Phase measurement issue using loopback timing

[rasykora]

Hi John and all,

Am working on a 2-way active speaker and using VituixCAD with REW. Was using a UMIK-1 and now trying to move to an EMM-6 mic so I can sync individual driver measurements. As audio interfaces go, have tried both a SoundBlaster Audigy FX and a QuantAsylum QA401. Naturally, the QA401 is much better but getting the same issue with phase measurement in either case. Have also tried both Java and ASIO drivers and the released and Beta versions of REW.

Here is a look at the results of SPL & Phase sweep (also showing the soundcard and mic calibrations)...

The frequency plot is as expected, but phase is jagged as shown in the lower half. Since I forgot the legend, sound cal is the dotted line and the mic is the solid black line.

If I switch to "no timing" I get the expected phase plot (in this case for a Purifi 6.5 midwoofer)..

Please help so I can finish this project.

Thanks!

Rick

 

[John Mulcahy]

You need to remove the delay caused by the distance of the mic from the speaker. Easiest is to use the Estimate IR Delay button in the graph controls and then choose the option to shift the IR and update the timing offset, then REW will remove that delay from further measurements you make. Note that for that to work properly you will need to keep exactly the same mic distance for any other measurements you make.

 

[rasykora]

You need to remove the delay caused by the distance of the mic from the speaker. Easiest is to use the Estimate IR Delay button in the graph controls and then choose the option to shift the IR and update the timing offset, then REW will remove that delay from further measurements you make. Note that for that to work properly you will need to keep exactly the same mic distance for any other measurements you make.

Thanks John!
Had tried some settings in the Beta for compensating for the distance but did not work. Your instructions work just fine in the released version and so am back in business.

Take care,

Rick