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5.1 calibration

All about the tools and techniques involved in capturing sound, in the studio or on location.

5.1 calibration

Postby Mac the Naif » Mon May 05, 2008 12:57 am

I'd like to get some information about how to calibrate a 5.1 system. This is, from an installed set or 6 speakers, know where to place the calibration mics to make the measurements with a RTA and a SPL meter.

I once saw a guy do this placing five calibration mikes creating a star and passing through an audio matrix to read the measurements in the RTA separately and mixing them to see how they affect each other. It was a pity I could only be there for a couple of minutes and ask him some questions about this.

Some friends have created and association to make "shows" for blind children and I talked to them about doing it in 5.1 in an old abandoned theater the townhall lends them, so we could rent some gear to make the PA system work finer. It's obviously something not professional, and instead of a professional set of calibration mikes I probably can ask some friends for his ECM8000s (though the SPL meter will have to be rented), but at least it will be better than leaving that PA system alone and do it using just ears.

Where should the SPL meter be located? In the last row of seats? in the middle of the venue? Should it be always facing the middle of the first row ("the screen" if it was a theater) or should the SPL meter be facing and pointing each way in every measurement at a given distance (I mean that surround measurements should be perpendicular to the L, R, C and .1 channels and that in case the surround was formed by more than a speaker they should be measured one by one? Well I guess the SPL levels won't be so difficult to find them out on wiki or so.

To equalize each channel I don't know what will be cheaper if getting a Dolby processor, or inserting cheap 15 band EQs on each channel, but going into the theorical part, where should the calibration mikes should be placed, for example making a star with the points set in the middle of the lines traced from the walls to the center of the venue?

Perhaps this project will finally not get into 5.1 and can't get that gear but at least I'm quite interested in this and though I might not be able to help them more, know the basics.

Thanks all your comments, suggestions and answers in advance.
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"Musical people always want one to be perfectly dumb at the very moment when one is longing to be perfectly deaf" (Oscar Wilde)

Re: 5.1 calibration

Postby The Red Bladder » Mon May 05, 2008 7:58 am

1. Put the SPL meter where the audience (or most of them or the middle of the bulk of them) is.

2. Set to C-Weighted.

3. Put pink noise filtered at the X-over frequency of your system, through each individual speaker. In other words, the five front and side speakers just get pink noise above your X-over F and the LF speaker gets PN below the X-over F.

4. If you have multiple side-rear speakers, bring them up as a single unit.

5. Bring up the volume of each speaker until it reaches a set value and each speaker is the same.

6. (For P.A.s only, not control rooms!) Now send PN (unfiltered) through the whole system and e.q. using a REAL TIME spectral analyser and e.q. in the usual way, looking for problem F that take longer to fall away and just e.q. until your ears and brain tell you that it sounds nicer.
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