Phase Setting on Subwoofer

[Otto Pylot]

My subwoofer (Emotiva BasX S10) developed a hum after about 5 years of use. The power is always on even when the receiver is off. I had the Phase Setting on the sub set to 0 (Normal) to match the sub setting in the receiver (Phase = Normal). I changed the sub Phase to 180, leaving the receiver setting at Normal. The hum went away and the sound is fine as far as I can tell (a couple of YT Dolby 5.1 tests and Subwoofer tests) so what exactly does the Phase Setting on the subwoofer do, and does it change anything if the receiver setting doesn't match the subwoofer setting? Cross-over is set to 80Hz for the speakers and 100Hz for the center.

OOPS: I meant to post this in the Subwoofer section. Can someone move it to where it belongs?

 

[TLS Guy]

My subwoofer (Emotiva BasX S10) developed a hum after about 5 years of use. The power is always on even when the receiver is off. I had the Phase Setting on the sub set to 0 (Normal) to match the sub setting in the receiver (Phase = Normal). I changed the sub Phase to 180, leaving the receiver setting at Normal. The hum went away and the sound is fine as far as I can tell (a couple of YT Dolby 5.1 tests and Subwoofer tests) so what exactly does the Phase Setting on the subwoofer do, and does it change anything if the receiver setting doesn't match the subwoofer setting? Cross-over is set to 80Hz for the speakers and 100Hz for the center.

OOPS: I meant to post this in the Subwoofer section. Can someone move it to where it belongs?

The phase setting changes the data point of a sine wave. So if the peak of a wave is positive, then if you change the phase 180 degrees then that deflection is now negative in the exactly opposite direction. Now the phase shift of a pre-out is 90 degrees, as the crossover is second order. The phase shift of the sub is fourth order so the phase shift is 180 degrees. When you combine the phase shifts then the crossover phase shift is 270 degrees. So altering the phase of the sub moves it in degrees. But you have to allow for the speed of sound, so the location of speakers and sub affects the situation greatly. The purpose of the phase knob is to allow you to get mains and sib in phase at crossover.

I suspect the hum was cured as you bumped the RCA connection which probably is a bit loose and not properly grounding your sub connection. Moving the phase control would not change hum.

 

[Otto Pylot]

The phase setting changes the data point of a sine wave. So if the peak of a wave is positive, then if you change the phase 180 degrees then that deflection is now negative in the exactly opposite direction. Now the phase shift of a pre-out is 90 degrees, as the crossover is second order. The phase shift of the sub is fourth order so the phase shift is 180 degrees. When you combine the phase shifts then the crossover phase shift is 270 degrees. So altering the phase of the sub moves it in degrees. But you have to allow for the speed of sound, so the location of speakers and sub affects the situation greatly. The purpose of the phase knob is to allow you to get mains and sib in phase at crossover.

I suspect the hum was cured as you bumped the RCA connection which probably is a bit loose and not properly grounding your sub connection. Moving the phase control would not change hum.

Thanks. But if I move the Phase control on the sub from 0 (Normal) to 180, the hum goes away. If I slowly turn the Phase control back to 0, the hum gets gradually louder the closer it gets to 0. I can move the Phase control without moving the sub so the connectors shouldn't have moved but I guess I can remove and then replace them.

As I mentioned, I don't really hear any audio quality differences with the receiver set to Normal Phase and the sub set to Phase 180 but that doesn't seem right just to get the hum to go away. Still confused.

 

[TLS Guy]

Thanks. But if I move the Phase control on the sub from 0 (Normal) to 180, the hum goes away. If I slowly turn the Phase control back to 0, the hum gets gradually louder the closer it gets to 0. I can move the Phase control without moving the sub so the connectors shouldn't have moved but I guess I can remove and then replace them.

As I mentioned, I don't really hear any audio quality differences with the receiver set to Normal Phase and the sub set to Phase 180 but that doesn't seem right just to get the hum to go away. Still confused.

With that information I have to revise my opinion.

I think that the hum may be decreasing as you turn the knob to the point where the sub and your mains are 180 degrees out of phase and cancellation is occurring. So I have to assume that there is also has to be hum coming from other speakers. If that is not so, then your sub amp is failing.

If the hum is on speakers other than your sub, then you have a ground loop, and if that is the case, then we will have to help you track it down.

 

[Otto Pylot]

Thanks. There is no hum at all coming from the other speakers with the receiver off. The only hum is coming from the sub, and, like I said, it goes away with the phase moved to 180. Someone mentioned switching the RCA cables around but I only have the single RCA sub cable coming from the receiver, it's not a red/black cable. I'll do some cable jiggling later on to see if I can get it to go away. If it does, it's either the cable connector, the sub connector, or a faulty/dying board. I've been trying to contact the mfr, Emotiva, but have been unsuccessful so far.

 

[TLS Guy]

Thanks. There is no hum at all coming from the other speakers with the receiver off. The only hum is coming from the sub, and, like I said, it goes away with the phase moved to 180. Someone mentioned switching the RCA cables around but I only have the single RCA sub cable coming from the receiver, it's not a red/black cable. I'll do some cable jiggling later on to see if I can get it to go away. If it does, it's either the cable connector, the sub connector, or a faulty/dying board. I've been trying to contact the mfr, Emotiva, but have been unsuccessful so far.

From what you tell me now, I would bet big money that the problem is in the sub amp.

 

[Otto Pylot]

From what you tell me now, I would bet big money that the problem is in the sub amp.

I don't want to admit that you're correct but I think you are . I finally go an email off to Emotiva but they'll probably just want to sell me one of their $800 subs, which is more than I need.

What about changing the receiver Phase setting to 180 to match the sub as a temporary fix? They would cancel each other out, like setting both to 0, at least in my way of thinking, but what would that do to the audio?