The Human Perception Of Loudness

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The Human Perception Of Loudness

  1. 1. The Human Perception of Loudness Introduction A change in the amplitude is not necessarily perceived as being an equal change in loudness. This is why sound pressure level is different to loudness as SPL is a physical quantity. Loudness is our perception of amplitude. The way we perceive loudness is influenced by the timbre and the frequency of a sound.[1] The best known example of a Visual representation of Loudness was the Fletcher and Munson curves of equal loudness level. [2] [3] http://www.maurograziani.org/text_pages/maxmsp/primer/lesson02/fletcher.gif This graph proves the point that when humans hear a sound at the same loudness they are not necessarily the same amplitude. As well as this the graph shows which frequencies our ears are sensitive and insensitive to. The lowest frequencies require high amplitude for us to hear but the same doesn’t apply to the higher mid frequencies as our ears are more sensitive to them. These frequencies are roughly that of the human voice which allows us to pick up voices clearly. Experiment The aim of the experiment was to investigate the human ear and our perceptions of sound. We would then compare these results to the Fletcher and Munson curves. We used a CEL-440 sound level meter kit to record readings of different places around campus. The device takes a decibel reading of loudness and sound pressure level, allowing for a comparison of the two. Before we began the experiment we predicted volumes for each of the rooms using the following scale: Very Quiet Quiet Moderate Loud Very Loud Extremely Loud
  2. 2. Once in the rooms we selected one of the above choices which best suited the volume. We then used the sound level meter to record loudness (dbA) and Sound pressure level (SPL.) We also made notes in each room of sounds we could hear and sounds we thought couldn’t be heard that could be picked up on the reader. We chose rooms we believed would vary a lot and cover the whole range of our scale. Results Studio control room: Our estimate: Very Quiet Result: Very Quiet Loudness: 18 dB Sound Pressure Level: 20dB The control room was extremely quiet as predicted. Although we could not hear any sound, there was a reading on our meter. After researching further I found that mains electricity produces a 50 Hz signal and from the “Fletcher and Munson curves” we can see this frequency is very insensitive to our ears and is very difficult to hear at low amplitude. [3] [4] Gym: Our estimate: Moderate Result: Loud Loudness: 86 dB Sound Pressure Level: 90 dB The Gym was much louder than we first thought. This was due to the equipment producing much more noise than we expected. Studio live room: (with musicians performing) Our estimate: Very Loud Result: Extremely Loud Loudness: 113 dB Sound Pressure Level: 115 dB We went into the studio live room to take a reading of someone playing guitar. We estimated the room to be very loud but it was even louder than expected. The guitar was at 115 dB SPL which is a dangerous level to our ears. After researching I found a recommended exposure time for 115 dB is 30 seconds. This shows how dangerous these high sound pressure levels are to our ears. [5] Bar: Our estimate: Loud Result: Moderate Loudness: 60dba Sound Pressure Level: 62dba The bar was mainly empty when we were taking a recording so this made our estimate wrong by a fair margin. Top Stairs: Our estimate: Quiet Result: Moderate Loudness: 63 dB Sound Pressure Level: 70 dB We expected the stairs be quiet but the echo from the room and people speaking whilst going up the steps gave a much higher reading than we thought. Food Court:
  3. 3. Our estimate: Moderate Result: Moderate Loudness: 64 dB Sound Pressure Level: 71 dB The food court was very busy at the time we took the reading and therefore there were a lot of people sat down talking. Going back to the Fletcher and Munson curve we saw that the human voice is a frequency our ears are very sensitive to. This was reflected in our results. The loudness reading was smaller than the sound pressure level which shows we hear the frequencies quieter than the actual amplitude of sound. Library: Our estimate: Quiet Result: Moderate Loudness: 67 dB Sound Pressure Level: 68 dB The library was very busy and a lot of people were talking. As said before this is a very sensitive sound to our ears so our estimate was wrong. The library was louder than we expected. The experiment demonstrated the difference between loudness and sound pressure level, and the dangers of loud sounds. Using a website I was able to conduct my own experiment to see if the Fletcher and Munson graph were accurate. The web page allows you to play sound to make your own loudness curve. I tried this for myself and a friend. My loudness curve: Katy’s loudness curve:
  4. 4. The curves produced are similar to the shape of the Fletcher and Munson graph with just slight differences between us. This experiment helped me prove that every human has slightly different hearing. My ear was less sensitive to the sounds where as Katy found certain frequencies almost unbearable. For me the highest frequency was very quiet this is likely due to hearing damage I have suffered. I found out that the high frequency area of the cochlea can be damaged by loud sounds. This explains my inability to hear the high frequencies well. [5] I also found out about the best volumes to use when creating a mix. From the Fletcher and Munson curves I can see the higher the amplitude the flatter response you get so this is the best possible volume to mix at. If you mix too low your mix could miss out on bass and high frequencies once turned up louder later. It is also important to make sure you have regular breaks as levels this loud will cause ear damage if listened to for too long. The information I have learned will help me in my future assignments and compositions. References: 1. Indiana university: Acoustics [Online] Available at: http://www.indiana.edu/~emusic/etext/acoustics/chapter1_loudness.shtml [Accessed 24th October 2009] 2. Electronic Musician: What is this thing called Loudness? [Online] Available at: http://emusician.com/tutorials/emusic_loud_louder_loudest/ [Accessed 24th October 2009] 3. Rossing, Moore & Wheeler (2002) The Science of sound third edition, San Francisco, Addison Wesley, p.107 4. All experts: Mains electricity [Online] Available at: http://en.allexperts.com/e/m/ma/mains_electricity.htm [Accessed 24th October 2009] 5. Dangerous Decibels: Hearing Loss [Online] http://www.dangerousdecibels.org/hearingloss.cfm [Accessed 24th October 2009]

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