B&O Tech: What is “ABL”?

Header info #1 for full disclosure: I’ve been given the green light from the communications department at Bang & Olufsen to write some articles describing some of the more technical aspects of B&O loudspeakers here on my own blog site. This is the first posting in what will be a series of articles.

Header info #2 for fuller disclosure: This particular posting will look familiar to some forum people at www.beoworld.org, since I wrote the original version of this as a response to one of the questions on their site. However, I’ve beefed up the response a little – so if you’ve come here from beoworld, there is only a little new information in here.

Almost all loudspeakers made by Bang & Olufsen include Adaptive Bass Linearisation or ABL. This includes not only our “stand alone” loudspeakers (the BeoLab series) but also our iPod docks and our televisions. The only exceptions at the moment are our passive loudspeakers, headphones, and the BeoLab 5.

There is no one technical definition for ABL, since it is in continual evolution – in fact it (almost) changes from product to product, as we learn more and as different products require different algorithms. Speaking very broadly, however, we could say that it reduces the low frequency content sent to the loudspeaker driver(s) (i.e. the woofer) when the loudspeaker is asked to play loudly – but even this is partially inaccurate.

It is important to note that it is not the case that this replaces a “loudness function” which may (or may not) be equalising for Equal Loudness Contours (sometimes called “Fletcher-Munson Curves”). However, since (generally) the bass is pulled back when things get loud, it is easy to assume this to be true.

When we are doing the sound design for a loudspeaker (which is based both on measurements and listening), we make sure that we are operating at a listening level that is well within the linear behaviour of the loudspeaker and its components. (To be more precise, when I’m doing the sound design, I typically use a standard-ish playback level where -20 dB FS full-band pink noise results in something like 70 dB (C) at the listening position (sometimes I use 75 dB (A) – but, depending on the amount of low end in the loudspeaker, this might result in the same volume setting).)

This means that

  • the drivers (i.e. the woofer and tweeter) aren’t being asked to move too far (in and out)
  • the amplifier is nowhere near clipping
  • the power supply is well within its limits, and
  • nothing (not the power supply, the amplifiers, or the voice coils) is getting so hot that the loudspeaker’s behaviour is altered.

This is what is meant by “linear” – it’s fancy word for “predictable”, (Not to mention the fact that if we were listening to loudspeakers at high levels all the time, we would get increasingly bad at our jobs due to hearing loss.)

So, we do the tuning at that low-ish listening level where we know things are behaving – remember that we always do it at the same calibrated level every time for every loudspeaker so that we don’t change sound design balance due to shifts associated with equal loudness contours. (If you tune a loudspeaker when it’s playing loudly, you’ll wind up with a loudspeaker with less bass than if you tuned it quietly. This is because you’re automatically compensating for differences in your own hearing at different listening levels.)

Once that tuning is done, then we go back to the measurements to see where things will fall apart. For example, in order to compensate for the relatively small cabinet behind the woofer(s) in the BeoSound 8 / BeoPlay A8, we increase the amount of bass that we send to the amplifiers for the woofers as part of the sound design. If we just left that bass boost in when you turn up the volume, the poor speaker would go up in smoke – or at least sound very bad. This could be because

  • the woofer is being pushed/pulled beyond its limits, or
  • because the amplifier clips or
  • the power supply runs out of steam or
  • something else.

(Note that BeoSound 8’s do not actually run on steam – but they do contain the magic smoke that keeps all audio gear functioning properly.) So, we put the loudspeaker in a small torture chamber (it’s about the size of a medium-sized clothes closet), put on some dance music (or some slightly more-boring modified pink noise) and turn up the volume… While that’s playing, we’re continually monitoring the signal that we’re sending to the loudspeaker, the driver excursion, the demands on the electronics (i.e. the amp’s, DAC’s, power supply, etc) and the temperature of various components in the loudspeaker, along with a bunch of other parameters…

beosound_8_last_prototype
One of the last BeoSound 8 prototypes. The orange/black wires connect directly to the woofers. The purple/white wires connect directly to the tweeters (at this stage of development, we are still using external amplifiers). Most of the other wires go into thermal sensors inside the device to see how hot things are getting inside. Some of these thermal sensors are actually in the final product that the customer buys. Some are just for development purposes and are not in the final product.

