Keith_W
New Member
Thread Starter
- Joined
- Apr 3, 2018
- Posts
- 11
Hello John, I normally use different measurement software but I am trying to develop some procedures in REW. I am using an XLR mic + RME Fireface UC to do all my measurements. The mic is on a proper mic tripod, and I moved all the furniture out of the way between mic and speaker. The mic was at the MLP.
The first thing I did was to check for consistency. These are three fullrange measurements (20Hz - 20kHz) of the left speaker with the tweeter chirp coming from the left speaker. I am expecting 0.0ms but I guess 0.0056ms is close enough. I decided to manually examine the impulse and determine the delay myself.
So I zoomed in on the impulse response and I found the tweeter timing chirp at about -760ms. I zoomed all the way in, placed the cursor at the peak negative deflection (I deliberately inverted the polarity of my tweeter, so I know that the main impulse should be negative), and set that as t=0.
Then I found the main impulse from the DUT, zoomed all the way in to the impulse peak, and placed a marker there. As you can see, it reads 762.47ms.
This struck me as a rather odd choice for delay between tweeter chirp and DUT so I tried looking up what the actual delay was. From REW's help pages on the acoustic timing reference it says "The timing signal is a sweep from 5 kHz to 20 kHz lasting about 700 ms." Clearly from my own measurement it is not 700ms. And I can't seem to obtain a value of 0.0056ms no matter which way I slice the cake.
Can I ask you what the acoustic chirp is actually measuring? What is the delay between chirp and DUT? And is the measurement between impulse peak of chirp to impulse peak of DUT?
The first thing I did was to check for consistency. These are three fullrange measurements (20Hz - 20kHz) of the left speaker with the tweeter chirp coming from the left speaker. I am expecting 0.0ms but I guess 0.0056ms is close enough. I decided to manually examine the impulse and determine the delay myself.
So I zoomed in on the impulse response and I found the tweeter timing chirp at about -760ms. I zoomed all the way in, placed the cursor at the peak negative deflection (I deliberately inverted the polarity of my tweeter, so I know that the main impulse should be negative), and set that as t=0.
Then I found the main impulse from the DUT, zoomed all the way in to the impulse peak, and placed a marker there. As you can see, it reads 762.47ms.
This struck me as a rather odd choice for delay between tweeter chirp and DUT so I tried looking up what the actual delay was. From REW's help pages on the acoustic timing reference it says "The timing signal is a sweep from 5 kHz to 20 kHz lasting about 700 ms." Clearly from my own measurement it is not 700ms. And I can't seem to obtain a value of 0.0056ms no matter which way I slice the cake.
Can I ask you what the acoustic chirp is actually measuring? What is the delay between chirp and DUT? And is the measurement between impulse peak of chirp to impulse peak of DUT?
