![]() However, to properly align the phase between two channels, it's necessary to use one channel for an absolute phase reference pre-sweep in REW so that when you measure the second channel that you want to phase-align with, both of the channels you are aligning to each other are measured in relationship to the phase reference channel that doesn't change between measurements. Then the pass band will gravitate toward 0 degrees or 180 degrees and you will be better able to see if it's sloped or twisted by radical phase shifts. It's better to measure without a phase reference channel and let REW choose the floating phase reference for you. Note that to easily see phase anomalies in a single subwoofer channel, it's best to measure the response of that subwoofer without using another channel as an absolute phase reference sweep, because a distance mismatch between the reference channel and the subwoofer that you are examining will cause a sharp slope in the measured phase. ![]() ![]() I ended up letting the phase rather than the frequency response be the ultimate determiner of where the 'best' placement is, because without independent sub channels there's no practical way to correct such things with room EQ. Especially for those subwoofers in a modal null on the sidewalls, a few inches of displacement toward the front or rear can induce a strong and sharp phase ripple that causes dramatic narrow-band cancellation between subwoofers. These qualities are highly sensitive to positioning, particularly the phase is highly sensitive although IME from reading these threads on AVS Forum people tend to neglect the importance of smooth subwoofer phase and often don't even examine it until after they've detected a problem with the integration. This got me good bass on the first calibration and I left it that way, but it took a while to figure out that smooth response and flat phase were both essential to aligning the subwoofers to each other. All three subs have a slight attenuation at 50Hz from that 45Hz burble, and since that's approximately mid-range in the band pass from 16Hz-80Hz, I decided to phase-align them and level-match them all at that 50Hz frequency to attempt to maximally smooth that 45Hz burble away. I'm driving them with an Onkyo TX-NR929 that has only a single subwoofer channel, although a second subwoofer channel would help a lot by separating the Mirage from the SVSs that have radically different acoustic placements.Īfter proper placement of all three subs for deep LFE, extended passband, and smooth flattish phase, I ended up with the 20-25Hz ported Mirage (not sure exactly what the spec is) at the center of the rear wall where the bass is strong in the 30-70Hz range but there's a slight bump and strong burble at 45Hz wrinkling the response, and the 18Hz ported SVSs on the sidewalls at approximately the 1/4 point toward the front wall where there's a 2nd order front-rear axial harmonic modal null near 45Hz attenuating that midband frequency range significantly. I am running two ancient SVS PB10's with adjustable phase and one ancient Mirage S12 that has only a polarity inversion switch.
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