It's been 50 years since I worked in the acoustic labs at Boeing where I posed the same question. One of the specialists in the passenger accommodation section of the lab explained it this way: the human ear is a SUBJECTIVE and dynamic instrument. In other words, the perception of sound pressure level (SPL) is a function of environment, how a person feels (is the person ill or have a runny nose, etc.), the listeners temperament (is he happy or upset), the nature of the sound (does the listener like the sound or does he find it annoying), how much has the listener had to drink, etc. As for the dynamic aspect, depending on the environment, you may hear a particular sound one way but a bit differently a moment later, depending on the above factors. Another factor is that sound can be much like water leaking into a boat. Both the water and SPL increases over time depending on the opening through which the water or sound enters a space. That type of sound can be measured with instruments but difficult to assess by ear. Sound in a restaurant can be much like water in a boat, people tend to talk louder which increases the overall SPL which causes them to talk even louder. In short, the rule of thumb is that it takes about a 10 dB increase in SPL for a person to perceive a doubling in the level of the sound. 3dB is almost imperceptible with most any kind of background noise.
On a tangential note, during the late 60s the Super Sonic Transport (SST) program was in progress and NASA conducted an extensive series of tests to determine objective and subjective aspects of sonic booms. The tests were conducted at Edwards Air Force Base in California over a three month period. Boeing, Lockheed, and other institutes participated. The base was building additional housing at the time so several of the new structures were used for the tests. Three of them were fitted out like regular homes with carpeting, window shades and curtains, furniture, etc., and a couple of the houses were configured more like offices or large department stores. Some of the homes had people in them and others did not. All of the buildings were extensively instrumented, both inside and out. All of my transducers were mounted on the outside of the buildings and my recording equipment was in a double garage of one of the houses. In my building, the garage door had been replaced with a large plate glass window to simulate a store front. The mounting assembly for the glass was changed from time to time to test various mounting designs. The subjective part of the test was done with people from the local communities who sat in various rooms and filled out forms designed to rate the effects of the sounds they heard. The sonic booms were generated by F104, B58, B70, and the then new SR71/YF12 aircraft. During some of the subjective tests, a KC135 (Boeing 707) airplane was used to simulate takeoff or low fly over sounds near airports. I never read the final report(s) of the tests but a few preliminary reports made the rounds. In the case of the subjective tests, people were all over the map. In many cases, people would give radically different scores for identical tests days or weeks apart. The objective tests often produced predictable results but there were times when repeat tests produced big surprises. Temperature, humidity, wind, and even doors open of closed, made noticeable differences in the measured data. For a quick look, we taped a ball point pen to the center of the large window and mounted a paper plate on the face of a clock so the plate was driven by the second hand. When the boom hit, the pen would produce a trace on the plate showing the displacement of the window. Some of the test were done with the garage being "tuned" by judiciously opening a door. A given aircraft would hit us with a boom then the door would be readjusted and the same aircraft would duplicate the boom minutes later. The difference could be startling. During one series of identical flights the first boom displaced the window 15mm but the second boom produced a displacement of 155mm. This type of testing is very expensive so, in an attempt to reduce the costs a ten foot diameter exponential horn which was mounted on a trailer. To test the efficacy of this device, the trailer was placed near one of the houses then two positive pressure pulses of gas were produced to simulate a sonic boom. The people in the house were told the boom was from an aircraft and asked to rate it in the usual way. (A sonic boom consists of a positive pressure spike followed by a negative spike. The amplitude, shape, and timing of the spike is a function of the speed and shape of the aircraft though the shape of the spike can be modified by structural and geologic features. The tests with the horn produced only positive spikes but the shape and timing could be adjusted mechanically. One day there was a lull in testing so I stepped outside for some air. Sitting on the ground a few feet in front of the horn was the neighborhood mutt. The dog must have noticed me because it cocked its head and looked at me. The image was right out of the logo for the RCA corporation. Doug, K7CUU -----Original Message----- From: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On Behalf Of Dauer, Edward Sent: Thursday, December 13, 2018 9:16 AM To: elecraft@mailman.qth.net Subject: [Elecraft] 10 dB or 3? A very unpleasant dinner last night at a restaurant with a reported noise level of 84 db – about the same as a gas engine lawn mower seated at the next table – raised what is probably an elementary question. 3 db is the familiar doubling of power, and in an audio environment is a doubling of acoustic energy, I understand. However, I have read that ten db is what results in an apparent doubling of the sound level as we hear it. Is the difference attributable to something like an AGC circuit in the human auditory system? And as for RF transmitter power, does it take a ten db increase rather than 3 to effect an apparent doubling of audio amplitude in the ears on the other end of the QSO? Never mind the S meter – I mean the actual ability to hear a signal over the noise, or over the QRM. Help, anyone? Ted, KN1CBR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to d_hud...@outlook.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
