Speaker selection is an important consideration in any quality system. And one of the most important, is low frequency, and how to obtain truly impressive performance, without the common mistakes made when designing this critical section of frequencies.
There is much more to consider when selecting subwoofers, their implementation and overall balance of the system. This is where Thiele-Small parameters dictate enclosure design and sizing, and one commonly ignored. There is much more to designing this system than just buying a driver and cabinet. The mechanical and electrical Q of a driver has to be properly matched to the cabinet. And one size (diameter) doesn’t match all cabinets. And any subwoofer driver not inside an enclosure, will not produce the effect you are seeking. The trunk itself doesn’t count, as it doesn’t match the Thiele-Small parameters of the driver originally used.
Rule #1, any sub driver outside a properly matched cabinet is only half a subwoofer.
Rule #2, never disconnect the driver from the cabin of the vehicle. You cannot overlook this rule, and often attempted. Disconnected designs where you place a sub in a cabinet, and place it in the trunk, is not a desirable design in any system. Imagine taking your home audio system in your listening room, and placing the subwoofer in the garage. The only result that will produce, is a very muddy, and over emphasized port chuffing monster that doesn’t lend itself to high quality reproduction… all it creates is noise. When you place a driver outside of the cabin, you lose the intricacies of the lower frequencies needed to reproduce music accurately. The primary frequency of low A (A-0) of a piano is 27.5Hz, and its second even harmonic is 55Hz, and it’s third even harmonic is 110Hz. And that’s only one example. These subtle harmonics are lost in disconnected designs, and lower volume levels will lose all detail.
And using that same piano note as an example, it is important that the amplifier is phase accurate, especially in this arena. It’s why attention to an amplifier’s signal path is so important, and why so much attention is paid in that area. It is the foundational building block to accurately create sinusoidal waves for the drivers. This is the arena in which realism and soundstage is created, those subtle harmonics and vibrato that are created during the recording process.
Another critical area, is the damping factor of the amp you connect your subwoofer to. This is one area that is misunderstood by many, and seldom executed well. As you decrease resistance, you decrease the damping factor of your amp. It’s why you should find a solution that has only one driver per amplifier channel, and at least 4 ohm. 2 ohm designs or less, while able to create more load, and in the end, more current, (watts) however, it is not conducive to damping factor. The amp has to be able to control driver excursion, and the closer one gets to 2 or 1 ohm, the less ability that amp will be able to control it. The net result is poor performance. Also, using anything less than 10 gauge wire for subs is not recommended. An amplifier that has a damping factor of 500 at 4 ohm, will be reduced to around 100 by using only 5ft of 14 gauge, and at 2 ohm it is almost 50. Damping factors that are at least >100 is a general rule for minimum, and the higher, the better. The function of using large wire gauge (10 gauge or larger) is not for current, but the amount of voltage drop.
From Crown; "Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing." In other words, the speaker produces sound waves that are not part of the original signal. Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a boomy throb. Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load impedance divided by amplifier output impedance. High damping factor equals tight bass."
The goal is to find a subwoofer driver that matches the wattage rating of the amp, placed in a properly designed cabinet to match its Thiele-Small parameters, and connected to the cabin of the vehicle, without using the boot as the enclosure itself.