Now that I got the Fountek FE85 and the Peerless DX20BF00-04 sorted out, it’s time to find the right woofer for a conventional 3-way design. The bass driver will be direct radiating, not a stand-alone bandpass sub.
Of all the woofers I’ve used in my projects, I eventually narrowed it down to the W20RC38-08. This 8″ Silver Flute offers the best price/performance ratio. At $38 (Masisound), it’s a bit too costly for a budget 3-way but I don’t have anything cheaper. I will work with this Silver Flute for the time being. What I want to see is how well it blends with the Fountek FE85 and the Peerless DX20BF00-04.
SuperMicro-DX2 with 250Hz High Pass
Fig 1 – 250Hz (24dB/oct) High Pass
Fig 1 is a plot of the SuperMicro-DX2 with my 24dB/oct electronic crossover high pass set at 250Hz. The steep slope is very effective in preventing the bass from entering the FE85.
Fig 2 – SuperMicro-DX2 without 250Hz high Pass filter
Fig 2 is of the SuperMicro-DX2 in a typical closed box alignment. since there’s no 250Hz high pass filter, the FE85 is even trying to produce 20Hz. Obviously this will soon destroy a 3″ woofer except that being a closed box design, the internal “air spring” stiffens considerably at low frequencies.
Harmonic Distortion SuperMicro-DX2
Fig 3 – SuperMicro-DX2 without 250Hz (24dB/oct) High Pass
Fig 3 shows what the FE85 is experiencing when it is trying to produce bass. The cone is pushed farther out, possibly out of it’s linear range. Hence, the increase in the 2nd (Red plot) and 3rd (Violet plot) harmonics.
Fig 4 – SuperMicro-DX with 250Hz (24dB/oct) High Pass Filter
Fig 4 shows the distortions have vanished when a 250Hz (24dB/oct) high pass filter is applied to cut-off the bass. This proofs that small woofers like the FE85 are prone to over excursion. This will be even worse in a bass reflex.
Integrating the Silver Flute W20RC38-08
Fig 5 – Black plot = W20RC38-08. Blue plot = FE85. RED plot = DX20BF00-04
Fig 5 shows the individual drivers’ responses. The 8″ Silver Flute W20RC38-08 is in a 24 liters bass reflex box tuned to a Fb of 36Hz. The crossover frequencies are 250Hz for W20RC38-08 to FE85 and 2.6kHz for FE85 to DX20BF00-04. All at 24dB/oct, Linkwitz Riley.
Apart from the filter responses, the plots also depict the relative sensitivities of the three drivers. Bear in mind that this is not at 1W/1m. That’s too loud for me. My main aim is to check whether the FE85 is going to be drowned out by the 8″ Silver Flute. If so, I won’t be able to use the W20RC38-08 in a passive crossover.
Fortunately, their sensitivities just about match. I may not even need to pad down the FE85.
SuperMicro-DX3 Frequency Response
Fig 6 – Summed Response of W20RC38-08, FE85 and DX20BF00-04
The final frequency response of the SuperMicro-DX3 is shown in Fig 6. The bass is adjusted for room gain. Any more bass and it’ll overwhelm the mids and highs.
The null at 150Hz followed by a peak at 200Hz are caused by standing waves in my room. They are not caused by the drivers. If I want a smoother plot, I will have to make my measurements in a much larger room or outdoors.
Auditioning the SuperMicro-DX3
I am surprised at how well the Silver Flute W20RC38-08 blended with the Fountek FE85 and the Peerless DX20BF00-04.
The SuperMicro-DX3 sounds like expensive speakers. The midrange is crystal clear, no veil and no glare. The treble doesn’t sound like glass being scratched. And lastly, the bass is tight and articulate.
II will definitely proceed with a passive 3-way. The SuperMicro-DX3 deserves it.
Note: Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.