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Passive filters design

2014-11-14 03:41  
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In high-fidelity audio systems is necessary to use multiple speakers for clear sound . Because that one speaker can’t play all frequency of the audio band it’s is necessary to use multiple speakers and some audio filters . Filters are used to select or pass desired signals and reject or block undesired signals. In our case , an audio filter will let to pass some of audio frequencies ( from the audio band ) or block some audio frequencies ( from the audio band )

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The audio band is divided into three main parts:
- low frequency area
- average frequency zone
- high frequencies zone

Why we need a “specialized “ speaker for each part of the audio band ? because the non specialized is not suitable for all frequencies of the audio band (the speaker can not play all frequencies of the audio band ) . These specialized speakers that reproduce each of them a part of the audio spectrum are :
-speakers for low frequencies or woofer (or subwoofer for very low frequencies )
-speakers for medium frequencies or midrange
-speakers for high frequency or tweeter
For dividing the frequency band into three parts is necessary to use filters frequency dividers (cross-over).
Often we was bothered by quality of the sound played by speakers (audio speakers).
To remove speakers distortions (acoustic enclosures) need a separate audio band by fitting on each speaker an audio filter .
In these page we will present how to design the passive audio filters (not active filters) .

By how filter does its job, filters can be broken down into four basic types :

a) low-pass filter

b) high-pass filter

c) band-pass filter

d) band-stop filter

Low-pass filters pass all low frequencies up to a certain frequency; from that frequency and above significant attenuation begins to occur.

High-pass filters pass all high frequencies down to certain frequency; from that frequency and below significant attenuation begins to occur.

Band-pass filters pass a band or range of frequencies only; outside this band of frequencies significant attenuation occurs.

Band-stop filters stop or attenuate a band or range of frequencies only; outside this band of frequencies all frequencies are passed with minimal attenuation ( band-stop filters are sometimes referred to as a notch filters).

To design passive audio filters  is necessary to know the following formula:

Capacitive reactance
capacitive reactance formula

where
Xc value needed for capacity
π = 3.14

FC=filter frequency

R-speaker impedance


Inductive reaction equation
reactanta inductiva
were :
XL= needed  inductance value
π =3.14
Fc= filter frequency
R-speaker impedance

Calculation and design passive audio filters Crossovers for speakers , grade I , II , III  and IV for speakers

Two way audio filter first order

Two way audio filter first order circuit Two way audio filter first order formula

Three way first order audio filter

Three way first order audio filter Three way first order audio filter formula

Two way audio filter second order

Two way audio filter second order circuit Two way audio filter second order formula

Three way audio filter second order

Three way audio filter second order circuit Three way audio filter second order formula

Two way audio filter third order

Two way audio filter third order circuit Two way audio filter third order formula

Three way audio filter third order

Three way audio filter third order circuit Three way audio filter third order formula

Two way audio filter fourth order

Two way audio filter fourth order circuit Two way audio filter fourth order formula

Three way audio filter fourth order

Three way audio filter (grade four ) circuit Three way audio filter fourth order formula

Notation

RH-tweeter impedance
RM-midrange impedanta
RL-woofer impedance
FH- tweeter cut frequency
FL- woofer cut frequency
FM-midrage(FHxFL) cut frequency
F-filter cut frequency