[GreenKeys] Re: teletype machine noise levels

[Don Robert House]

Leave it to an Aussie to come up with the best description yet!
;-)

Don



>Hi Gill,
>
>Sound, its all relative!
>
>I have scanned a chart of levels and it is at:
>http://www.shlrc.mq.edu.au/~robinson/Information/SPL.jpg
>It doesn't have TTYs on it, but perhaps they come in at 80db SPL.
>and another table here:
>http://home.new.rr.com/trumpetb/audio/dBexamp.html
>
>How loud is it?
>Depends upon how close are you to the source, and what frequency it is.
>I've forgotten, but I think you hold the SPL meter 1 meter away
>and to the side of the noise source.
>That is, if measuring a vehicle noise output, you don't shove it up 
>the tail pipe.
>
>========================================
>Some definitions:
>
>SPL (Sound Pressure Level) is used to measure sound (equivalent to 
>voltage ie volts)
>The ratio between the actual SOUND PRESSURE and a fixed reference pressure.
>This reference pressure is the THRESHOLD OF HEARING (defined as 0db SPL)
>which has been internationally agreed upon as having the value .0002 
>dynes/cm2.
>
>SI (Sound Intensity) is the sound energy transmitted per unit time 
>through a unit area,
>being a measure of the magnitude of a sound (equivalent to power ie watts).
>The unit of measurement is the erg per second per square centimeter,
>or the watt per square meter.
>
>Which means, instantaneous level is SPL, and dosage over time is SI.
>
>The THRESHOLD OF HEARING lies at 10-12  watts/m2
>The THRESHOLD OF PAIN is about 1 watt/m2.
>
>A normal SPL meter measures sound with a flat frequency response,
>but is has several weighting curves that can be switched in.
>The weighting "A" approximates the normal human ear.
>With this switched in, the SPL meter now measures SOUND LEVEL.
>Just to complicate things,
>the curve changes depending on how loud the sound is.
>Thats why you have a loudness tap on the volume control in your stereo,
>it increases the Low frequencies at low volumes.
>
>There is more techo info here:
>http://www2.sfu.ca/sonic-studio/handbook/Sound_Pressure_Level.html
>and I've quoted some of the stuff above from it.
>
>All this stuff applies to the real world.
>When sound gets coverted to voltage
>and starts running around inside an amplifier,
>things are different, VUs, dbM, and other rules apply.
>
>========================================
>
>I work in this area and have to deal with people talking this stuff,
>and I have to pretend to understand it.
>Sorry to get techo.
>
>Regards
>Ray vk2ilv
>
>_______________________________________________
>GreenKeys mailing list
>GreenKeys at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/greenkeys


-- 
---------------------------------------------------
Don R. House
4716 Patty Lane, Ringwood, IL 60072
Tel: 815-653-0683
FAX: 815-653-0684
*****************************************
North American Data Communications Dept. of CMA
URL: http://www.nadcomm.org
Computer Museum of America (CMA)
URL: http://www.computer-museum.org