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. #1 Matt Grant, Feb 10, 2014
    Last edited: Jun 30, 2023
    Timbre matched family of Hi-Fi/HT speakers all based on the same midwoofer (Dayton DS135-8) and tweeter (ND28F-8).

    These designs came about from my interest in building a conventional 3-way design (which there seem to be a lack of kits for) and one which would allow for an ideal horizontal center channel use. I wanted to use drivers that would offer very good performance yet keep the cost of the design in reach of those looking not looking to spend an arm and a leg. I also wanted the drivers to match if possible and give a nominal 8 ohm load so it would be safe for even the most anemic AVR or those super cautious users who just don’t want to risk driver a lower impedance speaker. Finally I wanted the midrange/midbass able to be used in a compact two way surround with decent power handling and extension in a small ported enclosure.

    I settled on the Dayton ND28F-6 for the tweeter, the Dayton DS135-8 as the midrange and two Dayton SD215-88A’s as woofers. Visually they match well, the DS and SD drivers sharing the same frame style and cone material and all the drivers looked to perform well within their respective bandwidths.

    I’ll update and post links to each of the respective designs below when I get them written up.

    TM 2-way

    MTM 2-way

    WTMW Center channel 3-way (configurable in vertical WTMW cabinet or TMWW tower form)

    MTMWW Tower

    Here is a nice picture someone got of the tower designs I brought to the 2014 Midwest Audio Fest:
    Toneb210 likes this.
  2. Re: Project NEXUS...


    They say the measure of man is his family....... :)
  3. #3 Matt Grant, Feb 15, 2014
    Last edited: Feb 5, 2024
    Re: Project NEXUS... (Warning photo heavy, lots of graphs and schematics)

    TM/MTM designs

    Update 1/13/17, Enclosure and crossover redesign for the TM and MTM, not as tight of a squeeze on the baffle and larger volume improves bass response. Crossover updated for new baffle size and for slight changes in newer batches of tweeters.


    I ended up
    putting large 5/8" round overs on the sides of these cabinets which I feel look better then the square edges. I'll end up wrapping them in the same veneer as the towers and get a photo of them at that point.

    -Nexus Cabinet Cutlists-

    These designs can put out a lot of sound for their size. The DS135 is quite capable of running fullrange in a small ported enclosure (0.15-0.25cuft) tuned to 55-65hz but is best used with a subwoofer. My original test enclosure was about 0.15cuft, 6"w x 9"h x 8.5"d tuned to 60hz with the 1-3/8" adjustable port from PE. New 2018 enclosure is 7"w x 10"h x 9"d, built from 1/2" MDF, using the 1-5/8" flared port from PE (port left at full length). I have the port installed on the back directly behind the tweeter for both this design and the MTM.

    The crossover is about 2100hz, fairly low but the ND28 handles it well without any rise in distortion. The low crossover and tight driver spacing allows this design to work quite well as a nearfield monitor with very little distance needed for proper summation between the drivers. It also allows a decently large vertical listening window. Don't let the nearfield comment scare you away from using it in a larger listening space, with a highpass filter at 80hz it will handle more power then pretty much any AVR is capable of delivering.

    The MTM is 7"w x 16"h x 10.5"d (1/2" material though you can use a 3/4" baffle). It uses the 2-1/2" flared port tube from parts express cut to 6" long. The bass output pair of those woofers can produce is quite impressive considering the size of the enclosure. The MTM has the advantage of a reduction in distortion of about 6dB below the crossover from the use of two woofers handling the content vs. the single woofer in the TM design.

    I chose to add a decent amount of BSC into these designs which gives them a very full sound. The midrange is very clear but not overbearing, and the treble smooth without sounding dull. Bass is again very good for such a compact speaker.

    Crossover schematic and parts list which includes drivers, crossover parts and port tube.

    -Nexus TM-:

    2021 Nexus MT Crossover Modification/Update:

    After testing on my new outdoor turntable rig which provides much better frequency response resolution I decided to make some adjustments to the crossover to eliminate a peak in the response which was masked in my previous measurements .

