A little help needed with REW and house curves please.

[wilsonj]

Hello,

I have spent the last couple days trying to get my head around how to use the REW, but I am still unsure about a few aspects.

My equipment
M-audio 24/96 USB soundcard
EC8000 mic
Behringer 802 mic power
DSP1124P
gereric digital SPL meter

Funny enough I have had this equipment for 2+years and never really got around to using it properly!

OK, so I have managed to calibrate my soundcard, checked leverls and entered in the cal file for the mic.

A question on the next step, checking levels. The REW notes say to increase the vol. until the meter reads 7db. Do they mean my digital SPL meter? C pr A??

Next question, weighting for SPL calibration. Should I have my SPL meter set to C or A. I assume A, as the REW notes say untick the C box if using a mic.....

SPL calibration procedure. I untick the C weighting box, so I assume I don't use C weighting on my digital SPL meter either?

I managed to take some measurements. Everything seemed to go ok here.

Question about the graph. Should I smooth out the freq curve or leave the tab set to "none" ?

Should I look to try and smooth out bumps greater than 3db?

Final questions relate to the house curve. I set up a house curve to give me 10db more at 20hz than at 80hz (0db). When I use this curve and take a reading my frequency plot is always lower than the target curve, so consequently there are no peaks to correct. I manually dragged the target down to where I liked it and worked from there. But this doesn't seem ideal, or correct to me.

I'm not sure I get the target level concept entirely...

Once finished I used my digital SPL meter to calibrate my processor sub output. But find it way under what it was. No problems I wind the level up to 75db like all other channels. Then when watching movies the sub is waaaay overpowering. It feels about 10db too loud.

I have tried to read as many posts here as I could before asking silly questions. Sorry if they have been covered before.

Thanks

Jamie

[brucek]

A question on the next step, checking levels. The REW notes say to increase the vol. until the meter reads 75db. Do they mean my digital SPL meter?

Increase the volume of your receiver (the soundcard feeds the CD or AUX input of the receiver) until your digital SPL meter reads 75dB at the listening position. Then you match the REW meter to that level to get a rough calibration between the two (do this by clicking the MIC/METER tab in the Settings routine and select Calibrate SPL).

Note, if you're using a ECM8000 and preamp, after you set the 75dB with the receiver and digital SPL meter, adjust the ECM8000 output and the input level control in REW to get a good input level, then don't touch the ECM8000 preamp level after that. Then Calibrate SPL in the REW program.

Should I have my SPL meter set to C or A. I assume A, as the REW notes say untick the C box if using a mic.....

Meter to 'C' weight. The REW has 'C'-weight unticked because the meter calibration file is used in its place. The 'C'-weight of most meters isn't a correct curve down at low frequencies, so we substitute our own file.

Remember in your case, the only reason you're using the SPL meter is to get an initial calibration in the room of 75dB and to match the REW SPL meter to it. After that you use the ECM8000.

Should I smooth out the freq curve or leave the tab set to "none" ?

Set smoothing to none. It's only used at higher frequencies where combing causes the graphs to be somewhat unreadable.

When I use this curve and take a reading my frequency plot is always lower than the target curve, so consequently there are no peaks to correct. I manually dragged the target down to where I liked it and worked from there. But this doesn't seem ideal, or correct to me.

Attempting a house curve when your natural response is much lower than the target requires manual intervention. Sometimes it just ain't possible to get the curve you want, given the sub and the room.
Take your reading and then place your target at the spot you like and then let REW suggest filters. Then manually see what you can do. Keep in mind that gain is not advised.

But find it way under what it was. No problems I wind the level up to 75db like all other channels.

Yeah, filtering lowers the level somewhat and to compensate you have to raise the sub amp a bit. That should be correct if it is balanced with the mains. Shows us a sub only and a sub+mains graph (using vertical scale of 45dB to 105dB and a horizontal scale of 15Hz to 200Hz).

brucek

[wilsonj]

Hi Bruce,

Thanks for your replies. Looks like I have things working right now. I spent some time today with the mains also, playing with xovers in the lexicon. Now I think they integrate nicely with the sub.

Movies now sound more balanced with better bass extension. I can't believe I hadn't done this earlier!!

I'm off to setup Dad's system now.

Thanks again for your help, it was greatly appreciated.

Cheers
Jamie