等响曲线 五

等响曲线 五 等响曲线五 经过大量实验测得纯音的等响度曲线如图等响曲线-听阈曲线所示，它表达了典型听者认为响度相同的纯音的声压级同频率的关系，图中纵坐标是声压级，横坐标是频率，二者是声音的客观物理量。 因为频率不同时，人耳的主观感觉不同，所以对应每个频率都有各自的听阈声压级和痛阈声压级，把它们联结起来就能得到听阈线。两线之间按响度不同又分为十三个响度级、单位为方。 听阈线为零方响度线，痛阈线为120方响度线。凡在同一条曲线上的各点，虽然它们代表着不同频率和声压级，但其响度是相同的，故称等响曲线。 每条等响曲线所代表的响度级(方)的大小，由该曲线在1000Hz时的声压级的分贝值而定。例如，噪声听起来与频 1 率1000Hz的声压级为85dB的基准音一样响，则该噪声的响度级就是85方。 等响曲线 对於纯音来说，等响曲线表明了响度与频率的关系。人耳对不同频率的声音闻阈和痛阈不一样，灵敏度也不一样.例如，200Hz的30dB的声音和1kHz的10dB的声音在人耳听起来具有相同的响度，这就是所谓的―等响‖不同的频率，具有不同的强度，但它们确有同等的响度级，单位是方(phon)，如40方或60方等响曲线。在低强度时，等响线的图形类似於听阈曲线。因此，如果声音的强度相等，那麼中频声听起来会比低频或高频声更响一些。随著响度级或声压级的增加，等响曲线渐趋於平直。也就是说，不同频率的响度级的增长速度是不同的，低频声的响度级随声音强度的增长比中频声要快，这表明在高声强时，人耳对低频声变得比较敏感了。一个由线谱或连续谱组成的复合声，一般来讲，它所包括的频率范围越宽，其声音也越响，尽管这时所包含的总声能保持不变。研究证明，响度与频宽的这种关系，只有当频宽超过某一最小值即临界带宽之后才会产生。而在其临界带宽之内，响度基本上不依赖於频宽，这种效应通常叫做响度综合，声音的响度也与声音持续作用的时间有关。在一定范围内(大约15,150毫秒)，持续时间越长声音也越响。超过这个范围，这种关系便不存在了。 2 实验表明，闻阈和痛阈是随声压、频率变化的。闻阈和痛阈随频率变化的等响度曲线(弗莱彻—芒森曲线)之间的区域就是人耳的听觉范围。通常认为，对于1kHz纯音，0dB—20dB为宁静声， 30dB--40dB为微弱声，50dB—70dB为正常声，80dB—100dB为响音声，110dB—130dB为极响声。而对于1kHz以外的可听声，在同一级等响度曲线上有无数个等效的声压—频率值，例如，200Hz的30dB的声音和1kHz的10dB的声音在人耳听起来具有相同的响度，这就是所谓的―等响‖。 等响曲线 把响度水 平相同的各频率的纯音的声压级连成的曲线。在该曲线圈上，横坐标为各纯音的频率，纵坐标为达到各响度水平所需的声压级(分贝)，每一条曲线代表一个响度水平(如标有40song的曲线上各点所代表的声音响度是相同的，它们的响度水平都是40song。() 人类的听音特性曲线，是反映人们对声音振幅范围心理因素的曲线，每条曲线上对应于不 3 同频率的声压级是不相同的，但人耳感觉到的响应却是一样，因此称为等响曲线，每条曲线上注有 一个数字，为响度单位，由等响曲线族可以得知，当音量较小时，人耳对高低音感觉不足而音量较 大时，高低音感觉充分，人对1000HZ-4000HZ之间声音最为敏感。北京市经贸高级技术学校教师田胜平 在18Hz—18KJz可闻声频率范围内，听者感受声刺激的响度，并不与声振动的振幅一致。响度与声音的频率有关，在低声强级时，人耳对中频段1-3KHz的声音最为灵敏，对高、低频段的声音，特别是低频声变得迟钝。另外，对高声强级的声音信号，听者感觉其响度与频率的关系不太大，相同振幅的各频率声音，听者感觉其响度与频率的关系不太大，相同振幅的各频率声音，听起来感觉响度差不多;但对低志强级信号的响应，则感觉与频率关系甚大，对于振幅相同的信号，人耳感到高、低频的声音比中频声音小得多，而且这种现象随着声音振幅的减小更为明显。 这种现象称为弗莱彻—芒森效应。把许多听觉正常的人的这种效应的特征进行平均，所得到的就是著名的弗莱彻-芒森等响度曲线，该曲线反映了人耳对声音强度的心理和生理因素的主观感觉曲线。 等响度曲线，即把不同频率和不同强度的纯音和1kHz的 4 纯音做等响度的配对。把1kHz的某纯音的强度值作为在其等响度曲线上别的频率的纯音的响度级。 获得等响曲线的条件是:听者要面对声源入射方向;当听者不在 时，声场为平面自由行波;声场的声压级应在听者不在场时测得。 Fletcher-Munson 曲线。Fletcher 和Munson是20世纪30年代的研究学者，他们首次准确的测量出并且公布了一系列表现人耳对频率响度敏感性的曲线。他们最终证明人的听力是极其依赖于响度的。该曲线表明人耳对声音最敏感的区域是在3 kHz到4 kHz之间，这意味着3-4 kHz以上或以下的声音必须经过放大才能够被人耳听到。因此， Fletcher-Munson曲线又被认为是声音响度等高线。这一系列曲线包括从―刚刚被听到‖的声音(0 dB SPL)一直到对人耳有害的声音(130 dB SPL)，通常情况下他们都被加上了10 dB的响度增量。 等响曲线是响度水平相同的各频率的纯音的声压级连成的曲线。在 5 该曲线圈上，横坐标为各纯音的频率，纵坐标为达到各响 度水平所需的声压级(分贝)，每一条曲线代表一个响度水 平(如标有40分贝的曲线上各点所代表的声音响度是相同 的，它们的响度水平都是40分贝(dB)。 Equal-loudness contour From Wikipedia, the free encyclopedia (Redirected from Equal-loudness contours) An equal-loudness contour is a measure of sound pressure (dB SPL), over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon, and is arrived at by reference to equal-loudness contours. By definition two sine waves, of differing frequencies, are said to have equal-loudness level measured in phons if they appear equally loud to the average young person without significant hearing impairment. Equal-loudness contours are often referred to as &Fletcher-Munson&' curves, after the earliest researchers, but those studies have been superseded and incorporated into newer standards. The definitive curves are 6 those defined in the international standard ISO 226:2003 which are based on a review of several modern determinations made in various countries. Contents [hide] 1 Experimental determination 2 Recent revision aimed at more precise determination - ISO 226:2003 3 Side versus frontal presentation 4 Headphones versus loudspeaker testing 5 Relevance to sound level measurement and noise measurement 6 See also 7 Notes 8 References 9 External links [edit]Experimental determination The human auditory system is sensitive to frequencies from about 20 Hz to a maximum of around 20,000 Hz, although the upper hearing limit decreases with age. Within this range, the human ear is most sensitive between 1 and 5 kHz, largely due to the resonance of the ear canal and the transfer function of the ossicles of the middle ear. 7 Equal-loudness contours were first measured by Fletcher and Munson using headphones (1933). In their study, listeners were presented with pure tones at various frequencies and over 10 dB increments in stimulus intensity. For each frequency and intensity, the listener was also presented with a reference tone at 1000 Hz. The reference tone was adjusted until it was perceived to be of the same loudness as the test tone. Loudness, being a psychological quantity, is difficult to measure, so Fletcher and Munson averaged their results over many test subjects to derive reasonable averages. The lowest equal-loudness contour represents the quietest audible tone and is also known as the absolute threshold of hearing. The highest contour is the threshold of pain. A second determination was carried out by Churcher and King in 1937, but these two investigations showed considerable discrepancies over parts of the auditory diagram.