To Clear Calibration Process Set Up Concepts

[puneet_dh]

Dear HTShack-mites

I am about top start sound calibration of my first HT.Before I start thread of my own just need some inputs to get my basics right for calibration process.

1) For sound clalibration ,do you take readings from individual speakers(L,C,R etc) or just from Right speaker

2) My front speakers are full range but I would cut over them at 80 hz for movies and would run them full range for music.Do you calibrate front left and right full range or only as bass limited speaker or should I do both?

3) Mostly I have seen people working on low frequencies an applying filters etc but what about high range frequencies between 200 Hz and 20000 Hz? How do you make them flat. Do you EQ them as well or absorption is the answer?

4) I have a velodyne SPL 1200R which has inbuilt parametric Equalizer, Do I still need BFD?

5) I am running pre and pro and have adjusted the power amps individual gain level to sound at 75 DB with receivers sound level set to 0 DB. All my speakers are now sounding(Pink Noise from CD) 75 Db at 0 Db of receiver.Is that a right approach?

6) when I had set Levels using REWS, the SPL meters output gain is so low that I have to increase receivers volume to +7db for SPL meter to show 75 DB.Now my Test CD adjustments and REWS Level adjustments are 7 DB apart. Which one should use as reference for 75 DB volume?

7) I am using Radio shack SPL meter and when I generate measurement tone from REWS I get different sound pressure level as compared to what I get If I run test tone CD.Which is the right approach?

So far I have calibrated my Creative x-fI sound card, set the levels and calibrated SPL reading between shack meter and REWS.

Thanks,
Puneet

[brucek]

Before I start thread of my own just need some inputs to get my basics right

You've already started a thread. Hopefully you'll stick to this one, since multiple threads are hard to follow.

1) For sound calibration ,do you take readings from individual speakers(L,C,R etc) or just from Right speaker

REW is a mono signal, and as such your receiver must be in the stereo mode at all times when using REW. A Y-splitter may be used at the receivers input to left and right channels. This results in the ability to measure the sub, left, right and any combination of those three. If you wish to check the remaining HT speakers, you would remove the speaker cable of a left or right main and substitute a different speaker to test.

2) My front speakers are full range but I would cut over them at 80 hz for movies and would run them full range for music.

Why? Bass management is advised for music and HT. The range that causes the most peaks and dips in the response is below 80Hz and best assigned to a sub that can be equalized and moved to get the best response. Sending less than 80Hz to a main is not a great idea.

Do you calibrate front left and right full range or only as bass limited speaker or should I do both?

Bass limited, since that's how they will be used in the system.

3) Mostly I have seen people working on low frequencies an applying filters etc but what about high range frequencies between 200 Hz and 20000 Hz? How do you make them flat. Do you EQ them as well or absorption is the answer?

Above 100Hz is best served with room treatment and speaker position - not EQ.

4) I have a velodyne SPL 1200R which has inbuilt parametric Equalizer, Do I still need BFD?

Usually the built in EQ will be suffice, but you have to measure to find out.

5) I am running pre and pro and have adjusted the power amps individual gain level to sound at 75 DB with receivers sound level set to 0 DB. All my speakers are now sounding(Pink Noise from CD) 75 Db at 0 Db of receiver.Is that a right approach?

Matters not. You would like to start by ensuring that all your speakers are set to the same level with the receivers test tones. If its 75dB or 55dB or 100db, it has no effect on REW or equalizing the system.

6) when I had set Levels using REWS, the SPL meters output gain is so low that I have to increase receivers volume to +7db for SPL meter to show 75 DB.Now my Test CD adjustments and REWS Level adjustments are 7 DB apart. Which one should use as reference for 75 DB volume?

Forget your test CD. REW has all the tones required to set up the EQ of your system. If you want to set some reference level that calibrates your volume dial, then you can do that at any time. It has nothing to do with REW. REW is a measurement tool designed to obtain a smooth response from a sub and mains, through positioning and equalization.

7) I am using Radio shack SPL meter and when I generate measurement tone from REWS I get different sound pressure level as compared to what I get If I run test tone CD.Which is the right approach?

Put your Test tone CD aside and measure your system with REW. Again, REW isn't concerning itself with absolute levels. That's not its purpose. The REW setup puts the measurement levels at approximately 75dB. Once you have the sub equalized and positioned, and the mains positions and all the room treatment complete, if you want to set up some reference levels with a Test CD, then do it once you've finished with REW. Use your receivers test tones to balance the levels and trims and then start REW measurements.

