Why is ”bad phase tracking” really that bad?

[dlr]

To Lasse, understand that phase-tracking is not by default equal phase response of two drivers, it is achieving the intended phase response of the desired filtered responses. For instance, all odd-order Butterworth filters are intended to be 90 degrees out-of-phase or some multiple of that number (i.e. BW3 is 270 degrees) and are acceptable crossovers types for speaker systems with first order being the most used to my knowledge when it comes to Butterworth.

From your 1st graph, I can see your Fc is near 2.5kHz (don't know if this is a sim, or actual measurement... whatever).
Right at your Fc, it looks like the 2 drivers are "summing" +2-1/2dB (LR is typically +6, and BW is +3).
I can also see that at Fc your drivers are OOP (out of phase) by about 100*. Theoretically, I'd reverse the tweeter to get them only 80* OOP. (They'd probably sum +3.5dB @ Fc then.)

I think you mean that the filters are down, -6 or -3 db, at Fc. But that's not complete. LR sums flat on-axis with no off-axis lobing. Even-order Butterworth sums to +3db on-axis. Odd-order sums flat. All Butterworth filters have lobing off-axis as will pretty much all filters other than LR.

dlr

[Dave Bullet]

That looks really good - I recall seeing your thread on HTGuide - you've put a lot of work into that crossover and it shows. Nice job!

Cheers. It's been 11 years in the making. Largely because i put the hobby on hold. The tweeters' ferrofluid is probably drying up :-)

I had a "phase perfect" LR4 M/T @ 2KHz design. ruler flat on-axis (yes power response matters). Anyway - it sounded worse than the tapered slope 3KHz steeper design I'm listening to now. Even though the mid and tweeter were padded to match sensitivity, the tweeter would dominate the mid on many recordings. Moving the Fc up fixed this, at the expense of increasing 3rd order HD on the mid. I might move it back down again. I'm also only playing on one speaker so have no idea of the imaging and soundstage presentation haha. I'm building the final cabinets as I'm pretty happy with the diffraction and driver placement.

[ernperkins]

I had a "phase perfect" LR4 M/T @ 2KHz design. ruler flat on-axis (yes power response matters)..

Just to be clear, are you talking about a simulation or actual measured response?

[Dave Bullet]

Just to be clear, are you talking about a simulation or actual measured response?

Measured response. By phase perfect I meant good tracking either side of of both Fc.

[lasse]

Hi all,

first I would like to thank you all for all the feedback on my initial questions in this thread. I have been offline for the better part of this day for pressing personal reasons and really need a good day to "digest" all the advice given by all of you.

One thing stads out for me and that it really is a good idea to strive for good phase tracking in the overlap region and I will remodel my system to try to achieve that.

I Will be back!!

Thanks!!

Best regards//lasse

[Dave Bullet]

I don't have a lot of build experience, and my theoretical knowledge is even less.... so take this with a grain of salt.

Through all my reading, it seems the factors dominating the sound are:
1. power response - avoiding slopes and baffle geometries that cause severe on axis or off axis peaks. Designing and measuring for just on-axis then finding you have a +3dB peak in the sensitive 2.5Khz - 4.5KHz area will make the speaker forward sounding and increase fatigue.

2. Distortion. Asking a tweeter to play too low / shallow slope or a harder coned / domed woofer or mid playing too high (where primary breakup node non linear distortion lower down) will make a speaker harsh

Phase seems to be mentioned after the above when it comes to designer trade offs and concerns. I'm not saying it should be ignored - but questioning its relative importance.

I wonder therefore whether we focus too much on phase - knowing the measuring axis is never the listening axis in a real world situation, and therefore phase is different purely due to location.

[jhollander]

I wonder therefore whether we focus too much on phase - knowing the measuring axis is never the listening axis in a real world situation, and therefore phase is different purely due to location.

The measuring axis can be your listening axis. Certainly the design axis should be where you intend to listen. You should measure off axis to look for issues where you might have messed up the phase alignment.

[craigk]

http://sound.whsites.net/ptd.htm#s4

[a4eaudio]

http://sound.whsites.net/ptd.htm#s4

Regardless where you stand or sit, you will most likely be a different distance from each instrument. One could insinuate oneself into the very centre of the performers' space, but this is more likely to lead to your eviction from the venue than to improve your listening enjoyment.

Craig - thanks for that link. Not only for the good technical info, but for the humor that Rod imparts in his writings. Laughed out loud reading about speakers on a Friday night.

[craigk]

Craig - thanks for that link. Not only for the good technical info, but for the humor that Rod imparts in his writings. Laughed out loud reading about speakers on a Friday night.

Glad you liked it.