K-System Speaker Level Calibration

Robert Katz Leave a Comment

Name: Stephane
Subject: Monitor calibration
Message: Hello Bob, I want to setup K14 system in my studio. I use to mix pop music and I am working in stereo with Genelec 8050A as frontfield and Genelec 1037C as midfield, in a “not so bad” LEDE control room. (90 percent of the time with 8050A). I see in the EBU documentation about R128 implementation that they recommend a listening level of 82dBA SPL per loudspeaker (using -18dBFS RMS). I understand that this listening level is for working at -23LUFS and not with K14. My question in about the weithing of my SPL meter. When I calibrate for K14 (0 dB on the meter yields 83dBC SPL per channel, slow speed), I need to boost the Genelec 1037C 2 or 3 dB and read 86dBC SPL to have an homogeneous sound pressure sensation when switching from one monitor to another. Metering with A weigthing (despite the SPL reading is diferent) give a more homogeneous response to my ear between the to monitor sets. As EBU recommend C weghting for 5.1 and A weighting for stereo I would like you to confirm that the right way to setup K14 is metering my monitors with C weighting. Thank you for all your fantastical educational work!!!

                   Dear Steph:

You are clearly a knowledgeable audio engineer! This subject is more complex than “just measure it and use it.” There are nuances:

Midfields and nearfields actually require different calibration levels because of perception. The nearfield will sound louder at the identical SPL. Why you have to boost the little Genelec might have something to do with its limited frequency response but normally the situation would be reversed, they should sound too loud.Furthermore, full range pink noise invites issues of speaker bandwidth. The speaker with the wider bandwidth will measure a higher SPL. That’s one reason why the EBU was recommending A weighting to exclude low frequencies where different models of loudspeakers vary. But A weighting is just a convenience for people who only have a wide band pink noise signal. The reason you are more successful with A weighting is the obvious loss in low frequency response in the 1037 compared to the 8050. And the A weighted measurement ignores most of the bass.

The SMPTE recommends a special “wide range” pink noise signal which can only be found in a Dolby system generator….   If you use the Dolby generator and your speakers are well standardized within less than 2 dB from 100-10 kHz then you’ll have success but only with that generator. So the assumption in all cases is the loudpeaker is flat. Standards have a long way to go.

In all cases it’s a compromise to some degree because differences (especially in low frequency) in frequency response will skew the measurement. At high frequencies the position (angle) of the microphone is critical, so another reason to reject high frequencies. Thanks to Tom Holman for pointing that issue out long ago, in his book, “5.1 Surround Sound”.

But there are more exacting ways to measure. I think you will be happier with the narrow band pink noise from my site at digido.com. At that point weighting won’t make a difference. Try working with 83 dB for the midfield per speaker and probably turn it down approximately 2 dB for the near field depending on how close the loudspeakers are to you. let me know if it helps, anyway to equalize the two loudspeakers. Once you have a difference in distance and in frequency response, it’s both an art and a science!

The narrow 500-2 kHZ band signal will help you. But then again, two loudspeakers, both of which are nominally flat, but one has a slightly depressed 500 Hz range and the other a slightly depressed 1 kHz range, will measure differently with the narrow band signal. However, assuming both pairs of loudspeakers are reasonably flat in the 250-2 kHz range you’ll be most successful with the narrow band signal. But honestly, I wouldn’t expect the 1037’s to be very flat as they are older technology… I wouldn’t mix to those, ever, personally….  why not get a pair of 8040’s so you have the same family as the 8050.

Does this help?

Best wishes,

Bob

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