[1] A new experimental determination was made by Robinson and Dadson (1956) which was believed to be more accurate, and this be 8 came the basis for a standard (ISO 226) which was considered definitive until 2003, when the standard was revised on the basis of recent assessments by research groups worldwide. [edit]Recent revision aimed at more precise determination - ISO 226:2003 Because of perceived discrepancies between early and more recent determinations, the International Organization for Standardization (ISO) recently revised its standard curves as defined in ISO 226, in response to the recommendations of a study coordinated by the Research Institute of Electrical Communication, Tohoku University, Japan. The study produced new curves by combining the results of several studies, by researchers in Japan, Germany, Denmark, UK, and USA. (Japan was the greatest contributor with about 40% of the data.) This has resulted in the recent acceptance of a new set of curves standardized as ISO 226:2003. The report comments on the surprisingly large differences, and the fact that the original Fletcher-Munson contours are in better agreement with 9 recent results than the Robinson-Dadson, which appear to differ by as much as 10–15 dB especially in the low-frequency region, for reasons that are not explained.[2] [edit]Side versus frontal presentation Equal-loudness curves derived using headphones are valid only for the special case of what is called 'side-presentation', which is not how we normally hear. Real-life sounds arrive as planar wavefronts, if from a reasonably distant source. If the source of sound is directly in front of the listener, then both ears receive equal intensity, but at frequencies above about 1 kHz the sound that enters the ear canal is partially reduced by the masking effect of the head, and also highly dependent on reflection off the pinna (outer ear). Off-centre sounds result in increased head masking at one ear, and subtle changes in the effect of the pinna, especially at the other ear. This combined effect of head-masking and pinna reflection is quantified in as set of curves in three-dimensional space referred to as head-related transfer functions (HRTFs). Frontal presentation is now regarded as preferable when deriving equal-loudness contours, and the latest ISO 10 standard is specifically based on frontal and central presentation. The Robinson-Dadson determination used loudspeakers, and for a long time the difference from the Fletcher-Munson curves was explained partly on the basis that the latter used headphones. However, the ISO report actually lists the latter as using &compensatedheadphones, though how this was achieved is not made clear. [edit]Headphones versus loudspeaker testing Good headphones, well sealed to the ear, can provide a very flat low-frequency pressure response measured at the ear canal, with low distortion even at high intensities, and at low frequencies the ear is purely pressure sensitive and the cavity formed between headphones and ear is too small to introduce any modifying resonances. Headphone testing is therefore a good way to derive equal-loudness contours below about 500 Hz, although reservations have been expressed about the validity of headphone measurements when determining the 11 actual threshold of hearing, based on observation that closing off the ear canal produces increased sensitivity to the sound of blood flow within the ear which appears to be cleverly cancelled by the brain in normal listening conditions[citation needed]. It is at high frequencies that headphone measurement gets dubious, and the various resonances of pinnae (outer ear) and ear canal are severely affected by proximity to the headphone cavity. With speakers, exactly the opposite is true, a flat low-frequency response being very hard to obtain