"Thiele/Small" commonly refers to a set of electromechanical parameters that define the specified low frequency performance of a loudspeaker driver. These parameters are published in specification sheets by driver manufacturers so that designers have a guide in selecting off-the-shelf drivers for loudspeaker designs. Many of the parameters are strictly defined only at the resonant frequency, but the approach is generally applicable in the frequency range where the diaphragm motion is largely pistonic, i.e. when the entire cone moves in and out as a unit without cone breakup.
Using these parameters, a loudspeaker designer may simulate the position, velocity and acceleration of the diaphragm, the input impedance and the sound output of a system comprising a loudspeaker and enclosure. Rather than purchase off-the-shelf components, loudspeaker design engineers often define desired performance and work backwards to a set of parameters and manufacture a driver with said characteristics or order it from a driver manufacturer. This process of generating parameters from a target response is known as synthesis. Thiele/Small parameters are named after A. Neville Thiele of the Australian Broadcasting Commission, and Richard H. Small of the University of Sydney, who pioneered this line of analysis for loudspeakers. These measurements are also used for designing enclosures for Subwoofers.
The main cause of subwoofer failure is overdriving or driving a clipped or distorted signal continuously to your sub. This can result in a mechanical or electrical failure. With electrical failure the result is normally a burnt voice coil causing the sub to go open circuit or in some cases short circuit to ground.
It is important to match the “RMS” ratings of your sub to your amplifier to avoid overdriving. Clipping or distortion is the audible sign of an unclean signal and this can originate from any piece of equipment in the signal chain. What this means is you may be only driving your amplifier at, say, half power yet your head unit/source may be driving at close to its maximum output which could be supplying a clipped or distorted signal to the amp, thus creating the audible distortion.
Mechanical failure occurs when the spider or butyl surround rips or tears, or sometimes the voice coil jumps the gap. What we mean by 'jumps the gap' is that when the sub is being mechanically overdriven it can result in over excursion or over travel. This results in the voice coil leaving the gap that it travels in, resulting in failure.
Mechanical failures in general are all symptoms of over excursion which can be caused by having the wrong size enclosure and/or overdriving. It is very important to follow the recommended enclosure volumes to ensure optimum performance of your sub and to protect it from these types of failures. It is also important to note the port length and diameter in relation to the tuning of the enclosure, as this also could adversely affect performance and reliability.
My speakers are 300 Watts “Max” and 90 Watts “Rated Power”. What size amplifier do I need to drive them to achieve the best performance?
When you are choosing an amplifier to drive speakers or a Subwoofer, you should use the “RMS” per channel ratings (amplifier) and the “Rated Power” (speaker/subwoofer) as the reference for your choice. Always define which ratings you are comparing and try and get them as close as you can.
“Max/Peak” Power Rating
The “MAX/PEAK” power rating of a speaker is the amount of power that the speaker can handle in short bursts or peaks without causing permanent damage to the voice coil. If this rating is exceeded constantly, you will risk burning the voice coil.
“Rated Power” Power Rating
The “Rated Power” rating of the speaker is generally considered to be the nominal constant power that the speaker will handle continuously without causing damage.
Therefore if your speakers are rated at 90 Watts (rated power) you should drive them with an amplifier that is capable of supplying 90 Watts RMS per channel or as close to that as possible. That is not to say that an amplifier capable of a higher output cannot be used if the amplifier settings are managed responsibly, remembering the potential to overdrive your speakers exists. This rule also applies to using an amplifier that is under driving your speakers. Constantly driving a distorted signal from an overdriven source to your speakers can cause damage to the voice coils.
The first thing to do is check that your amplifier is not in protection. If it is, this could be a sign that you have a problem with your subwoofer or amplifier. The easiest way to check if your subwoofer is causing your amp to go into protection is to disconnect the subwoofer and power up the amplifier. If it does not go into protection with it disconnected, your subwoofer is the problem. Check for a burnt smell, or try to move the cone gently by pressing down in the center to see if it has seized or is rubbing. It should move freely if the coil is not damaged. If the amp still goes into protection when you disconnect the sub, there is every reason to suspect your amp may have an internal fault. Unfortunately this does not mean your sub is guaranteed to be fault-free as the amp may have suffered as a result of the sub failing or vice versa, so at this point we would recommend that you return either one or both of the units to your place of purchase for inspection by the authorized dealer under the warranty provision of the product (if applicable).
All Fusion subwoofers have an optimum enclosure volume which is based on a specific tuning point. To calculate volume, you need a calculator and a tape measure, and the following formula:
Length (in inches) x Width (in inches) x Depth (in inches) divided by 1728 = volume in cubic feet.
Length (in centimeters) x Width (in centimeters) x Depth (in centimeters) divided by 1000 = volume in cubic litres.
Always allow for the volume of the subwoofer that will be inside the enclosure and the port if applicable. Ensure you measure the inside dimension allowing for the enclosure material thickness.