PREFACE: Any time you read a review about speakers that was not conducted in a lab with calibrated tools, it is going to be subjective. This review is subjective. It means that the results of my test are only as I my ears & brain perceive them. Everyone hears the exact same audio differently. Everyone has a preference as to what sounds “best”. You hear people refer to music as “warm” or “bright” or “tiring” or “smooth”. I like to think of it like this: You probably have an EQ on your car radio or home audio system. How do you have it set? What does the ‘curve’ look like? Some people don’t like the obnoxious thump of bass, so they turn that frequency range down. Some people don’t like the ‘hissing’ sound of cymbals, so they turn those frequencies down. My preference is a curve that is high on the ends (Bass and Treble) and low in the middle (Midrange). This directly impacts what is heard in music.This particular review is specific to the Harman Kardon Onyx series and the Bose SoundLink Revolve+. My spending cap was $300 on Amazon, so that ruled out other speakers like the Vifa Oslo and B&W Zeppelin. I’d still like to try the HK Play+Go, but don’t have the resources right now. (Unless someone would like to gift me one to review 😊)------------------I’ve just spent the past month with the Oontz Angle 3XL Ultra ($100), the DOSS Soundbox XL ($70), Bose SoundLink Revolve+ ($270), the Harman Kardon Onyx Studio 1 (n/a), Studio 4 ($175), and Studio 5 ($164).I wanted to find the best speaker that fits MY listening profile. My primary focus is on audio quality via Bluetooth with a $300 max price on Amazon. Other factors like portability, water resistance, and battery life are not heavily weighted for me because this speaker is primarily intended for indoor use with AC power.So…”Long review short”…my preference in order of “Best” to “Really Good”. (None of them are bad.)The HK Onyx Studio 5 is my favorite. Why? It sounds the best (to me) and costs the least.Followed by the Onyx 4, and then the Bose Revolve+. The HK Onyx 1 is purely for reference and is no longer available to purchase. I decided not to include the Oontz and the DOSS in this writeup because after hours of testing, they just aren’t in the same game, let alone same sport. They will have a separate review. (Summary of that review: Get the DOSS @$70 or spend an extra $100 to get the HK Onyx Studio 5. That extra $100 will easily justify itself after years of listening pleasure!)To get the speakers setup, all speakers were plugged in to AC power. If a speaker had an available firmware update, it was applied. All speakers were connected via Bluetooth to an iPhone XS. I used the Amazon Music app (w/full Amazon Music subscription) to test. I selected specific songs that I know well across a variety of music types. The following is a small sampling of the Artists & Albums. Some albums I listened to in their entirety, some I just chose particular songs.Techmaster PEB – BassgasmChris Stapleton – TravellerDonovan – Beat CaféChristian McBride – Live at TonicPink Floyd – Dark Side Of The MoonGustav Holst – The PlanetsAudiolab – Audio Test TonesThe first thing I wanted was something that matched my listening preference as noted above. An upside-down bell curve. Strong bass and treble, and a flat midrange. To me, too much lower-midrange causes most music to sound muddy. Too much higher-midrange and it sounds hollow or echo-y.The Bose is definitely last place in the bass frequencies. Its single, smaller downfiring speaker just isn’t up to the task of creating bass you can actually feel (or hear at the really low frequencies). You can tell the Bose unit is making an effort, but it doesn’t have that deep sound that you get from the larger drivers on the HK Onyx units, particularly the Onyx Studio 4 & 5. I did try to cheat a little with the Bose by putting it on a surface that would allow it to act like a bass transducer. Unfortunately for that idea, Bose does a fantastic job of isolating its sound from the surface it’s on, so there’s no buzzing or resonance on any surface. This speaker is not going to vibrate itself off any flat surface.Where the Bose Soundlink Revolve+ shines is because it is a downfiring speaker, it does a much better job dispersing sound evenly throughout a room. The staging of its output just has a certain ‘something’ that is best explained by listening and not with words. Unfortunately, while the overall sound is smooth, it’s missing the low end that I require. Lack of bass response notwithstanding, the Bose most closely resembles the sound of the Onyx 4.Now on to the Harman Kardon Onyx Studio, models 1, 4, and 5.As I noted, the Onyx 1 is for reference. A family member has had it for years and I’ve always been impressed. It was time to see what improvements HK has made to its newer models.The Studio 4 and 5 definitely sound better than the original, but it’s not a HUGE improvement. If they weren’t side by side, most people would be hard pressed to discern a