PMC Twenty5 Sub Subwoofer

The PMC Twenty5 sub-subwoofer is a high-end unit delivering 400 watts of class D power and powerful bass. The two 170mm long-throw woofers provide bass down to 30Hz. Moreover, this is a relatively compact unit and can be used to make bookshelf speakers sound like three-way floor-standers.

Lastly, like the rest of the Twenty5 series, there are two Laminair bass ports at the rear and the spiked feet are adjustable from the top. Balanced line-level inputs are provided along with an RCA adaptor.

Two PMC designed Bass drivers

The two 170mm bass drivers used in the PMC Twenty5 sub-subwoofer are made of g-weave material. This is a kind of woven fibre-glass that is stronger than paper. However, it still adds no colouration to the sound. The cone has a long throw and a cast alloy chassis. Finally, the motor and magnet assembly have been upgraded and have 80% more power handling capacity.

Class D power

Most subwoofers and active speakers use class B amplifiers. This is far more efficient than the class A/B units used in standard amplifiers. In fact, it is up to 90% efficient. It also generates less heat and has a smaller form factor, making it perfect for cramped spaces such as a speaker cabinet.

The built-in amplifier is ultra-low-distortion and a subwoofer will enhance music as well as movies. Class D amplifies digitally. The output consists of a series of high-frequency pulses that are fed to MOSFET transistors.

This is known as pulse width modulation. The closer together the pulses are the higher the output. The output is passed through a low-pass filter to remove the pulses and recover the audio.

Connectivity and control

The PMC Twenty5 sub-subwoofer has two balanced XLR inputs, one for each channel. There is also an adaptor so that standard RCA leads can be used. Additionally, there is a screen at the back of the unit, along with controls so that the EQ and filters can be set easily. This speaker makes an excellent addition to any music or movie setup.

Laminair airflow port

Two Laminair bass ports are provided with the Twenty5 sub-subwoofer, these make the bass even more impressive and were inspired by the air intakes of Formula-One racing cars. The design reduces turbulence and drag and also reduces air noise. The result is a dynamic and powerful bass with good timing.

About home cinema systems

Subwoofers can be used both to enhance music and movies. However, they are more common in home cinema systems. They add impact to explosions as well as increasing immersion in the action. An AV amplifier is needed to make a home cinema system. These have the required decoding capability and enough built-in amplifiers to drive the speakers.

The simplest system is known as 5.1 and features a front left and right pair of speakers along with a rear pair. There is also usually a centre speaker and a subwoofer such as the PMC Twenty5 sub Subwoofer. However, there are more complex systems, such as Dolby Atmos that can have up to eleven channels, including ceiling speakers. Some amplifiers can also drive two subwoofers.

Connecting a subwoofer

The PMC Twenty5 sub-subwoofer is intended for high-end systems and consequently only has a line-level input. Subwoofers are usually driven from a dedicated output on an AV receiver. However, budget subwoofer models also have a speaker-level input that can be connected to the speaker outputs on older amplifiers.

For example, some amplifiers have outputs for two sets of speakers and one of those could be used.

This combines perfectly with the PMC Centre Speaker and are also the perfect accompaniment for any setup of the PMC Twenty5 speakers to make anything from a 2.1 speaker system to 5.1.