Do You Need an External Power Amp for Your AVR?

I wanted to cover this topic as I have some amplifier reviews coming in soon so I wanted to introduce the topic a bit more broadly before we get into it.

Aspects to Consider

There are 4 issues to consider when trying to answer this question:

1. The type of AVR you have
2. The type of speakers you have
3. Whether you run your speakers as small or large (full-range)
4. The volume you prefer to listen at

Let’s cover each of these in turn then.

Issue 1: AVR Type

AVRs try and cram a LOT of technology into a single chassis that needs to drive the pre-amp, video and audio processing and more and more channels with one power supply feeding all these elements from a single power cord. I don’t think it takes a genius to figure out that ultimately, there’s only so much power you can draw from the wall – partly because of the law of physics and partly because of regulations in different parts of the World.

In a real-world scenario, even if we weren’t doing anything else with that power but drive speakers, you will only get around 1000 to 1200 Watts of power into 8 ohms. Divide that by the number of channels and that’s kind of your theoretical maximum.

Of course, not all AVRs are made the same. Lower-end models will typically include rather weak amplifiers and a weak power supply feeding those amps, while higher-end models will include better components, larger power supplies and beefier amps. This will improve the number of channels that can be driven simultaneously, provide cleaner power at higher volumes and a larger dynamic range when the action gets going.

Of course, this isn’t the only issue to consider. Some AVR manufacturers like to “voice” the amps in their AVRs to sound more laid back or forward and this can impart some colouration to the sound. I know this because connecting an external power amp to some receivers will actually provide a slightly different sound – with everything else being equal – and even after re-calibrating the system multiple times, it consistently sounds different. I am not a huge fan of this “voicing” by certain brands to be perfectly honest – whether deliberate or “an accident of the design process”.

Issue 2: Speakers

The second issue is speakers. There are two main things to consider with speakers:

1. Speaker impedance
2. Speaker sensitivity

Speaker Impedance

The lower the impedance of a speaker, the more power it needs to drive and therefore will be more difficult for a weaker AVR with its weaker amps to do so. An 8Ohm speaker will be easier to drive than a 4Ohm speaker, and a 4Ohm speaker is easier to drive than a 2Ohm load.

Of course, life would be simple if it was that clear cut. Unfortunately, impedance is not uniform across the frequency spectrum. The odd high-end manufacturer will quote the MINIMUM impedance the speaker has next to the overall impedance. For example, they may say it is a 4Ohm speaker with a minimum impedance of 3.2Ohms (at such and such frequency). But this is more the exception than the rule.

What you need to remember is this: just because a speaker is rated at 4Ohms doesn’t mean that it won’t dip down lower into 3 or 2Ohms in certain parts of the frequency spectrum. My experience is that – even though some beefier AVRs are rated for 4Ohms – they will still struggle to deliver enough power to 4Ohm speakers cleanly and there will be some areas of the frequency spectrum that will sound strained / not clear, even at lower volumes.

Take for example Jamo’s or M&K’s THX speakers. While they can be run using a high-end AVR, ultimately they won’t sound their best. I find that they need a dedicated amplifier to run well even at lower volumes. Once they have enough clean power, imaging tightens up and dialogue becomes clearer.

This is likely because the speakers will dip into 2Ohms in places and the AVR is struggling to cleanly drive the speaker drivers at that point. When a good-quality high-power amplifier is driving such speakers, they will likely produce a cleaner impulse response with less noise or ringing / break up of the sound waves as those dips into lower ohms happen.

This is why, I now recommend that people who want to keep driving speakers using an AVR, get speakers that are rated at 8Ohms. Even if the speaker dips down into 4Ohms in places, the AVR won’t struggle to drive them.

Speaker Sensitivity

The second issue with speakers is sensitivity. The sensitivity rating tells us how loud the speaker will play when driven by 1 watt of power at 1m distance (of course the manufacturer can fudge this by measuring differently so pay attention to the small print). The higher the sensitivity, the more loud the speaker will play when driven by the same amount of power. Each doubling of loudness will take 3dBs of extra sensitivity and will require double the watts. (Please note that this is not the truth and is only true if we ignore equal-loudness curves.)

I wanted to give you some guidance regarding speaker sensitivity ratings so here is one:

• Below 85dB: Poor
• Between 85dB and 90dB: Ok
• Between 90dB and 94dB: Great
• Over 94dB: Excellent

If you enter “Speaker SPL calculator” into Google, you will find lots of different calculators (e.g. https://mehlau.net/audio/spl/) that you can use to figure out how much power you will need to drive a speaker with a specific sensitivity to produce a particular sound pressure level. Please note that to play a soundtrack at reference level, all speakers need to be able to produce 85dBs continuously and 105dB peaks of sound pressure at the listening position. Of course, most people don’t listen to movies nearly as loud but listen -25dBs to -15dBs below reference with -20dB being around the average.

