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Author Topic: Phase shift  (Read 2483 times)

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ALEXZ

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Phase shift
« on: February 21, 2015, 01:10:02 PM »
Hi,
What line level baffle compensation filter does with the signal phase above the step ?
Thank you,
Alex

ALEXZ

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Re: Phase shift
« Reply #1 on: February 23, 2015, 03:54:52 PM »
Let me try again ... does any one noticed any changes in soundstage depth and imaging  after inserting the Fix into the system ?

4krow

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Re: Phase shift
« Reply #2 on: February 23, 2015, 07:34:27 PM »
 My understanding of this circuit is that it would have minimal phase shift due to it's 1st order slope. As far as soundstage, I never noticed any difference in my system. Makes me think that you have one channel out of phase with the other, but I don't see how that might happen with this circuit.

Online Paul Joppa

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Re: Phase shift
« Reply #3 on: February 23, 2015, 07:51:45 PM »
If some capacitors were swapped by accident, that would make a difference between channels, both phase and frequency response, which could well disturb the image. In theory, of course.
Paul Joppa

ALEXZ

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Re: Phase shift
« Reply #4 on: February 24, 2015, 02:01:32 AM »
I'm using a "complex" filter consisted of  2 resistors and one cap as per publications by PJ ;-) and
Rod Elliot.  So capacitors mismatch or phase reversal in one side is out of questions.
1st order filter in theory shift phase 90 dig, right ? In baffle loss comp. filter  this shift is in a mid range where it is most sensitive. With any additional phase delay we are now more close to the 180 deg. phase (inverted) then original.  Am i wrong somewhere ?

« Last Edit: February 24, 2015, 03:27:27 AM by Alexz »

Offline Bonzo

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Re: Phase shift
« Reply #5 on: February 24, 2015, 02:10:48 AM »
I'm about to build that filter too, but with two potentiometers and a switch to select the second cap (for hights booster).

You are speaking about the line level BSC published on the t-line-speakers website, aren't you?

Ciao
Bisogna avere orecchio!

ALEXZ

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Re: Phase shift
« Reply #6 on: February 24, 2015, 02:59:19 AM »
Today I would just buy the Fix ...

Online Paul Joppa

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Re: Phase shift
« Reply #7 on: February 24, 2015, 10:34:00 AM »
A first order filter shifts the phase 45 degrees at the corner frequency, approaching zero as you move into the pass band, and approaching 90 degrees as you move deeper into the rejected frequencies. One way to look at it is that the phase shift is proportional to the slope of the magnitude. (Technically, they are Hilbert transforms of each other.)

A BSC filter is a step filter, where there is a first order pole and a first order zero that are close to each other - less than an octave apart when the boost is less than 6dB. The phase shift of the pole is in the opposite direction from that of the zero, so they partially cancel. The biggest phase shift is at the middle of the transition where the frequency response is steepest, and is about 20 degrees for a 6dB boost. At 4dB (the highest setting of the Fix) it's 14 degrees, and at 2dB boost it's 6.5 degrees. Outside of the transition region there is essentially no phase shift at all, neither above nor below the transition frequency.
Paul Joppa

4krow

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Re: Phase shift
« Reply #8 on: February 24, 2015, 01:07:21 PM »
 That is a good description for me to understand. I think that what I meant to say is that the first order slope is least guilty of phase shift, compared to steeper sloped filters. I was not aware of the step filter cancellation effect however, which is one of those happy coincidences working for us. Of course I realize that your reply was not meant for me so much as to answer the OP, but it is useful knowledge non the less.

ALEXZ

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Re: Phase shift
« Reply #9 on: February 24, 2015, 01:49:58 PM »
Thanks, Paul.
That is what I was trying to find out : how second pole is interacting with the first one.  Sure enough 14 deg. are not remotly close to phase-inversion. or anything significant...

« Last Edit: February 24, 2015, 03:14:14 PM by Alexz »