There is no exact proper setting for delays.
If you get it "perfect" on axis, then move to one side and the delay time is now wrong.
The old idea of the HAAS effect (adding 25ms or so to the actual delay time) is fine for blown or bowed instruments, but not for percussive ones.
"generally (there are cases when it varies)" I set the on axis delay time as close to "perfect" as I can. Then when you move to the side the additional delay difference starts creating a bit of the HAAS effect.
You can't make it "perfect" in every location
The Haas effect is the definition of a phenomenon. And has been twisted and misinterpreted by a lot of people. You don’t just add delay.
The Haas effect or the precedence effect explains the parameters that are acceptable that vary from (as close to) perfectly timed delay speaker that you can achieve and within those parameters the sound will still be perceived as coming from the direction of the first speaker. If a delayed speaker system is done right people will think that the delayed speaker is off. Because of this I have had clients that don’t want delayed speakers installed because they are tired of having to deal with people telling them that the speakers are off. Even though the room and situation calls for delayed speakers to work the best for what they are trying to do. I have said to people that I think it would be great if you can hide the delayed speakers so the people won’t be listening with their eyes.
Keep in mind that you really can’t delay speakers perfectly except for one location. So you have to find a delay that works for all of the areas that the 2 speakers overlap. And it is a compromise. And that is where the Haas effect comes into play but not that you just add delay to the speakers.
“The Haas effect is a psychoacoustic phenomenon discovered by Dr. Helmut Haas in 1949. Also known as the “precedence effect,” the law states that when one sound is followed by another with a delay time of approximately 40 ms or less (below humans’ echo threshold), the two are perceived as a single sound.
This relates to how we determine spatial location by sound. Because two noises with a very short delay between them are perceived as one, spatial location is determined by the first heard, dominant sound–regardless of where the second came.
To summarize, we determine the source of a sound based on what arrives at our ears first. Any subsequent reflections or noises arriving after a short delay give the sense of depth and spaciousness and do not appear to be individual sounds.”