Armed with that information, we are able to “know” how those parameters behave with respect to the characteristics of the music that is being played (i.e. how loud it is, in various frequency bands, for how long, in both the short term and the long term). This means that, when you play music on the loudspeaker, it “knows”

  • how hot it is at various locations inside,
  • the loudspeaker drivers’ excursions,
  • amplifier demands,
  • power supply demands,
  • and so on. (The actual list varies according to product – these are just some typical examples…)

So, when something gets close to a maximum (i.e. the amplifier starts to get too hot, or the woofer is nearing maximum allowable excursion) then SOMETHING will be pulled back.

WHAT is pulled back? It depends on the product and the conditions at the time you’re playing the music. It could be a band of frequencies in the bass region, it could be the level of the woofer. In a worst-case-last-ditch situation, the loudspeaker might even be required to shut itself down to protect itself from you. Of course, there is no guarantee that you cannot destroy the loudspeaker somehow – but we do our best to build in enough protection to cover as many conditions as we can.

HOW is it pulled back (i.e. how quickly and by how much)? That also depends on the product and some decisions we made during the sound design process, as well as what kind of state-of-emergency your loudspeaker is in (some people are very mean to loudspeakers…).

Note that all this is done based on the signals that the loudspeaker is being asked to produce. So it doesn’t know whether you’ve turned up the bass or the volume – it just knows you’re asking it to play this signal right now and what the implications of that demand are on the current conditions (voice coil temperature, for example) This is similar to the fact that the seat belts in my car don’t know why the car is stopping quickly – maybe it’s because I hit the brakes, maybe it’s because I hit a concrete wall – the seat belts just lock up when they’re asked to move too quickly. Your woofer’s voice coil doesn’t know the difference between Eminem and Stravinsky with a bass boost – it just knows it’s hot and it doesn’t want to get hotter.

It’s important to note that some of what I’ve said here is not true for some products. Bang & Olufsen’s analogue loudspeakers cannot have the same amount of “self-knowledge” as the digital loudspeakers because they don’t have the same “processing power”.  However, we make every effort to ensure that you get as much as is possible out of your loudspeaker while still ensuring that you can’t do any permanent damage to it. However, it’s fair to say that, the more recent the model, the closer we are able to get to the maximum limits of the total system for a longer listening period.

Bang & Olufsen BeoLab 14 reviews

b-o_beolab_14_0

 

recordere.dk’s review

“Beolab 14 er et harmonisk sæt, der lyder godt som en samlet enhed. Netop det at det spiller som én samlet enhed, hvor der er kælet for detaljerne, er med til at løfte det flere niveauer op. Bassen virker stram og velafballanceret, men med rigeligt power til effektscenerne i actionfilmene. Mellemtonen virker klar og naturlig, og selv vokaler i highend audio (24-bit) gengives sprødt og realistisk. Diskanten runder det hele fint af i toppen.”

 

hifi4all.dk’s review

“Beolab 14 sættet lyder ganske enkelt rigtig godt. Der er den rette mængde bas (hvilket man jo egentlig selv bestemmer), et mellemtoneområde, som bare er der uden at gøre væsen af sig, og en diskant som har den rette afrunding mod toppen, hvilket giver god mening sammen med 2,5” enhederne, som per design ikke er konstrueret til ultra høje frekvenser. Og så hænger det hele rigtig godt sammen! Altså det man kalder en homogen gengivelse af musikken.”

 

 

Bang & Olufsen BeoPlay A9 Reviews

I was the final sound designer for the A9, so my job was deciding on its final tonal balance.

