stupid polarity question.

[Learnincurve]

I'm building an active sub and still planning the electronics to go in front of the bridged power amp. I know this is a really stupid question for those who know the answer, but:

What is the point of a 180 deg. phase switch circuit? won't simply reversing the polarity of the speaker dp the same thing? Yes, I did search.

OK! SHOOT ME NOW!

[Pan]

Yes, just changing the cable to speaker will do the same thing BUT, many subs have a continous setting that can be used to alter phase anything between 0 and 180 degrees. But if it´s only a simple switch it´s only to make it a little easier than having to unscrew the cable.

/Peter

[Learnincurve]

Thanks for the reply. The consensus about continuous adjustment seems to be that it's a waste of time as it's only correct at one frequency. The (limited) modelling I've done suggests that I'll be around 160deg. out at crossover frequency (40Hz), so 180 deg is probably near enough.

[Artmaster]

Originally posted by Learnincurve
so 180 deg is probably near enough.

gday!
furthermore, you need modulating control of phase for subwoofer.
it's absolutely necessary for your system instalation.

[Jim York]

You only need for it to be correct at one frequency, and that's the crossover frequency between the sub and the mains. The phase switch allows the sub and mains to be in phase in the overlap zone of their outputs, and you adjust it simply by using whichever position delivers the higher system bass output. If you can't hear the difference don't worry about it, it only matters if you can hear the difference.

[Learnincurve]

modulating control? (ignorance shining through). Sorry. I got bogged down in a driver discussion as I can't use the one I have.

[BillFitzmaurice]

you need modulating control of phase

Don't feel ignorant, I have no idea what he means by that either. Sounds like a line from 'Star Trek' to me: "More power to the shields, Scotty, and modulate the phase frequency!"

[BassAwdyO]

Bill you make me laugh...

I dont know exactly how variable phase controls all work, but I'd imagine most dont perform ideally. Phase and polarity are related, but in audio they are often considered to be the same thing. They are not!

For a function F(x)= sinX

a function with reverse polarity is written
F(x)= -sinX
A function out of phase is written
F(X)= sin(X+pi)

[simon5]

Yes, but F(X) = -sinX = sin(X+pi)

[BassAwdyO]

Try changing the frequency.

instead of using sinX use sin2X as this represents a double in frequency.


I believe the standard form of a sin function is written

Asin(B(x+c))
where A determines amplitude. B determines frequency and C determines phase shift.

for sinx A=1 B=1 and C=0
For sin(x+pi) A=1 B=1 and C=pi
for -sinx A=-1 B=1 and C=0

Now if we go to the equation Sin2X and reverse the polarity we get -Sin2X... An equivilant equation would be Sin(2(x+pi/2))
Now this could be simplified into Sin(2x+pi), but the phase change is still pi/2 and NOT pi