    Link to the new set of full measurements with the updated crossover.

    Here is the new Schematic:
    Nexus MT v1.03 crossover.png

    Parts List:
    C1 - 10uF Poly
    C2 - 3uF Poly
    C3 - 22uF NPE
    C4 - 0.47uF Poly
    C5 - 68uF NPE
    C6 - 6.8uF NPE

    L1 - 1.5mH 18 AWG I-core
    L2 - 0.60mH 20 AWG Air Core
    L3 - 0.40mH 18 AWG Air Core

    R1 - 10 Ohm 10W Wirewound
    R2 - 15 / 16 Ohm 10W Wirewound

    If you wish to upgrade from the prevoius version of the crossover to this version the existing 50uF cap (C3) should to be changed to 22uF.
    Then 6.8uF and 68uF NPE capacitors and a 0.40mH air core (18 gauge) should all be wired in parallel and placed inline on the positive woofer lead.

    If you are using a class D amplifier you may want to add an ~8-20 ohm resistor in series with the C4 capacitor. This will not change the frequency response of the speaker but prevents issues from the capacitive load in the ultrasonic range which some switching amps do not like. This resistor can be small anything over a 1 watt rating should work.

    -Updated set of crossover PCBs available for the Nexus MT-

    Nexus MT-1.jpg
    This set of boards puts the new network on a separate board for ease of mounting. I felt one board for everything would be a very tight squeeze through the woofer cutout or to mount in the box. The additional board is wired inline between the main crossover board and the woofer.

    -Nexus MTM-:



    (The 15uF NPE could be upgraded to a poly cap if designed, #027-432)

    If you are using a class D amplifier you may want to add an ~8-20 ohm resistor in series with the C4 capacitor. This will not change the frequency response of the speaker but prevents issues from the capacitive load in the ultrasonic range which some switching amps do not like. This resistor can be small anything over a 1 watt rating should work.


    -2021 new detailed measurements of the Nexus MTM can be found here-

    Link to Crossover PCBs for the Nexus MTM design:
    -Nexus MTM Crossover PCB-
    Nexus MT-MTM-1.jpg
  4. #4 Matt Grant, Feb 15, 2014
    Last edited: Jan 13, 2018
    Re: Project NEXUS...

    TMW 3-way design - Update, no real advantage with this design when compared with the MTM and far less cost effective.
  5. #5 Matt Grant, Feb 15, 2014
    Last edited: Feb 5, 2024
    Re: Project NEXUS...

    WTMW Center
    Edit: Could also be built as a vertical WTMW sealed or ported


    This 3 way design uses two of the Dayton SD215A-88 subwoofer drivers for the the low end.

    The designs like the TMW puts the midrange and tweeter in a separate chamber that extends to the top/sides or top/bottom for the center channel layout. The chamber is just deep enough to fit the midrange, 3.75" from the front baffle face to the rear of the chamber (driver flush mounted).


    The center channel measures 10" high x 26" wide x 12.5" deep (built from 3/4"). This gives the woofers about 1cuft of volume, they are run sealed and f3 is approximately 58hz. The midrange chamber is 6.5" wide x 3" deep internal and run the height of the cabinet. I run the side panels of that midrange chamber all the way to the back for added bracing and cut some holes in them behind the midrange chamber o allow airflow around the back of the cabinet between the woofers. Driver center positions are marked in the 3d model above.

    Nexus Center Cabinet Cutlist:
    Sized for 3/4" cabinet material, Overall Cabinet Dimensions - 10"H x 26"W 12.5"D:
    Baffle/Back (3/4") x2: 10" H x 26" W
    Sides (3/4") x2: 8.5" H x 11" W
    Top/Bottom (3/4") x2: 26" L x 11" W
    Front to Back Braces (3/4") x2: 8.5"H x 11"W - Openings should be added behind midrange chamber)
    Mid/High Chamber Back (3/4"): 8.5"H x 6.5"W - This one gets sandwiched between the other two braces to form the sealed midrange chamber.

