AE/KEF Hybrid 3Way Center Channel


  • Member
    LocknLoad on #1315

    Hello All,

    Looking for some help and advice please. Sadly the slippery slope that is DIY has bitten me and my front stage can no longer keep up with my DIY subs.
    Never built a speaker as passive crossovers always seemed like a dark art that I should be wary of.
    I want to do my center first and then front L+R later.
    All my speakers are KEF as I like to coaxial they use… that said I am looking to get more performance in the 60-2Khz range.
    I currently run my AVR crossover at 80hz but would like to take it to 60hz if the center could handle it.
    Leaving it at 80hz is also fine as I imagine I will generate far more SPL with lower distortion with this setup vs my current KEF center.
    The goal is to run the two TD8X-8 drivers in parallel and present a 4ohm to the AMP.

    I would like some guidance and advice regarding the possibility of using a simple passive crossover for the coaxial driver+tweeter.
    This would save me an additional channel of amplification. I will probably use a inuke 3k DSP for the center channel especially if going with passive.
    If the consensus is fully active then was thinking about using a minidsp 4×10. That would give a 3x 3way for the front stage.

    Here are the models I did in Winisd
    SPL

    Filter and Cone Excursion

    This is what I have come up with so far. The crossover points most probably need to be moved around but I want to limit the movement of the coax in order not to interfere with the tweeter.
    The net volume required by the coax needs to be confirmed. Once I finalize the AE portion I will open and measure my Q900.

    I will be using the KEF Q900 Coax – here are some measurements http://www.stereophile.com/content/kef-q900-loudspeaker-measurements

    Ideal Feedback
    1 – What is the general consensus regarding the design
    2 – How complex would a 2way passive x-over be to build for the coax with the inclusion of a Notch/LCR filter around 4-5kHz
    3 – Comments/Suggestions on x-over frequencies and roll off to be used
    4 – Worthwhile looking at dropping AVR xover to 40hz? Winisd shows 100db at 40hz…

    Would really appreciate any help or guidance from those with experience.

    Thanks.


    Member
    Face on #11234

    @locknload wrote:

    Ideal Feedback
    1 – What is the general consensus regarding the design
    2 – How complex would a 2way passive x-over be to build for the coax with the inclusion of a Notch/LCR filter around 4-5kHz
    3 – Comments/Suggestions on x-over frequencies and roll off to be used
    4 – Worthwhile looking at dropping AVR xover to 40hz? Winisd shows 100db at 40hz…

    Would really appreciate any help or guidance from those with experience.

    Thanks.

    Too much overlap. Cross the mid to the woofers around 300-400hz to minimize cone movement and to keep the coax a point source. Do not play the woofers up the tweeter’s crossover point, it will be a mess.

    Keep the original crossover and use a Mini-DSP to add a LR2 slope between 300-400hz. There’s also the possibility of the AE woofers being more efficient than the KEF coax, another reason active will be advantageous.

    As far as the AVR’s crossover point…due to the drop off, I would recommend either a larger and/or ported enclosure, or a crossover freq of 80hz.


    Participant
    stryke on #11235

    Agreeing with most of what was said. I think that 300hz xover point is probably going to be about right for the distance between centers of the two outer drivers. Active is definitely the way to go for that.


    Member
    LocknLoad on #11236

    Thanks Face and Stryke for the feedback.

    I have a CSS calibrated usb MIC and would no doubt have to measure each driver in order to tweak filters based on the enclosure response.
    I have updated my proposed design. If there a formula for estimating the better crossover point based on the distance between driver centers?

    Two Drivers in 15L with 500W.

    I included two filters to reduce sub 100hz roll off and protect cone excursion

    Still debating passive vs active – Came across this – worth a look?
    http://www.parts-express.com/prv-audio-3df400-1800-three-way-crossover-board-400-1800-hz-with-selectable-attenuation–294-2869

    Again…. thanks for all the help.


