DIY Variable Phase Shifter

[FireWalker877]

Hey guys,
I have noticed that there is a phase control on many commercial subs, and some plate amps. My pro amp does not have that control, and I don't think there is any way to compensate for phase on my rather basic receiver. I am hoping that I won't have any real trouble meshing my sub with my mains, but I am trying to prepare for the worst. Most of my listening will be music, so I want everything to match up as best it can. I plan to build a vented LLT once I am back in my apartment, so phase disparity will only get worse. If anyone has built a variable phase controller and would be interested in throwing out some suggestions, let me know!

Thanks!
Charlie

[brucek]

You may use the receivers speaker time delay (speaker distance adjustments) as a substitute for not having a phase control. It will perform essentially the same function. Use REW to observe the crossover region between the sub and mains and alter the subs speaker distance to get the best transition..

brucek

[Mike P.]

Rod Elliott has a Phase Controller Schematic on his site. Here is a link to it.
http://sound.westhost.com/project103.htm
Here is an excellent article on Phase Shift Vs.Time Delay, also from the same site.
http://sound.westhost.com/pcmm.htm

[brucek]

Here is an excellent article on Phase Shift Vs.Time Delay

Yep, and certainly over wide ranges, phase shift and time delay are quite different, but over a reasonable range, a phaseshift network is a reasonable approximation to a time delay. A well designed phase shift network's all pass filter aspires to remain linear over as wide a range as possible. It's never as black and white as a digital time delay, but close enough. If you are without a phase shift network, it is quite acceptable to substitute the time delay of the subwoofer output of the reciever - and much preferred than adding extra electronics.

brucek

[FireWalker877]

Thanks for the help! I have a pioneer vsx-516k. I know it does have a listening position adjustment, but I think it is only "Front," "Center," or "Rear." I don't believe I can adjust each speaker's position independently. (I bought the receiver for really cheap on black friday.) Anyway, you are probably right Bruce, all kinds of bad stuff can happen when you throw this kind of stuff in the mix. I will check my receiver when I go back home in a week or two. If it's as I remember, I might just have an excuse to upgrade my receiver. Then again, I might as well apply some of my curriculum to something useful. We shall see!

[phaseshift]

If you want the most simplified phase inversion, you can apply a DPDT switch to the amplifier output to the driver. This limits you to direct inversion only and you cna even go more low-tech with a pair of banana jacks and a jumper on the back or side of the cabinet.

For variable phase, you need to look at the circuit above. This is very similar to how it is done in a lot of plate amps and it works OK. To go completely variable, you will have to have some changes to add a Vr and perhaps some adjustments to the capacitance depending on the Vr you use.