I bought a new Klipsch Subwoofer(SW-10) and hooked it up to my old Yamaha HTr 5240 (I think) receiver. I guess setting the subwoofer's "power level" and "low pass filter" dials is merely a personal taste issue( am I wrong?) -- pick whatever combination sounds best, but what about the "0 & 180 phase" selection? Obviously they are opposites and I have no idea what the difference is--

How should I choose?

By the way, due to space\layout limitations, the sub is not in line with the front speakers, but almost in line with the rear surrounds-- a little bit closer to the front and off to the left-- Not ideal , I know, but no other place to put it in my situation.

Thanks

Barry

Yeah, talk about a confusing "feature."

There are two major ways that phase shift is introduced into a system. First, amplifier stages can either reverse the polarity of a signal, which is a 180 degree shift, or not, depending on the design; any particular preamp and amp will have reversed the phase many times, and the output at the speaker terminals might be in phase or out, depending on how many times the phase was reversed.

Second, tone controls and equalization introduce slight phase shifts, and at different portions of the audio spectrum, depending on the frequency, Q and intensity of the equalization.

The sub, connected to the high level output, that is, amp output, has a connection with zero phase shift relative to the main speakers. However, the sub has a crossover at whatever frequency you set it at, and that introduces a phase shift into the sub output.

Your assignment is to somehow figure out where to set the phase control so that you get totally smooth frequency response in the transition from the sub's sound to the mid bass coming out of the other speakers in the system. The sub's placement will also affect this a bit, as speakers that are in phase when next to one another will not be in phase when spearated. Distance between speakers makes signals come out at different times when seen from some location in the room; that time difference is a phase shift. And just to make it crazier, a particular time difference caused by physical separation is a different phase difference in degrees at different frequencies because different frequencies have different wavelengths.

So...

Forget all of this and mess with the control to see if you can find a setting that seems to give a "hole" in the bass response. If you have a sense what musical notes are at the transition from sub to mains, that will help you perceive this "hole." After you have found the hole, set the switch 180 degrees away from that position; you do it this way because it is easier to hear a null than a peak.

Once you have set the phase, you can adjust the volume for the smoothest transition.

Then reverse the polarity and see if you still have a hole in the response...and so on and so forth.

By the way, chances are that, if you do not adjust the knob at all, or do not have it properly adjusted, you will never know it. Every speaker system has a non-flat response curve, and every room affects the levels of sound output from the speakers, so we are used to hearing, and quite loving, systems with peaks and valleys of response.

Adjust it. If that makes the system sound smoother, you have improved it. If you make it sound worse, try to make it as bad as possible and then reverse the phase by 180 degrees.

There are a couple of ways to properly set the phase of a subwoofer. Ideally a sub will have a variable phase adjustment, but the majority have a 0/180 switch. The easiest way to set this but definately the least accurate is to sit in your listening position and have someone switch back and forth between o and 180; whichever one sounds better is the one to go with.

The better way takes a little more work. The first step involves reversing the leads (flip the + and - negative speaker wire on each speaker)wire on your front speakers. Next your gonna need a disc that will provide a relatively constant low frequency signal, a good set-up disc will have this. Play this disc, and while sitting in your listening position, have someone switch from 0 to 180 until you get the LEAST amount of bass. The reason this works better than the first method is because it is much easier to hear an absence of sound than just better or more bass. (Incidentally, what should be happening is the bass from the out of phase front speakers is being canceled out by the subwoofer when it is at the proper degree of phase. When you put the front speakers back in phase, then the bass from them and sub will reach your listening position at close to the exact same time. Which is what you want.) This is not a foolproof method. That is why more expensive subwoofers have a variable phase adjustment. To get the phase set up perfectly you need to have some flexibility in the placement of your subwoofer. It is rare that where you decide to put it for aesthetic reasons is going to meet all the criteria for proper sub placement. This is not to say the sub won't sound good where you have it, so don't freak out.

P.S. - Don't forget to reverse the leads back when you are done.

You can/should use an RTA. You are looking for a smooth blend with the mains at the crossover point.

