I sure hope I am doing something wrong

**grn1969c10** · **10-24-08, 08:00 PM**

I attempted to plot the response of three different subs. REW output connected to the CD input on receiver. Sub - Yes. Mains - Large. (Mains disconnected.) My room is quite large, but the lack of bass below 35hz seems rather exaggerated. I'm hoping I have made an error in the setup somehow.

I profiled the sound (rather old onboard audio) saved the cal and then loaded the RS meter cal. The waterfall for the sound card was curved below 40hz. Maybe its a problem?

Also, the waterfalls don't seem to scale properly on the X-axis. If I zoom in and out, the graphed data seems to expand and contract totally different than the axis. i.e. A 3D plot originally went 10-120hz, I zoom in and back out, now the 3D plot shows 10-200hz, etc. each time I do it the data changes scale.

edit: The waterfall shown is from the 3rd sub, CSX-15 shown in teal.

Sorry to include so many goofups in one post!

**salvasol** · **10-24-08, 08:23 PM**

Quote:

grn1969c10 wrote:

I profiled the sound (rather old onboard audio) saved the cal and then loaded the RS meter cal. The waterfall for the sound card was curved below 40hz. Maybe its a problem?

They look valid to me ...

If you can, post the brand and model of your subs ... os the expert can tell you if they're correct or not

**grn1969c10** · **10-24-08, 08:40 PM**

1st Green - JBL PSW-1200
2nd Purple- Velodyne CT-100
3rd Teal - Cadence CSX-15

I was expecting useable bass to 25Hz with the 15". I need to plot my mains to compare. It seems like they went down to 40Hz with authority. (Of course I think there is a peak at 40 caused by the room)

**grn1969c10** · **10-24-08, 09:42 PM**

Here (in purple) is the CSX-15 and PSW-1200 (set for similar output with pink noise) in opposite corners of the front wall. Following that, is my mains with the subs turned off (in blue).

**grn1969c10** · **10-24-08, 10:28 PM**

I finally put it all together to see the full range plot (10-500 Hz). This is two subs and both mains. Call me crazy but I'm a bit miffed that things are going to moo.
I am not sure what is meant by "reference levels" but I didn't think 85dB was asking too much.

**brucek** · **10-25-08, 08:09 AM**

When you post waterfall, use the same standard that all response plots should be posted with.

Use vertical = 45dB-105db and horizontal = 15Hz-200Hz. Use a target of 75dBSPL for measuring.

Hopefully you have calibrated your soundcard and have the correct calibration file for the SPL meter you are using. If not, the results would be meaningless.

To verify the soundcard calibration file is correct, connect a loopback on the right channel and run a response measure (be sure the meter cal file is cleared for this test). The result should be a perfectly flat line. This now ensures that the problem isn't with the measuring equipment.

brucek

**grn1969c10** · **10-25-08, 09:13 AM**

Just for drill, I just went to mic/meter and cleared the cal file, I then went to soundcard and cleared the cal file. The output was looped back into the input and I clicked on measure, next, next. The input appeared about 6 db too hot. (Output at -9 db and input at -3 db). I reduced the line-in level until the input was about -8 db (bringing the input and output within 1 db of each other) and the peak line about -4.5 db. Clicked next, next and let the calibration run.

The settings windows was minimized and the soundcard response graph captured. I then clicked on waterfall, set the graph boundaries as per standard, generated the waterfall, and captured that. Finally, I clicked make cal and saved it as the current sound card cal file.

Hopefully, the soundcard cal file is good, I can reinstate the RS meter correction file, and proceed?

**brucek** · **10-25-08, 09:33 AM**

Quote:

Hopefully, the soundcard cal file is good, I can reinstate the RS meter correction file, and proceed?

Yeah, it all looks good.

The final check, once the soundcard cal file is loaded (and the meter cal cleared) is to measure the loopback cable just as you would a normal measure. The result should of course be a flat line, since the response of a cable is flat and any response weakness of the soundcard is compensated for with the soundcardcal file you just made.

