digiZoid ZO2 Personal (not a) Subwoofer Review

digiZoid ZO2 Introduction

In the world of high-end audio bigger is better. Bigger screens, bigger receivers, and bigger amps. Sure, your phone might be getting smaller and thinner but not the screen, right? No, those are only getting bigger.

When we first took a look at the digiZoid ZO², we had a few questions. First, what the heck is a "personal subwoofer" anyhow? Then we wanted to know how it worked and whether it would really provide the performance it promises. So we did what any good review mag would do - we asked for a sample. Even with shipping to Australia (digiZoid provides free, worldwide shipping for the ZO²), the ZO² arrived faster than nearly every other product we've ever requested. In our minds, that was a good start.

digiZoid ZO2 First Impressions and Overview

What the heck is it?

Personal Subwoofer is not what the ZO² is. In reality, it is a tiny headphone amp with a built in bass-boost. According to the designer, the ZO² is a "analog sound enhancement device that happens to have high power headphone drivers at its outputs." This means that everything is kept in the analogue domain negating need for ADCs and DACs within the device  If that doesn't sound like something you might be interested in, I beg you to read on. This is the sort of product that I didn't think could even exist.

Measuring 2.75 by 1.5 by 0.38 inches, the ZO² has a smaller surface area than a credit card and is just thick enough to mount a 3.5mm input and output. There is a front mounted light and a small button on the side. The button can be depressed or clicked (it doesn't make a noise but it isn't a scroll wheel) up or down. There is a side-mounted mini-USB port for charging with a very small red light on the side to let you know when it is charging (red light illuminated) and fully charged (red light off). The Li-Polymer battery has a recharge time of under an hour but will last for up to 17 hours of playback.

The top has a 3.5mm port for input and output. Inside is a Class-A headphone amplifier that uses an ultra-low noise pre-amp. The ZO² has two settings - headphone out and line-out. The main difference is that the headphone out uses the volume control of your device. The Line-out (designed to be used when connected to a 3.5mm-to-dock connector cable or source without volume control) allows the ZO² to control the volume. The ZO² has a 32 step volume control.

First Impressions

The ZO² is tiny and light. It really doesn't feel like it should be capable if amplifying anything. At less than an ounce, the cable on your headphones probably weighs more. The case has a "soft-touch" coat on the plastic which feels, for lack of a better word, weird. Not bad, mind you. Even after weeks of testing, I occasionally find myself looking at it to see if there is any sort of velvet on the outside.

The digiZoid ZO²'s front light is color coded. When you first turn it on, it will be in headphone mode. It's color-coded pink. Insert "why-the-heck-did-they-go-with-pink" joke here. In all honesty, once you select the mode, you never see the pink again so it isn't a big deal. Line out mode is color-coded purple though that color changes based on what volume you chose. After you set your volume, you go into bass-boost mode.

Integrating the ZO² into your system is a snap. digiZoid includes a small 3.5mm jumper cable for your use. You plug the jumper into the headphone out on your phone/player and into the input (labeled with a musical note) on the ZO². You then plug your headphone into the output on the ZO² and you are good to go. digiZoid did well to flush-mount the 3.5mm jacks on the ZO² so as to not impede use of headphones with larger connectors. Since they intend (based on their marketing material) the ZO² to be used with high-end headphones, that was a smart design choice.

digiZoid ZO2 Installation and Use

There are two ways to install the ZO² Personal (not a) Subwoofer. You can use the 3.5mm jumper cable from your source to the ZO² or you can use some sort of line out cable that terminates into a 3.5mm jack. In the latter case, you'll have to provide your own cable as digiZoid only provides the 3.5mm jumper. This seems reasonable considering the multitude of uses a consumer might have for the ZO².

While the obvious use is between your headphones and your phone or portable music player, there are tons of other applications. If you connect your phone to your car stereo via a 3.5mm cable, you can easily integrate the ZO². Between your computer and headphones or desktop speakers? No problem. With the size of the ZO², the problem is not going to be portability (other than possibly losing the thing) as it goes everywhere. Plus, it is so light you can leave it dangling on the cable and not have to worry about any damage to your ports.