difference. The aural differences between the 4 and 5 are even less. What intrigued me the most between the 4 and 5 was HK’s decision to go from a 2x2 driver setup to a 1x1, respectively. My first thought was that any sound staging would be diminished with the newest model. Surprisingly, there is almost no difference between the two, so “props to HK” for being able to re-engineer the Onyx Studio 5 for better overall sound. If I didn’t have all the speakers side by side, I wouldn’t be able to tell the difference between the 4 & 5. However, ‘they were’ so ‘I could’. HK’s switch to the larger woofer in the 5 makes a notable difference, specifically when testing for sub frequencies. Both in music and using the Audiolabs test album, the 5 was absolutely able to respond down to 40Hz. This is also where the Techmaster PEB album came in to play. The Bose wanted nothing to do with it and didn’t bother to show up to the game. The Onyx Studio 1 at least showed up, but it was the 4 & 5 that actually hit the field to play. The 5 just barely edged out the 4. Again, that single, larger driver in the 5 is what works.The Studio 5 also managed to have better overall staging and ever-so-slightly better vocals and treble.On any albums that have more of a “live” sound, the 5 fared slightly better, giving the vocals more presence in the room. The Bose also did very well, but the vocals weren’t quite as forward on the stage.If classical music is more your thing, it’s a toss up between the Bose and the Onyx Studio 5. Again, the Bose does a fantastic job giving you a full stage of instruments, at the expense of some of them not being quite as crisp or pronounced. You know the individual orchestra pieces are there, but sometimes it sounds like some of them are behind the curtain. Again, it’s really a toss up. Listening to “Holst: The Planets”, there are some very quiet moments that both speakers handle with aplomb. In a perfectly quite environment, I suspect classical aficionados may prefer the Bose for the way it separates the stage, even if it’s only slightly better than the 5.Summary: Reference Graph #2- This unscientific, subjective graph is how I hear their respective tuning. The Onyx 4 has a relatively flat response curve. Hence a bit more of the midrange that I don’t like. Around 90Hz, the speakers are pretty even. You can see the Bose falls pretty much in line with the Onyx 4 and 5, but seriously lacks the initial bass response, and overcompensates with additional midrange.Thus, as I noted at the beginning, the HK Onyx Studio 5 is the speaker that most closely matches the way I like to hear music and wins the overall award.Now that I’ve determined the speaker that sounds the best to me, let’s discuss the other factors that distinguish these units.Overall Volume / Loudness:Reference Graph #1This graph is how I perceived their volume at given frequencies. This is a very unscientific way to do this. (Again, it’s all subjective.) I first set all speakers to approximately the same perceived volume using 1000Hz as the frequency to normalize the volume. The volume does not get adjusted for the remainder of this test. Next, I went back and started with 40Hz and stepped up to 16kHz. The graph represents where I perceived an increase or decrease in volume relative to 1000Hz. This is completely unscientific because higher frequencies will seem louder than lower ones. Once in the higher frequencies, its more about which speaker seemed louder than the other at that frequency. Take the graph for what you will. (I’m doing this review for free. I’m not spending the additional time & effort & equipment required to record a channel sweep of each speaker and display the results. *laughing*)Worth noting on this volume graph… There was essentially no perceived volume at 16kHz. And none of the speakers are crystal clear at their max volume. But this could be due to numerous compounded factors: The encoded bitrate of the Audiolabs album that is streaming from Amazon; The usable frequency spectrum handled by the Bluetooth protocol. From this testing, I also believe that once you push Bluetooth past about 80%, the BT itself becomes the primary source of distortion, not the speaker & its amplifier. If I had done a direct line-in using my actual/physical Test CD, that would entirely eliminate any of those possibilities. Again, I didn’t feel it worth additional time & effort. 😊- I found it interesting that while the Bose wasn’t as loud at lower volumes (a percentage of total volume adjustment), ultimately the Bose did play louder than the Onyx 5. It would seem that the Onyx ramps up and plateaus faster. The Bose also had a flatter volume response, whereas the Onyx units got a little peaky in some areas. If someone is paying attention, the graph would seem to run counter to my claim that the Bose was overall louder at max volume. Subjectivity at its finest!