    The tower you see in the first post was 10" wide x 36" tall x 16" deep, however that was just a test box and I personally would build it taller and shallower. The tower was ported and tuned to the high 20's. The pair of woofers can be used ported from 1.5 to 3 cu ft. tuned between 24-32hz.

    As expected bass performance from a pair 8" subwoofers is very good, plenty of excursion capability means you aren't likely to bottom the drivers without using a power amp. A pair of the towers feed with 100w each will outperform a decent 15" sealed subwoofer in a 3cuft box with 500w. Don't let all that bass talk let give you the impression the center channel makes vocals sounds boomy, I feel the crossover blends the drivers very well and you are left with a rich full midrange without any sign of overbearing or peaky bass.

    The design can handle amplifiers up to 200-400w.

    Detailed measurements for the Nexus Center posted here.

    Crossover info.
    (Note Inverted Polarity on Tweeter and Midrange, dual voice coils on woofers are wired in series then the two woofers tied in parallel to the crossover):

    Parts list (drivers & crossovers components):
    The 50uF and 12uF get tied in parallel to make 62uF. The 15uF and 8uF NPE caps on the midrange could be upgraded to poly caps if designed, parts 027-432 and 027-426.

    Crossover Photo:
    Nexus Tower-Center1.jpg
    -Link to Crossover PCB if you are interested in purchasing one-
  6. #6 Matt Grant, Feb 15, 2014
    Last edited: Feb 5, 2024
    Re: Project NEXUS...

    MTMWW tower / WTMMW center design, could also be configured as a WMTMW design

    Edit: It comes to life at last!

    This design took 3rd place in Dayton Audio category at 2014 MWAF! :D

    I ended building them without that bevel at the top of the cabinet but instead made the grills beveled.

    New Photos (2023) they have a couple scrapes and dings now from loading them in and out of my vehicle a few times but still sound just as good.







    A couple shots I took of them at MWAF:



    Here is the crossover info
    Note Inverted Polarity on Tweeter and Midrange. Dual voice coils on woofers are wired in series then the two woofers tied in parallel to the crossover:

    Note the crossover BOM specs non-polarized electrolytic caps for the midrange 12uF and 39uF (22uF+17uF) however feel free to upgrade those to poly caps if you wish (027-430 & 027-442). I do have poly caps in mine.

    -Link to Crossover PCBs for sale-

    Nexus MTMWW Tower Crossover PCB Assembled.jpg

    Enclosure construction info, I built the enclosure out of 3/4" MDF, outer dimensions (not including base plate) are 46" high, 15" deep, 10" wide. The midrange chamber is small, it runs the internal width of the cabinet, the depth of that chamber is 3" (internal) which gives about an inch of clearance for the mids, the height of that chamber is 14.75". The angle on the back of the cabinet is mostly for appearance and starts at the top 10" back and runs down to 30.5" high. The cabinet can be built without the angled back if desired as just a regular rectangular shaped cabinet, no real change in performance. There is window bracing above/below and in-between the two woofers. The midrange chamber itself adds to the bracing on the top part of the cabinet but there are a couple braces running front to back inside the mid chamber (between the mids and tweeter) and a brace behind the chamber to the angled rear section (I forgot to add that on the 3d model).

    Nexus MTMWW Tower Cabinet Cutlist (Rectangular, no sloped back):
    Sized for 3/4" cabinet material, Overall Cabinet Dimensions - 46"H x 10"W 15"D (not including baseplate/feet):
    Baffle (3/4"): 46" H x 10" W
    Back (3/4"): 46" H x 8.5" W
    Sides (3/4") x2: 46" H x 14.25" W
    Top/Bottom (3/4") x2: 13.5 L" x 8.5" W
    Window Brace (3/4") x3: 13.5" x 8.5" - Two should be full window braces and are placed below/between the woofers, the third above the woofers forms the bottom of the midrange chamber and should only have openings behind that chamber.
    Internal Midrange Chamber Back (3/4") x1: 14.75" H x 8.5" W.
    Another window brace could be added behind the midrange chamber, in this case it would be: 9.75" x 8.5", otherwise you can add stick bracing there.


