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Phase 0-180


Fotog

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1. I am not clear on how/where the search function is for this forum. Any help there would be appreciated. Hopefully it isn't too obvious.

2. On the rear of my KSW-150 subwoffer, there is a toggle labeled Phase with positions 0 and 180.

a). what function does this switch have?

B). when do I use it?

3. There is an "auto" mode for on/off. Is there any detriment or risk to leaving the sub on auto continuously?

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a). what function does this switch have?

B). when do I use it?

Phase and Polarity Controls

That's a very good question!

Many units have a variable phase adjustment that allows you to variably tune the phase between 0 and 180 degrees.

Since it doesn't tell you at what frequency, we all get to guess.

I wish that it were as simple as specifying "the crossover frequency".

It has very little function, but it is impressive as Hell, isn't it?

If the delay were more sophisticated (literally, meaning it cost more and they actually spent a few more minutes designing and building it) it would be calibrated in time. Instead you have some form of LC circuit or a pot and an all-pass filter that is pretty much useless. And they are seemingly everywhere. I wish I had better news regarding these 'controls'.

If it is a variable phase adjustment, I would set it at "0" (hopefully
to pull this function 'out' of the circuit) and use the "set-up" delay
function on your receiver to set the distance(time) from the sub to the
listening position.

The irony is that most instruction booklets use the terms "phase" and "polarity" as if they are interchangeable (which should give you an idea of how much time went into their design!). My guess is about 180 degrees worth. And since phase is a measure of time, your guess is as good as mine as to how much time that actually was!!

With luck, by a phase switch, they actually mean "polarity", which should simply be a toggle switch
which determines if the woofer moves in, or out, with the application
of voltage. This should be "in polarity" with the main system, otherwise, phase cancellation can occur.

If it is 'polarity', you can attempt to listen for the switch position that provides for the greater amount of bass. But depending upon placement, you may still be experiencing the superposition of two signals that will result in the cancellation of particular frequencies. Changing polarity is not normally an optimal solution for this!

In order to determine proper polarity, a good tool for this is track #52 of the ProSonus SRD Studio Reference Test CD to verify polarity (as well as use the pink noise source on the CD to determine room modes),. An even better option providing much greater acuity can be gained by obtaining the ETF/RPlusD software for $150 to check the impulse response. This will allow you to accurately adjust and fine tune the signal alignment of your sub in addition to all of your various speaker sources. (and much more!)

------------------------------------------------------

Is the difference between phase and polarity becoming apparent?
They are not simply interchangeable. And while with a perfect
continuous sine wave we can say hat polarity is simply 180 degrees out of phase,
in the real world with time variant material, this is not correct!

Comparing two drivers in polarity means having both sources begin by moving in the same direction at the same time with the application of a voltage. Out of polarity would imply that one driver moves forward while the other moves backwards with the application of voltage.

Phase, on the other hand, refers to time. And it is a relationship between two signals of the same frequency. And as such, if we focus on the start times, it means that one source begins vibrating before the other source. The time differential is refered to in terms of degrees of a cycle or in units of time.

We are able to synchronize two signals in time realtive to a point by adjusting the delay of one signal relative to another source. Assuming that the sub was closer to the listener than the satellite speaker with which it is crossed over, then the signal to the sub can be delayed to a degree (depending upon the circuitry employed).

But phase relationships are frequency dependent, meaning that you can potentially adjust the relative phase between two signals at a particular frequency.

And this is further complicated by the fact that the 'general' phase adjustment is not calibrated. It is often simply a potentimeter attached to an all-pass filter. And you are left with a most inelegant tool that provides you with little reference by which to determine the optimal setting. At most you are able to determine a polar null at your particular lovcation relative only to a particular frequency - as the lobes vary in spacing and number with frequency!

But let me muddy this up a bit more, as what you need to be dealing with is absolute phase - having two or more signals be in sync (in phase with proper polarity) from the absolute beginning), not simply in relative phase. What do I mean by this?

Let me try to create a simple analogy.Let's say that I run track, and that I run at a rate of 1 stride a second. If you also run track and run at the same rate, if we begin running in the same direction (in polarity) at the same time, we will run with our strides matched for the entire race (assuming we never tire). We will be in polarity, and in phase.

