Here's some exerts from my paper so far. I'm too lazy to edit them right now or to actually blog about the experiments. So here's expiriments 9 through 11
Experiment 9: Underwater Recording
For this experiment I developed 3 techniques for recording underwater.
Cover a dynamic mic with a condom
Cover a dynamic mic with a sandwich bag
Cover a dynamic mic with a plastic grocery bag
Cover a dynamic mic with plasti-dip
Use an actual hydrophone
Dry as recorded above water with a dynamic mic
In order to record, I had to overcome several challenges. How would I project sound underwater, and how do I keep the microphone’s dry? One of my dissertation committee members had experience with recording an electric guitar, I assumed since he hadn’t died of electrocution, he was successful. During my first committee meeting, I borrowed his hydrophone, and I finally had gotten around to this experiment. His advice for making underwater speakers was to take a midrange horn driver and cover it with a polyurethane coating. After doing some research and talking with a couple music store salesmen, I finally found a small audio components store that sold midrange horn drivers on the boarder of Gresham. What I didn’t realize when I got there were there were multiple types of midrange horn drivers. I went for the cheapest, smallest horn driver I could find due to my low budget and limited working space. Next I had to find polyurethane so I could coat the speaker. After a trip to A-boy, I realized I didn’t know what to buy, so I came home empty handed until I could research which product to buy. At first I was rather nervous about buying a can of Polyurethane coating because a can of it was in the price range of $40 to $50. This was getting my worried. After a while of searching, I found a product called Plasti-Dip which is used for coating the handles of tools. With a bit more research I found a site that had Plasti-Dipped a microphone in order to record underwater. I decided that this would be a good substitute for the polyurethane coating and took a short trip over to A-boy one more time. Luckly they had 3 cans left, I bought their last can of black plasti-dip and a 5’ length of audio cable to soldier to my speaker. Another step I had to take was learning how to soldier wires together which I found out is fairly simple. Next I applied the first coat on the speaker. This turned out well, but I found many tiny holes where air bubbles had popped and left the speaker exposed. Because I didn’t want the cone of the speaker to get covered too much, I took a pencil and liberally applied plasti-dip in the spots that had holes. Because it takes 4 hours to dry and I only have about 5 hours of free time a day, I was only able to apply a new layer once or twice a day. The process of waterproofing the speaker took about 4 days so that no part of the speaker had any exposure to the water. Once the speaker was done, I attached the wires to a stripped 1/4” wire to the audio wire that I had stripped and soldiered to the speaker. Unfortunately the speaker was 4ohms and the amp was an 8ohm amp, I believe this is why the speaker was giving me an ungodly 60hz hum. Next I tried hooking my speaker up to the banana jacks from my stereo’s amp to the exposed wires using gator clips. This removed the buzzing, but I couldn’t move my entire audio system from my living room down to the bathroom. My last ditch effort was hooking a modified stereo system I had borrowed from Random to the cables, success.
Now that I had my speakers out of the way, I had to figure out how to use the hydrophone that I borrowed. At first I was under the impression that the hydrophone had a single large wire protruding from it because it had been stripped and the end was tangled covering the fact it was a coaxial cable and was constructed of two different wires. Once that this was pointed out to me, I took the stripped 1/4” cable and soldiered alligator clips to the end of it, then clipped the ends of the clips to the raw wires of the hydrophone. Unfortunately I had wasted a day trying several different ways to attach the wire to my pre amp.
Before submerging my only $40 dynamic mic, I decided to go and buy the cheapest mic I could find so that if anything went wrong I wouldn’t lose a decent mic. Coincidentally my dad was going to frys that night so I hitched a ride and found the perfect karaoke mic for $10. Everything else fell into place, and I carried out my first tests. First thing I tested was covering the mic in a condom. Unfortunately the first one broke, so I used the second one which also broke. Rather than using the given rubber band at the end, I took a rubber band I found laying around which worked fine. In each test I held the mic partially submerged in 5” of water 1” away from the cone of the speaker. Nothing particularly exciting happened during the next couple tests. My last test was covering the mic in plasti-dip then submerging it. The only challenge I faced was that the holes in the grating over the mic bit kept popping holes when I dried the dip.
Track order by Number:
84. Sandwich Bag
Experiment 10: Atmospheric Pressure by Depth
I had this idea if I recorded underwater with a hydrophone, the atmospheric pressure would play into the fact that the Piezo electrical device measures sounds by the pressure it displaces. So if there are various amounts of pressure being caused by the weight of the water, would this affect the overall sound of the recording? It appears that it does. Another reason for a change in sound may be a acoustical change due to new volume of the recording space, although I would have no way to determine this.
[Listen to tracks ______ through ______]
There is a difference between tracks 1 and 3 in sound, but the second track sounds very similar to track one although it has a higher intensity in reading the higher frequencies between 7000 and 8000kh range. I started at a depth of 5” and worked up from there to 7.5” and 10”. I recorded each depth twice one at 5” away from the cone of the speaker and once at 1” from the speaker.
I had the idea of putting a waterproofed dynamic mic underwater in order to compare the sound of a piezo based mic and a diaphragm mic, but after a bit of research, I realized that each mic just converts different pressures and that each mic is just acoustically tuned for the fluid it’s exposed to. Basically the only thing I would be getting out of a waterproofed mic is having the sound traveling through the water hitting the plastic rubber diaphragm then traveling through the trapped air. I went ahead and did it in experiment 9, the track is called Plasti-dip if you would like to compare
Track order by Number:
Track 87 : 5” of water
Track 88 : 7.5” of water
Track 89 : 10” of water
Experiment 11: Cones
For this experiment, I decided since I was testing things underwater, I may as well test how cones sound underwater as well. When I was building a underwater speaker out of a mid range driver, the speaker came with two cones attached a single cell loudspeaker cone and a small metal cone, these cones are supposed to be used in tandem in order to amplify the small speaker. I started getting curious if cones amplified underwater, which to me would be common sense, but I thought I would try it anyway. The final result was against my expectations. The cones were actually blocking the sound. I’m not sure why this was the final result, it’s exactly counter intuitive. The probable reason for this is I originally put the speaker 1” away from the hydrophone but with the cones I was setting the end of the cone 1” away from the hydrophone. I don’t think that this is the reason for the result is because I attached the horn to the speaker correctly, although I was holding the cone to the speaker and my hand may have muted the wave when I hit the initial chamber before leaving through the horn.
Track order by Number:
Track 90 No cone
Track 91 W/ horn only
Track 92 W/ metal only
Track 93 W/ both