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Cardioid Microphones Ated from: hp://.acrchsound.com/ACS/edarmicsi.html Piup Paerns. For ve sound, tre are two main types of microphone pickup erns: 1mni-directil 2Cardioid Omni-directil micrs "r" or pick up sound from all directis eqy. Wther you speak into the front, the side, or even the back, the microphone will pick up yr voice at the same volume. Omni-directil micrare not il for ve sound reinforcement since they can pick up the ampfisound and other ises in the rm very sand cause feedback and other prlems. A cardioid microphone blocks sound from the rear. If a chwere to hold a cardioid microphone upside-wny wld not be heard too we. On the other , if a sker is vering a prepared speech, the audience would hear less rustng of tes from in front of the speaker (auming the rear of the mike is towards the ience)The graphs low ustrate how ssitive each pickup paeris at diergles from the top; the audibty thresld curve for the cardioid microphone is an example of a cardioid curve, and this explains the reason for such a microphone’s me. The ibty at the side of the cardioid microphone is t lf the audibty at the fron Infoation about the ics of rdioid micres ars on the next two pag. How A Cardioid Microphone Works Bruce BarettEdor Adapted om hp://rosoundweb.constall/sght/rdioid/cardioidcs.shtml As if by magic, rdioicres n pick up what they are aed at, but reject sounds to the side and rr For example, talk into a cardioid ke om all sides whe stening to s tput. Your reproduice will be lest when you talk into the t of the knd softest when you talk into the rear. Buse they discrnate against ss to the sides and rrrdioids help rejt unwanted sounds such as rm scs everbera), fr lkage. Cardioids are the most lar cice for this rs How do they work? In other words, how do you make a ke direcal? Start by making an omni-diral mike. Take a ktransr, made of a diaragm and some hardware that changes diaragm motion into a signal. Then put this transdur in the end of a sealed so that incoming sound contts the diaphragm ly on s t su. Sound om the t prees on the t of the diaragm and makes a signal. Sound om the side or rbes around to the t of the ke. This sound also prees on the t of the diaragm and makes a signal. So the kress the same to sounds om all dirs. In other words, it has an omni-diral lar paern. Note that the omni mike becomes diral at high eencies. That’s buse the ke sing blocks high eencies that aive o-axis. Now sse we t some les in the can behind the diaragm. We carefuy size these les and add sc damping such as felt or foam to crte an sc ase-shift network. It’s ke an RLC circu, which delays the signal paing through The holes or “rrts” let sound into the back of the diaragm. Also, the rts delay the sound rhing the back of the diaragm. FE. Sound wave travetside and inside a cardioid mike How es this aangement ncel sound om the rear? Suppose a sound wave approhes the kom the rrIt travels to the diaragm by two paths: tside the kand inside the kthrgh the ports (See the Figure at the left). Some of the sound wave travels to the t of the diaragm, outside the ke. The sound travel time, om the rear rt loto the t, is what we ll T. Some sound also enters the rear rts and is delayed. If the delay inside the kis set the same as the delay tside the ke, sounds aive at the t and rr of the diaphragm at the same e, in phase. Sounds sh on oppose sides of the diaragm, also in phase. The diaragm t me, so sounds om the rear make a very wk signal. Rr ss ncel t. You have created a cardioid polar paer Sounds cong om the t do not ncet. Why? Frtal sound waves travel to the rear rts ring e T. Inside the ke, the ase-shift network further delays the sound by e T. The total delay is 2T. Since there is a big delay or ase shift betwn the signals at the diaragm's t and rra tal sound makes a strg signal. High eencies do not rthe rear of the diaragm buse they are fered out by the rear rt's RLC fer. The cardioid ke is diral at high eencies buse s housing blocks high eencies o-axis. How at a bidirecal ribbon ke? The ribbon is fuy en to sound on s t and rrSounds om the t and rr experience a asshift as they travel around the ribbon, so you get an output signal. But ss om the side press eay on the t and rr of the ribbon, in phase. The ribbon t me, so you get a weak output om side ss. By changing the delay of the rear rts, you get almost any paern betwbidiral and rdioisuch as supercardioid or hypercardioid (graphs of the pickup paerns for these types of micres are given at the previslted se hp://rosoundweb.constall/sght/rdioid/cardioidcs.shtml). Ef these two paerns has a rr le that is in oppose lary wh the t le.