If you're looking for a rich, immersive, and exciting audio experience for your music or videos, you'll want a speaker with a good soundstage. It's the 'stage' for your audio, comprised of the width, depth, and height of the projected audio image as you perceive it. Another way to understand this is to imagine yourself at a concert in which all the musicians surround you. Based on their arrangement, you can perceive where their sound is coming from without necessarily seeing where they're located. A good soundstage can also help separate instruments and make your audio sound clear from different angles.
There are a couple of factors that we test for that can influence how you'll perceive a soundstage: the speaker's directivity performance and if the speaker is stereo or mono.
If you like music or movies, a wide and natural soundstage can improve your audio experience by giving you a sense of depth, height, and width. Objects in the soundstage like voices or instruments seem like they're coming from precise and distinct areas around you, rather than from the front of the speaker. Your audio also sounds more immersive, which can be especially good for movies or videos. A good soundstage is also important if you want your audio to sound clear, even if the speaker is pointed away from you.
To measure a speaker's soundstage, we measure its directivity index and whether it's a stereo or mono speaker. These two components can tell us how wide and natural the soundstage seems. It also indicates if the audio sounds clear at different angles or if there's deviation, which could make it harder for you to hear your audio if the speaker is turned a certain way.
Our soundstage test is conducted at the same time as the frequency response and dynamics tests. We use a room that's 18' (L) x 16' (W) x 9' (H). There's one couch, and there's minimal acoustic treatment. The speaker is placed one meter away from the tip of the central microphone. Using a laser measuring tool, we ensure that the microphone array, table, and speaker are all at equal distance from the side walls. We also check that the speaker is placed at an equal distance to all of the table's sides. Finally, we also run this test using the speaker's battery, if applicable, and pair the speaker to our test phone via Bluetooth or Wi-Fi.
Speakers come in lots of different shapes and sizes, which can impact its soundstage. There are two general designs: a front-facing speaker that plays audio in one general direction, and an omnidirectional (or 360-degree) speaker, which plays audio in all directions. A 360-degree speaker can help create a wider soundstage while ensuring that your audio sounds clear from all angles. We measure a speaker's performance at different angles using the directivity index. This index measures in decibels how directional a speaker's pattern is, and how narrow or wide the soundstage seems.
To test a speaker's directivity, we place it on a moveable table one meter away from our mic setup. We play an audio file to measure its frequency response and turn the table to seven different angles (0, 30, 60, 90, 120, 150, and 180) while recording each pass. In the graph, the 0 line is the flattened frequency response at 0 degrees. Each thin line corresponds to a different degree and is the difference between the 0-degree frequency response and the corresponding angle. The red line indicates the average difference. In short, the smaller the directivity index or the flatter the graphed responses, the better a speaker's directivity.
Directivity is important for creating a large soundstage, especially if you like to listen to music or movies. Also, 360-degree speakers can be beneficial for gatherings so that everyone hears the audio clearly. That said, while some speakers have a poor directivity index, they're designed to be paired with another unit like the Sonos One Gen 2, which can be added to your pre-existing Sonos soundbar setup for a more immersive audio experience. You can also pair them with multiple other units if you want to cover a large space.
If you like to listen to music from your speaker, you'll want to know whether your speaker is mono or stereo. This refers to whether it can play either monophonic (mono) or stereophonic (stereo) signals. Mono signals contain a single audio channel, while stereo signals contain two channels, left and right, which sound somewhat different from each other. We test whether a speaker is mono or stereo by checking the user specifications or tech drawings. We also use a test signal to see whether the speaker can play the left channel and then use a different test signal to see if it can play the right channel.
To play stereo signals, speakers like the DOSS SoundBox Plus or Sonos Five have to have separate left and right channels. These two channels play stereo signals to help create the impression that sound is coming from localized areas rather than from the front of the speaker. For example, if you're streaming video with your speaker, someone can speak on the left-hand side of your screen, and the stereo speaker can then localize that voice so that you perceive it as coming from your left. This can help its soundstage seem wide and accurate.
Speakers like the Amazon Echo Dot Gen 4 are mono speakers, so they only have one channel to playback audio. When it receives a stereo signal, it has to downmix it into mono to play it. Mono speakers don't create a very immersive soundstage, as the objects they produce are two-dimensional and lack width. That said, stereo speakers can still play mono content. They play the same mono signal from both the left and right speakers, which creates a phantom mono sound source. You may even want your speaker to play mono signals if the original track was recorded in mono, like AM radio or older albums.
In addition to width, there are two other components of a 3D sound, height and depth, which also play a role in creating an immersive soundstage. However, note that we don't currently test for height or depth when evaluating a speaker's soundstage and it's a limitation of our testing at the moment. That said, height is created by frequency or the sound's pitch in relation to other sounds in your mix. For example, sibilants like cymbals are localized higher than low-frequency sounds such as a bass guitar, which creates a perception of height. In contrast, depth is a mix of dynamic range, reverberation, and level. Depending on this, sound can be perceived as if coming from closer or further away from you. Stereo and mono signals can both reproduce height and depth. However, only stereo can create width, which is why some people may describe mono audio as 2D.
A good soundstage can make all the difference if you want a rich audio experience. A narrow directivity index can make your audio sound clear from all angles, while a stereo design can help your mixes seem wide and accurate. Depending on your setup, a speaker with a wide directivity index or a mono channel may not necessarily be a bad thing if you have several units placed elsewhere throughout your room. You may also prefer a 360-degree speaker if you have a gathering. That said, if you're a fan of immersive content like music or movies, and you only plan to use one speaker, you'll want to prioritize a stereo design and a narrow directivity index to get a natural, wide, and accurate soundstage.