The HomePod Is a Mono Speaker

Stereophonic sound uses two speakers to deliver two very different sound channels (depending on how the music was recorded) to deliver sound that approximates what we hear when we hear music live. It uses two channels, because we have two ears. The HomePod is a mono speaker. It uses a ring of seven tweeters to adjust the volume of the mono sound it sends out in an attempt to provide balanced sound anywhere in a room. It does not create any form of stereophonic sound reproduction.

I’m correcting a statement that Daniel Eran Dilger on AppleInsider posted in a rebuttal to my recent article about the HomePod. While I’m happy to disagree on some points, he makes the statement below about the HomePod not being a mono speaker, which is simply incorrect.

He also makes the bizarre claim that “it’s a mono speaker.” HomePod is not a mono speaker. A mono speaker is a single speaker that can only deliver a single channel of audio, resulting in its sound clearly appearing to come from one source. Stereophonic sound uses multiple speakers to deliver at least two slightly different sound channels to create a wider soundscape. HomePod is a stereo speaker. It uses a ring of seven tweeters to send out stereo sound that creates a wide, surrounding sense of stereophonic sound reproduction.

Also, “a mono speaker is a single speaker” is not correct. A mono speaker can have multiple “speakers” – aka drivers – such as a woofer, midrange, and tweeter. Or use one floor standing speaker, that may have four or five drivers, for mono sound. At a minimum, most – though not all – speakers that aren’t portable have two drivers, a woofer and a tweeter.

Apple sells the HomePod as having “room-filling sound.” But they never suggest that it’s stereo. It’s not hard to test it: put on I Saw Her Standing There, on The Beatles’ 1963 album Please, Please Me. Paul’s voice is on the right channel, and the main guitar and the drums are on the left. This was common practice in the early days of stereo.

Listen to that song on a single HomePod and you’ll quickly understand that it’s not stereo. The two channels are in a single stream, and you don’t hear the voice on one side and the guitar and drums on the other. It’s logical: how would the HomePod know where the listener is to know how to separate channels? This would be possible; they could have, say, an iPhone emit a tone that the HomePod could identify, but aside from that, it’s just guesswork. In fact, go to your favorite streaming service and find the stereo and mono versions of this song. Listen to both of them on the HomePod: skip back-and-forth from one track to another. With the exception of the fact that the mono version is a bit louder, you will note that the sound is exactly the same.

In addition, Mr Dilger seems to ignore that stereo sound requires separation. There are plenty of “stereo” speakers that aren’t really stereo, because their two speakers (generally two tweeters; a single woofer can be used in such cases) are too close together. So even if the HomePod was an actual stereo speaker, with different audio coming out of the left and right sides, it wouldn’t sound like stereo, because there would be no separation. You’d get a sort of spatial effect if you were far enough away, but only if there are walls close enough to the HomePod for the different channels to reflect off.

Discussing my presentation of two HomePods on either side of an iMac – it’s not just “someone on Reddit” who imagined this; a lot of people hoped they could do this – he says:

This is purely ridiculous, as one HomePod delivers far more than enough sound to be placed within an arm’s reach of a seated computer user. Placing one on either side of an iMac to deliver “stereo” is simply a dumb idea, based on the misconception that HomePod is a “mono speaker” and that a Mac user would need to have two of them.

So he’s suggesting that one put the HomePod in front of the iMac to get a stereo effect…?

I’m not looking to get into an argument, but sometimes there are facts that can’t be explained away by fanciful marketing.

Source: Editorial: After taking the premium tier, HomePod will expand in markets Amazon and Google can’t

One more thing. I think what is confusing people about this is what Apple says about the HomePod:

HomePod combines Apple-engineered audio technology and advanced software to set a new audio quality standard for a small speaker, delivering high-fidelity sound and a wide soundstage. Featuring a large, Apple-designed woofer for deep, clean bass, a custom array of seven beamforming tweeters that provide pure high frequency acoustics with incredible directional control and powerful technologies built right in, HomePod is able to preserve the richness and intent of the original recordings.

