Speaker and Sub Measurements (REW)

[Greg_SA]

Hi,

I have a few questions wrt REW and the speaker measurements I have made.

I got a Radio Shack SPL meter and use the correct calibration file. I haven't used sound card calibration - I am using SPDIF out to my HTPC. Is this a serious problem?

I am using the line-in on my on-board sound or a SB Live Value card (both work the same).

The first thing I noticed is that my sub level was about 8dB higher than my main speakers Ooops...

I then started playing around with the sub and main speakers...

Firstly just full range (no crossover, large) on the main speakers (sweep from 10hz to 500hz). I seem to get a big boost at around 50Hz - is this the room gain?

I get the same type of peak from the sub-only test that I did.

Can someone explain?

1st graph = Full range Mains (Fronts) only (Monitor Audio RS6)
2nd graph = Sub + Mains (80Hz cross-over)

Regards,
Greg

[brucek]

I haven't used sound card calibration - I am using SPDIF out to my HTPC. Is this a serious problem?

Yes, the results aren't very meaningful. You need to use analog out and in and create a proper soundcard calibration file.

I seem to get a big boost at around 50Hz - is this the room gain?

It is a modal peak caused by the size of the room. Subwoofer placement or listening position placement or EQ are required to lower it for the listening position.

1st graph = Full range Mains (Fronts) only (Monitor Audio RS6)
2nd graph = Sub + Mains (80Hz cross-over)

Please post all subwoofer plots using the standard graph axis of vertical=45dB-105dB and horizontal 15Hz-200Hz.
What would you like explained about your graphs?

brucek

[Greg_SA]

Hi,

Thanks for the feedback

brucek wrote:

Yes, the results aren't very meaningful. You need to use analog out and in and create a proper soundcard calibration file.

When you say "the results aren't very meaningful", do you mean that my graphs aren't really meaningful until I do calibration? So I must do soundcard calibration? (Some other posts I read mention that it is not really necessary).

I'll try the calibration anyway, and check the results (using the correct formatting).

I just wanted to confirm that the peak was related to the room and seems normal (Room is about 12 x 14ftm 8ft high ceiling).

The subwoofer I am using is a 12" DIY sub that I built for my car, so it is a sealed 1.25 cu foot enclosure which is rather small - I think I should build a Linkwitz Transform Circuit for it, to boost the lower 30Hz region, and maybe drop the peak at 45Hz a bit.

Regards,
Greg

[brucek]

When you say "the results aren't very meaningful", do you mean that my graphs aren't really meaningful until I do calibration? So I must do soundcard calibration? (Some other posts I read mention that it is not really necessary).

Suppose your soundcards response is down -10dB at 20Hz. The graph you produce without a soundcard calibration would show the signal down -10dB at 20Hz.

I presume the purpose of taking a measurement is to display the response of your speakers and room, not the poor response of your soundcard. How meaningful are the results when you don't zero out and remove the soundcards influence from the equation? I'll let you answer that.

brucek

[Greg_SA]

brucek wrote:

Suppose your soundcards response is down -10dB at 20Hz. The graph you produce without a soundcard calibration would show the signal down -10dB at 20Hz.

I presume the purpose of taking a measurement is to display the response of your speakers and room, not the poor response of your soundcard. How meaningful are the results when you don't zero out and remove the soundcards influence from the equation? I'll let you answer that.

brucek

Cool, I'll do the calibration - it just seemed like a lot of people don't think it is necessary... but I'd like the results to be accurate, so I'll do the calibration Thanks for the help.

[Wayne A. Pflughaupt]

Greg_SA wrote:

Cool, I'll do the calibration - it just seemed like a lot of people don't think it is necessary...

Just curious where you came across that? It's the standard recommendation around here...

Regards,
Wayne

[counsil]

Greg_SA wrote:

Cool, I'll do the calibration - it just seemed like a lot of people don't think it is necessary... but I'd like the results to be accurate, so I'll do the calibration Thanks for the help.

It only takes a moment to create a calibration file for your soundcard. If you are having trouble understanding how to do it, just ask. Here are some rather straightforward instructions on how to do it...

http://www.hometheatershack.com/room...tml#calmeasure

[Greg_SA]

Hi,

The main reason I wanted to avoid the calibration, was that I already have SPDIF connected from my HTPC (in another room) to my amp. But I suppose an extra cable from the PC line-out to the amp ins't going to be a problem.

I'll definitely do the calibration and retest

Thanks,
Cheers
Greg