Flex-8 - Dayton SD215A-88
This one is for the bass lovers! The Dayton SD215A-88 has the best bass response of all the woofers with an f3 of nearly 40Hz (4pi) so depending on placement and room gain you may have extension into the 30's in room. Due to the response shape from the woofer it's left with a bit of a bump below 150hz, not enough to make things muddy but certainly gives some extra weight to the bass from the design. The bass performance and extension come at the cost of efficiency, this one is only ~85dB @ 2.83v or 82dB @ 1W/1M.
Both this woofer and the DS series which shares the cone/surround have a narrow dip around 1.2kHz, I assume some kind of resonance from the cone or surround. Being a narrow dip it's not an obvious issue in listening. I'd say this design has the weakest midrange of the bunch, don't get me wrong I'm not trying to say it's bad, just outperformed by the others woofers. I probably could have lifted it a bit more using a smaller L2 inductor but it also left a larger valley in the 200-400Hz range.
Distortion performance from the woofer is also the worst of the bunch producing quite a large amount of 2nd harmonic distortion at higher output levels. It's generally non-offensive and mostly masked in playback but it's certainly not the mark of a quality driver.
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.
Due to the lower sensitivity you definitely want a decent 4 ohm stable amp, 200w seems just enough to make full use of the woofer and get things to exciting levels (100dB+ peaks). Though a smaller amp can certainly be used if you aren't listening quite that loud.
I feel for smaller rooms assuming the placement and room modes fall in your favor you can easily get away without a separate subwoofer for most music.
Crossover Schematic:
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 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 - 27uF NPE (15uF + 12uF) or (17uF + 10uF)
C3 - 17uF NPE
C4 - 5.6uF NPE
L2 - 1.25mH 18awg I-core (a 1.2mH value can also be used)
R1 - 10 Ohm 10w - Alternate
R3 - 5.6 Ohm 10w
Loudspeaker Drivers / Horn:
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Full measurements for the Flex-8 Dayton SD215A-88 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. (Since this is a 4 ohm design subtract 3dB for the nominal 1w/1m efficiency)
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 (SD) Harmonic Distortion at 85, 95, 100 and 105dB/1m
Compression at 85/95/100/105dB normalized against 75dB:
Flex-8 (SD) Impedance:
