# Development and Evaluation of Light-Weight Active Noise Cancellation Earphones
## 3 Real-Time Experiments
### Real-Time Noise Reductions Results
Since the in-ear ANC earphone's error microphone is inside the ear canal and its loudspeaker has good frequency response as shown in Figure 5 (red lines), it can reduce broadband noise efficiently. Figure 6: Reduction of tonal noise: clip (green), earbud (blue), and in-ear (red); the commercial type A (brown), type B (black), and type C (pink) earphones. Figure 8a shows the measured noise at the KEMAR's ear for the commercial type A headphone. It shows that the type A headphone cannot passively attenuate the MRI noise by its ear caps. After ANC is turned on, there is 10 dB noise reduction from 100 Hz to 500 Hz. However, there is no noise reduction from 600 Hz to 3200 Hz. The commercial type A headphone even amplifies 5 dB of MRI noise for high frequency from 1800 Hz to 2900 Hz. Figure 8b shows the measured noise at the KEMAR's ear for the commercial type B headphone. It shows that the commercial type B headphone can passively attenuate  
Figure 7: Spectra of noise measured at the [PERSON]’s ear without earphone on it (black), with earphone but without ANC (blue), and after ANC is turned on (red). (**a**) Clip earphone; (**b**) earbud earphone; (**c**) in-ear earphone. the MRI noise about 10 dB to 20 dB passively by its earmuffs from 300 Hz to 3200 Hz. After ANC is turned on, there is 15 dB noise reduction from 100 Hz to 900 Hz. However, the commercial type B headphone amplifies 2 dB to 5 dB of MRI noise from 900 Hz to 3200 Hz. Figure 8c shows the measured noise at the [PERSON]'s ear for the commercial type C in-ear earphone. It shows the type C earphone can passively attenuate about 15 dB to 25 dB by its ear caps from 500 Hz to 3200 Hz. After ANC is turned on, there is about 5 dB to 10 dB noise reduction from 100 Hz to 1000 Hz, and 2 dB to 5 dB noise reduction from 1100 Hz to 3000 Hz. Figure 8: Spectra of noise measured at the [PERSON]’s ear without earphone on it (black), with earphone but without ANC (blue), and after ANC is turned on (red). (**a**) Type A; (**b**) type B; (**c**) type C.  
Comparing the similar ANC clip earphone (Figure 7a) with the type A headphone (Figure 8a), we found that neither can passively attenuate high frequency noise. However, when ANC is turned on, there is no noise reduction of the type A headphone beyond 500 Hz, but there is 20 dB noise reduction of the developed ANC clip earphone. Therefore, the developed ANC clip earphone has better performance than the type A headphone. Besides, comparing the earbud ANC earphone (Figure 7b) with the commercial type B headphone (Figure 8b), both the earphones speakers are outside the ear canal. However, after ANC is turned on, the commercial type B headphone amplifies the noise from 900 Hz to 3200 Hz, but the developed earphone still performs well to cancel noise. Comparing the similar style of the developed in-ear ANC earphone (Figure 7c) with the commercial type C earphone (Figure 8c), both are in-ear earphones and can passively attenuate high frequency MRI noise. However, the developed in-ear ANC earphone has better average noise reduction than the commercial type C earphone. In summary, the ANC earphones developed by this paper are more efficient for noise reduction, and more portable and comfortable to wear than the ANC headphones, especially for outdoor activities. Besides, the developed light-weight ANC earphones only integrate error microphone and ANC filter, which is the same setup as commercial headsets. Thus, the price of the developed earphones in this paper should be acceptable as a consumer electronic device. The stability of the adaptive feedback ANC system can be assured by properly choosing the step size [17].