Accurate low-frequency reproduction – whether it's for home theatre or hi-fi – is a highly complex subject. Just ask Dr Mathias Johansson, co-founder of Dirac, the audio technology giant known for its advanced room equalisation and calibration technologies. To learn more, I sat down with him to talk about how to harness deep, seismic bass. Some of his views may surprise you, even inspire you to experiment with your own system…

If you think subwoofers have no place in a stereo hi-fi system, then the man from Dirac begs to differ – and he doesn't believe big is necessarily better, either. We explored the depths that audio can sink to, and to be honest, we could have kept going for much longer. But to kick off our ramble about rumble, we touched on CEDIA's (the trade body for the custom install industry) new RP22 guidelines for immersive audio systems. Does this new rulebook offer any revelations?

“RP22 provides guidelines on all aspects of what superior sound is, but doesn't provide the solutions,” says Mathias. “It does a good job of actually compiling the state of the knowledge of the (AV) industry, explaining what is important in good sound. It talks about spatial resolution, different characteristics, dynamics, timbre and frequency response. It does a good job of highlighting the importance of bass and seat-to-seat variations, which is a bigger problem than many people realise. I might be having a fantastic bass experience, but those sitting next might think it's really off.”

I put it to Mathias that this highlights the need for multiple subwoofers, which seems like a trend in general. “We're seeing more and more multi-subwoofer systems”, he says. “The obvious problem with these is where to put them. In the end, you need to experiment, see what happens, because it's notoriously difficult to predict… Regardless of the setup you have, you can improve the seat-to-seat variation with digital optimisation. Dirac Live Bass Control, recently launched in Denon and Marantz AV receivers and amplifiers, is a huge step forward. We're not the first ones to think of this idea at all, but it's not been readily available to people.”

He continues: “With bass control, just by adjusting the delays and the gains and some all-pass filters, you're able to get a more even response, both in the sweet spot and in the seats around you. I experimented in our lab here and measured multiple-subwoofer systems. They had reasonably placed subwoofers, but we had huge suck-outs, areas where we simply didn't have anywhere close to the response that I was aiming for.”

For those not in the know, Dirac Live Bass Control uses AI and machine learning to optimise multiple subwoofers and speakers in a system, regardless of your listening position or surroundings. The software cleverly aggregates measurement and location data from each subwoofer to determine how to distribute bass throughout the room. It then looks to distribute 'bassfill' in any gaps in the sound waves. The software time-aligns speakers and adjusts phase at low frequencies to cover all seating positions. From a practical point of view, it also allows subwoofers to be positioned anywhere in the room. But naturally, you have to pay for the privilege…

Johansson: “Yes, it's an optional upgrade, and you pay a fee for it. Depending on whether it's a single subsystem or multiple subsystems. Onkyo and Integra are also offering it as an upgrade and NAD is coming out with it in the new M66 preamplifier and DAC; this has four subwoofer outputs; it's also on the Sonoro Maestro Quantum receiver. We also have high end systems from Stormaudio, JBL Synthesis, McIntosh and Bryston, where it's included with the units.”

“In the past”, adds Mathias, “there were more dedicated listening rooms. Those are still around, but there's a much larger population now that wants to have good sound in a multi-purpose room. I think a lot of people still don't understand that bass is to some extent, more dependent on the room than the bass speaker itself. Of course, you need subwoofers to put the energy into the room, but the environment itself has a huge impact.” 

SIZE MATTERS

So what does Mathias recommend for readers looking to bolster bass in a media room or living room system? Would he suggest people look at maybe several 8” subwoofers rather than one big 12- or 18-incher?

“We would advocate a system with two or three smaller subwoofers, than one big one – even in the case where you already have a dedicated sweet spot. The problem with one sub is you're still going to get uneven frequency response. There might be things that you simply cannot correct for in the sweet spot because of (hard surface) reflections. You can't really do that much about fixing that. So multiple subwoofers help bring all the frequencies up to your target response, and you can also control seat-to-seat variability.” 

The pros and cons of subwoofers have been hotly debated by hi-fi enthusiasts and home theatre fans for years, with one camp insisting they really don't need them because they're not musical, and the other trying to accommodate as many as possible. So does a hi-fi system need a sub? 

Mathias says it's more than just a simple case of subwoofer use being right or wrong. “It also depends on your options in terms of space. A large speaker takes up much more space and costs a lot more money. In many instances, even for stereo, it's better to have a smaller speaker pair combined with a good subwoofer. That's a very good way in terms of price and performance to get great sound.”

He also advocates digital optimisation for classic two-channel stereo setups. “It absolutely works. Although you'll find Dirac in many home theatre systems, most of our users are using room correction for stereo setups, 2.1 or 2.2. When we started out, stereo was the main use case. We are seeing tremendous interest in the stereo side, and in my mind, it's a no-brainer. In terms of price and performance, it's quite a reasonable approach to have a 2.2 or a 2.3 configuration. We know from scientific studies that bass response is a huge factor in the overall preference rating of a system. It's an extremely important area, and if you make sure that you have more than one bass source, you are able with these more advanced room optimisation technologies to get something which is extremely powerful, and extends further than you might be able to otherwise.” 

Mathias says that Dirac room optimisation still remains the preserve of the higher end. “We have worked historically with very high level brands, but the idea is to make better sound more accessible to more people. The software isn't free, but in terms of price and performance, it's a good ratio. We also want to make system optimisation more accessible. We're working on things to make that whole process of setting it up easier, and more streamlined.”

It's often forgotten that the room itself is a key part of an audio system. You can upgrade components in the pursuit of better sound, but making changes to a layout or soft furnishings point of view, could be even more impactful. Mathias contends that when you look at the whole chain, from the source to your ears, the biggest degradations are typically not on the electronics side…

“In my mind, you really can't separate the speaker from the room when it comes to low frequencies. Your speaker is emitting energy, and has to be able to handle power well, but in the end, it's how it interacts with your room that determines what you're going to get. That makes things complicated, it also means that it is required to do some sort of digital room optimisation will get good bass output.”

IN THE END

So Dirac's Mathias Johansson is unequivocal. He says that in order of magnitude terms, to get a better sound you need to begin by looking at your room. “Obviously you should consider what you can do physically, because the better the foundation is, the better the result (of digital optimisation) will be. A large part of the audio community still isn't thinking enough about their listening space. If there's one piece of advice I could give those looking for better sound, then it is to view the listening room as a key component in your audio chain – because that is truly what it is. What we hear is at our ears, not the output of a loudspeaker…”

For more information visit Dirac