No, not ever. In fact, aside from rather unimpressive SPL levels, all transducers actually perform their absolute best at very low power levels. This is where TSP's are measured and you can expect virtual linear results and zero thermal compression , flux modulation and other dynamic distortion mechanisms to be absent from the system. The problem is, with very low singles and power levels comes very low SPL. Transducers are grossly in efficient, around only 3 to 5%! That means for every 100 watts you put into the system, you get about ~3 watts of acoustic sound.
Can I harm a driver with a clipped single?
No, not unless the single is high enough to potentially cause mechanical or thermal failure. A clipped single of relatively small magnitude is harmless. The issue is that normally amplifiers clip at high power levels near or beyond the subwoofers mechanical and/or thermal limits which is why people associate clipping with damage.
Do sealed subwoofers really sound better than ported?
In short no, and if you want to get into he details more, it would be wise to study system design. One of the most critical aspects of a subwoofer system is linear response. And it tends to be easier to get linear response in a sealed system because less can go wrong and most drivers have Qts's above 0.4 which makes them work rather well in averaged sized sealed box. Depending in the TS parameters of the driver, some woofers are difficult to achieve linear response in either a sealed or ported box. People tend to think it's the box's fault when really it's a function of the driver with the box and with the equalization settings or better yet, lack there of. Unfortunately in car audio, equalization is not discussed enough, and it can be a very crucial component into making a subwoofer sound good or at least protecting it in the case of a higher ordered system such as vented boxes. Eq is also especially important in a car where certain frequencies can be peaky and others can be un accentuated to room coupling or standing waves.
What is a passive radiator?
Its very simple: It's a resonator much like a port. A port consists of air in the port (mass) and internal air pressure in the box (spring). The area and length of the port affects how the pressure of that moving mass resonates. This resonator physically displaces air for a very narrow frequency range when it resonates by the active driver much like pushing on a child on a swing at the exact time they reach you again. Careful alignment can lead to linear frequency response with an active woofer and a port resonator. Together they make a 4th (or more complex higher order) system that is more efficient than a sealed or infinite baffle type of system. Ported systems are often able to extend to lower frequencies where linear response demands displacement requirements beyond the woofer and hence a resonator is required.
Passive radiators do the exact same thing, but use weight for the mass and a spider suspension system for the spring. Passives radiators like ports resonate and low frequencies and when used in a box with an active driver can create a 4th (or higher) order system. As far as frequency response and SPL, passive radiators and ports should perform about the same, however passive radiators have several advantages over ports such as the ability to adjust frequency at which they resonant simply by adding or removing mass. The only way to do that in a port is the physically change the port length (a much more difficult feat) Passive radiator also commonly display low compression characteristics and don't produce unwanted port resonance distortion which can plague larger ports.
What is a subsonic filter?
A subsonic filter is truly a high pass filter that cuts off frequencies below a give frequency. Ideally subsonic filters should be used to protect woofers in (usually) 4th order bass reflex (vented) systems where driver excursion increases exponentially with no compliance protection below resonance. In a sealed box, the internal air pressure acts as a protection against over excursion. Secondly, in a sealed box, woofer excursion does not increase as fast below resonance so it's not a big of a concern.
In a typical bass reflex system the filter should cut off the woofer below tuning. In a 4th order system, you will see a peak in the driver's excursion at a frequency above the tuning frequency. Below that, the driver starts to approach a point of almost no movement. At that point, the port air velocity will be at the absolute max, the phase will be zero and the impedance will be at a minimum for the system. The woofer will be drawing the most power from the amplifier and it will be at its greatest risk of thermal failure. This is tuning! Below that the resonator (port) quickly becomes out of phase with the active and they cancel each other out. There is truly no more useful bass left and the excursion becomes widely out of control. It is necessary to cut off the active driver at that point. The high pass filter does this, but it should do it in such a way that the woofer's excursion below tuning should match that of what it did above. There will be two peaks and ideally they should be symmetrical and of equal amplitude (excursion). This is an appropriate high pass filter and it can be done with the naked eye (no modeling software) if need be. But you will need a sinwave generator (they can be downloaded).
What is the difference between SVC, DVC and QVC?
There is really no advantage to any of these voice coil configurations. Ideally speaking, they are the same coil but broken up into smaller pieces in order to wire them at difference resistance and ultimately impedance loads. The idea is to match a driver to an amplifier's maximum performance. There are differences in the TSP parameters, but ideally speaking, these differences typically cancel out. But because wire gauge and gap dimensions don't always completely match up, there are always small advantages from one coil option to the next, however these differences may only result in 0.25 to 0.5db sensitivity advantage from a higher BL^2/Re factor, but such difference are not audible. And you should really not concern yourself as a consumer with these differences. Many DIY gurus nit pick TPS's and forget the real proprieties of drivers such as dynamic linearity, or power compression for example. It is not wise to get wrapped up in the TSP nick pick game when it comes to coil configurations but rather to match the driver to an amplifier to maximum the performance of the system.
A simple way to understand the coils is like this:
SVC (single voice coil) can only be wired one way.
DVC (dual voice coil) can only be wired at twice the coil load or half the coil load. IE: D2 = 1 ohm or 4 ohms, or it can be driven with a 2 channel amp at 2 ohms per channel.
QVC (quad voice coil) can only be wired at the ohm load or one quarter or four times. IE: Q2 = 0.5, 2 or 8. Or a two channel amp at either 4 or 1 ohm per channel.
More complex methods can be integrated using multiple woofers.
It's important to understand that impedance is not a single number and in fact it is rarely ever the number listed. Impedance is a complex relationship of the resistance, reactance and frequency. Normally we list a nominal impedance load that is at best, a guess as to what the amplifier will see on average. There is no mathematical basis for this "nominal" load and what you should consider is that the DCR is the absolute minimum load that the amplifier will see, however it's never quite that low due to non-linear inductance effects and other aberrations beyond this academic explanation. Because most amplifiers are constant voltage, you can see that the at the impedance peak, there will be very little current and power going into the driver, but at the impedance dip, there will be a lot more current and power going thought the driver but the SPL will pretty much be at the same level.
Can I just use one of the coils because it's a better match for my amp?
Absolutely not! Drastic TSP differences and huge performance losses will occur including unpredictable distortion and irregular mechanical behaviors from the unused voice coil. You should expect no more than half the performance on virtually all fronts of the transducer and you're better off using a less demanding driver that is a better match for the amplifier.
Where should I place my subwoofer in my vehicle?
Ideally the subwoofer should be placed to that it has high acoustic mode coupling with the internal dimensions of the vehicle used. If the car is a wagon or SUV, the rear, or front (if possible) corners serve best for this. If the vehicle is a truck, than it becomes exceeding difficult because the internal cabin is very close to a square and unwanted cancellations can occur resulting is loss of system efficiency. In that case, some experimentation may be required.
