2010年7月28日 星期三

AUDIO CROSSOVER

What is a crossover? People can hear sound frequencies from 20-20000Hz. There is no one speaker capable of producing all frequencies throughout this range. Therefore, multiple speakers must be used. Usually, it is damaging for a speaker to produce frequencies lower than what it was designed for. Also, if two speakers produce sound at the same frequencies, then the sound at those frequencies will be louder. For these reasons, some type of circuit is necessary to make sure that each speaker only produces a certain set of frequencies. That circuit is a crossover

Audio crossovers are a class of electronic filters designed specifically for use in audio applications, especially hi-fi. Individual loudspeaker drivers are incapable of covering the entire audio spectrum, from low frequencies to high frequencies, with acceptable volume and lack of distortion by themselves.

Therefore a combination of multiple loudspeakers or drivers, each catering to a different frequency band, is the design pattern for most hi-fi speaker systems. Crossovers serve the purpose of splitting the audio signal into separate frequency bands which can be handled by individual loudspeaker drivers optimized for those bands. An audio crossover may also be constructed mechanically and is commonly found in full-range speakers, portions of whose cones/dust caps/whizzer cones are decoupled at progressively higher frequencies.




 
Reference:
1.http://www.lenardaudio.com/education/06_x-over.html
2.http://en.wikipedia.org/wiki/Audio_crossover
3.http://en.wikipedia.org/wiki/Linkwitz-Riley_filter

2010年7月21日 星期三

LC RF filter circuits: Low-pass filters

LC RF filter circuits: Low-pass filters: "Low-pass LC filters are recognized by having the inductor (or inductors) in series with the signal path and the capacitors shunted across t..."

LC RF filter circuits: High-pass filters

LC RF filter circuits: High-pass filters: "A high-pass filter (HPF) attenuates signal frequencies below the -3-dB cutoff frequency and passes signal frequencies above the cutoff frequ..."

2010年7月13日 星期二

LINE OUT , HEADPHONE OUT

Line out


The signal out of line out remains at a constant level, regardless of the current setting of the volume control. You can connect recording equipment to line out and record the signal, without having to listen to it through the device's speaker, and without the loudness of the recording changing if you change the volume control setting of the device while you are recording.



The impedance is around 100 Ω, the voltage can reach 2 volts peak-to-peak with levels referenced to -10 dBV (300 mV) at 10 kΩ, and frequency response of most modern equipment is advertised as 20 Hz - 20 000 Hz (although other factors influence frequency response).[citation needed]
This impedance level is much higher than the usual 4 - 8 Ω of a speaker or 32 Ω of headphones, such that a speaker connected to line out essentially short circuits the op-amp. Even if the impedances would match, yielding the theoretical maximum power transfer of 50%, the power supplied through line out is not enough to drive a speaker.


Headphone amplifier
headphone amplifier is a small power amplifier that can be connected to a standard headphone jack or (usually) the line output of an audio source. The headphone amplifier improves the sound quality by increasing the amount of power available to move the transducer, increasing the control that the source has over just where the transducer is in space.

Many headphone amplifiers have an output impedance in the range of 20 - 50 Ohms. The 1996 IEC 61938 standard recommended an output impedance of 120 Ohms.

2010年7月7日 星期三

今天一早上班的時候

最近因為剛"又"換新工作(前一個工作只撐了3個月), 很討厭的是又要重新的熟悉環境, 一剛始來公司同期其實也有一個比我早2個禮拜來的新人(我們兩個其實也不算新人, 都是有工作經驗的), 但是另一個新人好像都跟大家都不錯, 我卻大家都不太想理我, 難道Design house大家都這麼獨立冷漠,也沒有迎新這回事..跟系統廠差好多...


Adjacent Channel Selectivity

Adjacent Channel Selectivity
This characteristic deals with stations immediately adjacent i.e.(200KHz away) that might intrude on the station you have tuned. If the tuner is equipped with switchable IF bandwidth, this position would be known as 'wide'. It offers the widest bandwidth through which the signal must pass through to be decoded. A typical level is 8dB. (higher number value = better).



Alternate Channel Selectivity
 This characteristic deals with stations adjacent (400KHz away) that might intrude on the station you have tuned. If the tuner is equipped with a switchable IF bandwidth, this position would be known as 'wide'. A typical level is about 50dB. (higher number value = better).





 

2010年7月1日 星期四

OLED

Organic light-emitting diode (OLED)
compared to the incumbent liquid-crystal display (LCD) technology.

  • faster response time
  • wider viewing angles
  • lower power consumption
  • brighter or higher-contrast images
  • OLEDs are an emissive technology and require no backlight