Stage monitor headphones are experiencing a boom in popularity
Traditionally worn by artists and musicians while on stage performing, or by live sound engineers to check stage performance, an interest in the audio that the pros are listening to and an appreciation for the high acoustic isolation and fit of stage monitors is on the increase. This means there is a movement towards regular music lovers using them for listening, so they are fast becoming a popular genre of headphone. From autumn 2018, Sony enters this blossoming market with its newly developed stage monitors, the IER-M9 and IER-M7. We asked the designers about their focus during the design process.
(Interviewees) V&S Division, Product Design Div.Acoustic Engineer, Eiji Kuwahara
V&S Division, Product Design Div.Acoustic Engineer, Hayami Tobise
The IER-M9 and IER-M7 are new models of stage monitor that Sony has created from the ground up, utilising the latest technologies. To start with, could you tell us about the thinking and objectives you had regarding their development?
As an engineer, when it came to the IER-M9 and IER-M7, I wanted to start by thoroughly re-examining stage monitors in terms of their sound quality. It’s only recently that stage-use floor monitors have been replaced by in-ear monitors, and I thought there might still be room for further improvement. It seemed like it would be an interesting thing to look into.
What sort of sound is desirable in a stage monitor?
As the name suggests, studio monitors are used by Audio engineers in recording studios. Reproduction of the sound just as the microphone recorded, is what you are looking for. In contrast to that, what should a stage monitor that an artist wear on stage be like? We defined it as a tool that helps artists maximise their power of expression and did a breakdown of the acoustic qualities required to fulfil that role.
As a result of that breakdown, there were three essential elements which became clear to us.
The first of these is that the sound produced by the artist must be accurately reproduced, just as it was originally expressed. An important function of a stage monitor is making it possible to check for yourself how things like the smallest differences in singing, including breathing and the faintest vocals, are conveyed to the audience. The same is true for instruments like the guitar and bass.
The second element is the ability to properly ascertain the balance between the instruments. It’s important that the sound of the vocals and instruments on stage stand out and can be heard distinctly. Obviously, if these are all mixed up you can’t play your part. A stage monitor must accurately express the sound and emotion intended by the artist.
At a classical music performance, a conductor does these things, but at a concert it would typically be the stage monitor which would handle such things.
Exactly. Finally, the third element is rhythm. To ensure proper timings during performances, the vocalist and guitarist need to be able to properly hear the sound from the drums and bass in the rhythm section. This is another important function of the stage monitor.
This is a major point of differentiation when it comes to the IER-M9 and IER-M7. They allow you to clearly pick out the attack of the sound. We have also put a lot of our focus on making sure you can feel the groove of the music. This is because artists need to acutely feel the waves and swells of performances and respond to them accordingly in order to raise the expressive power of their music. So in practice this means we have made significant changes to the way low frequency sounds are created.
So far, we’ve discussed the ideal stage monitor sound. Can you now tell us about the technology that is used in the IER-M9 and IER-M7 to make this a reality?
To make this new stage monitor sound a reality, we’ve developed a new multi-BA system just for these models. We chose to use a balanced armature (BA) driver unit because the attack transient is suited for creating the rhythm expression required in an in-ear monitor. Also, to realise an accurate monitor sound, it is necessary to perform fine acoustic adjustment within the low to high frequency range. But with a multi-BA system, each BA handles a specific range making it the best approach for what we want to do.
You said “incorporated more than three BA units”, exactly how many BA units are there in these models?
There are five BA units in the IER-M9 and four in the IER-M7. And the main ranges handled by each of the BAs are also separated. This means that the IER-M9 is a 5BA-5WAY system and the IER-M7 is a 4BA-4WAY system. We actually tried making versions with more than six, but upon testing we found that more isn’t always better. To achieve the desired sound, we feel that, at the moment, a 5BA-5WAY set up is best. Furthermore, for the miniaturised BA, in addition to developing a new woofer and full range system, we are also developing a super tweeter.
What is really important here is that the IER-M9 is ‘5BA-5WAY’. There are systems that have multiple BA units handling the same ranges, such as 12BA 3WAY systems. But, we have not done that sort of thing with this device..
There are certainly benefits to having multiple BA units handling the same range, but one of the great things at Sony is that we are able to have the same engineer oversee everything from the in-house development of the BA units to the design and manufacture of the in-ear headphones. From the wires and diaphragm of the BA to the shape and the materials, we were able to follow through with exactly how we believed each BA should be. As a result, we were able to realise high acoustic quality with the fewest possible units.
I would like to talk a bit about the unfailing attention to detail Sony gave the BA units. Take the woofer, for example. This unit has very small holes through which the sound passes. These small holes, depending on their sizes, cut out high frequencies. We adjusted and tested these holes at a micron level to achieve our core aim of being able to express groove within music and adopted those which produced the sound closest to our ideal.
The path taken by the sound output from each BA is also important. With BA headphones, a path for the sound is usually created using narrow tubes connected to the BA. There are disadvantages to this method though, such as the high frequency range from the tweeter being dampened. To avoid this, we have adopted a method in which the BA units are mounted directly onto the inner housing. This method has allowed us to make a wider sound path and directly deliver the natural high frequencies produced by the BA (an optimised sound path). The inner housing is also made of highly rigid, high internal loss magnesium alloy. By securing the BA and reducing any unnecessary housing vibration, we were able to raise the clarity of the audio even further.
Were there any other issues that caused you trouble when assembling the multi-BA system?
