Project NEXUS... A timbre matched family of Hi-Fi/HT speakers

Discussion in 'DIY Speakers and Subwoofers' started by Matt Grant, Feb 10, 2014.

  1. In this post, it states that the woofers in the MTM are wired in series. In the xover schematic it appears to be wired in parallel. Series would be positive into woofer one and negative from woofer one into positive of woofer two and then minus from woofer two back to ground. Correct?
  2. Yeah that reply was referring to a earlier version of the crossover when I had the woofers wired in series. I have them wired in parallel on the current/latest crossover design which makes it a 4 ohm nominal design. Everything still holds true about that statement besides the AVR running cooler.

    In parallel you see roughly a 6dB gain in sensitivity compared to the series crossover design because it is able to extract more current/power from the amplifier. Most amplifiers and AVRs are capable of driving a 4 ohm load which is why I decided to go with parallel wiring and gain that extra 6dB in output.

    Now because of the extra sensitivity of the 4 ohm parallel MTM design it will not draw any more current then the 8 ohm TM design when both are played back at the same volume level. Which means an amplifier or AVR won't run any hotter powering the 4 ohm MTM vs the 8 ohm TM (again at the same volume levels).
  3. I have seen discussions that are intriguing about an older speaker that I think you designed . The Fusion 6. Are parts and design still available for that speaker?
  4. #130 mga2009, Oct 28, 2019
    Last edited: Oct 28, 2019
    Just finished my Nexus TM.

    They look almost nice (at least for me)... I just had a little trouble with the veneer, as I made the holes before veneering, and cutting the circular shape of the veneer was not possible with the router bit I had so I did it by hand with a Dremel Multipro and a sanding disc. The results... a not quite circular shape.

    Anyways... I am quite happy with the sound. Here is a FR measurement in my room which is untreated and has a TON of reverb. This measurement was made at the MLP with the subwoofer turned on, and before running the receiver's auto calibration. It has a 1/12 smoothing.

    And as you see on the picture, the speakers are not properly positioned as I need to finish the veneer on the second subwoofer.

    I don't know much about measurements, but it seems quite flat for me.

    Thanks Matt for this great design. Looking forward to build a couple more and get a complete 7.1 Nexus HT. My next approach will be an On Wall Nexus TM (or MTM? which would be better) for surround duty. The room is very small so these will be on the side of the couch, so I am planning on make them very shallow, a lot taller and the same width, and probably with a little closed angle to aim them to the MLP.

  5. Can the sealed WTMW center channel be modified to use it as L and R? Any changes in the XO?

    I really hope this thread come back from the grave... these are really nice designs
  6. You should be able to get away with the standard crossover if you wanted to use them for left/right with the midrange and tweeter centered between the woofers but turned upright.
  7. Between the subwoofers there is only 7 inches, which is not enough to fir the tweeter and mid woofer.

    Should I bring the tweeter and the mid closer and make them fit or should I separate the woofers?
  8. Yeah you will want to make the box a little taller and spread the woofers out to fit the midrange and tweeter between them.
  9. Would this be too much??

  10. That's perfectly fine.

    There is more leeway to give the woofers wiggle room, I didn't intend for you to think like you have to keep everything as tight as possible. Unless you are purposely trying to keep things fairly compact in which case carry on.
  11. Correct me if I am wrong, but it's better to have all the drivers as close as possible, correct?

    Also, considering I do not listen in to high SPL (around 80db), can I expect a performance improvement from MTM to WTMW in L-C-R channels? Maybe in the midbass?
  12. It is beneficial to try and keep the driver spacing as close as possible but for the woofers with the frequency range they cover having them spaced even an inch or two further would hardly be detrimental. I didn't place them super tight on the original center channel design for this reason, I thought the extra space was more aesthetically pleasing and the impact on performance is practically negligible.

    I do think the WTMW does sound better then the MTM even at low volumes, so I think that alone answers your question.
  13. Matt,

    Thanks for your reply. Now in my country the USD$ valuation has gone to the roof in the last days, and I might need to reduce my budget on LCR speakers, so... back to the Nexus MTM design...

    Now, If I use the MTM for the center channel, I would like to bring the port up to the front (speaker is located in a closed-back rack). One alternative is to locate it beneath the tweeter (haven't make the measurements, so I don't know if it fits) and another alternative is to make the enclosure a little bigger (wider) and locate them next to the woofers in the outer side of the speaker.... in this case If I would like to use 2 ports to make it look like the Elac Debut 2.0 B5.2 Center, should I use two equal ports of half the lenght? Or, should you recommend tune it to a different frequency, as I will be making a "bigger" enclosure"?

    Thanks in advance for taking the time to reply.
  14. What you can do is reduce the depth of the enclosure to keep the internal volume the same then use two ports around 1.5" (38mm) diameter and 5" long (127mm), this should give the same tuning as the original single port.
  15. Thanks! Will do.

    Whats the total net volume of the MTM? According to my calculations it's near 0.50 ft3
  16. That's correct, actually anywhere between 0.45 and 0.55 ft3 would work just fine.
  17. Matt, thanks for your reply!

    I think I am really pushing it with so many questions but... is there any possibility to replace the tweeter cap with 2 cap in series to sum the correct amount? I am getting a very good price on Jantzen Superior Z-Caps and it seems they don't have the "correct" values... So I thought I might use 2 caps to sum them and get the correct amount...
  18. What values do you have access to? It's easier and more economical to use two capacitors in parallel to get the correct value rather then placing them in series. Something like a 2.2uF + 3.9uF in parallel to replace the 6.2uF, Could also use a 3.9uF instead of the 4uF.
  19. Thanks Matt, parallel is what I meant (sorry, not an electronic guy)...

    So I just need to get the correct sum, and wire them like this:

  20. Yes that's correct.
  21. Thanks!

    Hey Matt, I noticed there are not any frequency response plots for the Nexus line... is there any reason for it? My TM Nexus's FR look very nice compared to some more expensive 2 way's, but it would be great to take a glimpse to the MTM and Nexus Center plots.
  22. Hi Matt,

    I love the idea of these speakers and am considering building a pair. Do you happen to have any more of the PCB boards for the tower and center speakers left?
  23. I only have two PCBs for those left and one may be spoken for but I'll likely get more made up soon.
  24. I forgot to get measurements with the new crossover updates but there isn't a huge change in the shape of the response from the older crossovers especially in regards to off axis behavior. I'll attach those below.

    Nexus MT:
    On axis
    TM on axis.png

    Off axis horizontal 0-90 degrees
    TM horizontal.png

    Nexus MTM:
    On axis
    MTM on axis.png

    Off axis horizontal 0-90 degrees
    MTM horizontal.png

    Off axis vertical 0-90 degrees
    MTM vertical.png

    Nexus Center:
    On Axis
    wtmw center on axis + phase 8-23-2014.png

    Off axis horizontal 0-90 degrees
    wtmw center 0-90 degrees horizontal.png

    Nexus Tower:
    On Axis in room
    on axis 8-21-2014.png
    mga2009 likes this.

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