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At the resonance frequency of the subwoofer system, the impedance will either peak at its highest level (sealed enclosures), or it is going to dip to its lowest level (ported and band pass enclosures). If you own a hatchback, for example, you will have to calculate the cubic feet of the hatch area, keeping in mind that you'll still need to be able to get to your spare tire. As I have already shown you about wiring your speakers to your subwoofer box, this is the easy part. Try listening with the boost on and off to determine what you like best.
subwoofer ohm
In practice we would probably make the enclosure half this size, or similar to the size of the sealed enclosure. If we connect (2) four ohm speakers (R1 and R2) in series to an amplifier the total resistance will be:The fact is that installing car stereo equipment is not much fun. When you increase the level of the low and high frequencies at lower volume levels, you will see that the volume goes up the level of boost at these frequencies is reduced. Position the brackets and mark the positions to pre-drill mounting holes.
When you are trying to build a subwoofer box of your own so that your car is the best sound quality that you could possibly find, it helps to really understand the basics of car audio. That is what this section will talk about.
Webster's dictionary defines sound as:
The perceived object occasioned by the impulse or vibration of a material substance affecting the ear; a sensation or perception of the mind received through the ear, and produced by the impulse or vibration of the air or other medium with which the ear is in contact; the effect of an impression made on the organs of hearing by an impulse or vibration of the air caused by a collision of bodies, or by other means; noise; report; as, the sound of a drum; the sound of the human voice; a horrid sound; a charming sound; a sharp, high, or shrill sound.
Thats funny; considering that sound is a lot easier to explain. Its noise, or at the least something we sense with our ears. Clearly sound is basically nothing more that the vibration of the air that is based on something moving. As this book deals with car audio we will be talking about the movement being our speakers.
When you are using speakers to conduct your sound actually causes a vibration in the air that our ear receives and we hear music. Below is a diagram of what sound looks like as a wave:
A sound wave like the one above goes through a cycle of 360 degrees. As the speaker moves forward it goes 0 degrees through one quarter of its cycle to 90 degrees. When this starts to go back to rest it then travels another 90 degrees to the 180 degree mark before it begins moving completely rearward to 270 degrees.
As it moves back to the rest position it then travels the final 90 degrees to the 360 degree mark. Then the cycle will start all over again and we hear the result as music. As the speaker moves up and down it travels throughout one complete cycle which is about 360 degrees. These cycles are measured in Hertz (Hz) with one Hertz meaning one cycle.
The lower the number of Hz the lower the sound is. A human can hear the sounds between 20 Hz and 20,000 Hz (also known as 20 kHz). We do not hear all of the sounds in the same way though. Our ears are less sensitive to sounds that are further down the scale. This was discovered through research done by Fletcher and Munson and the drawing below shows the "Fletcher-Munson" curve.
Take a look at how the curve goes up at both ends of the scale. You should also notice how the curve is higher when the volume is set lower. This is what the loudness circuit on a head unit tries to do.
When you increase the level of the low and high frequencies at lower volume levels, you will see that the volume goes up the level of boost at these frequencies is reduced. However, some loudness circuits do nothing more than boost the low and high frequencies by a constant amount.
If you've seen a car that has an in-dash equalizer the chances are very good that the vertical sliders were arranged in the same way as the Fletcher-Munson curve. This is sometimes called "making your EQ smile".
The information and diagrams above has been adapted from information found at
http://www.caraudiohelp.com/car_audio_basics/car_audio_basics.htm.
I hope that this has let you understand the basics of sound enough for you to really see how it travels. This little bit of information has been put together so that you can build a better subwoofer.