Once you've installed it, you need to press the button to turn it on. It will default the first time to the typical bass boost in headphone mode. This is signified with a yellow light on the front. Pressing the button again will sent it into mode select. As it defaults in Headphone mode, the front will glow pink. Press the button down (roll it toward the bottom of the ZO²) and you'll switch to a blue/purple color. This is Line mode where you have volume control. Up and down on the button will control your volume. To switch back into Headphone mode, hold the scroll button up for about 10 seconds until the light turns pink again.

When in mode select, a single button press will send you back to the bass boost selection mode. Here you have 32 degrees of bass boost from nothing (flat) which will show green to maximum bass boost which will glow red. The levels of bass boost vary and become less dramatic as you go up (meaning at first you get a big difference between the amount of boost with each level while at the top a level up represents much less boost). You can press the button for each level or hold it down to scroll through the levels faster. One long press turns the ZO² off and a single press turns it back on. After you adjust the settings on the ZO², it stores those settings.

Use

For this review I used the ZO² with a number of different headphones. I have a large number at my disposal with price points between $40 and $300. For the most part the headphones used were the Arctic P402 ($40), the Moshi Vortex Pro ($150), and the Pioneer SE-MJ591 ($300). Each of these headphones have a different sonic signature with completely different "problems" that may or may not be made better or worse by the inclusion of the digiZoid ZO² Personal (not a) Subwoofer.

Before I go on, I believe I may lose some of you after this paragraph. Just remember that the ZO² has more uses than with your phone. If you have headphones with in-line controls or an in-line mic, the ZO² renders them inoperable. It does not, for whatever reason, pass the signals back to the phone needed for control and voice. It also doesn't fool your phone into thinking that those controls and mic are operational so you end up being able to use the phone just as you would if you were wearing headphones without in-line controls and mic. An annoyance? For sure. And maybe a deal-breaker for some. But the ZO² still has many uses that may outweigh this downside.

Charging the ZO² took very little time and the run time is so long that I didn't think to charge the thing for days at a time. There is a secondary red light at the bottom of the light bar on the front that will blink when your battery gets low but that rarely happened to me even after days without a charge (and I was using the ZO² nearly constantly). Charging the ZO² while in use adds no audible noise to playback (unlike charging and using my phone at the same time) unless your source and the charging connection are the same (charging the ZO² with the same computer that is providing the musical output).

While the ZO² is very light and portable, I did wish there was some way of securing it to your phone. While it wasn't too much of a hassle to stick it in your pocket with your phone, I wanted a way to connect it to the back of my phone case. In what was probably a fit of madness, I attached a piece of Velcro to the back of my Samsung Galaxy Nexus Otterbox Commuter case and to the back of the ZO². This created the perfect way to store the ZO² when I was out and about and the ZO² was thin enough that I could still stick the phone with the ZO² attached in my back pocket. Since then, I've racked my brain for a solution that digiZoid could include with the ZO² but I've come up empty. The Velcro works well but the connection is so strong that you have to be careful removing the ZO² as you can feel the case flex if you put too much pressure on it.

digiZoid ZO2 Amplification and Control

There are two basic changes the digiZoid makes to your sound - it makes it louder and it can apply a measure of bass boost. From the manufacturer: The ZO² is "actually not a headphone amp with bass boost, rather it's an analog sound enhancement device that happens to have high power headphone drivers at its outputs." This means that the output should stay constant as long as you have the ZO² at the lowest level since the high power headphone drivers shouldn't change the sound - only increase it. This is very hard to test as the change in volume is enough to trick the ear into hearing a difference. At the same time, it is near impossible to equalize the volume quickly enough even if you didn't have to switch the headphone cable at the same time.

