A microphone that responds to the difference in acoustic pressure between the front and rear of the diaphragm. A bi-directional microphone.
"Dr. Coban, Thank you so much for transferring my high school choir album to a CD. It has been many years since I was able to listen to this record, so now I can enjoy it again. What great memories! The quality is good, the customer service you provided was superb, and the communication was the best; we are very happy with the final product. ..."