Automotive Measurements

[RobertM]

I have the UMIK-1 and have already taken some speaker measurements using the basic tutorials, I got this primarily for home speaker assessment and speaker building. But I would also like to fool around with in-car measurements. I have several different car speaker systems I would like to install and test, mostly for the fun of it. So far, what I have figured is I can burn the Pink Noise signal onto a disk and play it back on the car stereo. The microphone I would install at the head position pointing upward. I would use 90 degree calibration file. Is this the proper way to do this? Am I missing anything? I did search various corners of the internet, but there isn't a great deal out there in terms of support for using REW and UMIK-1 for in-car measurements.

 

[RobertM]

A bit more research. The PN file would be used with the SPL meter to set the proper volume at 75dB. I would then play the logarithmic sine wave sweep. Under "Measure", click start measuring when this file is playing and then stop measuring when done?

 

[luegotelodigo]

I read the last version can import recorded sweeps so It would be better to play the sweep by the different speakers in the car and make the deconvolution into IR by postprocessing

 

[John Mulcahy]

When you save the measurement sweep to file select the option to include the timing reference. To make a measurement select the "Wait for timing reference" option on the Measure dialog, start the measurement (which should capture the background noise then pause saying "Waiting for timing reference") then play back the file. To get a valid result the settings used when you save the measurement sweep should be exactly the same as those you use when making the measurement, including the sample rate.

 

[luegotelodigo]

When you save the measurement sweep to file select the option to include the timing reference.

I can't find that option, maybe that's why when I try to import the stymulus it says: "The sweep does not contain data REW requires to generate..."

 

[John Mulcahy]

Sweeps need to be saved from the signal generator, when doing that a dialog pops up with the options. A bit of metadata is inserted in the first samples so that REW can determine the parameters that were used to generate the sweep.

 

[luegotelodigo]

I can't make it work using 5,20 beta 1 on Win7

 

[John Mulcahy]

You need to select Measurement sweep rather than log sweep.

 

[RobertM]

I think I'm missing something here, is it because I'm using v5.18? Under Generator, I understand I can make a .wav of PN to set the level. I can also make a log sweep .wav, but there is no option there to insert a timing reference. Also, the log sweep .wav created by Generator is 10s long and the measurement sweep under Measure only has a 5s duration. What I believe needs to be done is to be able to create a log sweep that has a timing reference in front of it (under Generator). Burn that to disk and insert in CD player of car. Go to Measure, start measuring and then play the CD with the log sweep .wav. The microphone picks up the timing reference of the log sweep and begins measuring and does so for the duration of the log sweep. Is this not the process?

EDIT: Okay, I just discovered that if you scroll down the different waveforms menu, there is a "meas sweep" there, did not realize there was more entries on that menu. Will give this a try now, I think I have finally figured it out.

 

[RobertM]

One last related question before I burn the CD. Under Generator, the default RMS Level dBFS is -20. Does this need to be changed to -12 to match the Level dBFS that is listed along with the frequency on the Log Sweep and other waveform selection or under the Measure, which also has -12 dBFS or does it not matter that they match?

 

[John Mulcahy]

It doesn't matter if they match, but better using a higher level in the WAV and using the replay volume to control how loud it is.