That being said, I did try to ascertain if the ZO² modified the sound when set on the lowest bass boost level, which is supposed to be a flat level. I tried switching the headphone cable from the ZO² to the player as quickly as possible while changing the volume. With a physical volume button on the side of my Galaxy Nexus, this was easier than it could have been. While non-scientific and certainly nothing that could be objectively verified, I could not hear any difference when when I used my most sensitive headphones - the Pioneer SE-MJ591.

But that's not to mean that I couldn't hear anything. When no content was playing, I did notice a slight hiss when using some of my headphones with some of my devices. Specifically with the Pioneer cans, there was often a slight hiss when using the digiZoid ZO². It was an easy thing to ignore for the most part as it was completely inaudible if there was anything playing or a reasonable amount of background noise, but it was definitely there.

After extensive testing, it because clear that the hiss was coming from the source and not the ZO². This points out an obvious problem with a device that amplifies everything. Any noise from the source is amplified as well. With my computer headphone output it was most noticeable. With my phone, for the most part, I didn't hear it unless there was nothing else being played back and I was in a quiet place. In all cases, it wasn't something that bothered me but it is something to consider. With harder to drive headphones like the Denon AH-D1000 I could only barely make out the hiss while the Arctic P402s covered the noise completely. It was only with the Pioneer headphones did I think that the hiss was loud enough that I would forgo the use of the ZO² because of it. With most of the pairs of headphones, it was either inaudible or inaudible enough for me. What does this mean for you the consumer? Well, if you have a particularly revealing and easy to drive set of cans, the ZO² may not be for you (if your source is not great). Otherwise, it will probably work just fine. Using the Line-out option may be a workaround as well.

The amplification aspect of the ZO² should take much of the load off your portable device. This should result in increased battery life of your player. While I didn't test this, it does make sense. The ZO² easily increased the volume by a factor of two or more (depending on the headphones I was using). This does mean that you will need to make sure your settings on your phone are appropriate for the new level or risk damaging your headphones or ears. Also, once you start using the ZO², going without it requires you to change your settings back. An annoyance unless you have an app that stores different audio profiles.

The last thing I'll mention is about the user interface. The color-coded display is so hard to read as to be pointless. If the colors between the different levels were more distinct, or if there was some sort of audible or tactile indication that you had switched a level, it may have been useful. As it is, 32 gradations of color between green, yellow, orange, and red are impossible to read. I know that for some headphones I liked the bass boost completely off, with others I liked it around yellowish. Yellowish is not a setting. Since I'm not going to sit there and count my button presses, I don't know exactly what setting I liked for any given set of cans. Even if I did count the number of times I hit the button, without any user feedback, it is impossible to know that each press was registered once, twice, or at all.

I went through all the colors one click at a time and could more easily hear the difference than I could see it from the color. If you are okay with this sort of muddiness of control, don't worry about it. In actual practice, "yellowish" was good enough. But as a high-end device (they like to talk about how people pair their ZO² with $300+ pairs of headphones), I'd think a little more feedback would be in order. With the color coding of the volume on the Line mode going between blue and purple, I can only imagine how confusing that would be.

digiZoid ZO2 Listening

The first thing I was worried about with the ZO² was that it would affect non-bass frequencies in some way. I did extensive listening tests with the ZO² and I could find no evidence that it affected any frequencies other than bass in any way. If I was listening to music that had no bass (songs with a cappella openings for example), I could push the bass boost all the way into red without hearing any sort of change to the presentation.

With that, I focused on the bass end. Regardless of the name, the ZO² Personal (not a) Subwoofer will not create bass where none exists. It can't cause a driver to recreate frequencies that are outside of its range. What it will do is give the driver more power (amplification) to work with and accentuate (bass boost) those lower frequencies.

The bass boost was smooth and lifelike. Unlike some of the digital solutions I've experienced, the ZO² boosts bass in such a way that it truly sounds like it was recorded that way. With bass heavy headphones like the Moshi Vortex Pro, I preferred little or no bass boost. But with bass light ones like the Pioneer SE-MJ591s, I really fell in love with my headphones all over again. This is what the headphone lacked and the ZO² has such a natural and lifelike presentation that I couldn't believe that it was an external force creating the extra bass.

