n00bz first measurements!

**assemblyworker** · **10-22-09, 11:48 AM**

Howdy folks, after some initial dramas getting the software to work I've just taken my first measurements. The top end looks very spiky, are these sort of measurements normal or am I getting some interference in my chain?

Many thanks...

Matt

**tonyvdb** · **10-22-09, 11:57 AM**

Hi Matt, You need to post 5 times befor you can post any pictures or graphs. Use our post padding thread to achieve this if you wish.

What Mic are you using with REW?

**brucek** · **10-22-09, 12:27 PM**

Quote:

The top end looks very spiky

I assume by top end you refer to > 200Hz?

This is comb filtering caused by relections and is normal. To view the underlying trend of the signal response, select smoothing in the left pane.

BTW, if you are using a Radio Shack meter, the highest frequency you should be testing to is 3KHz.

brucek

**assemblyworker** · **10-22-09, 04:23 PM**

I'm using a Behringer ECM8000, via a very good pre-amp to a M-Audio Fast Track pro.....

Here's the pic....

**brucek** · **10-22-09, 05:39 PM**

Quote:

I'm using a Behringer ECM8000

I note you haven't loaded the microphone calibration file for the ECM8000. Go to our download page and get the cal file and load it into REW. You can apply it with the IR Windows popup or take another measure to include it in your measurements.

Note the little floppy icon in the lower left hand corner of your graph. This is used to save an 800 bit wide jpg of your plot suitable for posting so that you don't have to include the entire REW page.

brucek

**assemblyworker** · **10-22-09, 06:52 PM**

Ah cool, thanks for the help Sir!

**assemblyworker** · **10-23-09, 10:30 AM**

Ok I've applied the ECM calibration file.... This is the latest read out.

As you can see there are sharp dips at 700Hz, 900Hz and the three sharp dips between 2-7kHz...

Most likely comb filtering? I'm curious about the amount of high roll off, these are studio monitors, is such a roll off common?

**brucek** · **10-23-09, 11:06 AM**

Quote:

Most likely comb filtering?

Yes, use smoothing on full range plots as previously mentioned.

Quote:

I'm curious about the amount of high roll off, these are studio monitors, is such a roll off common?

Measuring high frequency response of your speakers requires closer mic location in a horizontal 0 degree position (pointed at the drivers). The standard vertical position with a 20 degree cant is a good all round technique to use at the listening position, but it will usually result in a roll off of the upper frequencies.

Note, for subwoofer plots, always use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - 200Hz) using the Graph Limits button in the top right corner of REW. Use a measurement start frequency of 0Hz and an end frequency of 200Hz. Use the appropriate target line that matches your crossover.

For full range plots, use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - upper limits) you desire, i.e. 15KHz -20KHz. Use a full range target line.

For full range only, enable smoothing (1/3 octave) to eliminate the comb filtering.

brucek

**assemblyworker** · **10-23-09, 12:03 PM**

Cheers Bruce, that's me done for the day but i'll likely get onto more testing over the weekend.

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