This graph is going the wrong way

[Sean]

I dont understand why as I set my sweeps to start at a lower frequency the db's start high and lower. Should it start lower then go high. I finaly calibrated the sound card and my spl meter so Im not sure what the problem is.

Sean

[thewire]

That is the loudest I can get REW to measure.

Try setting the SPL meter with an external source (such as pink noise from your player, receiver, pre/pro, nifty amplifier plug in modules) first then adjust the output level from your soundcard to match. It should not be that high. There are ways to adjust the sweep level but I would try first adjusting the volume level starting from a very low setting, then raising it until it reaches a sweep like 20dB to match as close as possible. Adjust the sweep higher as necessary to match the system and the levels are stable. Be sure you using the subwoofer view, extra features on the soundcard such as eq or monitor all audio is disabled.

[JohnM]

Sean wrote:

I dont understand why as I set my sweeps to start at a lower frequency the db's start high and lower. Should it start lower then go high. I finaly calibrated the sound card and my spl meter so Im not sure what the problem is.

The loopback measurement curves up because C-weighting compensation is selected, which is not valid with a loopback connection. The other measurements don't look correct, the SPL meter connections may not be right or something else is wrong with the setup but generally room measurements don't come out like that. If you post a screenshot of the Scope page after a measurement that may give some clues.

[brucek]

I finaly calibrated the sound card and my spl meter so Im not sure what the problem is.

Let's start off by taking a simple measure of a loopback cable on the right channel from 0-20KHz with your soundcard.cal file loaded.

I would like to see the flat line response chart of that measure.

brucek

[Sean]

My scope page was blank so I will do more measurments like Brucek requested. Should I keep the loop back cables in place when measuring. I took them off for these set of measurments.

Thanks You for your help.

Sean

[brucek]

Have no other cables connected other than the loopback cable. It will be on the right channel. Only use the right channel. Measure the cable (with your soundcard cal file loaded). The result should be a perfect flat line.

Once the measure is done, you remove the loopback and connect the SPl meter and output cable to the right channel.

Post the flat line graph......

brucek

[Sean]

Here is the graph with the right side of the loop back cables connected only. I unchecked the c weighting and cleared the RS cal File.

[brucek]

Perfect.

Now remove the loopback cable and in its place, plug the SPL meter into the right line-in and then connect a cable from the right line-out to your receivers AUX or CD input. Do not use the left channel at all and do not click the checkbox for 'Use Left Channel as Calibration Reference'.

Load the RS meter calibration file.

Run the Check Levels routine, and then the Calibrate SPL routine.

Run the Measure routine....... post graphs with a vertical scale of 45dB-105dB and horizontal scale of 15Hz-200Hz.

brucek

[Sean]

Well I did it again at it seems to look ok. Tell me what you think. I seems like I have huge dip at 43hz and I verified it with Rives test audio cd and the dip is there also.

Sean

[salvasol]

... post graphs with a vertical scale of 45dB-105dB and horizontal scale of 15Hz-200Hz.

You better do it this way or the boss will scream at you

[Sean]

O no Sorry I forgot to check can I pull out my FOP card and get out of this one. The boss told me once but I got so dizzy when I saw that huge dip I lost my train of thought.

[brucek]

In addition to the axis of the graphs that needs to be corrected, I'm wondering why you're measuring at such a high level rather than 75dB?

Also, measure to 200Hz when testing a sub.

brucek