Days 1 to 3

As part of Phone Week here on TechRadar each member of the phones team is taking a top end phone and giving the key feature a stress test. I was handed the HTC One M9 and decided that the audio abilities the brand keeps making a noise about needed a good going over.

One of the key features on the One M9, and its two flagship predecessors, is the firm's focus on music with its BoomSound audio technology and dual front-facing speakers.

The Taiwanese firm has worked tirelessly over the past few years to improve the audio experience you receive from your smartphone and the M9 bears the fruits of the third generation of this technology.

HTC has teamed up with Dolby Audio for the BoomSound tech inside the One M9, so I've spent a week trying out all the features to find out if the noise is worth listening to.

Day 1 - Here comes the Boom(Sound)

Take the HTC One M9 out of its box and its musical potential is immediately obvious thanks to the sizable dual-speaker grills which adorn the front of the handset.

They're not quite as wide as those found on the One M8, but the holes have been drilled slightly larger, and there's more vertical space between them, offering a cleaner, fresher look and feel.

It may not have the Beats Audio technology - and the logo on the rear - like the original HTC One, but the Taiwanese firm has continued to develop its audio boosting tech even after the split between itself and Dr Dre's Beats.

I went directly to the YouTube app to get my first taste of BoomSound in action (Gangnam Style, PSY followed by Now You're Gone, Basshunter*) - and although the icon in the notification bar told me the audio tech was in full swing it wasn't necessarily immediately noticeable.

Sure music sounds good - surprisingly good actually for a smartphone - but in isolation and without the ability to toggle BoomSound on and off when using the internal speakers I struggled to really appreciate what was happening under the hood.

I enjoyed what I'd heard however and promptly downloaded Spotify, cranked up the volume and relaxed listening to an eclectic mix of dance, pop, DnB, dubstep and jazz - no closer to finding out if the One M9 is really delivering a superior audio experience.

*phone fans: check out the old school LG Shine and Nokia N73 used in this video!

Day 2 - Tunes on steroids

One of the good things about BoomSound is the fact it doesn't just work with the built-in speakers. HTC has stuck an amp on the 3.5mm headphone jack, allowing you to enjoy the enhanced beats on the move without distracting others.

Having plugged in my Panasonic RP-HC700 headphones I was pleased to find the 'HTC BoomSound with Dolby Audio' option in the Settings menu now allowed me to switch it on and off - giving me my first clear comparison between normal music and HTC's tunes-on-steroids version.

Is there a difference to be heard? Absolutely. Is it life changing? Err, no.

Flicking BoomSound on and off does give you a clear audible difference to the track you're listening too - no matter the genre - and the BoomSound enhancements provided a better listening experience.

Thanks to the over the ear headphones I was wearing I could really appreciate the subtle upgrades it was bringing to my songs, from deeper bass to better clarity in the trebles and vocals.

Switching to the bundled in-ear headphones the difference wasn't quite so pronounced, but it's still noticeable and I'd always pick BoomSound being on, rather than off.

Day 3 - Wired versus wireless

Wired headphones are all well and good, but they're a bit of a pain as I dash through London's underground train stations at the height of rush hour. The wire always seems to get in the way, or get snagged on a piece of clothing, unceremoniously ripping the buds from my ears.

I much prefer Bluetooth headphones, with their hassle-free wireless design allowing me to dart between bleary-eyed commuters. My Sony DR-BTN200 headphones however, did prove a problem for the One M9 and its BoomSound beats.

BoomSound is not available over Bluetooth, HDMI, Miracast or USB audio out - meaning I was instantly transported back to songs which sounded the same as pretty much any other smartphone I'd previously listened to them on.

Having spent the whole of the previous day enjoying the BoomSound enhancements through my wired Panasonics, the experience I was getting on my much-loved Sony cans was one of disappointment.

There are, of course, technical limitations and reasoning as to why the BoomSound technology can't be transferred wirelessly, but it feels like a huge disconnect in today's world where wireless is fast becoming king.

Days 4 to 7

Day 4 - New meets old

HTC made a lot of noise about the improved Boomsound experience on the One M9 over its predecessor, so when I fished out a One M8 to do a side-by-side comparison I was expecting some big differences.

Unfortunately the improvements made by HTC on the M9 aren't exactly obvious. I played several songs on both the M8 and M9 - listening for any differences in playback.

