How to read the chart:
When you look at your chart you will see a vertical line going up and down. This line represents the level of decibels your woofer is producing. Now look at the horizontal line running from left to right. This line is the frequency measurement.
Starting at the bottom left hand corner represents zero volume at zero frequencies. As the line traverses across the grid each point represents the performance of your sub box system. In our graph it reads that all things being equal (volume on amp and head unit locked) a note being played at 50 Hz will be 8 dB softer than a note being played at 100 Hz.
Definition of the 3 Most Popular Enclosure Designs
The Sealed design delivers the most acurate sound of the 3. If paired correctly with its subwoofers recommended air space, the sealed design will deliver a "max flat" frequency response or frequency curve. A max flat curve means the speaker system will reproduce a broad band of frequency or musical notes at the same decible level. For example, if your woofer has a max flat curve starting at 80Hz and ending at a crossover point of 1000Hz the musical instruments playing at these frequencies would be equal in volume to your ear.
The idea is to be able to hear the mixture of sound as the artist/producer in the studio created it to be heard for their audience. As we will see in some of the other designs, a box on its own can make a bass note at 80 Hz sound like it is kicking you in the back of the head while the punch of the kick drum at 100-120Hz is buried way off in the distance.
Labyrinth Slot Vent Design:
The Labyrinth Slot Vent Design is currently the most popular of the 3 in the car audio industry. The Slot Vent attracts the car audio crowd because of its added volume at the low frequency area (the area that shakes your car). Note that there are other designs that increase decibels like the Slot Vent but none that keep as smooth of a curve as the Labyrinth Slot Vent. The Slot Vent’s popularity comes from the fact that it performs more like a sealed enclosure just louder at an average 3-6 dB gain.
The bandpass design will take a band of 10-15 low frequencies and deliver a 6-10 dB gain within those specified frequencies. The advantage is tons more bass but a disadvantage summed up in the term given to the bandpass design “one note wonder.” Unfortunately, the bandpass design is accused of going to sleep thru the course of a normal song only to “explode” when the chosen frequency band width is played. However, brands of rap or certain pop styles of music exploit the advantages of the bandpass and somewhat diminish the disadvantages making it a more attractive choice for those types of music lovers.
30dB Very soft whisper voice
50dB Adverage living room with TV
70dB Typical Voice speaking
75dB Vacuum Cleaner
95dB Automobile on Freeway
110dB Very Loud Radio
120dB Jet Take Off
165dB Turbo Jet Engine with Afterburner
195dB Rocket Launch
Let’s put the decibel in perspective. For most people, a 10 dB change in sound level will sound twice as loud as the level before the change. A 3 dB change in sound level is very small but most everyone can hear it. A 2 dB change in sound level is very, very small and some people will have trouble hearing it. A 1 dB change is super small and very few people outside of trained hearing specialists can detect any difference.
Now, let’s talk about decibels in relation to amplifier power as well as driver cone excursion. To increase the sound pressure level just 3 dB, you have to Double the amplifier power and increase the cone excursion by 50%.
So, if you are paying $200 for your amplifier, simply by using a slot vent design that gives you an additional 6 dB’s essentially saves you $400 in the purchasing of power it would take to get there with a sealed box.