So far I have calibrated my Creative x-fI sound card, set the levels and calibrated SPL reading between shack meter and REWS.

Let's see the soundcard calibration file. Use the post padding thread if you need a minimum of threads to post graphs etc.
Did you run a measurement of the loopback cable and get a flat response after the soundcard cal was complete?

brucek

[puneet_dh]

Dear Brucek,

Thanks for your response.I may have sounded dump but pardon me as I am new to all this.
I have attached measurement after calibration of the loopback cable and of sound card calibration file.Does this look ok?

[brucek]

have attached measurement after calibration of the loopback cable and of sound card calibration file.Does this look ok?

I'd like to see the loopback response alone with a vertical axis of 45dB-105dB (the standard we use here), because it appears to drop at the low end as if you didn't have the soundcard cal loaded. The soundcard cal looks good though.

brucek

[Wayne A. Pflughaupt]

1) For sound clalibration ,do you take readings from individual speakers(L,C,R etc) or just from Right speaker

It's not clear from reading your post exactly what "calibration" is to you. The receiver's built-in calibration test tones are mainly for setting relative speaker levels. Not sure what all your test disc is supposed to do, but many of them provide a means to do the same thing.

REW isn't quite like that. It's mainly for examining the frequency response of your speakers and/or sub in your room, so that maybe you can do something about improving it (if need be). (Of course, it can do lots more than that, but that's usually where people start.) That could also be called "calibration," but as you can see it's a different sort of calibration. If all you're trying to do is set the relative levels of your speakers, then your receiver's built-in calibration or your test disc will work fine.

To answer your question about the L/C/R speakers, if you want to look at the in-room frequency response of your speakers, obviously you would want to check them one at a time. The Radio Shack SPL meter will only do that reliably up to about 3 kHz or so; if you want to check response full-range, you'll need a calibrated mic.

3) Mostly I have seen people working on low frequencies an applying filters etc but what about high range frequencies between 200 Hz and 20000 Hz? How do you make them flat. Do you EQ them as well or absorption is the answer?

Certainly, do all you can with treatments if your situation allows (not many people want acoustical panels hanging on the walls or bass traps piled high in the corners of their living rooms, for example). Same with placement, but to me placement is more about getting the best imaging than the best frequency response (just how many places can you reasonably move your center channel, for instance?).

And certainly, utilize whatever equalization your receiver or pre-pro provides, if it's needed and if it's powerful enough to do the job. It's there, and it's free.

Beyond that, if you feel you need to resort to outboard equalization, don't think you're going to do it on the cheap. Obviously you'll need an equalizer for each channel you want to equalize. You have an advantage going in if you already have outboard amplification, but even if you only want to do the front speaker suite, you're looking at a few hundred minimum, even for the cheapest equalizers suitable for main-channels use.

4) I have a velodyne SPL 1200R which has inbuilt parametric Equalizer, Do I still need BFD?

The built-in will certainly be useful. There's no way to know if you'll need more than that until we see your response graphs.

6) when I had set Levels using REWS, the SPL meters output gain is so low that I have to increase receivers volume to +7db for SPL meter to show 75 DB.Now my Test CD adjustments and REWS Level adjustments are 7 DB apart. Which one should use as reference for 75 DB volume?

7) I am using Radio shack SPL meter and when I generate measurement tone from REWS I get different sound pressure level as compared to what I get If I run test tone CD.Which is the right approach?

Again, it all depends on what you're trying to do with the test discs. If all you're doing is adjusting levels between the speakers, then the disc is fine to use. It and REW are their own self-contained systems, so don't worry about it if their reference settings don't transfer.

Regards,
Wayne

[puneet_dh]

Dear Wayne,
Thanks for taking your time out.
To me calibration is flatting the frequency response and I thought setting relative speaker levels is the starting point but as I understand now they don't have any relation.
By using disk I mean not only playing Pink noise for speaker leveling but also playing sweeps tone I download from real traps website. Since the out put of CD test tone was louder then what is produced by REWS connected via AUX I mis understood that I'll be reading frequencies excited with higher or lower sound output.
I'll be putting lot more effort in coming weeks to working with REWS and your and Brucek support is valuable.
I am currently at Saudi Arabia and I do not have any helping hand except this forum.
Rgds

[puneet_dh]

Dear Brucek,
I have remeasured my sound car loop back response.I hope this is what you are looking for.
Regards,
Puneet

[brucek]

I hope this is what you are looking for.

That's fine. Carry on.

When you do a measurement and post a graph in the future, please 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.

bruce