Whether you’re trying to overfill your car with bass or create the perfect sound, there is a set up that’s right for you . You may have heard of the terms “SQ” or “SPL” before. Understanding these terms will assist you with what kind of sound you are seeking.
SPL

SPL stands for sound pressure level which basically means how loud the subwoofer or speaker is producing sound. In regards to subwoofers, ported enclosures are usually favorable for SPL set ups. This is due mainly to the ports being able to push more air and create more pressure. Bigger subwoofers such as 15 or 18″ or multiple subwoofers are more common in these set ups as the more cone area you have the more air pressure you’re going to be able to produce. SPL is measured in decibels which means you will be able to tell just how loud your system is with an SPL meter. SPL systems are going to be higher powered and geared towards pushing your system to it’s maximum limits. Musical genres like rap and hip hop are ideal for this purpose Speakers can also play a role in an SPL system. Metal tweeters are ideal for obtaining louder highs which you will need to prevent the bass from draining out the high frequencies. If your goal is to make sure the whole neighborhood can hear you, then go SPL.
SQ

If SPL had an estranged brother, then it would be SQ. There are many differences to an SQ system. SQ is for sound quality which means there are no overbearing frequencies, excellent sound staging and superb tonal accuracy. Sealed enclosures are ideal for subwoofers in this application to give you a tighter and more accurate bass response. Genres of music with double bass pedals, such as rock, require subwoofers that are more responsive. For this reason, 10 and 12 inch subwoofers are more commonly used for this type of application. Sound quality can not really be measured. However, a good subwoofer should be able to produce +/- 3 dB. It is mostly about personal preference for sound quality. Go SQ if you are looking for a sound that will make you feel like your right in front of the artist.
Keep in mind that one is not necessarily better than the other. It all comes down to what you’re into. Its even possible to create an SQL system that can take the best of both worlds. Theres always going to be haters on both sides of the fence but only you can decide what is right for you!