Evan Kirkendall wrote on Tue, 27 April 2010 17:20 |
You want your phase trace to look similar to the pink trace in this shot:
Measurements were made 10' away from the cab in the ground plane. The pink trace is the combined sub and low of the system once they've been aligned.
Evan
|
Adam,
Not to confuse you further, but Evan's posted way of doing this and what Mac is describing are not using the phase information in the same way, though the end result is the same. The difference is why Mac's phase traces will not be flat near the XO point, but Evan's phase traces will be.
Mac is instructing you to pick a fixed reference delay time in Smaart (by using AutoSM/Delay Finder) and then adjust the top delay till the slope of the sub phase and the top phase are the same in the crossover region.
Evan's way is manually adjusting the reference delay till you have
zero apparent group delay at the desired XO point. You do this for each of the boxes, and then subtract the adjusted reference delay times from each other to find out the relative delay difference between the boxes.
In the specific example Evan posted, Evan appears to have done:
1. Adjust the SMAART reference delay time for the sub (i.e. Blue) trace until it looks like the blue trace on the screen. Typically starting with an AutoSM and then adding additional delay.
2. Shoot the top trace (i.e. Orange) using the current (i.e. Blue) reference delay time.
The next step would then be:
3. Adjust the Smaart reference delay until the Orange curve lays on top of the Blue curve.
4. Compare the reference delay of the Blue curve to the Orange, and apply the necessary
differential delay to the appropriate box. Usually that is the top box, but not always.
The final result of this, using the original Blue reference delay time, is the pink curve displayed.
Both this method and Mac's method achieve the same final result (i.e. phase alignment at the XO). Mac's method is easier to explain, but can be more difficult to perform.
I personally find the method Evan shows easier to do in difficult acoustic environments, and that is the method I teach new users first. Also, in a class setting, the method Evan is doing allows me to expound a deeper conceptual understanding of what is really going on.
Since I taught Evan this method, he can expound on whether he felt that it helped give him a deeper understanding of what the phase trace is really saying.