Getting started with REW speaker and amplifier comparison tests.

[agentpatience]

Hi,

I am relatively new to REW. I am trying to start some measurements comparing speakers and amplifiers using AKAI EIE Pro audio interface.

I have done the initial loopback calibration test but getting some steeper rolloffs on the high and low end that doesn't seem right to me for a loopback frequency response test. Please see the image attached.

I did the test with a different 6ft.RCA loopback cable and about the same length but a little newer. The strange thing is it has a little more loss which I had to compensate for to attain the -10dbFS signal level but the response didn't change much:

 

[John Mulcahy]

The loopback result graph uses a very small Y axis range, the roll-off is smaller than it might appear.

 

[sm52]

On your graphs, the -1 dB drop is at 6.5 hertz and 19 kHz. It is ok.

 

[agentpatience]

Hi Guys, Thanks for the replies but after researching expected passband flatness per MFG specifications it seems I should be achieving around +/- 0.5dB flatness? Am I looking at the data wrong or could something be wrong with my setup? There is a compromise between my master volume output and my pre-amp input level controls. I set my master to max and adjusted the pre-amp level to REW expected output of -10dBFS to help keep the pre-amplifier circuit noise level down but maybe I am short-sighted?

From the manual; corresponding IN/OUT I am measuring with:

 

[agentpatience]

John, I think I see what you mean but your application calculates it to be 1.1dB+/- Is there any errors? or am I being a Ninny!

 

[John Mulcahy]

The output spec may be for an unloaded output. A much shorter loopback might reduce the high end roll-off fractionally, some devices also have a choice of reconstruction filter which would also affect the high end roll-off shape. It looks fine though. Make sure you use the device names starting EXCL so that there is no OS resampling and you get full data resolution.