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Attackpoint AR - performance and training tools for adventure athletes

Discussion: bluetooth ??

in: jtorranc; jtorranc > 2009-09-16

Sep 17, 2009 9:45 AM # 
Are your headphones bluetooth?? I have never swam with headphones but would like to find a reliable set that I could use with my uber-phone (which plays MP3s and Audible audiobooks). I could keep it dry at midpool and stay in bluetooth range as I did laps, I think.
Any ideas ??
Sep 17, 2009 2:23 PM # 
I often thought about bluetooth headphones--which seem like they would be convenient. But, there is that issue of requiring power... so are likely bulkier.
Sep 17, 2009 3:40 PM # 
I have excellent Motorola bluetooth stereo headphones. The wraparound design would be perfect for swimming if they were waterproof.
Sep 17, 2009 4:21 PM # 
Given the frequency, my guess is the signal won't travel very far underwater. Maybe a foot or two - probably less? Bluetooth and wireless networks use the same unlicensed band as microwave ovens, and those work because of stong absorption by water at ~2 GHz.
Sep 17, 2009 4:54 PM # 
There's a nice discussion of the problem here. Absorption by fresh water at 2.3 GHz is 194 dB/m! (using their formula). That's 2dB/cm. 3dB is a factor of 2 signal strength loss. After about 5cm your signal is 1/10th its original strength. And there is interface loss at the surface, plus the change in wavelength in water which will make your for-air designed receiving antenna less efficient. Your best bet may be to shave and tape on some wires.
Sep 17, 2009 5:50 PM # 
Thanks for the technical explanation. I will put my headphones in a waterproof baggie, then on my head, then dunk, then report my findings here in Jon's hijacked log.
Sep 18, 2009 2:22 PM # 
For DWR, there might be no issue other than power consumption but it would be a pain for swimming to try to keep the crucial bits out of the water or barely submerged. My current setup is very much wired. Which is a pain since the wires get tangled up while not in use but it's an endurable pain.
Sep 23, 2009 1:05 AM # 
I ran my experiment today...
I tested the distance through air by placing the transmitter (phone playing music) at one end of the pool and the receiver (headphones in baggie) on my head was able to walk the full 25m to the other side with no apparent signal interruption. Then I returned to the near side and slowly dunked my head so the receiver moved underwater. The music cut out and the signal dropped as soon as it was an inch or two underwater.
Conclusion: "Bluetooth waves" experience the same underwater signal degradation as radio waves. ;)

This discussion thread is closed.