The reason for the extra removable cap on the bottom is to increasee the signal. That's where the sending antenna is. The metal blocks a good bit of signal.
Great and very helpful review. Which would you say is better in terms of sound quality between the PTU-2U and the PTU-7000 and how would you describe the differences? Personally for you, which would you choose considering the price difference?
I personally like the PTU-2U better. Remember, I'm a rapper. The PTU-2U seems to cut through a little better, has a better feel when holding it, is more durable, and the natural EQ to it seems to work better for me. That being said, if you're using them as speaking mics I don't think it really makes a difference. I would probably opt for the PTU-7000 for a speaking mic, but when it comes to performances I like the PTU-2U better.