AKARSH SHEKHAR
Why Should You Have a Cardioid Subwoofer ?
Cardioid is a term that is associated with microphones . However , here we are going to talk about cardioid subwoofers . Both speakers and microphones are transducers ( devices that convert between electricity and air pressure ) that are found at the ends of the audio chain . They are actually doing the same in opposite directions . So while we ' re talking cardioid when we ' re talking about mic pickup patterns and showing that nice heart-shaped diagram , we can apply the same idea to speakers and talk about dispersion patterns .
Are subwoofers omnidirectional ? Generally , all speakers tend to be directional . So the term cardioid can ’ t be used for them . All subwoofers are generally omnidirectional due to the laws of physics . To make an audio frequency directional , we need to have a box that is close to the length of the frequency we are trying to hit . Given that 100Hz is roughly 11 feet long , your sub box is unlikely to be that large . This means that a subwoofer is emitting approximately the same level in all directions .
The cons of omni directionality This omni directionality can cause us some headaches . When setting up a stage , we generally take care to keep the top boxes in front of the mics so we don ' t have to fight feedback , and we usually place the subwoofers just below the top boxes . This keeps them aligned in time and in phase with our top boxes .
Unfortunately , while our tops are good at focusing their energy forward , subs are firing as much energy directly into those open mics as they are into the crowd .
If you have more than one sub on stage because you want more bass , they will also tend to interfere with each other . This can happen as a result of time differences between the direct low frequencies or reflections that are more common because the low frequency is coming out in all directions . Also , that energy builds up and rolls across the stage . It can make a hollow stage ring , rattle drum hardware , and make life generally miserable .
What ’ s the solution ? Wouldn ' t it be great if we could get the power from a subwoofer to run primarily like our full-range speakers do ? It would solve feedback and hoarding problems and make the sub more efficient as you are driving more of your energy towards the audience . This is what led to the birth of cardioid subwoofers .'
The concept is not new . It was actually proposed in a paper in the late 1950s , and enterprising sound engineers have been assembling subwoofer arrays for a couple of decades to make low-frequency material more directional . They combine several different subwoofers and adjust the timing by changing the position forwards and backwards or using an electronic delay . By carefully calculating the position , they can make the bass more directional through a combination of sub-location and phase . You can grab a couple of subwoofers and move them around the stage yourself to play with the idea . If you stacked them on top of each other with one facing the wrong side , you ' d be halfway there .
The basic idea is that you have two sources creating the same low frequency material , with the polarity reversed in one of the sources . Then change the sync so that at the front of this subarray the frequencies are in phase and combine to boost the output by 6dB . The signal coming out of the rear of the subwoofer is calculated to be out of phase and tends to cancel out .
Cardioid subwoofers in a single , reasonably sized package also allow you to get the benefits of keeping all that bass off stage without having to move multiple heavy boxes each time .
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