If it measures flat, then yes, load the meter cal file (and remove the loopback) and carry on with your measurements of the subs...

brucek

**grn1969c10** · **10-25-08, 09:56 AM**

These plots don't look very good. I did a measurement - still using loopback cable; C-weighted checked but NO meter cal loaded; Sound card cal that we just created. Not very flat is it?

**grn1969c10** · **10-25-08, 10:03 AM**

I'm guessing that the waterfall is a mirror image of the one posted earlier which means somehow the sound card cal file is not being applied to the measurement? Thankfully, I'm doing something wrong!

**grn1969c10** · **10-25-08, 12:09 PM**

Well, since something is wrong but I don't know what; I closed REW, deleted all user created files and started over. I repeated the same steps as before with three changes. I lowered the sweep level from -9 to -12db and evened up the input level to exactly match the output, upped buffers to 64k and UNchecked the c-weighted box on the mic screen (no cal file loaded). Resulting in the first calibration measurement and waterfall. I then ran a measurement using the newly created cal which produced the second measurement and waterfall.

**grn1969c10** · **10-25-08, 12:36 PM**

With a new cal file, I can proceed by loading the RS-cal file, making meter and receiver connections and clicking Calibrate SPL which I adjust to 75db.

Then comes the first hitch. When I "check levels" on the soundcard settings screen, the input appears to be too low, around -26db. At this point, I need to raise the level up to -18db using the line in setting of the sound card properties, correct? This produces an output of -12db, 75db on the meter, and an input level of -18db which I save.

**grn1969c10** · **10-25-08, 01:12 PM**

New plots are looking just like the old ones. Just for giggles, I used the generator to loop a 15 second -10db sweep from 20 - 55hz and listened. Very quiet from 20 to 32hz and then really coming on strong from 33 to 55hz. My ears seem to agree with the plots.

The CSX-15 has a bass boost, but it is useless to me because it hits hard around 50hz and further exaggerates the low end rolloff, so I'm leaving it turned all the way down. One last thing I might try unless someone comes up with a suggestion, is running the output directly to the sub and eliminating the receiver from the signal chain.

**brucek** · **10-25-08, 02:18 PM**

Quote:

These plots don't look very good

That's because you had C-Weight selected. That's the same as a meter file. Clear it when doing the loopback test.
The C-Weigh box is used if you have a perfect C-Weight meter and don't need a meter calibration file. When you use a meter cal file it over-rides the C-Weight box.

Quote:

At this point, I need to raise the level up to -18db using the line in setting of the sound card properties, correct?

Yes.

Quote:

Just for giggles, I used the generator to loop

Well, it is easier to simply run the signal generator and select Frequency tracks cursor option and press play. Then put your mouse on the display and click and drag the cursor around to play any frequency you want. Then watch the REW SPL meter (press the red button to enable).

I guess you've tried your subs co-located in a corner?

brucek

**grn1969c10** · **10-25-08, 11:27 PM**

Well, after an entire day of wrestling both subs all over the place this was the best I could do. I must say I think I'm pleased with the Cadence sub. Well over 3000 cubic feet with no room treatments and no equalization can get pretty ugly, but there is no doubt the CSX-15 is a lot more sub than either the Veldodyne CT-100 or the JBL PSW1200. I'm running out of options for room placement so I may have to investigate other solutions for taming that mountain from 35 to 80 or the null at 100.

The extended family came over for movie night to see the Incredible Hulk. The sound track is a 30 second recording of a terrible car crash that is perpetually looped back over and over. Pretty cool! That was probably the loudest movie I have ever played (on my old 27" TV!)

The first plot and waterfall were done before everyone showed up. Perhaps later someone can expound on the waterfall as the significance of it is still somewhat lost on me. The last plot with 1/6 octave smoothing was done after they left and I wanted to give the sub frequencies a little context. I don't know what changed to cause the null to move around but I'm too tired to care now.

Over and Out

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