Interviews

Interview with Dean Hartley, Monitor Audio’s technical director

Dean Hartley, Monitor Audio

After obtaining a diploma in electronic sciences, Dean Hartley began his career in hi-fi by joining Fane Acoustics as a development engineer. Musician and sound enthusiast, he discovered a passion for audio restitution. After joining Wharfedale in 1990, Dean created the Keswick Audio Research company, which specialized in the design of audio monitors. He then joined Monitor Audio as technical director in 1998. Under his leadership, Monitor Audio revolutionized the design of their speakers and drivers. Often seen as the “ears of Monitor Audio” he is currently at the head of a team of twenty engineers.

Monitor Audio speakers are well known for their use of C-CAM technology, can you introduce it and sum up its benefits?

We have been designing speakers with metal cones and domes for around 30 years. Original materials were made from aluminium and anodized to form a hard surface layer, providing additional strength. When I joined Monitor Audio in 1997, we set about trying to improve the stiffness and damping of the metal cones. Stiffness and damping are sometime difficult to achieve, because one or the other usually prevails. As an example; a soft dome tweeter has good damping, but low stiffness. On the other hand, ceramic materials has high stiffness, but poor damping. We wanted to try and achieve the best of both worlds to ensure we had a uniform frequency response, yet a controlled cutoff frequency (i.e. beyond which the driver becomes very difficult to control).

Our research led to us to investigate the chemistry of materials and we worked with a metallurgy specialist to find a unique combination of aluminium and magnesium alloy. It had originally been developed for aerospace applications where high strength, low mass and resilience to vibrational stresses are of great importance. Conventional cone materials operate over the bandwidth which pushes their boundaries and this results in a large amount of audible distortion. The C-CAM cones are designed with the specific intention of having resistance to bending stress. We feel the C-CAM material exhibits almost ideal properties for loudspeaker domes and cones, resulting in increased clarity and reduced distortion.

La membrane C-CAM d'un haut-parleur de grave-médium Monitor Audio

With C-CAM technology, we decided to experiment with a new ceramic anodizing process. The material undergoes stress-relieving processes throughout its manufacture to avoid surface deformation and molecular weakness. This combination of material and processing we called C-CAM and has been the mainstay of our product ranges now for many years.

Some woofers also benefit from RST technology, can you tell us more about it?

RST (rigid surface technology) is a general name we applied to the development of techniques intended to increase the stiffness of a cone, by adding additional geometric shapes. The dimpled pattern we currently use provides the cone with an additional resistance to mechanical bending forces. The RST pattern effectively displaces any standing waves which would ordinarily propagate across the cone surface. The RST cone retains a constant shape and diameter throughout the working frequency range. In a conventional cone, the body starts to deform typically under 150 Hz in a 6.5” loudspeaker unit. We analyzed these mechanical behaviors and chose the right materials based on their resistance to deformation. The selection of material, profile and mechanical treatment (RST) is critical to almost the full working band of the loudspeaker, and not just the high frequency ‘break-up’ region. Typically, the RST cone driver is able to work higher in frequency as it pushes the break up modes higher up and out of the region where the crossover is providing suitable attenuation. Our RST based drivers remain pistonic to over one octave above the crossover point.

Hive technology is linked to bass-reflex ports : how does it improve low frequency reproduction?

HiVe (High Velocity Reflex Port) is essentially a conventional reflex port by characterization. However, it features a smooth rifled design which assists in accelerating the airflow and reduces turbulence as pressurized air moves quickly in and out of the port itself. HiVe technology has the ability to move air in and out much quicker than a conventional port. We wanted to ideally design a system that could benefit from the superior transient response a sealed box exhibits, with the acoustic power of a ported box. It works really well.

What are the benefits of the internal bracing and bolt fixing of drivers?

We developed the single bolt design for the radius series back in 2003, for aesthetic reasons. However, we noticed the bolt clamping force from front to back gave demonstrable improvements in cabinet stiffness. We have developed this over the years since, improving the results with every new range. Another advantage is that the driver periphery has an equal clamping force around the edge, which is not the case with a classic design. The sound is therefore much cleaner.

Monitor Audio Gold 100

High end Gold and Platinum II series use ribbon tweeters : can you describe the advantages over dome tweeters?

The main benefits are fundamental to the design and materials. A dome tweeter has a small surface area and components that contribute to its mass, such as the dome, voice coil, suspension … This is not the case with a ribbon tweeter. In addition to that, the dome needs to be rigid to provide high frequency output. We have developed our C-CAM dome tweeter now to achieve output to around 30 kHz. However, in the case of Gold and particularly Platinum, we wanted to achieve output to over 50 kHz, to make the best use of High definition recordings (24/96, 24/192 etc.) and meet the requirements of the newest HD players and amplifiers. Even making a dome tweeter from a rigid material such as Beryllium or Diamond will not allow it to reach 50 kHz. We use a ribbon tweeter for the Gold and the previous Platinum series because it overcomes these issues. We have now chosen to design and build our own MPD (Micro Pleated Diaphragm) tweeter for the new Platinum series, which will one day trickle down to other products. The MPD has a surface area around 8 times larger than a typical dome tweeter, its efficiency is therefore higher. It is composed of a soft and ultra light ribbon whose behavior differs from that of a dome tweeter, with no break up modes. It is able to reach beyond 50 kHz and delivers a detailed but very smooth sound.

In-wall and in-ceiling speakers use the same technologies as other ranges: can they be used for surround or Dolby Atmos applications?

There are no strict specifications or requirements for Dolby Atmos when speakers are mounted in a ceiling. We do recommend the use of our in-ceiling IDC products, as they can be directed towards the listening space and provide a more elevated performance in terms of the Atmos effect. We do also have in-ceiling speakers specifically designed for surround effect applications.

Do you plan to release a multiroom system?

We are interested in future technologies and keep a watchful eye on how the market develops, especially regarding new ways to enjoy music. Our commitment right now, as ever, is the improvement of sound reproduction. We are seeing a mini-resurgence in two channel hi-fi, with more people now concerned about high quality sound. We think this is fueled partly by the high-definition music sector and the rise in analogue turntable sales. However, the long-term future has to be with high definition digital audio files, but the exact format has yet to be decided.

Monitor Audio Trimless 300 CT380-IDC

Can you tell us about Monitor Audio future products?

Sadly, I am not in a position to discuss future products. I can only say that our major effort is designing better speakers with wider application for the custom installation sector. We feel that there is a big opportunity to educate the builders and architects in how to achieve better sound in the home by focusing on key construction materials and attributes.

Can you tell us about your personal audio equipment?

I currently use PL300 speakers and am looking to upgrade these to the most recent PL300II in the near future. These are powered by a Moon i7 dual mono integrated amplifier. The CD player is an old CDS from Naim, which still sounds very good. I use an oracle Delphi iV turntable with a combination of SME V with a Koetsu Urushi MC cartridge. The phono stage is a hand-built, low-noise, battery-operated kit, I built it around 25 years ago. It still works great for MC cartridges.

Lastly, what is your best musical recollection?

I guess my first recollection of music was from my father. He had a collection of ’70s rock and prog rock, which I listened to a lot. The first album I played a lot would have been Pink Floyd, “Wish you were here.”

This post is also available in: French

About the author

Tristan Jacquel

Tristan est rédacteur chez Son-Vidéo.com. Passionné de musique, d'acoustique et de high-tech, il réalise notamment les tests matériels pour notre blog.

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