The section I have put in italics is what makes some people think that the HomePod is actually a sort-of-stereo device. All it is doing with this “incredible directional control” is compensating for the shape of the HomePod. Most speakers point in a specific direction; the HomePod is omnidirectional. What it does, using its microphones and multiple tweeters, is modulate the volume from each tweeter according to the proximity of walls or other objects in rooms. And, using time delays and reverb, it can create a more spacious sound from a single speaker than one that is just pointing in one direction.

Look at this still from Apple’s animation about the HomePod:

You can see that two of the mauve circles point forward, and are larger than the two smaller ones that seem to reflect off the back wall. With these multiple tweeters, the HomePod can produce sound that can develop resonance if it is timed correctly according to the distance of walls. The blue circles are the bass, which, perhaps, also has a bit of delay. What is deceptive in this photo is that there are two pairs of mauve circles, suggesting that it might be stereo. It’s not, but the volume of each tweeter is adjusted using the “incredible directional control.” Hence the spatial impression that can make music sound less flat.

However, this fails totally when the HomePod is in the center of the room, but, in that case, the HomePod is far superior to a directional speaker, because it can send music in all directions. I would guess there is probably not much difference in volume when the HomePod detects that it’s far from walls, because the goal there is to fill the room completely. This is, in fact, the ideal use case for a single HomePod: in a central location, with people in many positions around it. Set it up on a table in the middle of a room when you have a party.

Apple continues:

With two HomePod speakers set up as a stereo pair, this soundstage gets even wider, delivering room-filling sound that is more spacious than a traditional stereo pair from a speaker that’s just under 7-inches tall. Using spatial awareness to sense their location in the room, each HomePod automatically adjusts the audio to sound great wherever it is placed and sound great together, using an Apple-designed wireless peer-to-peer direct link to communicate with each other and play music completely in sync.

This suggests that the “spatial awareness” is used to control which tweeters send audio. The HomePod knows it’s, say, a foot from a wall, and can tell that the other HomePod is at a certain direction, allowing it to figure out which way is intended to be the front. This probably doesn’t work if you set two HomePods, say, at ends of a table in the center of a room.

Note: some of this is educated guesses, based on what Apple has said, and the way the device is constructed (ie, seven tweeters and six microphones). For more details about this, watch Phil Schiller presenting the HomePod in 2017. Of course, you need to take with a grain of salt what he says about things like “ambient audio, the backing vocals and reverb.”

18 thoughts on “The HomePod Is a Mono Speaker

  1. Although traditional stereo is all about right left separation I think there is more to this than you are making out. To fully understand I would suggest you mix down the same song to mono and play it on the HomePod back to back with the stereo version. If you can’t hear a difference, then your claim that the HomePod is a Mono speaker will be solid! I agree with you that true stereo separation and musical imaging would be something that might be very difficult even in the best case where the HomePod was in a corner and you were sitting directly in front of it. But in theory that is exactly what it is trying to do and at such close proximity it might succeed.

    You argue that the speaker doesn’t know where you are but it knows where it is specially and knows the surfaces it can use to reflect sound. So your example would be an iMac with the HomePod directly behind it, with it pulled 12-18+ inches from the corner causing most of the forward directed sound to be blocked and the reflected sound is what you would mostly hear.

    • Oh, there is definitely a sort of faux-surround sound coming out of the HomePod, but it’s not “stereo.” There are cases when the HomePod can tell which way is front: if it’s got a wall behind it, and a lot of space in front, it can detect the time it takes for music to echo back. But nevertheless, it can’t be stereo for everyone, and can only really “point” in one direction.

      • To be fair, no “stereo” is “stereo for everyone”. That is why you setup listening locations to fully enjoy music. If you are too close to one speaker or the other it will completely destroy the imaging of the music.
        Also, you said it was “mono” and not that it was “not stereo” I get that you used those interchangeably, but there is a difference. That difference is the “faux-surround sound” it generates which includes it’s attempt at actual stereo.

        • It’s not an attempt at stereo; it’s trickery to make it sound fuller. And it’s very subtle; it’s not like the plugins that use phasing and timing to create a fake “immersive” soundstage.

