Question on REW estimated IR delay anomaly

[josersurg]

I have been playing around with a new centre channel, 3-way with twin woofers, twin mid panels and single ribbon tweeter. They are in a vertical line on the same baffle and closely aligned. I have taken measurements with REW of each of the 3 components and have been trying to use REW to time align them.
In the Impulse screen one can ask REW to estimate IR Delay and these are the results I got: BTW I have repeated these measurements multiple times on different days and the "anomaly" persists.
I have not used a timing reference.
Woofer -1,365.2757ms (-468.290m 1536 ft 5 in)
Mids 0.0431ms (15mm 0.58in)
Tweeter 0.0521 ms (18mm 0.7in)

The relative delays for the mids and tweeters are as expected. There is clearly a problem with the woofer delay. There is one 12" and one 15" running in parallel in the attached measurement but I get the same anomalous result when measuring the woofers on their own.
Interestingly, if I look at the actual graph and the maximal amplitude of the signal, the calculated woofer delay would be about 0.175ms

I would appreciate your views on what could be causing this incorrect woofer IR Delay calculation and any advice appreciated.

regards
Jose

 

[EarlK]

You must use a timing reference to get meaningful offset numbers.

At least you admit your mistake.

Time for you to do a lot more reading in the help files ( found at the top of this forum ).

 

[sm52]

In the Impulse screen one can ask REW to estimate IR Delay

read what Estimate IR delay does

SPL and Phase Graph

 

[josersurg]

Thanks for the replies.
I have tried to read up on the various functions but still cannot understand (probably due to ignorance) why the estimated delay for the woofers would be so different to that of the mids and tweeter.

 

[John Mulcahy]

That's a bug, triggered by the left hand IR window being very long and longer than the right. I'll fix it, but in the meantime I can't think of a reason to use a left window longer than the right, or one that is so long. If you set the left window to something much shorter the result will be correct.

 

[josersurg]

Many thanks John