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Home / News > Design and Implementation of Feedback Active Noise Canceling Headphones


Design and Implementation of Feedback Active Noise Canceling Headphones

Feed-forward headphones are generally easier to develop because design engineers often do not have to deal with stability issues. However, one of the major drawbacks of this topology is wind noise because its noise-canceling microphone is exposed directly to the environment. One way to overcome this shortcoming is to use feedback active noise reduction technology. This article will describe the steps required to design an feedback-powered active noise-canceling headset using the ams AS3435. Summary

As with the design feedforward headphones, feedback headphones also require specific equipment, the most important of which is the ability to measure the frequency response and phase response of the audio measurement system.

Audio equipment suitable for these measurements includes Audio Precision, Bruel & Kjaer and Soundcheck. The human ear simulator with different types of artificial ear can be used to simulate the acoustic response of the human ear. It is recommended to use Head Acoustics, Bruel & Kjaer or GRAS products.

The IEC711 coupler, which is commonly used in feed-in ear-type products, is not required in this application. In the feedback ear system, the placement of the microphone is subject to space constraints. Thus, 99% of the feedback headphones are generally on-ear or over-ear designs. Of course, the current market or still feedback into the ear design. In addition to simulating the human ear and measuring the gain and phase of the audio measurement equipment, the rest of the equipment used for feedforward design has included all the development of feedback active noise reduction headset needs. In order to measure the active noise reduction performance of the headset, a two-way speaker system (preferably a bidirectional coaxial loudspeaker) is also required to allow the active noise-canceling headphones to be exposed to the noise field for testing.

The last element required to design a feedback active noise reduction headset is the AS3435 evaluation board (EVB), which includes all the necessary connectors and preamplifiers to meet the needs of headphone acoustics.

How beats by dre sale to measure the acoustic characteristics of feedback headphones?

In addition to mechanical components such as cushions and loudspeakers, each active noise-canceling headset also requires an electro-acoustic component such as beats solo a loudspeaker and an active noise reduction microphone. These components are assembled together to determine the frequency and phase response of the headset. Different headphones will cheap beats by dre have different frequency and phase response, so the need for correct characteristics of the measurement to achieve the initiative to reduce the performance of each headset to achieve the maximum bandwidth.

Compared to the feedforward system, the active noise reduction characteristic of the feedback system is very simple and it is only necessary to measure the open loop between the headphone speaker and the active noise reduction microphone.

The measuring device includes the Audio DAQ (data acquisition) system, the artificial head and the active noise reduction headset shown in Fig. The output of the Data Acquisition system is connected to the input of the AS3435 evaluation board. The loudspeaker of the active noise reduction headset is connected to the headphone amplifier output of the AS3435 evaluation board and the active noise reduction microphone is connected to the microphone input of the evaluation board. The required beats headphones bias voltage for the design is provided by the evaluation board, so the microphone connection does not require additional external components.

The last important and necessary connection is the analog audio input from the QMICx pin (microphone preamplifier output) of the EV kit to the DAQ system. The AS3435 EV kit must be properly configured before the measurement starts. The screenshots of the evaluation board software are shown in Figure 2. It is important to set the microphone preamplifier gain to 0dB so that it can match the ams filter calculation template.

In addition, setting the headphone multi-input to the "unconnected" position is also necessary to help prevent the microphone signal from being fed back to the speaker. Of course, this is required during active noise reduction operations, not for open loop circuit characteristics.

When the evaluation board is properly configured, the DAQ system generates a sine sweep signal from 20kHz to 20Hz. The DAQ system then measures the gain and phase response of the microphone preamplifier output. This measurement includes all the information needed for all feedback filter designs.