It wasn’t just the pattern with which the BA units were put together. Including the shape of the acoustic paths for mixing the sound from each BA and tweaking the network circuits to split up the frequencies, there were a countless number of adjustment patterns possible. Trying all of these was truly a slow and difficult process.
The middle range for these models is split mainly between two full range BA units. One assists the woofer, increasing the groove, while the other works in conjunction with the tweeter to put out clean high-frequency audio. That direction was visible to us from early on in the process, but in the end, we were able to far exceed the audio quality we had imagined at the start. What made that a reality was the network circuitry that Tobise worked so hard on. By completely rethinking the design concept, he succeeded in improving the connection between each BA. We can proudly say that this is quality which goes far beyond our greatest expectations.
Besides audio quality, were there any other points that received special consideration?
During the development of the IER-M9 and IER-M7, you sought the assistance of live sound engineers and artists who actually use such devices. Could you tell us what sort of collaboration took place?
We have the technology to make headphones and we are confident in the technology to judge and improve audio. However, what we did lack was the knowledge regarding stage monitor usage and the required audio quality. So, the assistance of artists and engineers who specialise in Sound Reinforcement (SR) was invaluable. Thanks to Sony Music, we were introduced directly to a live sound engineer working hands on with such equipment and were able to acquire lots of helpful advice from them. (See column below)
IER-M9 headphones impart excitement through sound
During the development of the IER-M9 and IER-M7, the collaboration with live sound engineer Ryo Ohmura of Kim Co., Ltd became something of a totem. What type of exchange was there, and how did the audio evolve as a result? We spoke to Mr. Ohmura.
First of all, could you tell us what your thoughts were when Sony contacted you?
I was excited. One of the joys of working as a SR is the creation of a fully-working stage from zero. It’s what motivates me in my work. In a similar way, making an in-ear monitor gave me that same sense of joy and excitement. When they contacted me, I immediately thought “I definitely want to do this.”
Could you explain the specifics of how you assisted?
Once I received the prototypes I utilised the help of my engineer colleagues and some of the artists I work with to test them out. In the end, I was able to gather the opinions of several dozen people. Their responses were all different and some of them were a bit too much of a personal opinion, but out of those I picked the especially important things that were required for an in-ear monitor and passed them on to Kuwahara and Tobise.
What sort of sound does an artist want from their stage monitor?
For example, it’s important for a vocalist to have such things as the tone and speed of their voice reproduced authentically. Of course, I think that sort of basic feature was mostly realised as early as the prototype stage. However, the reproduction of the heavy and low sounds of the bass drum that are so important to drummers was a bit weak, so I requested that they do more in that regard. With small in-ear monitors, it's typically not possible to reproduce the type of heavy, low sound that makes the air move, but I told them that I wanted to be able to feel that.
That was something we were surprised by. We were thinking that if you just want to hear your own voice or the attack of the bass drum, it was fine to have the low frequencies subdued. We were under the impression that we were putting out more than enough, but he said that for the musicians to perform, that still wasn’t enough. That’s the biggest change from the prototype. We learned that to give a good performance on stage, the reproduction of heavy and low frequencies is important.
Was that advice reflected in the final product?
Yes. Yes. I just tried listening to audio using the final version, and I can say I could definitely feel the air move. (laughs)
We asked Ohmura the same question - how do you feel about general music fans like us being able to use the IER-M9 and IER-M7 stage monitors, even though they were developed for professional artists?
To a pro, a stage monitor is simply one of their work tools. They certainly wouldn’t typically be something that would be used by everyday music fans. But, and I think you may have got some sense of this from the discussion so far, the truth is, they are excellent for not only monitoring but also listening.
For example, just like the sound directed toward the audience, the sound that is broadcast to the vocalist’s stage monitor is usually a mix of all the instrumentation. The ability to make adjustments so that a well-balanced reproduction of that sound can be listened to is one of the main characteristics of a stage monitor. So, while it is a monitor, it can also be used for listening, killing two birds with one stone as it were.
This was a new challenge for Sony, and in carefully searching for direction in creating the sound, we discovered that the final product had a balance that was suitable for everyday listening. The sound of the instruments is accurate, as are the rhythm and balance, and on top of that we think it’s a product that plays audio in a way that’s exciting to listen to.
Are there any genres that the IER-M9 and IER-M7 are particularly suited for?
Fundamentally, they are made to accurately render any type of music, but I would say they are a great way to enjoy the grooves and intricate musical expressions found in genres where a stage monitor would be used such as pop, rock, jazz.
Please tell us the differences between the IER-M9 and IER-M7.
The IER-M9 has an additional tweeter for smoother and more refined reproduction of high frequencies, allowing the fine nuances of the timbre to be expressed. Because we put a lot of our focus onto reproducing sounds like the linger of cymbals and high hats, and the breathing of the artist, it would be the IER-M9 that I would recommend to anyone who wants that level of exacting reproduction. Of course, the IER-M7 also feature all the important parts so I believe you should be just as satisfied with a pair of them as well. We think that those who regard the mid-range frequencies, particularly the vocals, to be especially important will find them to their liking.
What level of music player or audio source are you imagining this will be connected to?
Try it first with your normally preferred music player, even if it’s a smartphone. After that, if you have the budget, try a Walkman® that supports balanced connections (NW-ZX300, NW-WM1A, and NW-WM1Z) to enjoy the pure acoustics of a balanced connection. I would also recommend using the highest quality audio source available. High quality headphones are able to properly express differences in source quality, so I think it would be fun to listen and compare.