- Earlier in my testing with the Bose, I found that controlling volume with the VOL+/- on the iPhone, there are 20 steps. However, using the volume buttons on the speaker, there were 5 steps for every 1 of the phone. So the Bose effectively has a volume adjustment of 0-100 when done manually at the speaker. I did not test manual volume control on the HK units.Portability & Aesthetics:- The Bose Soundlink Revolve+ definitely wins in the portability category. It’s definitely the lightest of this bunch and it’s super convenient to just pick it up by the fabric handle and be on your way. It also has the smallest footprint. However, the Bose is going to get dinged a little for its 3ft USB charging cable. 3ft is not a lot when you’re looking to have your speaker plugged in and use it at the same time. That being said, check out someplace like Amazon/Monoprice for longer USB cables to make this less of an issue.- Neither the 4 nor the 5 are particularly portable, as in, “throw it in a backpack and head out for a day trip”. The HK Onyx Studio 4 retains the same general setup since the original. A cup on the top-back to carry it, and two non-detachable legs sticking out the lower back. On the Studio 5, HK changed it up and went to a design that now looks more like a woman’s handbag, having a full handle on top. The Studio 5 is also quite a bit heavier than the 4. The plus side to it being a heavyweight is that it stays where you put it and is less prone to vibrate the surface it’s on. When specifically comparing the Studio 4 to the 5, the 4 seems like it would fall over easier if something knocked it from behind. That’s just an observation and not a likely scenario.- Of the four units, I like the Bose the best for button layout. The Onyx 1 & 4 next. The Onyx 5 is the least favorable for button layout. It hides its buttons on the top-front of the speaker fabric. And the audible feedback of the HK isn’t nearly as intuitive as the Bose. The Bose talks at you; The HKs just play tones (most of the time).- Due to the downfiring, 360° nature of the Bose SoundLink Revolve+, I think if you had high ceilings and hung them like light fixtures, the audio in the room would be amazing! Or if you’re using them outside, hang them on some really tall Shepard’s Hooks. Technically, you could do the same thing with the Onyx Studio 5, but the speaker is much more directional, so you’d probably want to have them in corners firing inward.Serviceability:I’m only calling this out because the original Onyx Studio 1 had both a removable grill so you could see all the speakers, as well as the ability to open up the body and replace any component, including the failed rechargeable battery (which I replaced while reviewing this lineup). The Bose and newer HK Onyx’s are sealed up tight with no apparent way to crack ‘em open.Extra features:- As I noted in the beginning, extra features aren’t really on my radar. I want a speaker that plays my music. The other stuff doesn’t really concern me as much.- The Bose and HKs are able to wirelessly connect to similar units. However, the Onyx Studio 5 is only able to pair up with other Studio 5. It doesn’t have HKConnect technology, so you can’t connect it to any previous Onyx models. As such, it’s also not recognized by the HKConnect app.Reviews for all the speakers have plenty of people complaining about the ability to pair their speaker with the exact same model. It would seem that grass isn’t perfectly green on either side of this fence.- I think both the HK and Bose handle incoming phone calls… Don’t know, didn’t try.- The Bose I received had an available firmware update that went very smooth. I hooked up the speaker to my Windows 10 system and it recognized it without issue. I downloaded Bose’s Windows app and updated the firmware without issue.Looking at HK’s site, neither the 4 nor 5 appeared to have a firmware update.Battery life:I didn’t do any rundown tests. I’m going to keep my speaker on a shelf and/or near AC power, so battery life isn’t a big factor for me. I will say that the Bose clearly speaks its battery capacity when you turn it on. It also speaks the name of exactly it’s connecting to. That’s a nice feature I wish the HK’s had.Price:As of this writing, the HK Onyx Studio 5 currently is the least expensive of this group. And it’s my favorite sounding speaker! That’s a WIN for me! The Onyx Studio 4’s audio quality is right up there in a close 2nd place to the 5, but it’s currently more expensive. And then there’s the Bose which is currently selling for more than $100 over the Onyx Studio 5. Apparently, you are going to pay for the Bose name and portability. And possibly the battery life or other features I didn’t cover. The Bose is nice, but I’ll keep the extra $100 thankyouverymuch!All in all, if you’re not nearly as particular as me, any of these three speakers will treat you well. I’m obviously recommending the HK Onyx Studio 5 because it sounds the best and cost the least. However, if you aren’t nearly as picky and have a concrete spend limit of $100, I’d go with the DOSS Soundbox XL for $70.