Say what?
*(Unless otherwise stated, all dB values are re 20*10^-6 Pa)
"Can my iPod to that?"
I ended my last post by promising things to come, mainly pictures and some rantings of Robert Randolph. I regret to inform you that these things will have to wait; I am in no mood for them now. Instead I will enlighten you on the subject of iPods and sound pressure levels. It all started with the headlines this morning, something about someone sueing Apple because their all-too-famous iPod can produce 115 dB. Now, there is quite a simple solution to this problem: don't turn the volume all the way up! Obviosuly. Well, this got me going, and it seems to me that someone who would sue over something to simple might be exagerating a bit. I knew what I had to do. My work was cut out for me.
The first task was to determine what pressure corresponds to 115 dB: 16 Pa. I then grabbed my iPod and my old headphones and headed for Rani's room. I explained the importance of this project to him, and he readily came into the hall to help out. I was to stand at one end of the hall, holding the headphone at shoulder level with the iPod volume turned all the way up, while Rani walked away from me until he could no longer hear the music. This approach didn't work so well. Rani made it to the end of the hall and he could still hear the music coming from my iPod. I went back to my room to find a message from John offering his help. I went to his room and explained everything. We decided the best approach was to go outside and measure the distance using an old baguette, which we estimated to be 22 inches using a $50 bill. We stopped by Dan's room, because what sane acoustics student wouldn't want in on this action?
Having finally left the building, the three of us stood by the path and prepared to make history. I was to hold the iPod, Dan and John were going to walk until they could no longer hear it. So we began. They walked. I stood there. They marked where they stopped. We measured the bricks that lined the path: three bricks to a baguette. John counted off the bricks to the point where he and Dan had stopped: about 46 meters. Now for the technical part of the experiment. Assuming spherical spreading (pressure * radius = constant), and that they stopped walking when the sound was at the threshold of human hearing (20*10^-6), we found the constant to be 0.00092. Then we assumed that, when placed in the ear, the source was at a distance of 1 mm. This yields results of 93 dB. That is quite a bit different from 115 dB. We decided that maybe the man had taken his reference in water instead of air. That calculation yielded 119 dB, which is closer, but an absurd assumption. We pondered together the effects of the source being to close to the ear, and the assumption of spherical spreading not holding for this specific case. We parted ways still having not answered our question in a satisfactory manner.
On our way downstairs, John and I had a thought: what if he and Dan had failed to hear the iPod due to background noise? That would mean that the pr constant was incorrect, and the pressure at 46 meters was actually that of typical background noise. Assuming a background noise of 25 dB, then pr=0.016, and the new sound pressure level was 118 dB! That actually makes sense. So it turns out that the guy wasn't totally crazy after all. We fully intend to get out hands on a sound pressure level meter and determine the background noise at the Technopole. Then we'll have a better idea as to how right or wrong we are.
And that is what today was all about: acoustics experiments at the Technopole. I'm sure you've enjoyed all this technological mumbo-jumbo. You never know when you might need it.
"Can my iPod to that?"
I ended my last post by promising things to come, mainly pictures and some rantings of Robert Randolph. I regret to inform you that these things will have to wait; I am in no mood for them now. Instead I will enlighten you on the subject of iPods and sound pressure levels. It all started with the headlines this morning, something about someone sueing Apple because their all-too-famous iPod can produce 115 dB. Now, there is quite a simple solution to this problem: don't turn the volume all the way up! Obviosuly. Well, this got me going, and it seems to me that someone who would sue over something to simple might be exagerating a bit. I knew what I had to do. My work was cut out for me.
The first task was to determine what pressure corresponds to 115 dB: 16 Pa. I then grabbed my iPod and my old headphones and headed for Rani's room. I explained the importance of this project to him, and he readily came into the hall to help out. I was to stand at one end of the hall, holding the headphone at shoulder level with the iPod volume turned all the way up, while Rani walked away from me until he could no longer hear the music. This approach didn't work so well. Rani made it to the end of the hall and he could still hear the music coming from my iPod. I went back to my room to find a message from John offering his help. I went to his room and explained everything. We decided the best approach was to go outside and measure the distance using an old baguette, which we estimated to be 22 inches using a $50 bill. We stopped by Dan's room, because what sane acoustics student wouldn't want in on this action?
Having finally left the building, the three of us stood by the path and prepared to make history. I was to hold the iPod, Dan and John were going to walk until they could no longer hear it. So we began. They walked. I stood there. They marked where they stopped. We measured the bricks that lined the path: three bricks to a baguette. John counted off the bricks to the point where he and Dan had stopped: about 46 meters. Now for the technical part of the experiment. Assuming spherical spreading (pressure * radius = constant), and that they stopped walking when the sound was at the threshold of human hearing (20*10^-6), we found the constant to be 0.00092. Then we assumed that, when placed in the ear, the source was at a distance of 1 mm. This yields results of 93 dB. That is quite a bit different from 115 dB. We decided that maybe the man had taken his reference in water instead of air. That calculation yielded 119 dB, which is closer, but an absurd assumption. We pondered together the effects of the source being to close to the ear, and the assumption of spherical spreading not holding for this specific case. We parted ways still having not answered our question in a satisfactory manner.
On our way downstairs, John and I had a thought: what if he and Dan had failed to hear the iPod due to background noise? That would mean that the pr constant was incorrect, and the pressure at 46 meters was actually that of typical background noise. Assuming a background noise of 25 dB, then pr=0.016, and the new sound pressure level was 118 dB! That actually makes sense. So it turns out that the guy wasn't totally crazy after all. We fully intend to get out hands on a sound pressure level meter and determine the background noise at the Technopole. Then we'll have a better idea as to how right or wrong we are.
And that is what today was all about: acoustics experiments at the Technopole. I'm sure you've enjoyed all this technological mumbo-jumbo. You never know when you might need it.
posted by David @ 11:59 PM
1 Comments:
At 12:23 AM ,
john said...
An old baguette, fifty dollars, and a really loud ipod... pure genius!
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