As part of my mini-series of blog posts regarding topics of common confusion in home theater, below I cover speaker resistance and analog vs. digital amps in AV receivers. This series features excerpts from my new Kindle book Home Theater for the Internet Age.
- Part 1: Volume in a zero dB world, updating firmware, and the disadvantages of Blu-ray
- Part 3: PCM vs. bitstream and Blu-ray player upscaling/upconversion
- Part 4: THX certification, DLNA network access, and distortion and THD
- Part 5: HDMI (including cable length and controversial expensive cables)
- Part 6: Closed-back vs. open-back around-ear headphones
- Part 7: Understanding your room and room dynamics
- Part 8: Room correction, speaker position, and more room dynamics
- Part 9: Ethernet, component separates, and broadband internet routers
Speaker Resistance: 4 ohm vs. 8 ohm
When it comes to amplification wattage, the general rule is that more is better. But, as mentioned, the clarity and lack of distortion of the audio and video produced by any receiver is as important as the sheer power level. While bigger is typically better, the proper receiver selection involves knowing the speakers you’re getting. In terms of power and electrical current, there are two types of speakers: 4 ohm and 8 ohm. In a nutshell, 4 ohm speakers require less power than their 8 ohm siblings. Technically, 4 ohm speakers feature lower resistance, allowing more electrical current from your amplifier to flow through them.
When researching and shopping for AV receivers, you may find amplification power quoted as two different wattage numbers, one when paired with 4 ohm speakers (the higher figure) and another for 8 ohm models. If a manufacturer or reviewer quotes only one number, it’s traditionally the lower wattage, reflecting the case of driving more common 8 ohm speakers. Beware: Don’t read the higher 4 ohms wattage number and mistake it for the 8 ohm figure. This could convince you that you were purchasing much more power than you were actually getting, possibly allowing your speakers to lag and not reach their full potential.
To get an idea of the difference in power output from an amplifier when powering 4 ohm and 8 ohm speakers, consider that an average 125-watt amp (receiver) when pushing 8 ohm speakers will provide roughly 200 watts when connected to a lower impedance speaker of only 4 ohm. If your speaker selection includes 8 ohm models, you’ll want to investigate if your AV receiver candidates will sufficiently power your particular high-resistance choice. This is an area where personal testimonials—taken with a grain of salt and easily found on YouTube and web forums—are a great way to learn from the mistakes and successes of others.
Generally, especially if you have 8 ohm speakers, you want 100 or more watts per channel (but, again, this is highly dependent on your particular speakers and their specs). Although this book doesn’t delve into the nuances of volts, amps, and watts, it should be noted that multi-channel amplifiers that provide audio to at least five speakers in your home theater pump more watts per channel when driving only a stereo, or two-channel arrangement (the available power is simply spread over fewer channels). Thus, your research project becomes even more complex, because receivers show different performance levels when operating in five channels (movies) or two channels (music and much TV programming). Are you listening to a Led Zeppelin CD or watching The LEGO Movie on Blu-ray? And at what volume? Your receiver, when paired with your speakers, should provide enough clean power to be good at both.
Note that some digital amps can’t power 4 ohm speakers, going only as low as 6 ohm. Carefully compare the specs of the speakers and receiver you choose to power them to ensure that you won’t run into any roadblocks (or have to fall back on a reseller’s return policy).
Digital vs. Analog Amps
Just as display technology is rapidly advancing, with OLED and 4K on the horizon, so too are other areas of home theater technology, specifically receivers and amplifiers. AV receivers have traditionally included analog amplifiers, called Class A/B amps, a technology in use for the past few decades. When digital amps, called Class D, first appeared, their expense put them out of the reach of the average consumer. Pioneer Elite’s first receiver featuring a digital amp, in 2008 (only six years ago), was $7,000.
Like all technology, this highly efficient binary amplification has become much more affordable and begun appearing in receivers priced under $1,500 (sometimes with sub-$1,000 street prices). Digital amplification basically does more with less, minimizing power consumption while producing more accurate, robust amplification when necessary. The advantages of digital amps are especially apparent at louder volumes and when the unit is being taxed, delivering in the neighborhood of 80-90% efficiency. This means that 80-90% of the energy consumed by the digital amp is converted into more powerful sound produced by your speakers (compare this with Class A/B analog amps that, while often producing stellar sonic performance, average 30-60% efficiency). However, preference between Class A/B and Class D digital amps is subjective. Not everyone prefers digital amps.
If Tesla is the next step in the evolution of the automobile, then Class D is the new species in the evolution of affordable home theater amplification. While there will always be those who prefer old school analog (sometimes really old school, as in the case of expensive retro tube amps), digital power processing is the wave of the future. Many who complain about performance issues will be pleasantly surprised with the high-quality and affordable models that will pour onto the market during the next decade.
However, you need to remember: There’s a lot more to a receiver than its amplifier class. As you’ll hear echoed throughout this book, I’d rather have a receiver featuring a really good Class A/B amp than one with a mediocre Class D type. The quality of the audio produced by a receiver when paired with your particular speakers—not whether it features analog or digital amplification—is the real issue.
Curt Robbins is author of the following books from Amazon Kindle:
- Home Theater for the Internet Age ($9.95)
- Understanding Personal Data Security ($4.99)
- Understanding Home Theater ($4.99)
- Understanding Cutting the Cord ($4.99)
- Understanding Digital Music ($4.99)