AllenB, your first remark above confuses me. Yes, the two points are there, in space, but those points aren't free to rotate on their axis independently. The baffle board fixes their position to the other drivers. If the AC's aren't aligned, like on a flat baffle perhaps, I fail to see how tilting those two points in space can attain AC'ing while rotating them on a common axis.
When you tilt the baffle back, the tweeter AC moves to be directly over the woofer AC, ie they are now vertically aligned.
It is important to ignore the fact that both drivers are now tilted. The reason for this is that time aligning is a point/pressure based affair. Two centres, one measurement position, two distances, nothing else. (Lobing can be analysed from the point of view of being extrapolated from these, and besides is extraneous to time aligning.)
Is there a justification for wanting to rotate on the plane of the baffle?
It is important to ignore the fact that both drivers are now tilted. The reason for this is that time aligning is a point/pressure based affair. Two centres, one measurement position, two distances, nothing else. (Lobing can be analysed from the point of view of being extrapolated from these, and besides is extraneous to time aligning.)
Is there a justification for wanting to rotate on the plane of the baffle?
Again, we should not conflating the two together - that is the AC of the drivers and the phase of the driver.
For example, let's say you have a stepped baffle so that the AC of the mid and tweeter are perfectly aligned and their AC's are exactly on the same plane. So acoustically the AC's are aligned.
But now the height of your listening axis will change the phase integration of the mid and the tweeter. For example, your xover may be optimized for one listening axis, but may have a null at some other listening axis, but both of which cannot fault the drivers' AC, that is it is not the fault of the AC alignment. AC alignment cannot do anything about it.
I think the reason for aligning the driver AC's for meant for low order filters. If you use 4th order roll off or asymmetric xover, then the driver AC's don't really matter, because even if the AC's are not aligned, the xover will fix all of that. That is the xover will align the phase of the drives inspite AC's not aligned. On the other hands, low order filters (for example first order) don't have that luxury.
Ultimately, at the end of the day, you want to align the drivers phase response regardless of the drivers AC's. The alignment of the driver AC's are meant to make your xover jobs easier. If your AC's are not aligned, it just makes the xover jobs a little more difficult such as having to use higher order filter or asymmetric xover but both of which are a compromise.
For example, let's say you have a stepped baffle so that the AC of the mid and tweeter are perfectly aligned and their AC's are exactly on the same plane. So acoustically the AC's are aligned.
But now the height of your listening axis will change the phase integration of the mid and the tweeter. For example, your xover may be optimized for one listening axis, but may have a null at some other listening axis, but both of which cannot fault the drivers' AC, that is it is not the fault of the AC alignment. AC alignment cannot do anything about it.
I think the reason for aligning the driver AC's for meant for low order filters. If you use 4th order roll off or asymmetric xover, then the driver AC's don't really matter, because even if the AC's are not aligned, the xover will fix all of that. That is the xover will align the phase of the drives inspite AC's not aligned. On the other hands, low order filters (for example first order) don't have that luxury.
Ultimately, at the end of the day, you want to align the drivers phase response regardless of the drivers AC's. The alignment of the driver AC's are meant to make your xover jobs easier. If your AC's are not aligned, it just makes the xover jobs a little more difficult such as having to use higher order filter or asymmetric xover but both of which are a compromise.
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The one advantage of having a tilted baffle over the stepped baffle is the diffraction. The stepped baffle physically will cause some unwanted diffraction that does not happen for a angled baffle.
I agree, but where I'm uncertain is what other differences you say there are between stepped and tilted. In my view the other differences are very minor in the context of time aligning.
If I could make an analogy - the drivers AC's and phase are like a car brake and accelerator pedals. Both of which can control the speed of the car and therefore they are related but they are not the same.
So, over tilting the baffle could make the AC spill out the back of the driver. 😱
Best not tilt the speaker back too far andy2.
AllenB .. I see it as perspective. Like two stars in the sky that look to be right next to each other but in reality are billions of light years apart. Or the pair of paintings that look like one image when you're positioned "just right" in front of them. The person to your right and left see something different. It's an illusion.
The speakers combined driver response doesn't change when you tilt it. It doesn't. So, in reality, the creamy acoustic center(s) don't move either. Not really. It's an acoustic illusion that works "best" for camplo while seated in the sweet spot.
The speakers combined driver response doesn't change when you tilt it. It doesn't. So, in reality, the creamy acoustic center(s) don't move either. Not really. It's an acoustic illusion that works "best" for camplo while seated in the sweet spot.
It seems like the discussions are being mis-interpreted with semantics.
Sure the acoustic center of the drive itself does not change. It's the alignment of the acoustic center with respect the tweeter and mid that is changed.
And again, please do not conflate the concept of acoustic alignment and acoustic phase of each driver.
Sure the acoustic center of the drive itself does not change. It's the alignment of the acoustic center with respect the tweeter and mid that is changed.
And again, please do not conflate the concept of acoustic alignment and acoustic phase of each driver.
Just to confirm I have got the idea. Am I right in saying with a tilted baffle one listens to the drivers off axis?
^ midrange, this is one of the minor secondary effects I was talking about. Sure, it has significance, but it doesn't exactly invalidate the idea of tilting the baffle.. it just adds something else to think about 😉
Yes, when you say 'tilt', the listening position is intended to stay the same. (Also, we're only talking about 7-8 degrees).
Where would you like to see this discussion go?
I was only saying sometimes the semantics can obscure the subject being discussed. It's not really up to me where this discussion will go. There are few posts seem to keep talking about acoustic alignment and phase alignment as if they are the same. Maybe it's just the semantics.