Auto speaker calibration question

[cbope]

My Sony DA2400ES AVR has an auto calibration function to set up the speakers, basically it sets the speaker distances for each speaker, levels, and crossover frequency. It overall seems to work well, usually with a bit of minor tweaking. But the speaker distances are somewhat off. Not a lot for main, center and surround, but the sub distance in particular. For example, my sub is exactly within a centimeter or two of my R front, but the distance for the R front is calculated as 4m 69cm while the sub ends up at 5m 92cm. A huge difference. The calibration mic was placed at the listening position for calibration.

Should I correct this manually or just leave it? I wonder if actually measuring the distances with a tape measure and entering the precise dimensions for each speaker is overkill. But perhaps not. Comments?

[cornfedksboy]

Someone can correct me if I'm wrong, but I think that the distance helps to put the speakers in phase so that they are all firing at the right time. You could certainly measure it and see what you get, but my guess is that the signal arrives at the sub-woofer faster via the coaxial cable than to the R/L/C via the speaker cable. My subs were similarly placed further away via auto-cal. Anyone agree with this shot from the hip?

[cbope]

Someone can correct me if I'm wrong, but I think that the distance helps to put the speakers in phase so that they are all firing at the right time. You could certainly measure it and see what you get, but my guess is that the signal arrives at the sub-woofer faster via the coaxial cable than to the R/L/C via the speaker cable. My subs were similarly placed further away via auto-cal. Anyone agree with this shot from the hip?

While I agree with your first point, your second point about the signals arriving faster violates the laws of physics. Assuming a copper conductor in both types of cables, there will be no difference in the speed of the signal between the two cables. Electrons travel at the same speed in the same material. However, it could be compensating for the speed of air pressure waves traveling through air to the listener. High and low frequencies do travel at different speeds although this is usually not noticeable at normal listening distances. I might have to experiment with the distance setting on the sub to see if there is any audible effect.

[Beechnut]

The resistance in ohms of the two types of cables in question may have small differences. Over short runs under 50ft, really doesn't matter. That's how something could technically travel faster over one cable versus another. And Coax is typicaly a solid conductor, not stranded/braided. A solid conductor versus stranded, all things being equal, will show the solid conductor having less resistance.

It's my understanding that when AVR's assess distances to the listening point, they adjust their "delay" so that the soundwaves hit the listening point at the same time.

[cornfedksboy]

I am not sure what the material is in my coax, or how it is arranged. I don't know if this would affect the phase or speed, but thought I would throw it out ther.

[StephenM]

It's my understanding that this can be normal behavior, and that some subwoofer amplifiers will slightly delay the signal.