Flex-8 - Dayton DS215-8
The Dayton DS215 uses the same cone and surround as the SD215A-88 subwoofer and it suffers from the same kind of dip just above 1kHz. It's a bit larger on this one and didn't show as strongly until I measured the design outdoors where I could get a longer gate time for higher resolution. Luckily the dip is mostly benign and does not impart any irritating qualities to the sound.
Bass extension is not quite as deep as the SD215, with the tuning I used at the port full length (~35Hz) F3 is roughly 50hz with an F6 in the low 40's (4pi). Since it's an 8 ohm design efficiency is higher then the SD215 but sensitivity is still just a hair lower at ~84.5dB - 1W/1M (2.83v/1M).
Distortion from this woofer in low midrange and bass is much lower compared to the other 8" woofer variants I've tested even though the design does not implement any additional distortion reducing measures in the motor itself. I suspect it's largely due to the larger motor/magnet system which minimizes flux modulation but I can't be entirely certain. I believe it might share the same spider as the SD215 so the motor system would be one of the only differences between that woofer and this one. It does have a spike in 3rd harmonic distortion around 1kHz which is made more prominent on the normalized distortion graph due to the dip in the fundamental near the same range. Though it's fortunate the relative level of that 3rd harmonic distortion spike stays roughly the same as output level is increased which keeps it from being an annoyance at higher levels.
Bass and midrange sound quality is actually quite nice, I think in part due to the lower distortion and low compression from this woofer. The bass has a quicker, snappier and cleaner feel to it that does not mask the low midrange. Vocals sound very good, clean with good detail and not too recessed nor to forward even with the ugly looking dip in the frequency response.
The high frequency performance/sound quality is largely the same in all the designs so this section will likely be a cut/paste for each. The LaVoce DF10.101LS with the Celestion H1SC-8050 is a very nice combo, the smooth easy to work with frequency response results a very clean clear uncolored high frequencies with remarkably low distortion and compression. The high frequency driver has to work very little in this design so its composure is maintained well beyond the point where the 8" woofers are begging for mercy. The only negatives are the slightly narrower coverage of the horn then I would have liked and the early drop in high frequency output past 16kHz. For the cost I don't mind as they are not glaring issues that you notice immediately and the narrow dispersion could actually be a benefit depending on the desired use of the speakers if wanting a more focused dispersion pattern to keep excessive energy off the walls.
Overall I did not expect sound quality to be this good from the DS215 when compared to the SD215, both midrange and bass is cleaner and more to my liking even though the frequency response looks worse. In fact I might even rank this one at least in bass quality above the Silver Flute variant and very close in the midrange sound quality as well.
Crossover Schematic:
Port Tube:
Port tube was used at full length for this woofer, but could also be cut a couple inches shorter to flatten the bass response if desired.
On this crossover the C1 cap on the high frequencies should be a polypropylene style cap but all the others in the crossover are designed to use non-polarized electrolytic. The ESR in the NPE capacitors adds additional damping in the low pass circuits which proves beneficial to the shaping of the frequency response without the need for additional resistors on the C2/C3 parallel legs. C2 and C3 can be changed to poly (18uF) but it will result in some additional output in the midrange near the crossover.
Resistors are standard 10w wire-wound.
L1 inductor should be a 20 gauge air core, L2 and L4 should be 18 gauge I-core, L3 should be a 18 gauge air core.
Crossover BOM with links to suitable parts.
C1 - 3.3uF Poly
C2 - 17uF NPE
C3 - 17uF NPE
C4 - 2.2uF NPE (can also be a 2.2uF Poly)
C5 - 22uF NPE
L2 - 2.5mH 18awg I-core (Alternate)
R1 - 10 Ohm 10w
R2* - 0.91 Ohm 10w (can use a 1 Ohm + 10 Ohm in parallel if 0.91Ohm cannot be found)
R3 - 10 Ohm 10w
*R2 could be made 0.82 Ohm which will result is slightly less treble output or 1 Ohm for slightly higher treble output (roughly +-0.6dB change to the level).
Loudspeaker Drivers / Horn:
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Full measurements for the Flex-8 Dayton DS215-8 Variant
The following measurements were performed on my 10' tall outdoor turntable, measurements taken at ~5.66v / 2M on the tweeter axis which provides the same approximate SPL as 2.83v / 1M. (Nominal 1W/1M)
The measurements were gated at 14ms and blended to diffraction adjusted nearfield woofer response below ~300hz.
No smoothing applied to the frequency response measurements.
On Axis Response
CTA-2034 Style Spin
Estimated In-Room Response
Flex-8 (DS215-8) Harmonic Distortion at 85, 95, 100, 104 and 105dB/1m
104dB sweep included as I saw the clip light flicker a bit at the 105dB level and wanted to make sure there wasn't any amp induced distortion.
Compression at 85/95/100/104/105dB normalized against 75dB:
Flex-8 (DS215-8) Impedance:
