Keta- Most subs are *not* like that.

Most subs just have a switch for 0 or 180 deg.

Some subs have a variable phase knob.

My sub has a variable phase knob that covers about 210 deg, but it also has an inverted input too. So for me... Between the inverted input and the std polarity input, and with the phase knob, I can get 0 to 360 deg. I wasn't aware of many subs with a knob that would do 360 deg alone...

Kevin you are correct that it is not a single knob, it's a toggle for 0 and 180 degrees and a rotory knob from 0 to 180 combined in the "Phase Control". The sub is an NHT Sub-Twoi which uses it's own controller. The controller has so many control options it sometimes make tweaking difficult because of the countless possibilities.

Ok, time to ask the experts out there because now I'm just really confused. In my short experience, a signal is either "in phase" or "out of phase." This would dictate a switch on the sub that selected between 0 degrees and the reverse of that which is 180 degrees. What's the deal with sub's offering "in between phase"? Please somebody help out this curious soul.

It will give you more adjustment to help give a smooth bass response. Your other speakers bass and the subs bass can cause peaks and dips in the frequency response depending where you are in the room. This adjustment allows you optimize the bass response for your listening position a little more closely by turning a knob instead of moving the sub to different locations. It actually does seem to work well compared to a different sub I own that just switches 0 to 180.

IIRC it's usually implemented as a variable all pass filter - basically an active crossover that doesn't discriminate based on frequency but still gives a phase shift. Some systems (generally in the processor) also give a delay adjustment.

It's not a digital effect: either "in phase" or "out of phase".

Essentially, "in phase" means you are getting perfect 100% constructive interference between the frequencies of the mains and the sub where they overlap (near the crossover freq). 0 deg phase diff. In other words, sound is comprised of waves at different freqs and amplitudes. When 2 signals are in phase, the peaks of one signal line up with the peaks of the other, at the same freqs. The 2 signals add together so that 2 + 2 = 4.

When something is 100% "out of phase", 180 deg out, the peaks of 1 signal perfectly line up with the valleys of the other. If you add peaks and valleys, typically you don't get much of anything. They cancel. 2 + -2 = 0. Hence the bass level is lowered near the crossover freqs. (A full wavelength is 360 deg.)

So if you can imagine 1 wave passing over another, the phase can be anywhere from 0 deg (perfectly in phase) to 180 deg (perfectly out of phase) back to 360 deg as the waves start to line up again, but where the peaks and peaks (or peaks and valleys) don't perfectly line up, for example, you can be 57 deg, or 235 deg out of phase.

What a lot of people don't understand is, if you are 360 deg out of phase, you are actually back in phase, but now one signal is 1 full wavelength after the other (or delayed from the other). So now ever though you are in phase, bam, your time alignment is now hosed.

Hopefully that helps!

(Much easier to illustrate with actual waves on 2 different pieces of paper.)


[This message has been edited by Kevin C Brown (edited January 24, 2003).]

Thanks for the replies...I do truly love the level of knowledge displayed on this forum.

Hello all. I'm glad this thread was brought up, because I still don't really understand the difference between 2-channel stereo analog bypass and 6-channel analog direct mode, for stereo sources. I hope you all can set me straight.

My DVD/CD player is a Sony ES9000. It has only stereo 2-channel outputs for analog, no 5.1 analog outputs. Can I plug these into 2 of the 6-channel analog direct inputs on the 950 and get better sound? The ES9000 probably has better DACs than on the 950. Right now I have the ES9000 stereo analog outputs plugged into the 950's stereo analog CD inputs.

I guess I thought I was already using only the ES9000 DACs by choosing analog stereo bypass mode on the 950. How is this different than using 6-channel direct with just the left and right cables plugged in?

My goal is to use the ES9000 DACs and get pure analog sound to the mains and the subwoofer to see how that sounds-- and to still have the other modes (digital) sound good and have bass set up correctly for movies or 5 channel stereo.

So, to do this I should plug the ES9000 into 2 of the 6-channel direct inputs on the 950, turn on the 80 hz crossover switch, and select 6-channel direct mode, correct?

Does anyone have a similar setup and noticed better sound this way? Maybe this is what SDWinder is describing, but I'm not entirely sure.

Two issues I with this approach: I set up the bass to use Small speakers and have a smooth crossover point in digital modes. So it seems like the bass transition may or may not be as smooth using the 80 hz crossover switch in analog direct mode. Also the issue of the sub being out of phase in 6-channel direct if it is in phase for other modes? If so, that seems like a problem. If I have to keep changing the phase switch between movies, 5 channel stereo, and 6 channel direct stereo music that may not be worth it. I wonder if the Outlaws could fix this by modifying the ICBM to include a phase control for sub? Ok, here is my summary from reading this thread:

Two channel analog bypass stereo mode:
Uses only ES-9000 DACs
Double bass
Sub stays in phase with mains for this mode and digital modes
No trim controls

Six channel direct mode:
Uses only ES-9000 DACs
No double bass
Sub out of phase with mains if it is in phase for other modes
Trim controls active

Comments and education welcome!
-HTLearner

I can't explain in any technical detail but the 6/bypass was a vast improvement for my ears. I dont mess with the sub phase (no adjustment) it is a noticable difference but not a bad one. The phase shift seems to smooth out the bass a little, and add a little too. I can locate the sub a little more in this setup. It is worth pointing out that when A/B'ing this you will get a little more volume with the 6/bypass. This will make it seem better than it really is at first, but after you live with this config for a while you start to really notice a better stage (at least I did). Good luck!

Thanks hardwood. I haven't gotten much feedback, so I re-posted this question under "950 2 channel bypass vs 6 channel bypass redux". Hopefully I will get some more replies there.

-HTLearner