Dell D620 Soundcard vs MobilePre Calib-both bad??

[mtbdudex]

HTS REW gurus.
I'm finally trying to use REW on my IB sub, when the young kids go to bed it's my only time to do this "geeky stuff" as my wife says.
Set up/cabling:
I'm using the Windows XP laptop off battery only, I have a Behringer ECM 8000 mic with a MobilePre USB - Bus-Powered Preamp and Audio Interface.
(The MobilePre was powered off my Panamax USB port for the internal soundcard testing not the laptop USB port)
Pict of equipment set-up (btw carpeting being installed Monday 1/26!!):



1st, I tried my Dell latitude LaptopD620 internal Soundcard (SigmaTel Audio), settings.


and came up with this, what's up with the low freq "missing" and all that noise in the signal?
My cables all tight and I did this 3-4 times and same result.


Here is the measure check for the internal Soundcard :


Then, since I have a MobilePre I tried that, settings, I had to adjust the gain sw on the MobilePre but got this :


Ok, more low freq but whats that noise spike up/down between 200 and 1k?


Here is the measure check for the MobilePre:


Should I just go with the MobilePre since for sub below 200hz is all that matters??
Once I get past this 1st hurdle hopefully the rest will be smooth sailing...........

[brucek]

1st, I tried my Dell latitude LaptopD620 internal Soundcard (SigmaTel Audio), settings.
and came up with this, what's up with the low freq "missing" and all that noise in the signal?
My cables all tight and I did this 3-4 times and same result.

Typical of an inexpensive internal soundcard. The noise is not an issue - look at the scale of the vertical axis. The low frequency drop is about what I would expect - poor, but still usable as you can see by the flat line measure when the soundcard cal is loaded.

Ok, more low freq but whats that noise spike up/down between 200 and 1k?

Just an oscillation. Simply try again until you get a clean response. The Mobile Pre is a better card.

Should I just go with the MobilePre since for sub below 200hz is all that matters??

Matters not if you're just measuring your sub. The Mobile Pre is a better card and I would probably go with that. Just clean up the soundcard cal as I mentioned above. Adjust the sweep level makes all the difference. Play with a few settings.

brucek

[mtbdudex]

Thx Bruce;

I brought the Mobile Pre to work and will play with the settings during lunch until I get a good cal file.

For me, besides subwoofer/bass tuning, I will use REW to confirm my acoustic improvements as I step up the acoustic "ladder":

-no absorption (can you say echo echo echo and long delay time...)
-to a broadband bass trap riser
-to carpeting (Install Mon 1/26)
-to creating and installing side wall panels per reflection points (2" OC 703, many threads on DIY those)
Then, possibly
-additional bass traps if needed via measurements
-possible ceiling absorption
-lastly possible rear wall DIY diffusers


For me, this will be a good learning experience, it's one thing to read about delay time, imaging, soundstage, etc in books/threads/etc.
Another to quantify that during the process with fact based data (REW) and subjective evaluations.

[mtbdudex]

Lunch time results:
I tweaked the setting and thought I was doing good and got this "warning" message:




I then put the controls as high as possible w/o hitting -1db




Cal file image:




But the confirm/measure is this, flat but -13db below 75db, can I proceed with "real" room measurements with this cal file?
Am I making this too hard?
I feel sorts stupid, or doing something obviously wrong.
I've read the help files countless times, , did I overlook something obvious?

[brucek]

But the confirm/measure is this, flat but -13db below 75db

This is because after you set the levels you didn't run the Calibrate routine to tell the REW SPL meter where to place your plot. You will normally select 75dB. The REW SPL meter has no reference at this point, so you have to tell it where to place the loopback measure.

Either way, it doesn't matter where the plot is in absolute terms. The important point is that you haven't got a clean soundcard cal measurement yet.

Where is the loopback cable connected, and what type of connector are you using?

brucek

[mtbdudex]

I got it!
Thx for your help.

Mobile Pre showing loopback:


Settings progressing thru the steps.
I had to tweak the sweep level, output volume, and the Mobile Pre gain knob a few times to get this.


Flat w/o noise!
Saved the calib file.


Now, going to sleep after taking some measurements, later I'll re-take (after carpeting down) to apply filters.
Here is the IB sub nearfield (2" from cone) & 32" away (I guessed at 1m but was a little close) to see if I've got everything done correct.
(I downloaded the 8000 mic cal file from your site earlier and used that mic cal file)
Set-up, the FBD is in bypass mode for now:


My first REW plot:
Top (brown) is near field, bottom (blue) is 32" away.

[brucek]

Top (brown) is near field, bottom (blue) is 32" away.

Yeah, as you said, near-field of ~12" is a bit more reasonable. The 2" is simply too close.

BTW, when graphing subwoofers, 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.

Also note the small floppy icon in the bottom left of your REW graph. That saves the plot only in a 800 wide jpg file perfect for posting.....

brucek

[mtbdudex]

Bruce;
I know you get and answer lots of Q's, so just saying a heart full "Thanks" for getting me going using REW.

[brucek]

You're welcome.....