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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Lounge FUD Forum Archive => Topic started by: Vic Wintergreen on March 03, 2007, 01:41:35 PM

Title: A weighting vs C weighting
Post by: Vic Wintergreen on March 03, 2007, 01:41:35 PM

I appreciate the difference between the two response curves, but where is the cross-over point between the two scales. C weighted is designed for higher SPL's and represents the way our hearing adjusts at high levels (correct me if I'm wrong), but at what SPL does sound become a high level.

Title: Re: A weighting vs C weighting
Post by: Mario Salazar on March 03, 2007, 10:54:40 PM

There is a thread on this somewhere in this site.  Try a search.  To answer your question, it is not C but A weighting that "gives an approximation of the actual response of the human ear, as determined by Fletcher Munson."-Yamaha SOundreinforcement handbook.
However, once you get past 100 db the ear's frequency response becomes more linear so C weighing would be more appropriate from this SPL up.

I hope that helps.
Good Luck!
Mario

Title: Re: A weighting vs C weighting
Post by: Mike MacWillie on March 03, 2007, 10:57:19 PM

Mario Salazar wrote on Sat, 03 March 2007 19:54

However, once you get past 100 db the ear's frequency response becomes more linear so C weighing would be more appropriate from this SPL up.

Now, is that 100DbA or 100DbC ?

 

Title: Re: A weighting vs C weighting
Post by: Mac Kerr on March 03, 2007, 11:09:35 PM

Mike MacWillie wrote on Sat, 03 March 2007 22:57

Mario Salazar wrote on Sat, 03 March 2007 19:54 However, once you get past 100 db the ear's frequency response becomes more linear so C weighing would be more appropriate from this SPL up. Now, is that 100DbA or 100DbC ?

I think you both mean dB.  

Mac

Title: Re: A weighting vs C weighting
Post by: Mario Salazar on March 04, 2007, 12:16:12 AM

  AAAArg!
I don't know what I mean any longer!

Title: Re: A weighting vs C weighting
Post by: Vic Wintergreen on March 04, 2007, 08:07:04 AM

thanks for the response
i tend to set the foh by ear - if it sounds good - it probably is
i bought a paa2 for measuring levels, as well as checking the mains eq
i am getting some bigger jobs and wanted to show the customers the spl's around the venue, many want it louder, but 110dB at mix point is loud enough i think
i just wondered what was the best scale to use flat/a/c
thanks
Vic

Title: Re: A weighting vs C weighting
Post by: Tom Young on March 04, 2007, 12:49:49 PM

The choice of weighting networks are of great importance for industrial and legal noise measurements. For example; when you make community/annoyance noise measurements, the local or state statute will provide very clear limits for C and B weighting and also for A-weighting during day and also for evening hours. When you conduct a noise survey, you need to record what weighting you use as well as the location, mounting methods, etc. that were employed. You must also calibrate the meter befor and after the field measurements.

In live sound, there is no clear technical reason to use one versus another, other than if you are relating the measurements to OSHA guidelines, which are A-weighted.

What is always important is that comparative measurements are weighted the same and that when you state SPL you quantify it with the appropriate suffix letter. An un-correlated SPL value means very little in pop music measurements because the bass energy has such a large impact on the measurements.

When dealing with the uninformed, live sound folks can "cheat" the rules (or some poser's cursory knowledge) by using the A-weighted filter so that measurements appear to be lower in SPL than a standard or rule that is based on a Flat or a C-weighted limit. Of course, the opposite trick can also be employed.

So I would not sweat the choice of filters. I happen to use C-weighting when measuring amplified/reinforced pop music and sometimes switch to A-weighting when measuring spoken word or lightly reinforced choir.

Title: Re: A weighting vs C weighting
Post by: Vic Wintergreen on March 04, 2007, 01:57:45 PM

Well thats pretty much what I thought. I use the C scale at gigs. However, due to the weighting, the way it is measured, the appears to be nl high-end, as the scale drifts gently down to the right over the high frequencies. I know the highs are there and was just wondering if for a frequency spectrum representation of the sound in the room that A weighted is used, but for an overall SPL reading, the C scale is used. Thanks for your help
Vic

Title: Re: A weighting vs C weighting
Post by: Bob Leonard on March 04, 2007, 02:23:49 PM

This may be helpful to you. As Tom said above the content will usually determine the weighting used for the measurement.

http://www.engineeringtoolbox.com/decibel-d_59.html

Title: Re: A weighting vs C weighting
Post by: Vic Wintergreen on March 05, 2007, 04:26:24 PM

Ta, funnily enough, just got to the measurement section in Audio Engineering. Always handy to have some other thoughts tho