phase in bandpass

[The Camry]

So I think I'm understanding crossovers, their slopes and how they effect phase.

Lets see if I got this right. So your speaker is going to be playing a waveform. That waveform will switch 180 degrees if you wire out of phase/digitally flip it, or you run a -12 db slope.

If you run a -24 db slope. You get in phase with whatever your speaker is wired at. Or just pos to pos. Neg to negative. Normal wiring.

Skipping the -6 and -18 because of odd phase relationships.

So here's where I'm a little lost. If I say run my sub lpf at 100hz at -24. Then run my midbass hpf at 24 db. I should have two in phase speakers. correct????

But if I run the midbass at -12db instead. Without flipping phase manually or digitally. Am I suddenly out of acoustic phase?

Also. How does the effect of a band pass filter work. If I have a -12db on my hpf but a -24db at my lpf. What the hell is going on to the waveform?

I'm not sure how it can be playing out of phase on one end and in phase on the other.

Click to read more...

 

[LosIsATool 5,000+ posts]

Setting phase is something you have to do by ear. Normally you will flip the mid bass in a 3 way plus sub but you might only need to on the passenger side.

 

[hispls 5,000+ posts]

The crossover slope is only how quickly frequencies are attenuated below the crossover point. This does NOT effect phase. The phase issue comes from the sound sources originating from different locations and waves reaching your ear not all at the same time. Between your mids and highs avoiding phase issues is as simple as keeping the coils of the tweeter and mid as close together (and equidistant from your ears) as possible. Between sub and fronts you need an actual phase adjustment on either/or to make sure both waves are in phase when they hit your ear.

 

[wew lad 5,000+ posts]

Setting phase is something you have to do by ear. Normally you will flip the mid bass in a 3 way plus sub but you might only need to on the passenger side.

when you have time go a little more in depth with what you mean, i haven't bothered with phase and everything sounds great, but im wondering what i should take into consideration because i have 6.5s in my door active and then my kick panels are HPF'd components with a passive x-over.

instead of worrying about the different crossover slopes per piece of equipment I'm using, is there something i can play that'll focus on phase and indicate if a certain speaker is out of phase?

 

[wew lad 5,000+ posts]

The crossover slope is only how quickly frequencies are attenuated below the crossover point. This does NOT effect phase. The phase issue comes from the sound sources originating from different locations and waves reaching your ear not all at the same time. Between your mids and highs avoiding phase issues is as simple as keeping the coils of the tweeter and mid as close together (and equidistant from your ears) as possible. Between sub and fronts you need an actual phase adjustment on either/or to make sure both waves are in phase when they hit your ear.

different types of crossover slopes can change the phase of a signal...

 

[hispls 5,000+ posts]

different types of crossover slopes can change the phase of a signal...

Really? How does that happen? Care to show me the math on that one?

 

[wew lad 5,000+ posts]

Really? How does that happen? Care to show me the math on that one?

I've read about it multiple times. Something about when using a specific 12db crossover slope it's almost always necessary to switch the phase of the signal.

You don't need math to understand theory in many circumstances.

here ya go: http://www.rane.com/note160.html that should be sufficient

and just to further prove my point since you're being super cereal:

 

[big scott]

yup i have read it to.

i have read you should use a 24db as that gives 0 phase .

i think its 24.....

 

[hispls 5,000+ posts]

I've read about it multiple times. Something about when using a specific 12db crossover slope it's almost always necessary to switch the phase of the signal.
You don't need math to understand theory in many circumstances.

here ya go: Linkwitz-Riley Crossovers: A Primer that should be sufficient

and just to further prove my point since you're being super cereal:

From the Rane article :

The cancellation nodes are not due to the crossover design, they are due to the vertically displaced drivers. (The crossover design controls where cancellation nodes occur, not that they occur.) The fact that the drivers are not coaxial means that any vertical deviation from the on-axis line results in a slight, but very significant difference in path lengths to the listener. This difference in distance traveled is effectively a phase shift between the drivers. And this causes cancellation nodes -- the greater the distance between drivers, the more nodes.

One can safely assume that the 180 degree phase flipping inherent in cascading Butterworth filters is rectified by either the active circuit or by simply marking polarity accordingly on your passive crossovers.

 

[big scott]

there was a chart i seen that showed what phase each slope was.

and i think it was 24db that give 0 phase.

im trying to find it...

 

[big scott]

this also talks about it..

plus a good read.

http://www2.bssaudio.com/product_downloads/App_Notes/Crossovers_Demysified.pdf

also this.

http://www.stereo.net.au/forums/index.php?/topic/23800-active-vs-passive-crossovers-and-phase-shift/

but the more reading i do, it sounds like if your active you dont have to worry about phase.

but if your passive then yes.

and i was right its 3rd order that has the 0 phase .

even the 80prs manual talks about it. and the 80prs offers phase adjustments...

so does that mean phase is an issue with active crossovers?

 

[wew lad 5,000+ posts]

From the Rane article :

One can safely assume that the 180 degree phase flipping inherent in cascading Butterworth filters is rectified by either the active circuit or by simply marking polarity accordingly on your passive crossovers.

Yes, you would invert the polarity on the active crossover if it was an option, or would invert the phase of a midrange driver on a 12db passive second order crossover. What happens when your active crossover is 12db, and doesn't allow you to invert the polarity? I would assume you simply invert one sides midrange driver.

So we can all agree now that this type of crossover slope inverts phase 180 degrees?

While I'm thinking about it, here's what I don't understand - why wouldn't the designers of these passive and active crossovers not account for this by inverting one channels phase?

 

[The Camry]

Seems alot of you don't know what I mean. Ha. Anyway. Everytime I run -12 db slopes. I switch phase on both midranges. doing it to just throws the acoustic phases wayyy out of wack. I've never had to flip just one.

 

[trumpet 5,000+ posts]

Phase constantly changes, and swapping polarity to "fix" phase when using -12 dB slopes is to specifically target the crossover corner frequency and surrounding frequencies for adjacent driver pairs. Optimizing phase response in a room is to serve the purpose of meeting a desired frequency response target. -24 dB LR crossovers help to minimize the phase changes, but that doesn't mean we're out of tools to fix phase problems, nor does it mean we won't have phase problems after selecting that type of crossover topology. All I know is I have the tools to measure phase, and in my car it's a crazy looking graph that I barely understand. I have a lot to learn about electric and acoustic phase.

 

[hispls 5,000+ posts]

why wouldn't the designers of these passive and active crossovers not account for this by inverting one channels phase?

The signal would be phased properly for easy plug and play by the user. If you are not designing your own LR crossover system this is a non-issue.