Tim Gideon of PCMag.com wrote in this review:

“The bass is intense without being over-the-top, as the system seems to primarily focus on high-mids and highs. The A9 is a crisp, bright system, balanced out by powerful low-end, for sure, but it is the higher frequencies that own the stage.”

 

Trusted Reviews wrote in this review:

“B&O has opted for a relatively neutral signature, but bass, mid and high frequencies all shine through with the A9 managing that difficult balancing act of tying accuracy and emotion.”

 

Nick Rego at tbreak.com wrote in this review:

“After all this though, how does the A9 sound? In a word, mesmerizing. The sheer power that the A9 can deliver is absolutely incredible, and if placed in a well furnished room it could be hard to figure out where this incredible sound is coming from. I decided to put the A9 to the ultimate test for a house party I was having in my back garden. I had positioned the A9 towards the top end of the garden path, and when I turned up the volume the music could be heard in almost every corner. There was no distortion at all on the music even when I cranked the A9 up as high as it could go (without waking up half the neighborhood). The A9 certainly delivers on B&O’s promise of sheer audio performance packaged in a sleek enclosure.”

Bang & Olufsen H6 headphone reviews

 

I was part of the development team, and one of the two persons who decided on the final sound design (aka tonal balance) of the B&O H6 headphones. So, I’m happy to share some of the blame for some of the comments (at least on the sound quality) from the reviews.

 

 

 

Audio.de reviewed the H6 paired with an Astell & Kern portable player. They said:

“Tatsächlich aber ertönte der H6 mit dem AK Junior erstaunlich präzise, extrem sauber und stabil und vor allem ungeahnt luftig. Das Zusammenspiel des speziell angefertigten Treibers mit dem ausgeklügelten Bassport stellte nicht etwa – wie oft üblich bei geschlossenen Hörern – die tiefen Frequenzen wummernd und brummend in den Vordergrund. Nein, besonders Stimmen und feine Details profitierten vom knochentrockenen und nicht zu gewaltigen Bass.

“Susanne Sundfos glockenhelle Stimme beispielsweise stand fest gemeißelt im erstaunlich großen Raum, umgeben von jederzeit verfolgbaren Bassdrum-Beats, echten Streichern und Synthesizer-Harmonien. Der kurze Probelauf mit H6 und AK Junior wurde zur ausführlichen Hörsession, die erste Begeisterung zur echten Liebe. Eben true love.”

Correction: That review stated that I said that the H6’s were tuned using the Grado’s as the reference. This is not really true. While we were tuning them, we listened to many different headphones. The Grado’s are one of the many hanging in the listening room…

 

Gramophone Magazine reviewed the H6 in the April 2014 edition. They said some very nice things about the headphones:

“…excellent clarity and weight, well-defined bass and a sense of openness and space unusual in closed-back headphones. The sound is rich, attractive and ever-so-easy to enjoy.”

and

“… by no means are these headphones designed only for those wanting a pounding bass-line and an exciting overall balance: as already mentioned the bass extension is impressive, but it’s matched with low-end definition and control that’s just as striking, while a smooth midband and airy, but sweet, treble complete the sonic picture.”

and

“As I may have made clear in the past, I haven’t been the greatest fan of headphone listening, much preferring a pair of small speakers on the desk. But with the arrival of fine headphones such as the BeoPlay H6, I’m having to do some re-thinking.”

 

Bobby Solomon wrote this review at thefoxisblack.com.

“The sound is refined, with the midrange coming through clearly, and the bass and treble are balanced perfectly.”

 

Kenneth Roberts wrote this review at head-if.org.

“I’d describe B&O’s “house sound” as natural and neutral, with a brilliant, feathery-light high-end that resolves a lot of detail. This describes the H6’s sound perfectly. It delivers a staggering amount of detail in its price-class. In fact, the H6 delivers an impressive amount of detail when compared to headphones well above its price-class! Cymbals, triangles, snares, and hi-hats all sound crisp and light, with nary a hint of sibilance or stridence. I’m guessing this deftly executed high-end lends much to the headphone’s spectacular imaging, which I’ll describe later.”

