Vortex-15+
15" Coaxial Two Way Design
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Design description and thoughts:
This is an updated crossover and cabinet design for the Vortex-15 coaxial speaker kit which was sold by DIY Sound Group (now Cinergy Audio).
The Vortex-15 was originally tested and tuned using a large ported tower cabinet and while that sizable cabinet did offer great bass extension from the pro sound coaxial the tall design with a single driver resulted in a minor standing wave/internal reflection dip which muddied the low midrange and caused some difficulties when I was trying to balance the sound during the initial crossover design. I had since regretted not offering a crossover designed in/around a more conventional cabinet but since the drivers were discontinued I did not pursue that at the time.
More recently I was convinced by Mickey D. to finally revamp the design when I suggested there was more potential that could be extracted from the original drivers with a better crossover and more conventional cabinet especially after the updates I had made to my measurement and testing process in the time since the original crossover was developed. Thus this updated crossover for the Vortex-15 in a more conventional cabinet design finally came about.
This crossover was originally designed as active but after it was finished I realized a passive solution was possible that could nearly match the response from the updated active crossover so both options are available below.
In comparison with the original passive crossover that shipped with the Vortex-15 from DIYSG the updated design reduces some response peaking that was apparent around crossover frequency and helps even out and fill in some dips in the lower midrange. It also drops the crossover point from ~1350Hz to ~1100Hz which improves the directivity handoff between the woofer and HF driver and does a better job suppressing the woofer breakup. Overall just a more even and balanced sound from the upper bass through the midrange and into the low treble.
I've always liked the sound quality from the Vortex-15 and now with the updated crossover it is even better. While the response linearity in the top octaves may be outclassed on a speaker using a well designed waveguide the point source nature of the coaxial provides a directivity hand off in the midrange free of lobes or nulls and a more cohesive sound quality that cannot be matched by a conventional multi-way design.
Enclosure Design:
Since these were almost certainly going to be paired with subs I went with a more moderately sized sealed enclosure of ~2.2cuft this time around which would let the driver hit 80hz naturally without having to worry about ports and potential resonances/chuffing/midrange leakage issues and providing a cleaner baffle and easier to build cabinet.
The cabinet dimensions are 17" wide x 30" high x 12" deep using 3/4" material. I used a double baffle sandwiching 3/4" and 1/2" (because I was running low on 3/4" I had on hand) but a double 3/4" baffle would simplify construction and is what I will show.
The driver should be flush mounted. I used 1/2" roundovers on the cabinet but those are not critical. Backside of the double baffle was chamfered around the driver cutout.
Cabinet Cut List (17" x 30" x 12", double 3/4" baffle):
Baffle(x2)/Back - 17" x 30"
Sides - 30" x 9.75"
Top/bottom - 15.5" x 9.75"
Braces - (3x) 15.5" x 9.75"
Damping:
The sealed cabinet should be fully stuffed with damping material, I used 1.5" recycled denim damping to line the walls then stuffed the rest of the cabinet with polyfil because that is what I had on hand. Filling with fiberglass or rockwool would also work fine.
Center Brace Dimensions:
Active crossover design & measurements can be found here.
Passive crossover design & measurements below:
Crossover Design:
The Vortex-15 has always been much easier to work with then most coaxials when it comes to getting a decent frequency response without requiring complex passive filters. The original crossover design it was a basic 3rd order electrical highpass + L-pad for the HF driver and a 4th order electrical lowpass on the woofer.
The new passive crossover was designed to closely match the updated active version that I designed and tuned first. In comparison to the original passive crossover the updated version adds an LCR filter on the HF side for some minor contouring just below 3kHz where there was just a bit of excess energy. The woofer side get a larger revamp, I switched that to a 3rd order design at a lower crossover point of ~1100hz vs ~1350hz before. It also has a couple of notch filters. The tank filter across L4 both increases the lowpass slope and helps knock down the woofer breakup while the LCR filter aids in the shaping of the response below the knee of the filter.
The result is a much flatter frequency response from the woofer and a steeper rolloff that starts sooner to help suppress the cone breakup for a cleaner midrange. The lower crossover point helps maintain a wider and more even directivity hand off between the woofer and compression driver. The tonality of the high frequencies isn't changed much with the exception of reducing a bit of response peaking that was present around 3Khz.
-Optional crossover PCB I developed for the Vortex-15+ design-
Suitable Crossover Parts that fit the PCB:
C1(8.2uF) - C3(10uF) - C3(2uF) - C4(22uF) - C5(1.5uF) - C6(8.2uF)
L1(1.2mH) - L2(1.5mH) - L3(2.5mH) - L4(2.2mH) - L5(6mH)
R1 (1 Ohm) - R2 (3.3 Ohm) - R3 (3.3 Ohm) - R4 (8 Ohm) - R5 (0.5 Ohm) - R6(8 Ohm) -
Crossover sim with individual driver responses and reverse polarity notch:
Crossover Filter Slopes:
Vortex-15+ Crossover Schematic:
All capacitors are designed to be standard metalized polypropylene.
For the inductors L1 and L2 should be 20 gauge air cores, L3 and L5 should be 18 gauge I-cores while L4 should be an 18 gauge air core.
Resistors should be 10w, standard wirewound style are suitable.
Vortex-15+ Design Measurements - Passive Crossover
Measurements taken 4pi at 2.83v/2m and scaled up 6dB to approximate 2.83v/1m (Nominal 1 watt / 1 meter)
Measurements gated at 14ms and blended to diffraction adjusted nearfield woofer response below 250hz.
No Smoothing Applied.
On Axis SPL
CTA-2034 Style Spin Data
Harmonic Distortion @ 85, 95, 100, 105, 110 & 115dB/1m - (Measured at 50cm)
Compression at 85/95/100/105/110/115dB normalized against 75dB:
Impedance does dip down to just over 5 Ohms near 900Hz, but most amps rated for 8 ohms should have not trouble driving the speaker due to it's high sensitivity.
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