1 frequency response curve;
2 effective frequency range;
3 unevenness.
1 frequency response curve
There are many devices for measuring the frequency response curve of the speaker. In addition to the regular anechoic chamber measuring equipment, various manufacturers and some professional quality inspection offices and some professional media use computer software to measure in the non-anechoic chamber (most of the production plants). No), the representative equipments are LMS, LAUD and DAAS in Germany, and the measurement results are basically reliable.
The frequency response curve of the speaker system is measured under the condition of 1M·1W, that is, the power of the input speaker system signal is 1W, and the measurement microphone is 1M from the reference axis of the speaker system under test. When inputting a 20-20000 Hz (or higher) pink noise signal (or other signal) of the speaker system, the sound pressure radiated from the speaker system is received by the microphone and converted into an electrical signal and recorded, which is depicted as a curve (horizontal coordinate) It is the frequency Hz, and the ordinate is the sound pressure dB), that is, the frequency response curve.
Measurement method in case of speaker system non-anechoic chamber
2 effective frequency range
The effective frequency range of the speaker system is often labeled in the product as: XXHz-XXkHz (where K is 1000), which means that the speaker system can respond effectively within this bandwidth. If the product does not indicate the fluctuation range of the frequency response curve, it should be regarded as the national standard, that is, the frequency response curve within the effective frequency range fluctuates within the range of 4 dB upper deviation and -8 dB lower deviation. The sound pressure difference from +4dB to -8dB is 12dB, the sound pressure is 3dB, the loudness difference is 1x, and the 12dB tolerance band is too wide, so many excellent speaker systems are marked with ±3dB when marking the effective bandwidth. The deviation band is only 25% of the national standard requirement.
The speaker system has a resonant frequency (discussed later). The International Electrotechnical Commission (IEC) stipulates that the resonant frequency of the speaker system is taken as the low-frequency lower limit frequency. The point is drawn along the X-axis. This line and the frequency response curve are at high frequencies. The intersection of the ends serves as the high frequency upper limit frequency of the speaker system, and the interval between the upper and lower limits is called the effective frequency range of the speaker system.
3 unevenness
The measured frequency response curve of the speaker system is an uneven curve with many peaks and valleys. The difference between the maximum sound pressure and the minimum sound pressure (ie the difference between the peaks and the valleys) in the effective frequency range is called the speaker system. Unevenness. In general, the smaller the unevenness of the speaker system, the better the frequency response curve will be flatter.
The frequency response curve is an objective measurement index of the speaker system. The author's understanding is: "The excellent frequency response curve of the excellent speaker system is excellent, but the excellent frequency response curve does not necessarily make a good sound." This theory looks a bit weird, but it makes sense.
1. The measuring instrument is mechanical. It can only judge the average sound pressure in the measurement interval, and cannot judge the quality of the sound. A speaker system is often composed of multiple speaker units. The frequency divider controls each unit to work in different frequency regions (as will be discussed later). If the sounds of the units are inconsistent, the difference is too large, and the overall sound is not good. of. The sound quality of the speaker unit vibration system is different, the sound color is very different, and controlling the consistency of the sound of the speaker system unit is also a problem, which is one of the keys to the success of the speaker system.
2. Some parts of the effective bandwidth of the speaker unit cannot be used. For example, the area where the distortion or resonance is obvious. If these areas are selected in the whole speaker system, the sound of the replay may be unbearable despite the sound pressure balance. . Experienced tuners often only use the best bandwidth portion of the speaker unit and filter out the weaker parts.
3. Because the design of the frequency division circuit is unreasonable, although the sound pressure is balanced, the curve is also good, but the phase is out of the problem (discussed later), and the sound coming out is always "weird".
4. A few years ago, the author proposed a new perspective, namely the physiological and psychological ideal frequency response curve. What does it mean? Many people who play audio know the "equal loudness curve", and many amplifiers also have equal loudness switches. Originally, the hearing of the human ear has a characteristic. When the sound pressure is not high, although the sound pressure of the equipment replay is very balanced, the sense of hearing always feels that the high frequency and the low frequency are not enough. The original human ear is most sensitive to the middle frequency band. At 1000Hz-4000Hz. If the frequency response curve of a speaker system is flat or higher in the medium-low frequency range from 1000Hz to 4000Hz, the sense of hearing will obviously feel that the medium-high frequency is too bright and too noisy and uncomfortable. Therefore, it is necessary to combine physiological characteristics with objective measurement indicators to seek an "unbalanced balance", that is, the curve is unbalanced (small amplitude) and the sense of hearing is balanced.
The bigger the people, the slower the response to high frequency; the different levels of culture, the different occupations have different taste requirements in the listening, which are the factors that experienced designers will fully consider when designing different positioning products. of.
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