    Participant
    stryke on #11237

    I would look at the minidsp as an active solution. I think you will be much better off than with the passive design. With the passive you won’t easily be able to time align and correct phase between the drivers. Just measure the distance between centers, then look at that wavelength. For example, 16″ between centers comes to 848hz. Divide that in half gives 424hz. So at 90 degrees to the face you would have nulls at 424hz with the 8″ drivers being 16″ apart center to center. Directly on axis you will be fine. As you start to get further off axis these begin to appear. I would cross low enough to keep that from being an issue in your off axis power response.


    Member
    LocknLoad on #11238

    Decided that I will be going 3 way active with minidsp 4×10

    Final question (hopefully) regarding box size and Qtc. Power applied is 200W per driver in all scenarios. Feel free to check my math for the TD8X-8.

    7L each driver = qtc 0.5 and Fsc 104Hz
    10L each driver = qtc 0.446 and Fsc 91Hz
    15L each driver = qtc 0.397 and Fsc 80Hz

    I have read conflicting comments regarding going below a Qtc of .5. General consensus seems to lean towards NOT going below .5
    I have the space so it makes no difference to me and it does not appear to effect much in Winisd either.

    With a planned crossover of either 60 or 80Hz on the AVR – What is the recommendation to best match qtc and planned crossover?

    Thanks again for the feedback.


    Member
    Face on #11239

    @locknload wrote:

    Still debating passive vs active – Came across this – worth a look?
    http://www.parts-express.com/prv-audio-3df400-1800-three-way-crossover-board-400-1800-hz-with-selectable-attenuation–294-2869

    Again…. thanks for all the help.

    I would avoid that crossover and every other generic passive crossover like the plague.
    @locknload wrote:

    Decided that I will be going 3 way active with minidsp 4×10

    Final question (hopefully) regarding box size and Qtc. Power applied is 200W per driver in all scenarios. Feel free to check my math for the TD8X-8.

    7L each driver = qtc 0.5 and Fsc 104Hz
    10L each driver = qtc 0.446 and Fsc 91Hz
    15L each driver = qtc 0.397 and Fsc 80Hz

    I have read conflicting comments regarding going below a Qtc of .5. General consensus seems to lean towards NOT going below .5
    I have the space so it makes no difference to me and it does not appear to effect much in Winisd either.

    With a planned crossover of either 60 or 80Hz on the AVR – What is the recommendation to best match qtc and planned crossover?

    Thanks again for the feedback.

    I would lean towards a crossover of 80-100hz if you decide to go sealed.

    I would lean towards a Q of .5 and then add EQ. According to your charts above you should be fine power handling wise. You possibly may have enough room for a slot port though… 😉


    Participant
    stryke on #11240

    Yes, as Face says, generic crossovers just do not work. There is a very important phase relationship between drivers that can only be worked out well with measuring and modelling a crossover for those drivers measured in their specific enclosure. Pick up a microphone like the Umik-1 from MiniDSP for $75 and Room EQ Wizard for free. Then you can measure and setup things with DSP.


    Member
    LocknLoad on #11241

    I got a CSS calibrated usb mic that I am currently using to measure my room with REW. My dismal room acoustics measurements convinced me to build floor to ceiling super chunk bass traps.
    Got some success out of them and I am currently building another 10 odd panels and traps to further tame the room. I have pretty bad decay times.
    I already use a minidsp 2×4 balanced for my subs, so I am familiar with the interface. The minidsp 4×10 is $500 but still less than what three passive crossovers would cost.

    I got my mind set on sealed with 2x TD8X units each in 7-8 liters with 200W power fed to each as well. I really hope to get decent output to be able to cross the AVR at 80hz.
    Winisd models to

    109db at 3 meters at 200hz
    106db at 3 meters at 100hz
    104db at 3 meters at 80hz (113db at 1m)

    Final sanity check – For my purpose the TD8X models much better than the TD8M

    Sealed boxes with 8L per driver

    AVR will be crossed at 80hz but HP filter included as backup

    Only thing left is to place the order and begin my virgin voyage into speaker building….


    Participant
    stryke on #11242

    The TD8X looks to be a very good way to go with this. Slightly less efficient but with the coax driver you currently have these will be a better match. It all looks good.

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