 

T3’s website has a review here

“Which rather handily leads us onto how they actually sound. The answer can be summed up with the word ‘balanced’. By this we mean that almost all ranges perform excellently, but never does one take precedence over the other.”

 

pocketlint.com has their review here

from the middle of the text: “As you might expect, audio quality is top-notch. While we can’t say it competes with some of the other stay-at-home audiophile grade kit, for a set of headphones you can listen to daily, they certainly deliver. Sound is nicely balanced with plenty of detail and not an overly punchy bass. The set of 40mm drivers and the internal bass port just keep everything as clean and simple as possible.”

 

Tim Gideon and PCMag.com has their review here

The concluding words state: “In the age of big, booming bass, it’s doing its own thing. This is by no means an anemic-sounding headphone pair, it just favors lows, mids, and highs over a wildly boosted sub-bass range. If a more refined, crisp mids-focused sound is what you seek, the H6 will not disappoint, and it’s refreshing to see such a unique sound signature in this field.”

 

Bang & Olufsen Finally Got It Right” at head-fi.org

“The sound is surprisingly flat, but a little bit on the warm side. The sound is not as airy as the open back cans, but the soundstage is very good for a portable closed back.”

 

whathifi.com has a thorough review here

“Based on my favorable impressions of the H6 with the first series of tracks which are heavy on electronic sounds, and also on the second group which feature more conventional bands and acoustic sounds, I’d say the H6 bridges these different genres very well. There are very few headphones that have a decent deep bass response and reasonable impact but don’t have any upper bass emphasis or bloat, and the B&O H6 is one of those few.”

 

soundandvision.com has a review here

“This is no head-banger headphone, but the bass goes low and it’s nicely articulated. The frequency response is remarkably smooth, without a hint of the rolled highs and boosted bottom common to more mainstream ’phones; the downside to this clarity is that the headphone won’t do anything to blunt the harshness of overcompressed MP3s.”

 

beforeitsnews.com has a review here

“The sound, however, is near flat and crisp. You’ll be able to hear the fine details of a song or a recording. There’s also no distortion at top volumes, while the midrange is great. Bass is balanced rather than strong, preferring accuracy and refinement to simple power. Think of these headphones as fine wine and other headphones as beers. When you start appreciating its beauty and fine sound, oh boy, where have you been all my life?”

 

 

Customer Comments at beoworld.org

There is a long user discussion on the forum here. Persons looking for real-world opinions will certainly get their fill at that site.

“I did not really like the H6 when it was released, a bit thin on an iPhone and a big headphone. And expensive. So I bought the B&W P5 instead. Quite good comfort and good sound. But.. I just had to give the H6 a try so I bought a pair a few days ago (the black model – after a lot of pondering). I now have a completely different feeling about the H6. They sound very natural and good. I like how detailed and precise the sound is.  You can hear so many details very well and how acoustic noises changes in frequencies in a wonderful way.”

“My wife has a pair of H6’s in tan, and I am consistently impressed by them.”

“Soundwise, also nice to hear your opinion (and Chris´s). I can’t remember hearing a pair of headphones with a more true sound.”

“I’ve now got a tan pair of my own (240£ for a new pair via eBay) and use them every day.  I’ve been listening to some of my favourite music which I’ve listened to for over 40 years on CD, vinyl, digital via an ipod and A8’s and can now pick out musical detail that up to now has eluded me.  The separation of instruments on some of my live recordings is incredible, so much so that I’ve found that even Steve Hackett playing live does make some mistakes!  None of the music is muddied and I have to say that I don’t find the volume when using an ipod too low.  If I want loud music I’ll play it at home on a bigger amp set-up with some bigger speakers.  When using the headphones I want the isolation of me and my music.”