Are Class D amplifiers better than Class AB?

by Andrew Bishop

Let's briefly study the pros and cons of Class D v Class AB and reach a conclusion on which one is the best for your PA system.

In short, all passive speakers made by BishopSound need a solid power amplifier. 

Power amplifiers for PA systems traditionally were always class AB and consisted of large heavy toroidal transformers and capacitors to ensure that when the music called for punch the power supply delivered.

Class AB run hot and are not very efficient, whereas Class D are lightweight and run cold with many only 1u in depth such as our BP2k, BP4k and BP44k.

What are the different types of amplifiers used for PA systems?

  1. Class AB
  2. Class D
  3. Hybrid (key features of Class AB and D combined)

Class D has come along way in the last 5 years and is constantly improving. They run cool, are lightweight and rely heavily on a solid mains supply.

OHMs law is (V=CxR) Voltage equals current times resistance. The speaker is the resistance and the voltage is the musical signal. Heavy or repetitive drum beats in the music demands a lot of current. If the current is not available then the music may suffer from distortion or unfaithful reproduction of the music.

A solid power supply means the amplifier:

  • Has a firm grip on on the woofers and musical notes are more clear and crisp.
  • Quickly follows reproduction of dynamic changes in the music
  • Can handle dynamic bursts of music found in drum n bass and garage
  • Has no problem feeding hungry low impedance subwoofer speakers
  • Takes the energy the woofer does not need and reabsorb it back into the system

RF interference is everywhere - large numbers of Wi-Fi and Bluetooth connections in an area effects the performance of a Class AB amplifier. Class D is not effected by this.

For mid range and low volume subwoofers and PA, class D is perfect. Once you get over 3,000w Hybrid amplification which has the benefits of a big stable power supply and efficiency of class D combined is perfect. You will see this used in the 10,000 watt RMS SAE PQM13. SAE PQM13 - 4 Channel Power Amplifier 10,000w RMS – BishopSound

The great news about Hybrid amps is they are not as heavy as the old class AB amps so portability is retained.

We recommend an amplifier for the subwoofers and an amplifier for the mid/tops or a 4 channel amp where channel 1&2 feed speakers handling 98 - 110 Hz and channels 3&4 catering for the speakers delivering 105Hz plus. If you're not sure, we have experts on hand to advise you.

Hybrid amplifiers deploy a range of specialist capacitors at precise moments to improve the performance and maintain the stability of the power supply, thereby improving the sound reproduction, quality and reliability. In the world of PA and sound reproduction, never cut corners with power amplifiers as you get what you pay for.

Dirty mains and low cost inferior components will severely damage amplifiers. Always protect and improve your sound with a Power Conditioner.

Impedance matters and generally speaking, research shows 4 ohm loads function better on class D than 8 ohm loads, as the frequency response tails off rapidly at 20kHz removing the brightness many comment on with class D.

Active speaker systems only use class D due to weight issues. Passive PA systems are far superior in sound quality especially for larger gatherings.

Summary

  • For small PA systems up to audiences of 500 inside, Class D will work fine.
  • For audiences over 500, a mix of Class D and Hybrid or pure Hybrid will deliver stability and perfect audio reproduction without distortion.
  • Never cut the budget on amplification.

For detailed advice on creating your perfect PA system for touring or installation contact andrew@bishopsound.com.