Archived from groups: rec.audio.tech (
More info?)
In <1114109867.794239.283100@l41g2000cwc.googlegroups.com>, on 04/21/05
at 11:57 AM, "mikeorb" <mike-nospam@orb.dreamhost.com> said:
>I have a noise problem and I am trying to explain it to someone. I
>took a sound level reading before the event that is loud occurs and
>during. I'd like to be able to express to someone the difference
>beyond dB. Is there any way to compute a "percentage" difference
>between the two? Like Z is n% louder than X?
Expressing sound pressure levels in dB *IS* quantifying the differences
in sound levels. I suspect that your problem is explaining what the
numbers mean.
If I can use analogy: Expressing a length measurement to someone who
does not understand the concept of "inch" does not convey much
understanding. The context of the measurement is also important. A
surface irregularity of 1/4 inch on a highway is not particularly
significant, while it may be a disaster on a writing surface.
For sounds, the annoyance factor depends on the character of the noise.
Coherent noises are more of a problem than wide band noise. A
"coherent" noise is something that we can easily recognize -- such as
speaking, an infant crying, a tone, etc. "Wideband" would be the gentle
sound of wind, the noise between radio stations, etc. Wideband noise is
more or less random sounds that cannot be identified as anything
specific. If you switch your audio system to PHONO when nothing is
connected to the PHONO input, you will hear some wideband noise, the
rushing sound, and you will hear some "hum". The hum is the coherent
component of the noise and it has a very low musical pitch associated
to it. Humans are very good at focusing on faint coherent sounds.
Sounds in the vocal frequency range are more of a nuisance than very
low or very high frequency sounds.
I don't have any specific references for you, but a basic text on
psychology usually has a section on human perception of sound. This
would be a good place to start. From there you can move on to acoustics
and noise control.
Play with your sound pressure meter in as many situations as possible.
How many dB louder must a noise measure until you can perceive a
difference? On your first day of these experiments, note your
thresholds. After you have some experience, you'll find that your
thresholds will shift. While you are playing a noncoherent noise
source, introduce a second coherent source such as some music. If you
are normal, the coherent source will become quite apparent, but the
sound pressure measurement will hardly change.
While listening to wideband noise, fuss with your volume and tone
controls while watching the sound pressure meter. Some settings of the
tone controls may result in a greater "annoyance factor" for you. Do
they result in much of a change in the meter reading? If you have them
on your meter, fuss with the "weighting" settings, particularly "A"
weighting. Do any of them result in the meter tracking the annoyance
factor a little better?
Annoyance thresholds vary from individual to individual, the same noise
can be vexing or unnoticed by two different individuals.
For very loud sounds, we eventually reach a threshold where extended
exposure will result in temporary or permanent hearing damage. If you
are dealing with very loud noises, there are specific measuring
techniques that should be used to document the problem. Once the noise
is properly documented, legal recourse is possible, but it is a lot of
trouble.
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