Lets talk about T/A (time alignment)!
I am currently aware of 4 ways to adjust T/A.
1&2. By ear
1. Use pink noise and listen for the Doppler effect while adjusting the T/A. Try to get the speaker right at one of the first peaks or troughs as the phase change.
2.Use music and listen for the center image to come into focus. When the sound waves are out of phase the image will sound wide and when T/A is in it's proper place everything should be in phase and focus in the center.
3. Measure the distance from each speaker to the listening position, then figure the difference between each speaker and the speaker that is furthest away. Adjust your T/A appropriately based on measured distance and the speed of sound.
4. Use software such as REW to measure an impulse response and align each drivers response to the base driver (the one with the most latent impulse).
Pros & Cons
1&2.
Pros:
-This is for music. So in the end its what you hear that really matters!
-This can take into account for reflection and diffraction going on inside the vehicle that measurements cant attain.
Cons:
-Its not easy. Listeners fatigue and other factors can reduce the sensitivity of our hearing.
-Psycho-acoustics come into play. Our ears can be deceiving!
-Sometimes its easy to hear the difference in two similar drivers on the left and right, but much more difficult when aligning say, a midbass to a midrange on the same side.
- You must find the peak in the center or in the Doppler effect with these two methods. This can be very difficult when the drivers are already closely aligned. It helps to be able to listen for the rising or falling phase on either side of an acoustic peak or trough. But when the drivers are already close to one of those peaks or troughs you don't have a phase change in both directions to judge symmetry.
3.
Pros:
-By far the easiest method
-Very little margin of error
-Gets you pretty close.... Maybe?
Cons:
-Does not take into account reflection, diffraction, and other vehicles acoustic issues that can effect the staging and image.
-Metal tape measure tongue can get sucked into a strong magnet and damage driver cone. (personal experience)
4.
Pros:
-Probably the most accurate method
Cons:
-Requires extra equipment such as: measuring devices that can get costly, extra cables, a computer and software.
-Requires research time. One must gain the knowledge of the software used to do this properly.
-Requires Mic and PC calibration.
So? Which method do you use?
I used to believe that T/A was black in white. I don't think i believe that anymore. I am coming to realize that T/A (like every other aspect of car audio tuning) is a game of give and take. Sometimes that gray area can be quite large!
So what kind of sacrifices are made for a tighter sound stage?
In what cases would you allow your T/A to be slightly off in order to gain elsewhere?
Do you even believe it is possible to dial in T/A 100% perfect?
How do you know it is perfect (please don't use "because my system sounds great" as an example)?
Do you believe the "impulse response" method can account for a car's acoustical issues as well adjusting by ear?