If you choose to use a lower-end AVR to drive 7-9 speakers at high listening volumes, it is important to choose speakers with Great or Excellent sensitivity making sure that the AVR will be able to deliver the required continuous (RMS) power to the channels and the required peaks of dynamic power when required. Otherwise, you will get distortion or compression and the soundtrack will not be faithfully reproduced – while also hurting your ears or shutting down the AVR.

Issue 3: Limited or Full Range

It is much easier to drive speakers in limited range (called small in most AVRs) and direct the bass to subwoofers than drive them as full-range. In fact, there are many advantages to this in home cinema applications from being able to control the bass better to getting better amplifier efficiency.

Side note: Anything below 80Hz is not localisable in a room unless you have something rattling or resonating along with your subs. As soon as people take the time to secure everything in the room and calibrate their subs with EQ to be flat, at the correct output relative to the main speakers and IN PHASE with the impulse response of the main speakers, anything below 80Hz will literally sound like it is coming from the speakers themselves, not from a sub or subs. Subs that have bloat or overhang might also produce somewhat more of a localisable sound due to not allowing for the above conditioned to be fully fulfilled. Of course, some people swear they can hear stereo subs, likely due to mono subs providing out of phase response relative to their speakers which might be audible but it isn’t an issue of physics but that of setup. However, there can be some benefit in larger rooms for dedicated front versus back subs especially for multiple rows of seating due getting in-phase response to all seats between front and back soundstage. Anyway, getting back on topic…

Much greater demands are placed on an AVR when two or more speakers are run as full-range. This is why most AVRs generally have a feature to allow an external amplifier to be connected to the front speakers at the minimum, and take the load off the AVR.

If you were putting undue power on your AVR already and driving speakers with a low impedance and low sensitivity, making them full-range might not be such a great idea. Even with 8Ohm speakers, I would recommend using bass management with subs and main speakers as small and using an external amp for speakers that need to be run as large. The only exception to this might be very high sensitivity 8Ohm speakers.

Issue 4: Listening Volume

Lastly, listening volume is an important factor. The better the speaker sensitivity, the higher volume your speakers will go without staining the amplifier. As I said earlier, the Speaker SPL calculators are a great tool to figure this out for your space.

Ultimately, if you want to play your system close to reference level (85dB continuous with 105dB peaks), you will need efficient speakers or a relatively small room. As it all depends on those factors.

My Personal Experience

Currently, we have a room that’s 5m by 3.6m with a ceiling height of 2.5m. I have 4Ohm Jamo D500 speakers currently, but I have had M&K S150 in it as well. Both sets have relatively low sensitivity and require tons of clean power to run effectively. Since they can dip down to 2Ohms in places, more power means a cleaner impulse response and better imaging.

So ultimately, anything lower than a Denon 4000 series or Marantz 6000 series is really not going to cut it. In fact, it’s borderline underpowered as it will start to strain above -20dB whereby clarity suffers – especially with dialogue.

So even in this small room, I need to have an AVR with 170Watts per channel – so really the top models from each manufacturer – to really make the speakers work well. This is why I chose to supplement my AVR with an external 7-channel equal power amplifier to run the bed layer / floor level speakers as I don’t want to have to shell out close to $5K every few years just to upgrade. This way, I can go for a lower-end processor and get very clean power with excellent clarity.

HOWEVER, my friend decided to invest in Klipsch speakers which have one of the highest sensitivity of any manufacturer. Even though, he decided to invest in an external amp to supplement his Yamaha RX-A3060 when he got his system, the external amp is not required like AT ALL. Those speakers produce incredibly clean sound and could run on a bloody battery-operated amplifier, I kid you not. So the Yamaha is more than unto the task, even when running the front L/R as full-range. I was always impressed by how effortless the system sounds even without the external amp. This is in stark contrast to my D500s which could guzzle up as much power as you can deliver to them.

So you say why do I stay with Jamo? That is a good question that is for another article. But ultimately, it is better the devil you know. Once you have figured out a particular set of speakers – as each have their quirks – you are able to integrate them better. My system sounds more like a commercial theatre than his system. This isn’t due to the choice of speaker brand, but due to some very careful choices in how the system is selected – including the surround speakers -, set up and integrated with the room and subwoofers. This takes time and effort, and ultimately better or more expensive speakers will not necessarily sound better if the user isn’t taking the time to do that.

All the pro guides below will help you fine-tune your system. However, I feel there is a need to talk more about speaker selection as well because more and more users ask me this question. In fact, I feel the HiFi crowd getting into home theatre bring a level of baggage that almost needs to be unlearnt to be successful in creating a kick-ass system so I’ve given it a lot of thought recently to bring them along tactfully but also not mince words. I think I have a strategy that will work so stay tuned!

Related Pro Guides

Secrets of Audyssey

YPAO – The Lost Manual

Dirac Live Perfection