except in free space high above ground or in a very large and anechoic chamber free from reflections down to 20 Hz. Until recently it was not possible to achieve high levels at frequencies down to 20 Hz without high levels of harmonic distortion, and even today the best speakers are likely to generate around 1 to 3% of total harmonic distortion, corresponding to 30 to 40 dB below fundamental. This is not really good enough, given the steep rise in loudness (of 6 to 10 dB per octave) with frequency revealed by the equal-loudness curves below about 50 Hz, and a good experimenter must ensure that trial subjects really are hearing the fundamental and not harmonics, 12 especially the third harmonic which will be especially pronounced as speaker cones become limited in travel as their suspensions reach the limit of compliance. A possible way around the problem is to use acoustic filtering, such as by resonant cavity, in the speaker setup. A flat free-field high-frequency response up to 20 kHz, on the other hand, is comparatively easy to achieve with modern speakers on-axis. These facts have to be borne in mind when comparing results of various attempts to measure equal-loudness contours. [edit]Relevance to sound level measurement and noise measurement Although the A-weighting curve, in widespread use for noise measurement, is said to have been based on the 40-phon Fletcher–Munson curve, research in the 1960s demonstrated that determinations of equal-loudness made using pure tones are not directly relevant to our perception of noise.[3] This is because the cochlea in our inner ear analyzes sounds in terms of spectral content, each &hair-cellresponding to a narrow band of frequencies known as a critical band. The 13 high-frequency bands are wider in absolute terms than the low frequency bands, and therefore &collectproportionately more power from a noise source. However, when more than one critical band is stimulated, the outputs of the various bands are summed by the brain to produce an impression of loudness. For these reasons Equal-loudness curves derived using noise bands show an upwards tilt above 1 kHz and a downward tilt below 1 kHz when compared to the curves derived using pure tones. Various weighting curves were derived in the 1960s, in particular as part of the DIN 4550 standard for audio quality measurement, which differed from the A-weighting curve, showing more of a peak around 6 kHz, and these were found to give a more meaningful subjective measure of noise on audio equipment; especially on the newly invented compact cassette tape recorders with Dolby noise reduction which were characterised by a noise spectrum dominated by high frequencies. The BBC research department conducted listening trials in an attempt to find the best weighting curve and rectifier combination for use when measuring noise in broadcast equipment, examining 14 the various new weighting curves in the context of noise rather than tones, confirming that they were much more valid than A-weighting when attempting to measure the subjective loudness of noise. This work also investigated the response of human hearing to tone-bursts, clicks, pink noise and a variety of other sounds which, because of their brief impulsive nature, do not give the ear and brain sufficient time to respond. The results were reported in BBC Research Report EL-17 1968/8 entitled The Assessment of Noise in Audio Frequency Circuits. The ITU-R 468 noise weighting curve, originally proposed in CCIR recommendation 468, but later adopted by numerous standards bodies (IEC, BSI, JIS, ITU) was based on the BBC Research, and incorporates a special Quasi-peak rectifier to account for our reduced sensitivity to short bursts and clicks.[4] It is widely used by Broadcasters and audio professionals when measuring noise on broadcast paths and audio equipment, enabling subjectively valid comparisons of different equipment types to be made even though they have different noise spectra and characteristics. [edit]See also 15 Audiometry Audiogram CCIR (ITU) 468 Noise Weighting dB(A) Kazuho Ono, and Setsu Komiyama, &A measurement of equal-loudness level contours for tone burst&, Acoustical Science and Technology, Vol. 22 (2001) , No. 1 pp.35–39. 百度搜索―就爱阅读‖,专业资料,生活学习,尽在就爱阅读网 92to.com,您的在线图书馆 16