FS: New Old Stock DIYSG Concentric-8 Coaxial Drivers

Discussion in 'Classified Section' started by Matt Grant, Oct 13, 2023.

  1. #1 Matt Grant, Oct 13, 2023
    Last edited: Nov 22, 2023
    Buried in the DIYSG warehouse were several dozen new Concentric-8 drivers, Erich and I dug them out on my recent visit and I've been slowly giving each a QC check and now have many tested and available for purchase. I also grabbed a smaller number of Concentric-6 drivers too.

    These were higher end coaxials with better dispersion characteristics then the Volt-8, much improved frequency response both on and off axis and lower distortion as well. That puts these much closer to the Vortex coaxials in terms of sound quality then the Volt line.

    They would be great for surrounds, LCR speakers in living room sized home theater setups, or just used as a stereo pair for two channel especially if you go with a larger ported cabinet. They would also be great if you want a set of coaxial studio / near-field monitors that you can really crank up.

    The HF side uses a 1.75" damped titanium diaphragm with a copper pole pole piece to lower inductance and distortion.

    Here are the T/S specs of the woofer:
    * Piston Diameter = 165.1 mm
    * f(s)= 72.00 Hz
    * R(e)= 5.18 Ohms
    * Z(max)= 75.35 Ohms
    * Q(ms)= 8.750
    * Q(es)= 0.646
    * Q(ts)= 0.602
    * V(as)= 14.350 liters (0.507 cubic feet)
    * L(e)= 0.46 mH
    * n(0)= 0.79 %
    * SPL= 91.08 1W/1m
    * M(ms)= 21.92 grams
    * C(ms)= 0.22 mm/N
    * BL= 8.92
    Power Handling = 250w

    Cabinet Design:
    I just did a new refresh on the crossover design in a sealed cabinet that measures 10" wide x 13" high x 10" deep which matched the original few sample cabinets Erich had assembled from Bamboo and Corian. In that size sealed cabinet it will just about hit 80Hz and should be usable with either an 80-100hz crossover.

    A larger ported cabinet could be made 10" wide x 16" tall x 12" deep tuned to 55Hz for better bass extension, that should give an f3 in the upper 50's. Additionally a ported tower cabinet could be used as well something around 1.5cuft tuned to 45-50Hz should yield an f3 in the low 40's.

    Like the Volt-10 these could also be used in an in-wall/in-ceiling infinite baffle installation and crossed at 80Hz without needing a backer box. Though you can certainly use an enclosure if wanting to increase sound isolation for the room or port it for additional bass extension/output. I have a alternate crossover design developed if using them In wall/IB like this which eliminates much of the baffle step compensation on the woofer and removes some padding on the HF driver to give a flatter frequency response and greater sensitivity in that kind of install.

    Photos of the original Bamboo/Corian Concentric-8 cabinets:


    Drivers Available:
    I have two different batches of these drivers, the first batch has a black HF cover and the dust cap is installed. The second got a custom machined aluminum back cover but the manufacture did not install the dust caps I will include a free dust cap with those drivers if you want to glue it on, otherwise it's perfectly safe to use the driver without the dust cap in a home environment. The back plate does not make a difference to the sound quality and the dust cap only makes a very minor difference to the frequency response.

    I currently have 20 drivers with the custom backplate and no dustcap installed, and 15 drivers with the dust cap and black backplate.

    Photos of the drivers:



    $200 each + shipping. I will include a bare crossover PCB for free with the drivers.

    $5 off if you don't want or need the crossover PCB.

    $10 off each driver if buying four or more.

    I can also assemble the crossovers if requested, a fully assembled crossover would be $80 for the standard version, the In-wall crossover variant costs $70.
  2. #2 Matt Grant, Oct 13, 2023
    Last edited: Nov 10, 2023
    Crossover Info:

    Like I said above I retested the design and made some slight adjustments to the crossover largely focused on improving midrange linearity. Here is the schematic for use in a standard cabinet, recommended baffle width of 10":
    Concentric-8 v1 Crossover Schematic (2023).png
    Recommended parts for use with the PCB:
    C1, C2, C3, C4 and C6 should be poly caps, C5 and C7 should be NPE.
    L1 and L2 should be 20 gauge air cores, L3 and L5 should be 18 gauge I-cores, L4 should be an 18 gauge air core.
    R1, 2, 3, 4 and 5 should be 10w while R6 and R7 were designed to be 5 watt to save space on the PCB since little power is dissipated by those two.

    Optional - The resistor R1 can be adjusted up or down to fine tune treble output, making it 12 Ohm will reduce output by about 1.5dB, or 15 ohm will reduce by 3dB if you like more laid back highs. Making it 8 Ohm will increase it by about 1dB, 7Ohm will be 2dB and 6 Ohm is about 3dB if you wanted a sharper sound or to give a flatter response off axis say if the MLP is off axis from these when used as surrounds.

    10, 12 Ohm and 7, 6, 5 Ohm are optional values that give similar results on the In-wall version of the crossover.

    Concentric-8 v1 (2023)-3.jpg
    Concentric-8 v1 (2023)-4.jpg
    Concentric-8 v1 (2023)-1.jpg

    In-Wall / In-Ceiling / IB install Crossover:
    Pretty self explanatory, this crossover should only be used if installing the cabinet or bare driver flush in a wall, column, or ceiling. It eliminates much of the baffle step compensation that's needed in a normal cabinet resulting in a more even response and greater sensitivity.
    Concentric-8 v1 In-Wall Crossover Schematic (2023).png


    It's been pretty poor here weather wise for outdoor measurements the past couple weeks so I have not had a chance to measure the speaker on my larger turntable. But here are some measurements from my indoor turntable which just offers reduced resolution (1 meter distance, 5ms gate, 1/6th octave smoothing) Concentric-8 tested in the sealed 10" x 13" x 10" cabinet:

    VituixCAD Power+DI.png
    Concentric-8 v1 Crossover (v1.00) 2023 Directivity (hor).png
    VituixCAD Directivity (hor).png

    I still need to gather a few more measurements, namely distortion, compression and impeadance. I'll post those when I have them.
    taloyd likes this.
  3. Hi Matt, i sent you a PM about getting some of these. Thanks!

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