Amplifiers are essential in most audio signal flow paths. When looking at power amplifiers to drive our loudspeakers, we come across many design variations, including the monoblock configuration.
What is a monoblock amplifier? A monoblock amplifier is a single unit (“block”) responsible for amplifying a single channel (“mono”). The components of a monoblock amplifier amplify a single channel rather than being shared between multiple channels. Monoblocks, therefore, are larger, heavier and more expensive (per channel).
This article will further our understanding of monoblock amplifiers and discuss whether monoblock(s) are for you.
What Are Monoblock Amplifiers Used For?
Put simply, monoblock amplifiers can be used to amplify any single channel in an audio system.
If there’s only one audio channel (a mono signal), then only one monoblock amplifier is needed. If there are two channels, like in a stereo recording, we would need two monoblock amplifiers (or a stereo amplifier).
If we had a stereo pair of speakers and a subwoofer to handle the low-end, we could use three monoblock amplifiers; a stereo amp and a monoblock subwoofer amp, or an all-in-one amplifier capable of driving a 2.1 setup.
Let’s discuss the basic situations where monoblock amplifiers tend to be used. These applications are:
Because music and television are often mixed in stereo, most entertainment systems will utilize stereo amplifiers, which we’ll discuss later in this article. Monoblock amps are most often used in car audio and higher-end audiophile systems that benefit from the isolation of separate “per-channel” amplifiers.
Bass frequencies, in the context of an audio mix, are typically mixed in mono. Bass frequencies of sound waves are omnidirectional by nature. An additional notion is that lower frequencies require more power to reproduce in speakers (and headphone drivers).
These two facts make it optimal to use subwoofers to reproduce low-end frequencies.
Subwoofers are generally placed in the centre of the playback system and often have their own dedicated amplifiers capable of supplying higher wattage ratings. More power means more movement of the relatively heavy subwoofer driver, which, of course, translates to more bass!
Monoblock amplifiers are particularly useful for driving subwoofers. A monoblock amp can even drive multiple subwoofers if need be (wired in series or parallel depending on impedance bridging needs).
My New Microphone articles related to speaker/amplifier impedance bridging:
• The Complete Guide To Speaker Impedance (2Ω, 4Ω, 8Ω & More)
• What Is Amplifier Impedance? (Actual Vs. Rated Impedance)
• Why Do Speakers Need Amplifiers? (And How To Match Them)
Speaking of connecting multiple speakers to a monoblock amplifier, some monoblocks will have two (or more) sets of terminals.
These terminals will be labelled by polarity as either positive (+) or negative (–). If you happen to see two side-by-side + terminals and two side-by-side – terminals, it means the amplifier can easily connect to two speakers (in parallel).
These terminals are not separate channels and the same signal will be outputted from each pair of terminals.
Stereo and other multi-channel amplifiers will have their output terminals labelled per channel (left, right, etc.).
The Boss Audio Systems AR4000D (link to check the price at Boss Audio) is an example of a monoblock subwoofer amplifier designed for car audio. You can see that there is only one set of output terminals.
The Polk Audio SWA500 (link to check the price on Amazon) is an example of a monoblock subwoofer amplifier for home audio. It is designed specifically for Polk Audio’s CSW in-floor subwoofers but can be used for other subwoofers as well. The SWA500 has double output terminals to connect to two separate subwoofers easily.
Polk Audio is featured in My New Microphone’s Top 11 Best Subwoofer Brands (Car, PA, Home & Studio).
Separate Left & Right Channel Stereo
Monoblock amplifiers can also be used to amplify individual channels for playback.
In a stereo setup, then, two (ideally identical) monoblock amplifiers can be used. One amp to amplify the left channel and drive the left speakers and another amp to amplify the right channel and drive the right speakers.
Again, these monoblock amplifiers may have multiple output terminals to drive multiple speakers with the same channel signal.
Monoblock Vs. Stereo Amplifiers
A stereo amplifier has two independent channels for left and right audio within a single unit/chassis.
The form factor of a stereo amplifier is generally smaller than two individual monoblock amplifiers. The price is often more affordable. Since so much of the audio we enjoy (particularly music and television) is mixed in stereo, it’s much easier to go with a stereo amplifier for our audio setups.
These advantages come with a few downsides, though. Because the stereo amp signal paths share the same chassis, transformers and power supply, they are not as isolated and will often inherit crosstalk, resulting in more noise, interference and distortion in the signal path.
This is often not the biggest deal. Most home theatre and stereo system amplifiers are built with this stereo amplifier design.
However, if you’re looking for the best possible audio, it’s often better to go with a matched pair of monoblock amplifiers over a stereo amplifier.
The Marantz MM7025 (link to check the price at B&H Photo/Video) is a great example of a stereo amplifier with up to 140W per channel at 8Ω.
What About Dual-Mono Amplifiers?
Note that dual-mono amplifiers, monoblock amplifiers and stereo amplifiers are not the same.
A dual-mono amplifier has two separate mono amplifiers within a single unit. However, they each have their own input circuit and their own power supply.
With dual-mono amplifiers, there is better stereo separation and no crosstalk. An added benefit of having a separate power supply for each channel is that the unit will tend to be capable of handling higher current/power demands.
Though a dual-mono amp could be used for improved stereo audio, it’s more often used (as the name would suggest) to amplifier two independent mono signals.
The ATC P1 Pro (link to check the price at Sweetwater) is a superb example of a dual-mono power amplifier.
Bridging is a method of connecting multiple amplifiers such that they drive a single floating load (bridge) or a single common load (parallel) with increased power.
Some stereo (and other multi-channel) amplifiers have “bridge modes” that effectively turn them into mono amplifiers. The bridged mono amplifier will have increased output power due to the combining of the two (or more) typical outputs.
Let’s look at an example of the popular Crown Audio XLi 2500 (link to check the price on Amazon) stereo power amplifier.
The power specifications of the Crown Audio XLi 2500 are as follows:
- 4Ω Dual: 750W
- 8Ω Dual: 500W
- 8Ω Bridged: 1500W
What does this mean?
Well, let’s begin by stating that lower-impedance speakers demand more power to be driven properly. Therefore, power amplifiers are required to output more power when driving lower loads. This is seen in the specification difference between 4Ω (750 W) and 8Ω (500 W).
But that’s beside the point we’re making here. Those specs refer to each channel (left and right) when the XLi 2500 is in stereo mode.
When we set the XLi 2500 to bridge mode, its two output channels are effectively combined into a single mono output.
As we can see from the above specifications, the bridged mono output is 1500 W into an 8Ω load. That’s three times more power than if the XLi 2500 was set up to drive two 8Ω speakers (via its left and right channel outputs).
So then, it’s not only monoblock amplifiers that can output mono signals.
Can you put 2 subs on a mono amp? It is possible to connect multiple speakers to a single amplifier by wiring them in series and/or parallel. Wiring in parallel will drop the overall load impedance as seen by the amplifier, while wiring in series will increase the overall load as seen by the amplifier.
What is a subwoofer? A subwoofer is a woofer-type (moving-coil dynamic) loudspeaker designed to produce low-end frequencies. Subwoofers generally have large diameters and are the biggest speakers in a system. These large diaphragms (and motors) are required to push and pull the air volume needed to produce low-end end bass and sub-bass frequencies. Subwoofers sometimes require their own monoblock amplifiers (bass is nearly always in mono).