First Non-EQ'ed room response...

[Vader]

OK, after playing with REW for about a week, I finally got a resonse curve for my HT room (I know, minor achievement, but for the noobies like me a major victory). Is my room in need of some serious help? I plan on getting a BFD when it is in the budget, but for now I simply have to make do (Moving the subs is not an option, due to room constraints)....

Raw Response.jpg

[brucek]

Looks like a fairly easy signal to equalize. No huge dips or peaks - but you do need a BFD.

brucek

[Vader]

Bruce, the subs are both SVS 20-39 PC+ tuned to 20Hz. Can I assume that the response below about 16Hz is "less than accurate" due to room response (I mean, shouldn't it continue to drop off here instead of going back up)?

[Sonnie]

Congrats Vader! Heck man... when I first started working with the BFD it took me a week to hook it up and another week to take my measurements. lol Exaggerating obviously, but it definitely took me a while to figure it all out.

If you are using the proper correction values then your response down to 10hz could very well be correct. I'm thinking really good room gain. How big is your room and where do you have the sub located?

As your sig says... SVS doesn't leave the bass behind...

[Vader]

Sonnie, The room is approx 3200 ft^3, and the subs are "kinda-sorta-pseudo corner loaded" (best I can do for the time being). In other words, the subs are about 6' from an actual corner on one side, and the fireplace on the other (which sticks out about 2 feet, at an angle of 135 degrees):

PartialLayout.JPG

Where F = the subs, K = Window shelf (closed), D = AV Rack, and E = Another shelf (LaserDiscs).

I'm using the (new) calibration file for the old Rat Shack meter, the calibration for my soundcard (SoundBlaster Live Value), and C-weighting (doesn't seem to matter to the graph whether I turn it on or off?!?)

[brucek]

doesn't seem to matter to the graph whether I turn it on or off?!?)

The C-Weight check switch in REW only affects frequency areas not covered by a meter .cal file, so in this case above ~100Hz. Make the scale of your graph go from 10Hz to 20,000Hz and observe the effect of the C-Weight switch. Also remove your .cal file and observe the effect of the C-Weight switch. The .cal file replaces those areas of the C-Weight compensation to create a more accurate curve to match your specific meter...

If the Radio Shack meters actually had an accurate C-Weight response, then a .cal file to over-ride the mathematical C-Weight compensation provided by REW wouldn't be necessary.

brucek

[Vader]

The more I play with this, the more I think I messed up somewhere. A few more questions:

1) It seems pretty coincidental that my room curve and the target response coincide at 10Hz (81dB). Since my subs are in 20Hz tune, they should begin falling off rather sharply around 17-18Hz, but I reading from this curve that (allowing for some perturbations that require a BFD) it remains "flat" down to 10 Hz. Can room response do that?

2) When the measurement is made and the data saved off, is the data dependent on the calibration files loaded at the time? In other words, is the data saved in completely raw form , independent of calibration files, which can then be applied later, or do the cal files somehow influence how the raw data is recorded?

3) My soundcard calibration (the dotted line above at 75dB, right?) is almost perfectly flat, only falling off above 20k. Is this normal?

[brucek]

Can room response do that?

Yes

In other words, is the data saved in completely raw form , independent of calibration files, which can then be applied later

No, it's saved with the inverse C-Weight or calibration file applied to the saved data. No effect on an mdat file loaded later.

My soundcard calibration (the dotted line above at 75dB, right?) is almost perfectly flat, only falling off above 20k. Is this normal?

Good soundcard perhaps. Change the vertical resolution to be a few dB from max to min and see how it looks. i.e 72dB to 75dB. This will exaggerate the small changes (if there are any - and there should be some change by 10Hz)
Or just look at the soundcard.cal file with notepad. It's easy to read.
Here's mine up to 30Hz. See it drop off a bit starting at 20Hz.
10 -0.17
11 -0.11
12 -0.10
13 -0.10
14 -0.08
15 -0.07
16 -0.06
17 -0.05
18 -0.05
19 -0.04
20 -0.04
21 -0.02
22 -0.01
23 0.00
24 0.01
25 0.01
26 0.01
27 0.01
28 0.01
29 0.01
30 0.01


brucek

[Vader]

Bruce, my soundcard is a Soundblaster Live Value (only 16-bit duplex, not 24). Here is my cal file up to 30Hz. Does this look normal to you?

0 -19.795
1 -8.423
2 -3.121
3 -1.598
4 -1.106
5 -0.670
6 -0.566
7 -0.407
8 -0.353
9 -0.298
10 -0.258
11 -0.233
12 -0.208
13 -0.190
14 -0.178
15 -0.165
16 -0.157
17 -0.151
18 -0.143
19 -0.137
20 -0.134
21 -0.129
22 -0.125
23 -0.122
24 -0.119
25 -0.117
26 -0.113
27 -0.113
28 -0.112
29 -0.109
30 -0.108

For future measurements, do all of the parameters used in the generation of this cal file (measurement level, input volume) need to be exactly the same?

[brucek]

Does this look normal to you?

Looks OK to me....

For future measurements, do all of the parameters used in the generation of this cal file (measurement level, input volume) need to be exactly the same?

Not at all. This file stands alone as compensation for the soundcard inadequacies. Just keep the file and leave it selected so it loads each time you start REW...

brucek

[Vader]

Thanx, Bruce. Assuming that the above graph is correct, I really have no need to go down to the 16Hz tune, and lose the headroom after all. Now, all I need is a BFD (I *might* have a few questions once I get it ). Someday, I'm hoping to understand enough about this stuff to just be dangerous....