Phase Adjustment

[wyliec2]

Not a newb to audio but working on my first IB setup - every active subwoofer I've ever used has had a phase adjustment for matching main speakers. What do people use for phase adjustment in IB setups.

I'm considering using a Crown or QSC amp (my processor has balanced output) to drive a couple of 18" subs but am concerned about no phase adjustment. My IB can only go in one place and my mains only have one ideal location so is there a way to match phase between mains and sub???

Thanks,
Wyliec2

[jman]

The sub distance on your receiver is a phase adjustment.

[wyliec2]

Yes, speaker distance changes phase but it also changes the time at which the signal is propagated. If I calculate correctly, to effect a 180 degree phase change at 60 Hz, would require a distance adjustment of about 9.5 feet - which seems quite substantial???

Now is an electronic phase adjustment on a subwoofer actually nothing more than a delay adjustment??

Some subs do not have variable phase but simply a 180 degree switch - in effect swapping the +/- leads on the driver. It seems with this method, a 180 degree shift occurs without a change in the moment of propagation..??

I don't know if this is simply semantics with the net results being identical or if there is a audible difference between a 8 millisecond (approx. for 9.5 distance change) delay and swapping driver leads??

[ThomasW]

Phase adjustment circuits operate only at the crossover frequency, and have no effect anywhere else in the sub's passband.

If one thinks this is going to be a major issue (for most it's not) they should test placement with a portable sub that has a phase adjustment.

Here's a link to Rod Elliot's outboard DIY phase controller
sound.westhost.com/project103.htm

I've used subs since the mid 1970's and never needed a phase adjustment.

[retsel]

I don't have an IB, but do have an open baffle subwoofer and I do have phasing issues. I cross over between the midrange and subwoofer at 100 hz which is high enough to make it really important to deal with phasing.

I biamp and my midrange and woofer drivers are in the same plane, so my strategy is to adjust the phasing of each amp. I noticed that my single ended tube amp has capacitors in the signal path. My strategy will be to adjust the capacitor values until the phasing is correct. My hope is that this will work OK as it will allow me to adjust the phasing without adding any additional components into the signal path. If it does not, then I will need to try something else.

Retsel