Subwoofer Delay setting using REW Time Alignment query

[Buckster]

Wondering if anyone can help please I might be doing something wrong.

After successfully time aligning the mains, rears, and Atmos speakers I'm now trying to time align the subwoofer

Subwoofer is SVS-Ultra 13 with the latest 1000d amplifier (old one failed)

I have been using Centre channel (8030c as can easily turn on and off) to time align, with timing reference played by Front Left

Subwoofer was still on original delay setting from post Audyssey calibration (which I'd left the delay for sub as was) - was about 4.3m or so for the subwoofer vs approximately 3.1m for fronts. The subwoofer is about 40cm behind and to side of the front left.

Method was

(1) Plotted centre channel on its own with subwoofer off
(2) Plotted subwoofer crossed over part of centre channel with centre channel off

Crossover is at 90hz

I picked this time point and clicked time alignment tool, align Phase Slopes in REW and it said I was nowhere near (something like 3 metres off). I changed the distance on av amplifier from 4.3m to 7.3m and then REW was showing only a 2ms missalignment which is much much better, but I'm not totally sure of my methodology as it is such a difference to previous settings.

One particular question I have please- do you align at the crossover value set on amplifier (90hz) or where the two plots (centre only, centre channel sub only) crossover - as this point is 65hz on plot. Results very different from each point

Subwoofer is set to inverse phase, but trying positive and negative phase didn't seem to massively change REW alignment results

many thanks for any help

 

[neRok]

I picked this time point and clicked time alignment tool, align Phase Slopes in REW and it said I was nowhere near (something like 3 metres off). I changed the distance on av amplifier from 4.3m to 7.3m and then REW was showing only a 2ms missalignment which is much much better, but I'm not totally sure of my methodology as it is such a difference to previous settings.

The first distance you set was only to correct the time difference caused by the different travel distances. Your second change was to increase the delay further to account for the subs group delay.

One particular question I have please- do you align at the crossover value set on amplifier (90hz) or where the two plots (centre only, centre channel sub only) crossover - as this point is 65hz on plot. Results very different from each point

A filter doesn't force a slope, it just applies an affect of a slope. This cuold be why the amp has it set at 90Hz, but the resulting slope is not at 90Hz. So if you want to cross at 90Hz, you will need more filters to get the slope looking right. Otherwise you can cross at 65Hz if you want. Either way, you just want to make the final slopes at whatever point the same, like this video outlines;

 

[Buckster]

thanks very much for the reply - will watch that video looks interesting thanks

ref the time delay/distance originally set for the subwoofer that was by Audyssey so should take into account the room, DSP delays etc - using time alignment tool in REW (assuming I did it right) - suggested an additional 3m on top of that measure by Audyssey which seemed a lot