Actually, I think this is more relevant than a phase adjustment given that you don't have a woofer wired with a reverse polarity somewhere in your system. Pahse isn't such an issue when the horizontal placement of the low frequencyspeakers in a room is somewhat equal. This doesn't mean that you won't have phase problems at certain frequencies, but as oex suggested, finding the right crossover point for your particular system will mitigate this problem. Most of these home audio systems will have a fairly intuitive process of determining this imperically. In a pro audio system where you are working with bi amplification or tri amplification of drivers it becomes a lot more challenging, however most of the top pro audio speaker manufacturers have DSp processor algorithms written for digital processors that are optimized for them.

Well, thanks for the responses, but basically everything after "pick what sounds best" was a little over my head. I wish I knew more about audio issues, but I don't even know what an RTA is.

My subwoofer has 2 positions "0" and "180". Honestly, I was playing with it the other day while watching an HD sci-fi movie with sound booming through and around the speakers in the room. Switching the "phase" made no discernable difference to my untrained ear, so I'm not going to lose any sleep over my lack of understanding.

I appreciate your efforts and I am sure that someone else reading the thread got a great lesson. For simple minded me, I am just glad to hear some boom boom bass which I never had before I got the subwoofer!

Keep up the great work. I thoroughly enjoy reading and learning on this site!

RTA = real time analyzer

which is a device that shows a graph of the frequency response of your system. The "real time" part means that it shows what is happening right now. If you make a change in the response of the system, it will show up on the graph of the RTA.

And the most important point of all of this is that you want to make the smoothest transition from the sub to the main speakers.

Sorry. Didn't mean to be so cursery in my response. I tend to be over brief at times. My bad!

Go on....

Other than places like Sencore, where do we go to get traning and/or equipment to DO these calibrations?

What do you guys think about this advice from MjAcoustics?

The Pro 50, Pro 100 and Reference I subs are all downward firing and should have their "phase" control set to 12 o'clock (90�), as this is the subs natural angle compared to your main speakers that are facing towards you. The Pro 500 and Pro 1650 subs are forward firing and should have their "phase" control set to either 7 o'clock (0�) when the sub faces the same way as your main speakers or 5 o'clock (180�) when the sub faces in the opposite direction to your main speakers. Most people never experience phasing problems, but going through the above procedure will eliminate any phasing problems should they occur.

Makes sense to me but Im average joe :) LOL
Ive not seen the same advice anywhere else though.

Can phase be sorted using a sound pressure meter? I seem to recall mention of it elsewhere.

BK, if you're still here, I'd like to give you a starter course so some of the above makes sense.

When a speaker reproduces sound, the speaker cones alternately pressurize and rarefy the air, as the audio signal from the amplifier alternates between the positive and negative halves of the signal. (When the voltage on the red (+) speaker terminal is positive at any given moment, as compared with the black (-) terminal, the signal is said to be positive, and vice versa.)

When two (or more) speakers are reproducing the same (or at least related) sound, it is possible that both speakers' cones may pressurize the air in synch, or one may pressurize while the other one rarefies. By being "in phase", we mean that both speakers' cones are moving together (assuming the audio signals are calling for this to happen). "Out of phase" means the opposite; they're not moving in synch.

This is known as "relative phase", which refers to the speakers in a ayatem moving in synch. If one speaker is not moving with the others, we can fix it by swapping the wires at one end of a speaker. (There is also "absolute phase", which means that a speaker is pressurizing and rarefying the air in synch with the original sound source, which some purists say is important, but not relevant here.)

Now, a phase control on a subwoofer allows one to make sure that the sub and the other speakers' woofers work in synch (usually desired) as they share some frequencies around the crossover frequency. Sometimes, the room dimensions and characteristics make it desirable to reduce the bass level around the crossover frequency, and intentionally setting the phase "wrong" can reduce the bass "hump".

Every speaker system sounds different in every room. There's no way to tell someone what settings will sound best without being there, so the "whatever-sounds-best" approach is often the best approach. Instrumentation can be used to "dial in" an audio system with the environment and the equipment and listening positioning setup, but can be expensive and time consuming; it's a matter of priority.

What Larry said!!!!
Thats about as 'clear' as it gets!

Thanks for all the info! I sort of get it now-- Just pick what sounds best!

Sometimes the most complicated things are so simple!

BK