# Influence of the Quality of Consumer Headphones in the Perception of Spatial Audio
## 7 Conclusions  
This study outlines the influence of different quality parameters in headphones in the context of spatial sound reproduction. Four different perceptual tests have been done to analyze: (1) the effects of the sensitivity disparity between the transducers; (2) the influence of the frequency response over the perception of quality and the spatial impression; (3) the effects of non-linear distortion; and (4) the influence of the frequency response over azimuth localization. The following main conclusions can be drawn:  
1. The sensitivity disparities between left and right transducers affect the localization of sound sources, starting from level differences of 1 dB. 2. The quality and uniformity of the frequency response have an important influence in the _spatial impression_. 3. Additionally, the _spatial impression_ has a high correlation with the subjective _perceived quality_. 4. The binaural recordings do not obtain significant better results for the parameter _spatial impression_ compared to two-channel stereo mixes. Figure 10: Deviation in degrees of the answers for every reproduced angle of sound. The reference, headphones under testing and anchor are represented. The distortion introduced by consumer level low quality headphones does not affect the perception of the spatial sound image. 6. It has been ratified that much front-back confusion is produced, both for high and low quality headphones. 7. We found that irregularities of the frequency response in the band of 100 to 1600 Hz seem to especially affect the front-back discrimination. 8. We also found that a poor response in the band of 4 to 7 kHz degrades the accuracy in lateral position localization. All of these conclusions have been supported with statistical and ANOVA analysis. Some other interesting comments and clarifications about these conclusions can be added:  
In addition to Conclusion 1, the angles chosen in the disparity test are a determining factor, whereby the more lateralized the angle, the larger the deviation. An increased number of angular positions may be of interest in later studies. In relation to Conclusions 2 and 3, it is worth remarking that the mono anchor signal (ANC2) has obtained equal or even better results for _spatial impression_ than some headphones ((e)-LCmul, (f)-AirL) and the stereo LPF anchor (ANC1). This fact seems to be in relation to a deficient high frequency reproduction and the general listening sensation, as evidenced by the high correlation statistics obtained with the parameter _perceived quality_. In relation to Conclusion 5, other works, such as [28], have not found significant perception of the distortion. However, this earlier study used high quality headphones, while ours does so also with low quality consumer headphones, and we have also analyzed the influence on spatial reproduction. Finally, taking into account these three characteristics, _perceived quality_, _spatial impression_ and accuracy in _azimuth localization_, we have concluded that the first two are highly correlated. Surprisingly, and contrary to how it might seem _a priori_, there is virtually no correlation between spatial impression and accuracy in localization, because the strong influence that the subjective perceived quality has over the spatial image perception. An illustrating example can be seen with the (f)-LCmul headphone. It would be interesting to deepen this relationship in future work. Based on the results of this study, some general guidelines for the design of headphones suitable for spatial sound reproduction can be suggested. A sensitivity difference between left-right transducers less than 1 dB should be assured in the manufacturing process to avoid azimuth localization errors. A flat frequency response between 100 to 1600 Hz is desirable to reduce front-back confusion. Finally, a good frequency response in the band 4 to 7 kHz would guarantee a good accuracy in the localization of lateral sources.