acoustic phase question

[crazyhub]

Hi,

Let us suppose a classical two-ways.
Three different filterings (slopes and\or Fx) show, under identical conditions of measure, a same or very close magnitude response.
The first filter shows a crossing of the acoustic phases of each driver exactly at Fx. Both drivers are thus exactly " in phase " at Fx.
The second filter shows no crossing of the phases at Fx, but close and parallel phases on a wide band of frequencies on both sides of Fx.
Third filter shows no crossing phases but phases going away one of the other one.


What do these differences of phases between drivers mean in physical terms, as well as their corollary in the listening?

Thank you.

[Syncroniq]

Hi,

Instead of looking at the phase, you can invert the polarity of the tweeter. If the summed response have a huge suckout at XO, the drivers are well in phase.

[crazyhub]

Originally posted by Syncroniq
[B]Hi,

Instead of looking at the phase, you can invert the polarity of the tweeter. If the summed response have a huge suckout at XO, the drivers are well in phase.

Hi,
Yes I knew this reverse nul effect; my question was about the effects of drivers not perfectly in phase at Fx however giving a straight fr magnitude.

[sreten]

Hi,

It is a none question, different filters cannot sum the same.
Define the filter functions with the properties you describe.
2 and 3 seem not feasible.

/sreten.

[Syncroniq]

Hey,

You can have a response from the mid and tweeter, giving a flat response, but not being in phase. Thats how alot of companies does it, but it doesnt sound good. image and perspective depends on phase.

The best way is the reversed null method. flat in phase, and deep null out of phase, and you have a very good startingpoint.

[djarchow]

Originally posted by Syncroniq
Hey,

You can have a response from the mid and tweeter, giving a flat response, but not being in phase. Thats how alot of companies does it, but it doesnt sound good. image and perspective depends on phase.

The best way is the reversed null method. flat in phase, and deep null out of phase, and you have a very good startingpoint.

However, that is only true for even order XO's. To sum properly, odd order XOs, i.e. 3rd order butterworth, the high pass and low pass have to be 90 degrees apart which doesn't yeild a null when reversed.

Regards,

Dennis

[crazyhub]

Originally posted by sreten
Hi,

It is a none question, different filters cannot sum the same.
Define the filter functions with the properties you describe.
2 and 3 seem not feasible.

/sreten.

I spoke of different filters using different slopes and/or Fx suming the same fr magnitude, no matter the functions; thus 2 and 3 are feasible, no?

[crazyhub]

Originally posted by djarchow


However, that is only true for even order XO's. To sum properly, odd order XOs, i.e. 3rd order butterworth, the high pass and low pass have to be 90 degrees apart which doesn't yeild a null when reversed.

Regards,

Dennis

That's interesting; so can I consider that if the summed phase looks unshifted + wanted (flat) fr magnitude, it's OK, at least for this type of filter?

[Syncroniq]

Hi,

In praksis, thats not quite true.

You will have a timedelay between the two drivers, so you will never be put in that situation as there will be a timedelay between the two drivers. If you get a flat response in phanse, and not "nulling" out when out of phase, the filter will not perform optimal. The drivers NEED to bee in phase at least at xo point. It will be reflected in stereoperspective, staging and so on.

Just becourse its "a type of filter", doesnt mean its good. There are thousands of "types of filters", most of them just havent been named yet.

You should forget about butterworth, bessel and so on. Its way to theoretical to work in pracsis. Find the rolloff that makes your drivers sum flat in phase, and null out when out of phase. You might end up with slopes of 27dB/oct on the tweeter and 14dB/oct on the bass (just an example).

[Syncroniq]

Hi,

Here you can see the slopes i came to, in order to get flat response, and good phase, on a 3 way.




If your drivers are timealigned, and have a flat response to begin with, Steen duelund have developed a filter that are in phase at all frequencies, and give a flat response. Read more here.

http://www.steenduelund.dk/download/duelund-filter.pdf
On his site, theres other interesting articles. He past away a couple of years ago.