From Blu-rays to popular streaming platforms like Hulu and Netflix, you can find more and more movies that support Dolby Atmos. Dolby Atmos is an object-based surround sound format that allows sound engineers to more accurately place objects like voices and footsteps in pinpoint locations in the sound image, resulting in a more immersive listening experience. While down-firing speakers found in home theater setups are considered the standard for Dolby Atmos technology, you can also find Atmos-enabled soundbars designed to create the illusion of height.
We perform several tests to measure a soundbar's height performance, including localization, slope, standard error, SPL @ Max Volume, and weighted total harmonic distortion at 80 dB SPL and max volume.
If you like to listen to Atmos-enabled content, you'll want a soundbar that can offer an immersive listening experience. Most new movies and video games support Atmos, so fans of this content want a soundbar that can reproduce a large soundstage and accurately localize objects like voices and footsteps in the sound image. It's also important for those who want to feel the deep, thumpy bass in action-packed scenes and hear clear and accurate dialogue. You may also want to crank up the volume when listening to Atmos content for a loud sound without a lot of distortion. Surround and stereo content like older movies and music don't have height channels, so this won't matter for listeners who prefer those types of audio content.
To test a soundbar's Atmos performance, we look to see how accurately it can reproduce an Atmos file with one object placed in the middle of the ceiling. We measure its frequency response by playing a sine wave tone at -6 dB FS between 20Hz and 20kHz and plotting its output, in dB, on a frequency response graph. Using our microphone array, we also measure how loud the bar gets on its height channels. Additionally, we apply a spectrally pure sine wave to measure the amount of total harmonic distortion, both at a normal listening volume and at max volume. While we only test for Atmos content, we expect similar results with DTS:X content.
We perform our Atmos channel tests with a similar setup to our stereo channel tests. We use a room that's 20' (L) x 16' (W) x 9.5' (H), with one couch and minimal sound treatment to represent a typical living room. We place the soundbar and the table it sits on 7.5 feet away from our microphone array. We also test the bar when it's 6.5 feet and 8.5 feet away from the microphone to get a better understanding of the sound profile from different places in the room. We use a laser measuring tool to ensure that the microphone array, table, and soundbar are at the appropriate distance from the side walls, as well as the subwoofer and the satellites if they're included in the setup. However, we test the Atmos channels using the same preset we selected for our stereo frequency response tests and not with preliminary calibration.
While many soundbars support Dolby Atmos content, not all of them reproduce this content in the same way. Localization describes how the soundbar is set up to playback height content and can impact how accurately objects reproduce in the soundstage.
Home theater setups tend to come with dedicated or discrete height channels that you can screw into your ceiling, which offer the most accurate and focused soundstage performance. However, soundbars may have a phantom setup, meaning they use up-firing or side-firing speakers to bounce sound off the ceiling and back down towards you to simulate height. Unfortunately, a phantom setup can't reproduce objects in the soundstage like voices and footsteps as clearly or accurately as a discrete setup. Other soundbars that lack Atmos capabilities have to downmix this content into surround to play it, which doesn't sound as immersive.
During our height tests, we measure the frequency response of the height channels by playing a sine wave tone at -6 dB FS between 20Hz and 20kHz and plotting its output on a graph. Ultimately, the frequency response graph shows us how accurately the soundbar can reproduce audio at each frequency, from the low bass to the high treble.
The slope of the frequency response describes the overall tonal balance of the bar's sound profile. If the slope is negative, the bar reproduces more bass than treble, resulting in a thumpy, punchy, or boomy sound. A positive slope represents a frequency response with more treble than bass, so your audio may sound bright, sparkling, or piercing. A slope closer to zero represents a more balanced sound.
As with our stereo frequency response tests, we don't score the slope for the height channels. Personal preferences play a role in determining the sound profile that you'll prefer. While a neutral, balanced sound is considered suitable for most types of audio content, some listeners may prefer a bass-heavy sound that adds more thump and punch to action-packed scenes.
Audio content like movies and video games are mixed to contain a wide range of frequencies, from the thumpy bass in action-packed scenes to the dialogue and lead instruments in the mid and treble ranges. Our standard error measurement shows the average deviation of the soundbar's in-room frequency response from the in-room target response, allowing you to see how accurately the soundbar reproduces audio at each of these frequencies.
For all of our sound tests, we use the Harman in-room response curve as our target response. Research has shown that this curve represents the sound most pleasing to most listeners, and it adds a little extra emphasis in the bass and a little less emphasis in the treble. Ideally, your soundbar will have a low amount of standard error, meaning that its audio reproduction is very similar to the target curve. This usually results in a cleaner, more even sound.
You can usually tell which soundbars have higher amounts of standard error just by looking at their respective frequency response graphs. A soundbar with a lower standard error will usually have a flat response that's close to the middle, while a response that deviates from the middle usually represents a higher amount of standard error.
Depending on where those fluctuations occur in the graph, you can get a better understanding of the bar's sound profile. The bass range is where the thump and punch in your audio reproduce, so an overemphasized bass could make your audio boomy, while an underemphasized bass could mean that you don't feel the rumble in action-packed scenes. Deviations in the mid-range can make vocals and lead instruments muddy or push them towards the back of the mix, while fluctuations in the treble range could make higher-frequency sounds either piercing and painful or dull and whispery.
If you listen to audio in a large room or at crowded parties, you may want to crank up the volume for a loud sound. We measure the soundbar's Sound Pressure Level in decibels (dB) when it's pushed to its max volume. This measurement shows us how loud the soundbar can get on its height channels.
We consider a good value to be above 92 dB SPL since this gives you a lot of flexibility in selecting how loud your soundbar can get. Most of the soundbars we've tested measure between 80 and 95 db SPL, but your personal preferences play a role in how loud you want your soundbar to get. You can also find soundbars that get a bit louder than that, like the Nakamichi Shockwafe Ultra 9.2Ch, which reaches 100.2 dB SPL on its height channels.
Total harmonic distortion, or THD, is a measurement that shows the number of unwanted frequencies that the soundbar reproduces alongside the intended frequencies. Essentially, it compares the input, or the audio that you're listening to, with the output reproduced by that soundbar. Ideally, a soundbar has a low amount of distortion since that means that your audio content reproduces the way it was meant to be heard by whoever mixed it.
We use an SPL meter to set the soundbar to a normal listening volume of 80 dB SPL. Then, we apply a spectrally pure sine wave and measure the output produced by the bar using our microphone array. By comparing the input to the output, we can determine the amount of total harmonic distortion. Our measurement applies more weight to higher frequencies since those are more likely to be audible. THD can be difficult to hear with real-life content, so it's mostly important for listeners who care about the fidelity of audio reproduction.
If you like to listen to your Atmos content at loud volumes, you'll want to see if your soundbar can maintain clear and pure audio reproduction when it's pushed to its max volume. We measure the amount of total harmonic distortion, or THD, reproduced by the soundbar at its max volume on its height channels. Our testing procedure is the same as above, only we set the volume to its maximum instead of 80 dB SPL.
Most of the soundbars we've tested see a jump in total harmonic distortion at their max volume. However, THD can be difficult to hear with real-life content, especially if the weighted total remains below one.
If you enjoy Atmos-enabled movies and video games, you'll want a soundbar that offers an immersive height channel performance. Our Atmos tests give you a better understanding of how accurately the bar can reproduce the thumpy bass and the dialogue in your movies and whether or not objects like voices accurately localize in the soundstage. You may also want a soundbar that can get loud on its height channels without a lot of distortion. However, if you only want a soundbar for listening to stereo and surround content like music and older movies, this may not be very important to you.