatar
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    Thanks!

    Now I have to build up a filter to see how close the sym is to the real deal. That slope is with an 18b electrical filter. It's quite a steep crossover around 900hz is where I think it will end up.

    Rob
    Last edited by Robh3606; 09-12-2013 at 07:54 PM.
    "I could be arguing in my spare time"

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    Senior Member Jakob's Avatar
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    Interesting thread! Are all 476Be and Mg's 16 Ohm?

  12. #12
    Administrator Robh3606's Avatar
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    Are all 476Be and Mg's 16 Ohm?
    Yes they are both 16 Ohm drivers. A bit less but not 8 that's for sure.

    Rob
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    Senior Member Jakob's Avatar
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    Sorry if it's off topic, but what's the most important gain when designing speakers in using higher impedance CD's as JBL do?

    Regarding your measurements; how close to the horn mouth are they made?


    Have you come up with any possible box designs yet?

    Really looking forward to see your progress in this project.

  14. #14
    Administrator Robh3606's Avatar
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    Hello Jakob

    Sorry if it's off topic, but what's the most important gain when designing speakers in using higher impedance CD's as JBL do?
    Not sure aside from the fact that the overall impedance curve stays reasonable even with the parallel notches. I doubt that's the reason though someone else is going to have to answer that one.

    Regarding your measurements; how close to the horn mouth are they made?
    They were 2 sets one close about 18" the other out about a meter or so. There is not much of a difference between the 2 measurements. Once I get a network built I will remeasure with the horns and woofer in the enclosure to see what happens compared to the test baffle that the waveguides were measured on.

    Have you come up with any possible box designs yet?
    Now that spring has sprung here, I hope anyway it's been a long cold winter, I have my table saw set-up so I can finally cut some wood. I am going to try something along the lines of my Array set-up. Curved front edges on the woofer cabinet with a separate waveguide enclosure also with the waveguide flush mounted with curved front edges there as well. The idea being I can try to time align with a physical offset on the upper enclosure.

    Not sure exactly how yet. I am concerned about how to visually integrate the two cabinets as well as not causing diffraction issues as I am sure it will end up back a bit from the woofer. I have to really take a good look at where I think the centers are with the two drivers. I have always used the pole piece and thats easy with the 476Mg. Not so easy with the 2216.

    The discussion about the M2 in the other threads is getting me really curiuos about what the 2216's are going to sound like.

    Rob
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    Administrator Robh3606's Avatar
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    Now I get to start all over again with the right M2 waveguides!

    Rob
    "I could be arguing in my spare time"

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