But if you really want to know where the digiZoid ZO² shone, it was with the Arctic P402s.

Yes, I know that pairing a $120 accessory with a $40 set of cans is idiotic. I admit that taking the $160 you'd have spent on the two and getting a better set of cans would be a much better investment. But I think of it this way - there are tons of high-end headphones out there that need external amplification because they are so hard to drive. While tube headphone amps may be pretty, they aren't exactly transportable. So, rather than focus on the cost of the Arctics, I'm going to focus on how hard they were to drive.

And they are hard to drive.

If any of my other headphones required 1/3rd volume to reach a comfortable listening level, the Artics required 2/3rds or more. Easily double. With the amplification inherent in the ZO², the volume increase was nullified. This takes a huge load off the source device (usually my phone, iDevice, or computer) and also provides much more headroom. The increase in sound quality was immediately noticeable. It was clear that even at moderate volumes, the amps within my source devices were near or at clipping with the Arctics. With the ZO² in place, the presentation was much less strained and constricted. Given that the Arctics weren't exactly the most bass heavy of headphones, the digiZoid ZO² really made a huge difference. So much so, that from the midrange down, the Arctics sounded like headphones two or three times their price. The high end gave them away, of course, but the difference was pretty amazing.

digiZoid ZO2 Suggestions

While the digiZoid ZO² Personal (not a) Subwoofer is a good product, there are some suggestions that I think would take it to greatness.

• In-Line Controls Pass-through - This is a must. Beyond the price, there can be no greater deterrent to sales than the fact that the ZO² makes the in-line controls and mic inoperable. There may be technical reasons why the ZO² cannot be made to do this. If so, digiZoid would do well to explain why on their website/marketing material.
• Hiss Filter - Noisy outputs are a fact of life. I'd like to see digiZoid add some sort of hiss filter to correct for that. A defeatable filter with a switch would be best.
  
• Control Feedback - Part of me wants to say that 32 levels of bass-boost is about 22 too many. But, honestly, I like how you can fine tune your boost. What I don't like is that there is no way of really knowing what setting you are using without counting your button presses.
  
• Phone Connection - While I'm at a loss for a specific solution, surely one of the engineers over at digiZoid can come up with some way to connect the ZO² to your phone for easier transport. The Velcro solution I use works great but I doubt it is something everyone would be interested in.
  
• Sturdier Case - Adding any sort of weight to the ZO² is a risky proposition. Part of the allure of the ZO² is that it is so small and light. But working with the Velcro made me realize just how fragile that case is. It will surely handle any fall or drop but I don't think it would do well if stepped on. Every time I pulled it off the back of my phone, I could feel the case flex. A better enclosure would be a nice upgrade and worth the added weight in my opinion.
  

digiZoid ZO2 Conclusion and Ratings

The old adage that you are hardest on the ones you love is true in the case of the digiZoid ZO². I really, really like this product. Even if it didn't increase battery life, I think the bass boost is one of the cleanest and most natural I've heard. The large number of adjustable levels means you can fine tune your experience to your exact preferences. The small size and light weight makes the ZO² easy to transport and use in multiple situations. While the product is not perfect, I think its performance easily justifies its price.

At $120, I don't think everyone will agree with that last statement. The digiZoid is certainly a niche product for those that really love their headphones and crave gadgets. With the large increase in volume taking some of the pressure off your phone's battery and a built-in analogue bass boost, the ZO² performs as promised. If I found one of these in my Christmas stocking, I'd be thrilled. I'm betting a lot of other audioholics would react the same.

digiZoid Z02 Personal Subwoofer

$119.95 (free worldwide shipping)

www.digizoid.com

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

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Ergonomics & Usability
Ease of Setup/Programming/Integration
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