Noise Measurement - Lpick dB(C)??

[rafletcher]

Any of the audio specialists recognise this mode of measurement of sound pressure levels, and know how it relates (if at all) to dB(A)?

[nicknack]

Pinched from wikiped:

dBc (decibels relative to the carrier) is the power ratio of a signal to a carrier signal, expresses in decibels. For example, phase noise is expressed in dBc/Hz at a given frequency offset from the carrier. dBc can also be used as a measurement of SFDR between the desired signal and unwanted spurious outputs resulting from the use of signal converters such as a digital-to-analog converter or a frequency mixer.

If the dBc figure is positive, then the relative signal strength is greater than the carrier signal strength. If the dBc figure is negative, then the relative signal strength is less than carrier signal strength.

Although the decibel (dB) is permitted for use alongside SI units, the dBc is not.[1]

So, I guess, not really related to dB(A) at all. Sorry, don't know where the Lpick bit comes in. Where did you come across it?

[rafletcher]

A noise spec from a client for a plant-room - so probably an error if dB(C) is signal-to-noise type thing, rather than free field sound pressure.

[nicknack]

Well, never rely on wikipedia to give the whole picture. Consulting Rossing, Moore and Wheeler (Science of Sound),  I find that dB(C) is just one the 3 weighting networks used for sound measurements. It has a much flatter response than A which has a low frequency roll-off which corresponds to the response of the ear. Inside a building with noisy machinery the C weighting would give a higher reading due to the presence of much low freq. stuff. So I suspect it might be quite relevant.

[nicknack]

Here could be useful.

[rafletcher]

ok, thanks! Though quite what I do with the info is another matter...

So, would 85dB(C) be a lesser sound pressure level that 85 dB(A)?

[nicknack]

Presumably it would sound quieter because our ears don't pick up so much of the low frequencies. But it would depend on the spectrum of the sound. If there are few low frequencies present then they should be similar.

[rafletcher]

Hmm, so theoretically harder not to exceed the (C) scale than the (A), but only if low frequencies present?  Most of our kit will be motors, pumps and fans, so mainly higher frequencies.

[nicknack]

Hmm, so theoretically harder not to exceed the (C) scale than the (A), but only if low frequencies present?  Most of our kit will be motors, pumps and fans, so mainly higher frequencies.

Are you sure? Depends on the size of these. Some spl meters will give you a spectrum just to be sure. Or a pc with the appropriate software come to that.

[rafletcher]

We'll just feed it back to our suppliers 

[gordon taylor]

OT, but related...

Why does my new wheelie bin have a dBA sticker?

I think it says 88 dBA but I'd have to look tonight.

[nicknack]

Err... You live at 88 deBeers Avenue?

[hellymedic]

OT, but related...

Why does my new wheelie bin have a dBA sticker?

I think it says 88 dBA but I'd have to look tonight.

Wheelie bins are noisy feckers and seem to set off nearby intruder alarms. Partner and I are in a BAD MOOD for this reason.

88dB is about the level of tthe loudest shout I can achieve.

[gordon taylor]

I don't think I'm going mad...

If anyone is at home now, please go and look at your wheelie bin. It'll have a dB(A) sticker on it , I'm sure.   

[Wombat]

Yes, they do.  its the noise they make when being emptied.  Completely ignores the sound of an effing great dustcart, and 5 refuse operatives effing and blinding at each other at 6am, but....

Actually ours come much later in the day, and are not excessively noisy, but they do have an issue about returning them to the correct house.

[SandyV]

I asked a friendly acoustic engineer in the next office and he wondered if it is meant to be Lpeak which is apparently quite a common measure used to set levels where hearing might be damaged.  (He said quite a lot more but it went over my head)

[rafletcher]

I asked a friendly acoustic engineer in the next office and he wondered if it is meant to be Lpeak which is apparently quite a common measure used to set levels where hearing might be damaged.  (He said quite a lot more but it went over my head)

Yes I bet it is - the text I have is in translation from Spanish original. So Lpeak it will be.