What is the subwoofer phase function?

[radovantz]

Good morning..

I wonder what is the purpose of the phase control at subwoofer rear panel. It has some kind of degree measurement from 0 to 180.

Does it shows angles that would be useful in placement setup?

Or does it influenced by North-South pole?

Thanks

 

[Andrew Everard]

It's designed to allow you to adjust the subwoofer so the the sub and the main speakers are in phase at the crossover frequency.

Ideally both will be in phase - ie the drivers moving in the same direction at the same time - but typically they may well be out of phase, so the sub driver is moving back while the main speaker drivers are moving forward, due to positioning, amplification design and so on. If this is so, there will be a degree ot bass cancellation, which isn't ideal.

By adjusting the phase control - some subs have a simple phase reverse switch, others a dial marked 0-180degrees - it's possible to reduce this cancellation effect, giving you better bass.

The simple way is to just do it by ear, adjusting the control to get the best-sounding bass, but there is a more complex and scientific way, for which you'll need a test disc carrying a range of frequency tones, such as this.

To use the test disc for this purpose, reverse the speaker connections for the main front left/right speakers, ie red to black and black to red, so they're connected out of phase.

In home cinema systems, either disconnect the other speakers or select pure stereo mode so they're not being used.

Now play the test tone from the CD corresponding to the crossover frequency between the sub and the main speakers - eg 80Hz if you're using the THX standard crossover, or whatever your sub/speaker system determines.

If you've used an automatic set-up system, the menus on your receiver should show what crossover frequency has been chosen.

With this tone playing, adjust the phase control so you get the minimum sound - ie maximum cancellation between the main speakers and the subwoofer, bearing in mind that the change will be fairly minimal if you're using tiny satellite speakers with a stonking great subwoofer.

When you achieve minimum bass/maximum cancellation, the phase is set correctly.

Return the main speakers connections to their correct phase, and you're good to go.

 

[radovantz]

Thank you Mr Andrew for the explanation.

I never knew about the conflict that may arise between subwoofer and speakers resulting bass cancellation. Of course, the bass cancellation would also happen to a single double bass speaker like centre unit if one of the woofer is not functioning.

It must be difficult to set the right phase without those test tone CD. I'm going to set my subwoofer again in any mean.

This is a new knowledge to me. Thank you.

 

[Anonymous]

Does anyone know if it is safe to use this procedure on an integrated amp?

I'm using a BK sub connected via the high level input to the amps binding posts.

 

[Andrew Everard]

Yes, totally safe.

 

[pete321]

Andrew Everard: a test disc carrying a range of frequency tones, such as this.

Andrew, what's the test disc, I can't get the link to work. Thanks

 

[Anonymous]

pete321:
Andrew Everard: a test disc carrying a range of frequency tones, such as this.

Andrew, what's the test disc, I can't get the link to work. Thanks

Me neither.

And thanks for the above info Andrew, new to me too.

 

[Anonymous]

Andrew Everard:Yes, totally safe.

Thanks ,

If i wanted to hear the sub on its own without the main speakers ,how would i do this ?

I'm guessing its possible while my amp is on to do this by pressing the button marked speakers set A. (my amp can power 2 sets of speakers and has a switch on the front to turn either set on and off )

Is switching this button safe while the sub is on?

 

[Sliced Bread]

Hi Andrew,

When doing it by ear, should you also listen for the minimum amount of bass. I always thought that if there was minimum bass then the speakers are out of phase as they are cancelling each other out. Have I miss-understood?

Thanks

 

[pete321]

JohnNewman:Hi Andrew, When doing it by ear, should you also listen for the minimum amount of bass. I always thought that if there was minimum bass then the speakers are out of phase as they are cancelling each other out. Have I miss-understood? Thanks

I think the idea is that it's easier to listen for no bass than the most bass. So by reversing the phase on your main (L&R front) speakers and adjusting the phase on the sub to get no bass, when you put your front's back in phase you should have maximum bass?