    • I just went back and forth between the stereo and mono versions of I Saw Her Standing There. With the exception of the fact that the mono version is a bit louder, there is absolutely no difference between the sound of the two versions. This is actually quite a convincing test to prove that the HomePod is mono: take the same song in stereo and mono and listen to them. Thank you for pointing that out.

  2. I like your rebuttal of the rebuttal, Kirk. Daniel Eran Dilger’s quoted ‘explanations’ of stereo and mono are silly and do not use standard terminology. Kirk, you have shown in the past how inaccurate writing about music reproduction often is. This is another example of faith-based technology writing.

  3. Those paragraphs from ai were a weirdly condescending rebuttal (Such as, “Anyone who calls HomePod a “mono speaker” does not understand elemental basics of sound reproduction.” Wow).

    I’m surprised that there’s any confusion about a single HomePod being mono or not. Especially since Apple’s own support page for creating a stereo pair has the following, “Learn how to create stereo sound with two HomePod speakers.” Sounds pretty cut and dry to me since “create” implies a lack thereof.

    Also: if a single HomePod were stereo, Apple would say so. The call it a “speaker” and not a “stereo”, and they use “all-encompassing sense of space” to describe the effect of a single HomePod rather than use a floridly embellished “stereo”. It being truly stereo would be a selling point, so hiding it makes no sense.

    Anyway, searching for “HomePod mono” on Google has revealed that a lot of people are confused about this as well. All of Apple’s jargon seems to have successfully obfuscated the mono reality of the device.

    • Exactly. I remain polite in these things, but that person was extremely tetchy.

      But, as you say, the idea that the HomePod is stereo is not uncommon, because some people just didn’t understand what Apple said about how it worked.

  4. Well, the HomePod isn’t really mono, it isn’t really stereo, and it definitely isn’t surround sound. The HomePod is a stereo-fed, multi-aural system that uses various speakers with different timing to project fake-3D sound in the room.

    That’s pretty much what it is.

      • Yeah sorry, “fake-3D sound” is the wrong term. The HomePod uses his 6 microphones to analyse the different reflections around it and the DSP adjusts the timing and power of each speaker accordingly. The result is a more transparent sound than you’d expect from a stand-alone speaker unit.

        Regarding “Stereo”: On the HomePod launch event, didn’t Apple announce that 2 HomePods could mimic Stereo sound when combined? Thought I heard something like that.

        • Yes, and I discuss a stereo pair of HomePods in the original article.

          I’m not sure the goal is transparency, but rather dosing the music indifferent directions to ensure similar volumes in different parts of a room. But in most cases, that doesn’t matter very much.

  5. This has all been guesswork really. The fact is a HomePod is either stereo, or mono and that has NOTHING to do with how many speakers it has, nor how it may digitally process the sound signal to create (i.e. fake) any sense of depth and anyone who claims otherwise has no business commenting on such matters.

    The fundamental difference is whether the HomePod deals with 2 channels of audio and processes them separately or it combines them into a mono signal and processes that. The former would make it stereo and the latter would mean it is mono and at this stage I’d say only Apple actually know the answer to that.

    However, how does a HomePod receive the audio signal? AirPlay? Bluetooth? It is possible that in either case. the receiver (i.e. HomePod) specifically requests mono data from the source which would save bandwidth and the HomePod from having to combine the channels at all. In this case it would only ever receive a mono signal. I have no idea if this is how AirPlay and BlueTooth audio function, but it’s certainly a possibility.

    In any case, Apple have made NO statement indicating any stereo capability of a single HomePod, but have made specific reference to using 2 HomePods combined to make a stereo pair and also there’s Kirk’s test results. I’d say that’s all pretty conclusive evidence that a single HomePod is a mono device, whatever fancy processing it does to the audio signal it receives.

  6. Something else occurs to me. I have a small stereo test track in which a voice repeats “left channel” and then “right channel” so it allows you to definitively hear where each channel is being sent. I would suggest sending this to a single HomePod (which I do not have) and see from where each channel emanates.

    Would that not be a good test?

    • To ensure that the HomePod doesn’t know left from right, I tried one of my speakers on my desk with some online tests. It’s exactly the same no matter which channel is sent to the HomePod.

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