Thursday, December 08, 2005

Sound

What is sound and how do our bodies deal with sound? That's what I'm going to talk about today. Most people would describe sound by saying it something you hear. It is actually sed to describe two different things: 1) it's an auditory sensation in the ear and more precisely, the ear drum and 2)the disturbance in the medium that causees this sensation. But there is a lot to be explained in these two definitions.
Sound is carried through gases, liquids, and solids by sound waves. When we think of "waves", we usually think of the ocean. But sound waves create a different motion but generally all waves--light waves, water waves, shock waves, and radio waves--have some similiar properties. They can be reflected or refracted, which means that they bend as they travel from 1 medium to another. Think ofa corridor with a bend. 1 side has a light and after the bend, there are no lights in the hallway. You are standing in the dark portion and you can't see where the light is coming from but you can still see light. [I'll be drawing a figure on the board]. THis is because ethe light waves are bouncinng off thew alls until they reach the bend and travel down the perpendicular corridor and into your eyes. The same thing would happen if a perso was talking in the same spot as our presupposed light bulb--you cant see the person but the sound waves are still hitting you ear. The waves transport information and enery through a medium without actually transportinng hte medium itself. In space, sound cannot travel because there is no medium for it to pass through. A sound is a disturbance or small movement that passes through the particles of the medium. Imagine air particles between a stereo and a persons ear. The sounds waves leave the stereo and bump into the air particles closest to it. [another figure drawn by me]. These particles quiver a ltitle and bump innto their neighboring particles. This chain reaction continues all the way to your ear, wehre the particles collide with yor ear drum and make it vibrate. This vibration sends a signal to yor brain that you are heaving something. The brain then interprets the sounds as music or words. Louder sounds are percieved to be such becasue the particles shake and collide with each other and consequently hit your ear faster and harder. The particles retrn to their calm state after the waves have passed. Sound waves are slower then other kinds of waves, traveling at 343 m/s or 1125 ft/s in air, compared to light waves which travel at 3*10^8 m/s or 186,000 ft/s.
The threshold of audibility is the minimum pressure flctuationns t which your ear can respond. For most people, the threshohld lies at one billionth of atmospheric pressure. On the flip side, the threshold of audibility is a sound pressure change of 1 million times greater but still less then 1/1000 of atmosphere pressure. [Table 3.2]
Sound pressure leverls are differnet than "loudness" because loudness is a subjective thing. After hearinng a rock concert, people usually talk louder than normal because their ears have gotten used o hearing loud noises and base all other noises on previous sounds. Loudness also depends on the frequency of the sound--high sounds will alwyas seem louder to our ears than lower sounds even though they might have the same sound pressure level. This is important to remember as musicians in order to keep a balance of sounds, whether you are a pianist or play in a group setting. HIgh sounds seem louder because they almost always fall in the range of 1000-4000 hz which is where the ears are most sensitive. Music usually falls inn the middle of the range of sounds in both Hz and dicibels. [ Table 3.3]
Music tries to express different levels of loudnes sby dynamics. THer are six common ones from pp to ff but research has shown that musicians rarley play all six dynammics throughouut any given cocert. As musicians, we need to remember that the loudness is all relative. A piece may be marked piano, bt htat doesn't mean that you necessarily have to start very soft--instead, you need to be able tto make a much louder sound relatvive to the beginning sound in order for your audience to recognize the differnet as p>>>f. Many wind and string instruments rarely go over 20 db althoguh thhere are multiple exceptions to this statement, for example: saxophones and violins. This also highly depends on how far the listener is from the instrument. Generally, it is established that the sound pressure level decreases 6 db as the distance doubles. It also depends on the source power of the innstument. This power, like elcticity, is measure in watts. However, to be practical in the numbers, people express the power level in decibels by using a reference level which is a power of 10-12 watts. THe most powerful instrument in the orchestra is the bass drum which emits a powere level of 20 W or 133 db at its loudest. At a distance of 1 meter, thhe db level is 122, while at 10 meters is still loud at 102 db. This explains why the bass drum can always be heard over the entire orchestra. This causes a problem in the balance of the orchestras sound because some tonns can be masked by other tones.
Masking the upward shift in nthe hearing threshold of hte weaker tone by the stronger one. Weak and stronng are just words used to describe the relationnship and do not correspond with the words softer and louder, althhough that obviously can happen. masking can happen when 2 tons hhappen simultaneously but more surprisin is the fact that masking can happen even when they are not.
Now taht I've discussed waht loudness is and how it related to the human ear, I want to discuss the differnece betwee the loudness of a short, impulsive sound capared to thhe loudness of a steady sound at hte same level. Previous experiments hahve shown that the ear averages sounds over 200 milliseconds so that teh sond grows over time up to that level. People cannot feel this growth in sound because 200 milliseconds is a really shohrt time.
The human ear has come up withh defenses to protect itself from the damage of very loud sounds. THe ear can give effective protection for up to 20 db by the muscles attached to hte eardum and the bones that are attched to the middle ear called ossicles. WHen the sound elvel reaches over 83 db, occicles muscles tighten another mscle called the ossicular chain and pull 2 bones called stapes away form the cochlea. This reactionn to loud sounds is call the acoustic effect. However, thihs reflex doesn't kick in until 30 or 40 milliseconds afterh sounds begins. Also, the reaction to cover the ears with you hands usually only occurs after 150 milliseconds. This means that loud, unexpected sounds can do damage to the ear before any reaction can occur. An interesting concept to think about is what kind of protection the human body would have developed had loud sounds of hte modern world hahd existe for millins of years. Maybe soemthing like earlids?

7 Comments:

Blogger Keely said...

My only comment is to maybe proofread your post a little better. There are no major mistakes, just little ones. As far as your presentation, great job!

Friday, December 09, 2005 10:48:00 AM  
Blogger dbu_us said...

Yes, I agree more proofing is needed but it is very nice and very good work.

Friday, December 09, 2005 1:04:00 PM  
Blogger Anna said...

Great drawing during your presentation. It is much braver to draw pictures on the board apposed to using a simple power point. Very clever ending.

Friday, December 09, 2005 3:50:00 PM  
Blogger gfunk5 said...

Great job using the Tables in your presentation. They were effective in teaching sound.

Friday, December 09, 2005 5:23:00 PM  
Blogger violinbrunetka said...

Let's see, well, I like that you had tables for your presentation. I think you should need to proof read your paragraph.

Friday, December 09, 2005 9:55:00 PM  
Blogger Annie said...

Very nice information--the language was easy to understand. But when you're drawing on the chalk board- or explaining tables-- make sure you dont stand in front of what your presenting.

Saturday, December 10, 2005 12:05:00 AM  
Blogger saxubatar said...

Overall, I agree with everyone else. Solid presenation, and I did not think any of the language was too much. Nice job!

Saturday, December 10, 2005 11:31:00 PM  

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