AC Wall Power Considerations for Your Home Theater System

 We often get asked how much AC wall power is needed to run a typical home theater system. There are lots of factors that determine this such as the number of AV components you have plugged into the same outlet and their associated power consumption, and whether or not that outlet is shared with other appliances or lighting on the same circuit. This article and related YouTube video discussion provides guidance on helping you decide whether you need dedicate outlets for your home theater to deliver 1.21 Gigawatts!

Most domestic homes have standard 120V/15A outlets but if you're building a new home, you can request dedicated 120V/20A lines for increased power capability.

• Standard 120V/15A outlet provides up to 120V * 15A = 1800 watts
• Standard 120V/20A outlet provides up to 120V * 20A = 2400 watts
  

That's a 33% increase in available power!!!

AC Power Considerations for Your Home Theater YouTube Review

The typical 20A line uses thicker 12AWG cabling while a typical 15A line uses 14AWG. Keep that in mind when pre-wiring a new home or retrofitting an existing home. A dedicated 20A line is NOT just about a large fuse at the panel. You also need a proper gauge wiring from the panel to your wall outlet.

If you are trying to determine if you need a 15A or 20A circuit, as a rule of thumb sum the maximum rated power of all your audio/subwoofer amplifiers and other devices connected to that outlet and divide by a factor of four (4).

IE. Typical Scenario

• HDTV:         200 watts
• AV Receiver:    800 watts
• Subwoofer:    1000 watts
• Source devices:    100 watts
• Total:  2,100 watts / 4 = 525 watts, which is < 1,800 watts. In this scenario, the standard 120V/15A outlets are fine.
  

But on a shared outlet, you may have lighting and other devices connected too!

(4) 60 watt recessed ceiling lights will consume 240 watts continuously!

For systems utilizing large powerful amplifiers, it's a good idea to run a dedicated 20A outlet to ensure they don't get starved of power.  

Consumer products for domestic products are designed to operate on 120VAC ± 10% or from 108Vrms to 132Vrms. Operating above or below the nominal VAC can damage your components.

Sagging line voltage can cause an amplifier to try to draw in more current which can damage your components. It also limits available supply voltage to the rails and thus reduces available power to the loudspeakers causing the amplifier to clip (or distort) sooner which can potentially damage the tweeters in your loudspeakers. 

Example Power Comparison of 15A vs 20A Line

I'm currently testing the Anthem STR Amplifier rated at 600 watts/ch with 2 channels driven.  Nominal power consumption for an amplifier like this under moderate loading conditions is between 600 watts - 1100 watts according to the manufacturer. 1100 watts is about 60% of available power from a 15A line. Throw in a few components like an HDTV, and some source components and a few lights and you're already at your power limits for that outlet. In addition, this amplifiers maximum power capability can actually consume the full 1800 watts of a 15A line so if other devices are also attached to the same line, you are limiting its maximum potential.

We decided to test the limits of this amplifier using a shared 15A line versus a dedicated 20A line to show you the power output differences.

 

Anthem STR Power Output (2CH driven, 4 ohms) tested on a shared 15A line

Anthem STR Power Output (2CH driven, 4 ohms) tested on 20A line

Anthem STR	Power Output (15A line)	Power Output (20A line)	% Increase
0.1%, 2CH, 4 ohms	536 watts/ch	671 watts/ch	25 %
1%, 2CH, 4 ohms	562 watts/ch	708 watts/ch	26 %

As you can see, having a dedicated 20A outlet to power this amplifier allowed it to produce 25% more power than when used on a shared outlet. In fact, the amplifier failed to meet its 600 watts/ch (2CH driven) spec when using a shared outlet but exceeded its spec when supplied with enough output power from the wall outlet to deliver it.

In the 15A case, the amplifier was consuming roughly 1440 watts ((562x2/.78)*100) to deliver its 562 watts/ch x 2 measured output. As it was doing this, I watched the line voltage drop from 119Vrms to 106Vrms, which not only caused my lights to dim during the test but it forced the amplifier to operate below its minimum 108Vrms input requirement. In contrast, the wall outlet never dropped below 112Vrms on the 20A line during my test despite the fact that it was pulling in over 1815 watts ((708x2/.78)*100) to deliver a whopping 708 watts/ch x 2.

Granted, bench testing an amplifier with continuous tones is a worst case scenario but it proves the point about how important providing a stable power source to a high power amplifier really is.

Amplifier Review Considerations

It's important to note when reading reviews of amplifiers online or in print, one should consider if the reviewer specifies the line conditions used when testing the amplifier in question. This is a particularly important point if the reviewer is complaining about the amplifier lacking sufficient power during their listening tests. At Audioholics, we do ALL of our listening tests and bench tests of amplifiers on a dedicated 20A outlet unless otherwise stated.

Recommendation

Get an electrician to run at least 1 (preferably 2) dedicated 20A line(s) to your home theater room and use that line to connect your power amplifiers and/or powered subwoofers to. All other devices that consumer less power (i.e. HDTV, source devices, game systems, etc) can be plugged into shared outlets.

15A Outlet (left pic); 20A Outlet (right pic)

If you don't have a way of measuring actual power consumption, we recommend doing load calculation estimates as shown in the prior example to determine how many dedicated outlets you will need for your home theater. In practical real-world tests, if you are currently using a shared 15A line for your home theater and notice the lights that share that outlet flicker or dim during loud music/movie passages, then you're definitely a candidate for running a dedicated outlet to your power-starved power amplifiers or powered subwoofers.

In the Audioholics Showcase theater room, we have five powered subwoofers, two of which are on a shared outlet with an array of ceiling lights. If I crank the bass up high enough with ALL of the lights turned on, you can see them flicker in unison with the bass notes. This is not a good thing and I still mumble curses under my breath at the electrician who wired my home and forgot to run a fourth dedicated 20A line to the area of my room where I have those subwoofers plugged in.

Next time a friend of yours brags about how many watts his home theater is, ask him what kind of AC wall power he is using to feed his amplifiers. Then you can politely tell him his 300 wpc x 7 amplifier running on a shared 15A outlet is likely only capable of delivering about half that power spec under his current wiring conditions.  Dr. Emmit Brown will not be impressed and neither should you.

Let us know in the comment section below what kind of AC power you have going to your home theater system and if you plan on upgrading after reading this article.