Loopback vs Acoustic reference

[Cardsin2005]

I'm getting wildly different delay measurements when using loopback reference as apposed to acoustic reference. Neither seem to be giving me accurate results. I mist be doing something wrong.
When measuring my subs for example. Loopback measurements estimate the sub to be about 32 feet away. When using acoustic timing reference it estimates the sub to be about 5 inches away. Neither case is correct as the subs are positioned right behind the drivers seat (listing position).
This is a car audio installation by the way.

 

[John Mulcahy]

The delays are relative to the reference, they are not physical distances to what you are measuring. With an acoustic reference, that means relative to the time the sound from the reference speaker reached the mic. With a loopback it is relative to the time the loopback signal was seen, usually instant, so there will be a time of flight delay to add and any processing delays in the head unit. In either case delays aren't much help for subs as their low bandwidth means their arrival time is not precise. To align a sub use the Alignment tool and match phase where you want it to cross to the mains.

 

[sm52]

Cardsin2005
Most likely you are doing something wrong. Can you post the mdat file with both measurements?

 

[Cardsin2005]

Thanks John,

The sub was the problem. Since it was calculated as the farthest away driver in the group it was the measurement that was used to calculate the delay needed for the rest of the drivers. I remeasured all the drivers using loopback timing reference and calculated the delay based on the largest delay in the in the group ignoring the subwoofer. I added these delays amounts into my DSP and remeasured. All drivers measure at virtually the same delay now. I then used the alignment tool to align the subwoofer to the mid bass driver at the crossover point. I added the delay to the subwoofer and took a new measurement. Ran the alignment tool again, and the delay required for alignment was almost zero. I explain all this just to verify that my theory of operation is correct. My question now is, do I go farther and use the alignment tool to align the mid-range driver to the mid bass and then the tweeter to the mid-range? Thank you for the help. I have attached the new measurements I took tonight (before and after).

 

[carsound]

Hi Cardsin.

Don't care loopback or acoustic , if subwoofer 12ms, and left mid bass 8 , bass is 9 tw is. 10, car audio dsp delay time setting is subwoofer = 12-12=0. mid bass =12-8=4 ,bass =12-9 =3 ,

tw=12-10=2 , so , measure again, you can get all driver=12ms.