    Driver centers down from top measured fractionally: 3-11/16", 7-7/8", 11-1/16", 20-1/2", 29-1/2".

    Port Center 6-1/8" up from bottom of cabinet:

    Edit here is a photo I took when I was dry fitting the cabinet:

    The cabinet uses a 4" precision port with the middle length cut to 5.5", this gives a total length of 12" with the flares added. The effective tuning is about 28 Hz, mid/low 20hz extension is possible with these and they have similar output capability of a sealed high excursion 15" subwoofer driver, so they can shake things. ;D

    I really like how these turned out they are very smooth and detailed especially after the last few adjustments. They are also capable of quite a bit of output for a design using a dome tweeter, sensitivity is ~88-89dB at 2.83v through the midrange/treble and closer to 90-91dB in the bass. I was pushing these with a 200w/channel amp up to a touch below clipping and they took it like a champ, which would be enough to fill a good sized room. Very dynamic for a design like this as well.
    m4bgringo likes this.
  7. Re: Project NEXUS...

    Nice. I was just searching for designs with the Designer Series speakers a week or two ago!
  8. Re: Project NEXUS...

    ^ thanks

    Updated posts to include more info.
  9. Re: Project NEXUS...

    I' m about to order this kit :

    But I have a quick question. In your opinion is it worth it to get the MTM ? ( )

    Both are in my budget. These will be used primarily for music in an office (but may get played decent levels) and would be eventually paired with sub.

    I plan to run them off an old school but higher end Yamaha AVR (too old for HDMI and all that) in stereo (with sub). I had a thread at AVS [SIZE=78%][/SIZE] where I was looking for a nice pair of $250 speakers - as opposed to buying PC speakers. My office is private room, I can mount them on the wall on a shelf rather than place on my desk. I could even use speaker stands if I wanted.

    Any advice for me ? Eric recommended I try these out and they look like a winner to my noob eyes. Just looking for some feedback before I pull the trigger. Whatcha think ?
  10. Re: Project NEXUS...

    The MTM does have a few advantages over the TM,

    Using two woofers you get 6dB more output headroom and at the same time close to a 6dB reduction in distortion (across the range where the woofers are playing) for any level compared to the single woofer.

    The MTM layout reduces some energy (again in the midrange) that would otherwise reflect off the floor/ceiling, that's usually always a good thing.

    The MTM is actually 16 ohms nominal across the woofer range (~10-12 ohms) as the woofers are wired in series. If running these off an AVR you may notice it running cooler as it is not pushing as much current.
  11. Re: Project NEXUS...

    OK! MTM it is. Ordering now! Thanks again for your help and awesome design. I'd like to get started on the boxes and wood working tomorrow in prep for the kit arriving. Where can I get the info I need on instructions for building it properly ?
  12. #12 Matt Grant, Mar 27, 2014
    Last edited: Jan 25, 2018
  13. Re: Project NEXUS...

    SWEET ! I just placed my order for the MTM NEXUS. I can't wait to build these :) Thanks again for the help!

    You think I should just make a full size panel for a brace inside then cut away with a jig saw or whatever ? Cut into a U shape ? Or should I just make braces that go across in both directions ?
    Does it really matter or is it just important to brace the box ? I could easily just cut a couple braces to go across in both directions where they fit and glue them up, holding in place with a quick brad to let it dry after the box is completed.

    Should I wait till the kit arrives and I have the top and components before I put in the brace ? Or secure it. I could make the box now, cut the brace but not install it yet. That makes sense ?

    I have some (a full sheet) of 3/4" MDF already. Any reason not to just use that for the box ? I could easily hit HD and buy anything else if it matters. Advice ?
  14. Re: Project NEXUS...

    I am not sure if the panel brace will fit unless you run it vertical in the box. The diameter of the port might be too large to place the braces between the woofers and tweeter (if that makes sense) so you might want to hold off gluing that in until you receive the parts for the kit to double check. The style of bracing does not matter much but simple dowels or strips of MDF will be easiest to cut and place where needed.