Through the internal speakers of both handsets there was very little difference. The One M9 sounded slightly crisper, with better clarity between vocals and music - but it was a minimal step up.

Switching to headphones, the close-quarters playback allowed me to notice more definition between the two, but again it's pretty small. Things sounded ever so slightly crisper, but I started to wonder if I was looking for the upgrades, rather than hearing much difference.

Day 5 - The party

It's all very well enjoying the musical benefits of the HTC One M9 on your own, but music is also a social activity and you'll want to share your tunes with your mates.

HTC has predicted this type of social gathering and offers up a Bluetooth speaker by the name of Boombass to give your tracks some added oomph.

At £45.99, $89.99 the Boombass isn't particularly cheap - you can pick it up for less if you shop around - although its neat cuboid design and sliding mechanisms sees it double as a stand for your HTC.

Now I instantly had a mini boom box sitting on my dining table with the dual speakers of the M9 joined by the bass driver in the Boombass.

Pairing is easy - just use NFC to make the initial connection and then Bluetooth will do the rest - although that's where the problem lies. As I found out on Day 3, BoomSound doesn't work when connected to a Bluetooth device and thus when you utilise the Boombass' deeper tones your music isn't being enhanced.

You need to be careful where you place the Boombass too, as it uses its surface to resonate the bass - so carpets and similar fabrics won't give you the full effect. My glass table worked nicely though, and while you won't get bone shaking bass, it's a welcome addition.

I found the syncing issues I'd heard about - where the bass and song get disjointed - weren't apparent, although I was annoyed to find the audio channels weren't separated. I would have expected voice to come out of the phone, and bass the speaker, but there were some muddy vocals coming out of the Boombass too.

Volume-wise the One M9 and Boombass combination is loud enough to fill an average room with a few people in it. It's not going to give you enough power to keep a house party rocking, and if you've got loads of buddies in a space it can be drowned out by chatter.

All is not lost though, and as the party gathered pace I rushed the HTC One M9 to my Sony SRS-D211 computer speakers - a relatively modest affair comprising of two satellite speakers and a decently sized sub.

Plugging the 3.5mm jack into the One M9 meant BoomSound was re-enabled and my beats were invigorated with HTC's musical technology. After that, things got a bit blurry...

Day 6 - The morning after

There's nothing like a long shower after a hard nights partying, and while the HTC One M9 doesn't have the waterproof skills of the Sony Xperia Z3+ it's still a great companion in the bathroom.

The front-facing speakers and high volume output means you can enjoy all your favourite recovery songs over the sound of the running water.

Jump out of the shower and you may have had enough music for a while, but BoomSound can continue to assist you when it comes to video playback.

Stick a movie or TV show on the One M9 and head to the notification bar to switch between 'music mode' and 'theatre mode'. The latter improves sound for motion pictures, with more cinematic acoustics and clearer dialogue.

You'll realise if you've left theatre mode on when you head back to listening to songs, as playback sounds echoey. A quick swipe down from the notification bar and a tap on the BoomSound card however switches the mode back to music.

Day 7 - Final thoughts

As the week drew to a close I took some time to look back on my time with the HTC One M9, to assess just what - if any - difference it had made to my musical listening habits.

First up, the fact you've got two speakers up front is so much better than on the base or rear of the handset. It channels the sound right into your face, and your hands don't cover them.

Volume can also be cranked up to a pretty decent level, although in busy rooms it still can't match dedicated speakers.

Then there's BoomSound, HTC's crowning jewel of its audio onslaught, and yes it does make a difference. Tracks sound meatier, with more emphasis on bass while lyrics also come across more defined.

But it doesn't blow your socks off, and for all the fanfare from HTC over the past couple of years it feels like it doesn't quite live up to the hype.

It's an improvement, and a nice feature to have if you happen to pick up a One M9, but even for the most discerning audiophiles it doesn't do enough to justify the purchase on its own.

• This article is part of Phone Week, celebrating the best bits about brilliant smartphones and tablets as part of the lead up to the TechRadar Phone Awards. To find out what the iPhone 7 could look like, how a phone could survive in space or how to buy the perfect smartphone for you, bookmark TechRadar's Phone Week hub and check out all the great new features coming throughout the week!

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