If, on the other hand, you begin running 20 strides in front of me, you will begin ahead of me and while in polarity, we will be 'out of phase' by 20 steps. .If we divide the circular track up into degrees, with 360 degrees equaling 1 trip around the track from starting point back to the starting point, the difference between our positions can be stated in terms of either time (seconds) or in terms of the number of degrees. And if it takes 360 strides to make one revolution of the track, you would lead in phase by 20 degrees.

Let's take this even further and say that I arrive and begin running this race much later than you. In fact, say you have already run two laps before I start running and you are now at a point where I can see you just a little ways off in front of me. This difference can be stated in absolute and relative terms of phase. In relative terms, if you are only a little ways 'in front' of me, you might be said to be leading me by say, 20 strides or degrees of the circle. But in absolute terms, you would be leading me by 2 revolutions (360 degrees each) plus the 20 degrees, for a total of 740 degrees absolute. To someone who just happened upon the scene, they would have no idea of the absolute difference, they would only be aware of the relative difference.

Does this matter? Sure it does! It may not matter much to someone watching the race, but what if these two runners were parts of a song. In fact, if they are part of the same word of a song, but one is carrying the low frequency component and the other is carrying the high frequency component of the sound. In order to understand the lyrics of the song with maximum intelligibility, you would want the various voices to be singing the same words at the same time. If they become too far out of sync - out of phase, the intelligibility goes down the toilet. (And the overlap in the frequency range between the two sources can cancel when they are 180 degrees out of phase.)

So, to oversimplify this a bit more, your goal is to make sure that the two sources, the sub and the satellite, are not only in absolute phase - meaning that they start at the same time, but that they are in sync. And unfortunately, the control, if it is variable, only gives yoiu enough latitude to adjust for a maximum difference of 1/2 cycle of cone motion; or, if it is indeed polarity, it allows you to make sure the runners are running around the track in the same direction, meaning that they are at least running in the same direction with a time/phase offset, or if they are out of polarity, meaning that they are in the same place only several times as they pass each other in opposite directions.

And if you are now totally confused, then my job is almost complete!

Your job, if you accept it, is to insure their agreement in polarity AND to try to align their phase - at least in tems of delaying one signal relative to the other at their starting times.

And as such, without more efficient measuring tools to see the signals with greater accuity, the best you can do is to attempt to make sure they start by moving in the same direction, and that their 'basic' delay is set so that their arrival times at your listening location will be the same. And the adjustment that comes closest to this (assuming it is calibrated!) is the setup fuction in your receiver, where you can specify the distance of each driver from your listening position to where you are seated.

I am going to reist going further, as the simple analogies fail to adequately address the issue.

And to put 'variable phase controls' into a wry perspective, while I DO advocate signal alignment in time, on the one hand, with variable 'phase' controls, you are basically told to adjust the system by ear, as fractions of a cycle (360 degrees being one cycle) can be easily heard and tuned by ear....hmmmm..., while on the other hand, many here will just as quickly also maintain that they can't even determine absolute polarity by ear... and that acoustic origin offsets in the order of multiple feet with the significant attendant group delay cannot be heard. Subsequently, passive crossovers for Heritage speakers are 'just fine'. Hmmm...

So, as with the legendary beneficial effects of tiptoes for speakers, the GROSS errors measured in feet are indistinguishable, while the miniscule fractional variations just jump out and are intolerable!

Group delay (the rate of change in the relative phase) is such fun!

In other words, the bank won't miss that million, but an inaccuracy of a few cents will bring the house of cards tumbling down! I hope the irony is apparent! .

(You will of course pardon my mixture of units for the example; everyone knowing that distance relative to the speed of sound has a correlative time value! )

[;)]

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3. There is an "auto" mode for on/off. Is there any detriment or risk to leaving the sub on auto continuously?


Auto is the usual setting. The sub will turn its amp on when it senses a signal and turn it off after a few minutes if it doesn't sense a signal (My Yamaha subs turn off after 7 minutes, the Paradigm after 17 minutes. Not important either way.). It's just a convenience so you have one less thing to think about when you want to hear some music.
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I've done some experiments with the control and the distance setting on my receiver and it can get frustrating, I listen for the most bass but at different frequencies, some are louder, then I switch it again and another frequency will be louder, I guess it comes down to personal preference. I have a down-firing subwoofer with a passive radiator on opposite sides of each other and I don't know weather to turn the sub so one is facing me or keep it facing to the sides, agaion, room setup and preference has an impact on what I like. Of course I want the best sounding I can so when someone else comes over they'll think WHOA that sounds awesome. Depending on the frequency, it does pound my chest!!!

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