    You could use 3/4" MDF but the enclosure volume will shrink if you keep the outer dimensions all the same. You would need to add 1.5" or so to the overall depth to maintain the correct volume. The adjustments to the panel sizes I gave below would be: top/bottom now 10" x 5", sides 10" x 15".
  15. Re: Project NEXUS...e

    Ok I could add the extra to account for 3/4"

    Otherwise I actually have some 1/2" too already so I'm good either way.

    The main question I have is what specific internal volume am I shooting for ?


    What is the exact dimensions of the faceplate that comes with this kit ?

    I want to start the boxes before the kit arrives and I want to make sure the front fits perfectly.
  16. Re: Project NEXUS...

    All that info is in the TM/MTM post,

    Volume should be ~0.3-0.4 cu ft.

    Baffle is 6.5"W x 15"H.
  17. Re: Project NEXUS...

    Was the MTM done 16ohm in order to keep the XO and timbre the same? I like that idea, nice work. The sensitivity increase of going 4ohm is tempting, but ultimately it's all the same isn't it 8)
  18. Re: Project NEXUS...

    Yes that and the tweeter does not have enough output to really match up with the two woofers paralleled. It does make things easier not having to change the tweeter crossover any between a TM and MTM when wiring in the series like that.

    I designed the Fusion-6 MTM that same way.
  19. I saw the schematic earlier in this thread. I think I'll probably end up running back here for some help, or at least post up a picture and recap and ask for a quick double check before I seal it up.
    Anything special I need to know about wiring it all up ?
  20. OK I think I need some help - or at least a double check and a thumbs up before I proceed.

    Since I have the MTM here is what it looks like:




    so here is what I have now on my table:


    My questions are:

    1.) The red areas- and what appears to be the negative or the end - where does it go ? Does it all go back to the [ - ] input terminal and back to the amp ?
    2.) Does this look ok ? Anything wrong ?
    3.) Could I use a piece of 1/8" or 1/4" Masonite to mount at the crossover board ?
    4..) These get soldered right ? Do they connect directly to each other ? Or wire in between ?
    5.) Anything else I need to know ?

    Thanks in advance
  21. [​IMG]

    Any reason I could not wire it like this ?
  22. I'm interested in the MTMWW design..... any update on it?
    If my eyes weren't deceiving me, I thought I saw it in a photo spread from PEs' MWAF last month, is that correct?

    will be watching this one...
  23. I think you're right, it was there. I think it won something too. mtg would know.

    BTW, is your name Matt Grant by any chance? Cause MTG90's name is,,, Matt Grant ;D
  24. No, my name is Mark, and I recently moved to Colorado Springs. I already have 8 of the older SD215-88 woofers and was in the process of trying to design a very similar MTMWW using the ND20FA-6 tweeter but was having a difficult time deciding on what mids to use. I like that the Designer Series has the same look as the SD215s and I was looking at either the DS90s, DS115s or DS135s....
    But since I'm new to the use of PCD, I have had to play with it a lot...
  25. Sorry, I meant to reply earlier but I would not had have much of an update to give.

    These were at the MWAF this year in the Dayton category and took third place. Quite respectable considering I only had two nights to work on the crossover in stereo.

    I wanted to try a few changes to the crossover that I had not had enough time to do before the MWAF, specifically changing the midrange high pass to first order which would alleviate a impedance dip to 4 ohms near 1k. That dip was sucking a lot of power through the midrange padding resistors, so much that I had ~80w in resistors there and placed them in front of the inside port termination for extra cooling.

    After I got back I noticed the red cherry vinyl veneer I had used did not like sitting in a hot car for a day that I spent at Erich's shop. It looks as though it expands in the heat causing it to bubble and press out at the edges, I was mad about that and pulled the drivers and tore the veneer off one. Then I decided to work on other things.

    I just got back to them the past few days and made the changes I wanted to try with the crossover now I have everything ready, the MTMWW post on the previous page will be updated shorty. Work on the WTMW center and TWM 3-ways will follow shortly.

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