Home theater power amplifiers act as the interface between sources and speakers - they take the low voltage at the output of the source and amplify it to the levels required to drive speakers.
One amplifier channel is required per speaker, so a common 7.1.4 setup with 11 speakers would require 11 amplifier channels. Subwoofers are generally powered via their own internal amplifiers. Most Audio Video Receivers (AVRs) include at least 7 channels of amplification, so often all that is required is a 4 channel amplifier to power the top (Atmos) speakers.
In higher performance systems with a pre-processor, separate power amplifiers are required for all channels.
Enough power to drive moderate sensitivity speakers (90dB / 2.83v@1m) to cinematic sound pressure levels. We've found that 80W/Ch for LCRs / surrounds and 50W/Ch for tops is sufficient for our typical home theaters. Lower sensitivity speakers and/or large home theaters will require more amplifier power.
Great sound quality. We prefer amps that offer a clean window to the sound and offer a neutral to slightly warm sonic signature. There are many poor quality amplifiers that reduce resolution and sound fatiguing.
A form factor that works in equipment racks. The amplifier should have dedicated rack mounts and should not be more than ~20" deep in order to fit in a standard 24" deep rack whilst allowing cable clearance to rear.
The Zonemaster series sounds good and offers extremely high value. There are four models available at 50W per channel (150W if bridged): the two channel 250, four channel 450, six channel 650 and twelve channel 1250.
All versions are easily rack mounted and very compact - you can fit 8 channels of amplification in a single rack space with two side-by-side 450s! We often use the Zonemaster 450 (MSRP $795) to drive top (Atmos) speakers in a 7.1.4 home theater, since our preferred NAD T777v3 and AudioControl AVR-7 AVRs only include 7 amplifier channels.
The main downsides to the Zonemaster are low(ish) power, RCA only input and screw down binding posts.
Good value, superb sounding amplification from ATI based on Hypex N-Core Class D technology.
Built-to-order, these amplifiers offers a configurable number of output channels at two power levels: 2, 3, 4, 5, 6, 7 or 8 channels at 200W (model number N52Xnc, where X = number of channels) or 2, 3 or 4 channels at 500W (N54Xnc).
The amp offers balanced inputs, runs cool and is easily rack mountable. The main downside is the sleep mode that cannot be disabled, included as an energy saving measure.
MSRP for a 7 channel 200W version is $3195. A 3 channel 500W variant is $2895. What's not to like?
Parasound, ATI and AudioControl are the main amplifier brands we use in our home theater projects. Other brands we use as project needs dictate include JBL Synthesis and Lab Gruppen.
The main amplifier related question we answer through our Audio Engineering service is an important one - "how many amplifier Watts are required to meet SPL requirements?". Amplifier wattage required depends on three main factors: speaker sensitivity, desired SPL and listening distance.
We've found that using a generic amplifier requirement calculator gives hugely exaggerated results, primarily because the sound fall off in small rooms does not follow the text book '-6dB per double distance rule' that is the key assumption in all calculators that we've seen. Our approach is based on real world fall off data culled from our installations.
Nyal Mellor, Founder, Acoustic Frontiers