Hi...i am a new user here.One way to test phase is to use a battery. This works for woofers and subwoofers. If the +ve terminal of the battery is connected to the +ve terminal of the woofer the cone will move out and if the +ve terminal of the battery is connected to the -ve terminal of the woofer the cone will move in. This can allow you to ensure that your subwoofers and woofers are electrically in phase. However since your subwoofer is usually in the trunk and your woofer is generally in the front door you may have to shift the phase of the subwoofer so that both woofer and subwoofer are acoustically in phase. I do this by ear. Using a piece of music I am familiar with I will have someone rotate the phase knob of the subwoofer amplifier till my ear tells me all is good. The best music for this is an isolated bass guitar that will cover the range from about 40Hz (Low E is 42hz) to 200hz. Stanley Clarke is a good option.
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