Rated power
The average (root mean square — RMS) power of the input signal, at which the subwoofer is able to work continuously without negative consequences (damage, failure) for at least an hour. The rated power of the subwoofer must be greater than the power of the amplifier connected to it — in order to avoid overloads.
Max. power
The maximum signal power that the subwoofer is able to withstand for a short time (up to several seconds) without any negative consequences. When selecting an amplifier-subwoofer pair, it is recommended to take a subwoofer with a maximum power of at least twice the maximum power of the amplifier. In general, the higher the maximum power, the more resistant the subwoofer is to overloads.
Frequency range
The range of audio frequencies reproduced by the subwoofer. It is believed that the human ear is capable of perceiving a frequency range of the order of 16 – 20,000 Hz, but in this case note that the subwoofer is designed to reproduce the lower frequency band (up to 200 Hz). Accordingly, in the case of the lower limit of the range, everything is simple: “the lower, the better”; the upper one should not be lower than the lower limit of the main car audio — otherwise there will be "gaps" in the frequencies, which will affect the sound quality.
Impedance
The electrical resistance of a subwoofer when a signal is applied to it. This parameter is important primarily for selecting a subwoofer-amplifier pair: at a lower impedance than that of the amplifier, the subwoofer will distort the sound, at a higher impedance the sound will be too quiet.
For dual voice coil models (see above), the impedance is specified for one of the voice coils.
Resonant frequency
The natural frequency of the cone in the subwoofer speaker, namely the frequency with which the cone will oscillate if the speaker is suspended freely in the air and a single impulse is transmitted to the cone (for example, by clicking on it with your finger). In subwoofers, this parameter determines, in particular, the lower limit of the frequency range (see above): at frequencies below the resonant sound power drops sharply. Accordingly, for deep rich bass, the resonant frequency should be as low as possible. This parameter is also used to calculate the size of the enclosure for the subwoofer.
Phase control
The ability
to change the phase of the sound coming from the subwoofer, in other words, the ability to adjust the sound from the subwoofer to lead or lag relative to the main speakers. This need may be due to the fact that the sound from the main speakers and from the subwoofer can reach the listener with different delays — due to the location of the speakers and the features of the electronics — which negatively affects the sound quality. Adjusting the phases allows you to harmonize this sound. This feature is usually found in active subwoofers.
Protective grille
The presence
of protective devices in front of the main speaker of the subwoofer — this can be the grill itself, metal rods, plastic elements, etc. Such devices protect the device from foreign objects to a certain extent, and they can also play an aesthetic role.
Diffuser material
The material from which the speaker cone in the subwoofer is made. Determines the sound quality and, to some extent, the cost of the device.
— Pulp/paper. Historically the first diffuser material. Its advantages are lightness (which ensures high speaker sensitivity), as well as a smooth frequency response (amplitude-frequency response), which positively affects the sound quality. Among the shortcomings — low strength, which limits the power of such subwoofers, as well as softness, somewhat "blurring" the sound in difficult moments. In addition, paper diffusers are sensitive to moisture.
— Polypropylene. Synthetic polymer, in some aspects similar to paper, but differing from it in higher strength and resistance to moisture. It also has a smooth frequency response. Somewhat more cruel, but still belongs to the soft.
— Polyurethane. Another polymer material. At a low cost, it is somewhat stiffer than polypropylene, and is also very resistant to mechanical stress, which allows you to create powerful speakers.
— Kevlar. Kevlar fibre is highly durable (higher than steel); it also has good rigidity, which has a positive effect on fidelity in difficult moments. However, such diffusers are not cheap.
— Carbon fibre. It belongs to premium materials: it has high strength at a very low weight, and in the case of subwoofers, it is also worth mentioning the good rigidity that ensures a clear sound. Among the shortcomings — a somew...hat uneven frequency response and an impressive cost.
— Carbon. Another name used for carbon fibre is mainly for promotional purposes, for brevity and “impressiveness” of sound. See above for more details on carbon fibre.
— Fibreglass. Such material consists of ordinary glass stretched into filaments; unlike the classical form of glass, such threads do not break or break. It's lightweight (respectively sensitive), relatively cheap, resistant to moisture and temperature changes, and still provides good (though not outstanding) sound quality.
— Composite materials. Composite is a material that consists of two or more materials with a clear separation between them. In subwoofer cones, carbon fibre composites (based on carbon fibre, see above) are most often used. Such diffusers have all the advantages of carbon fibre and are able to provide good sound quality — however, due to the characteristics of the frequency response of the material, rather complex electronic circuits have to be used to achieve this quality, which affects, in particular, the price of subwoofers.
— Aluminium. Aluminium cones have the highest rigidity of all, which ensures high fidelity of sound transmission even in difficult moments. The "reverse side of the coin" in this case are their own extraneous "ringing" that occurs in the diffuser. To eliminate them, you have to use various tricks that significantly complicate the design and increase the price of the subwoofer.
Note that each material has its own characteristics and shades of sound, which you should pay attention to when choosing — a more expensive and high-quality material will not necessarily give a sound that you personally will like more.
