The evolution of MEMS microphones marks a significant leap towards a future of seamless human-to-machine interaction, ensuring that AI can truly listen - and one day even "understand" - beyond our auditory limits.

Hearing Beyond Human Limits: Infineon's XENSIV™ MEMS Microphones Fuel Next-Gen AI

USound currently offers two MEMS loudspeakers that are part of the Ganymede series: Adap UT-P2019 and Achelous UT-P2018. Adap is optimized towards maximum acceleration, making it ideal for free-field applications, whereas Achelous is optimized towards maximum excursion, making it especially suitable for occluded-ear applications. Therefore, USound MEMS loudspeakers can be evaluated in both acoustic domains: baffle and coupler conditions. For baffle conditions, the IEC 60268-5 standard is used, while for coupler conditions, the relevant standard is the IEC 60318-4, formerly known as 60711, or simply &ldquo;711&rdquo;. For both setups, proprietary measurement adapters are used to fit USound speakers to the standardized setup. Using the adapters, it is possible to achieve the results shown on the Adap and Achelous datasheets. Measurements with the Carme Box UJ-R1020 can also assess the speakers&rsquo; performance even if they lead to slightly different results. In this article, we will show several possibilities to perform the measurements and the differences between those methods.<h2 id="isPasted">BAFFLE MEASUREMENT (IEC&nbsp;60268-5)</h2>To measure the loudspeaker in a&nbsp;baffle, it is necessary to place the MEMS speaker inside the measurement adapter. The following picture shows a drawing of the proprietary adapter used by&nbsp;USound.<figure><img data-fr-image-pasted="true" src="https://lh4.googleusercontent.com/J5XLouoWSuShn2kNsrXZlX7cw0jFZl5jQrjSL1EdbaFMATh5sfK1oVCd4B3D4nkMQWXAM0cgZFBTtXlW445rnkRFSDvZ_OB4v7qyiR53GGHtAIHN67NhwYzjFeitd6NnvWBOIlvs" alt="" class="fr-fic fr-dii"></figure>The electronic connection is achieved using pogo pins that press against the pads on the back of the loudspeaker. A gasket is placed in front of the speaker for sealing purposes, and an opening in the baffle enables the speaker to radiate towards the microphone, which is placed at a 10 cm distance from the baffle (as per the IEC 60268-5 standard). The SPL and THD results measured with this setup can be found on the&nbsp;<a href="https://www.usound.com/technical-documentation/" target="_blank">Adap UT-P2019&nbsp;datasheet</a>.<h3>COUPLER MEASUREMENT (IEC&nbsp;60318-4)</h3>For coupler measurements, a coupler adapter was designed to place the speaker close to the coupler without introducing additional resonances. This was obtained using a port of 3.6 mm diameter and 1.5 mm length (with an additional gasket of 0.5 mm, compressed to 0.3 mm). By using these dimensions, any emerging resonance is guaranteed to fall above the audible frequency range (&gt;20 kHz). With the use of USound&rsquo;s coupler adapter, the measurement can be performed without the earmold adapter. The SPL and THD results measured with this setup can be found on the&nbsp;<a href="https://www.usound.com/technical-documentation/" target="_blank">Achelous UT-P2018 datasheet.&nbsp;</a><h2>MEASURING MEMS SPEAKERS WITH THE CARME UJ-R1020 SPEAKER&nbsp;BOX.</h2>The two methods mentioned above require the use of proprietary coupler adapters. Another possibility to measure USound loudspeakers is by using the Carme UJ-R1020 speaker box. With a back volume of 100 mm&sup3;, it provides the necessary sealing to avoid an acoustic short circuit. It offers a convenient way to connect USound MEMS speakers to USound&lsquo;s linear amplifier Amalthea UA-R3010 or to the Helike UA-E3010 development board. With the Carme speaker box, both measurements in free-field and measurement on an artificial ear are&nbsp;possible.<h3>MEASUREMENT WITH CARME BOX IN&nbsp;FREE-FIELD</h3><figure><img data-fr-image-pasted="true" src="https://lh4.googleusercontent.com/U5uzyqnZLWRpXlwc1Gtv94bUBUlLcpX3s9UJe1VlHTHF_9lVpc0SFpNX6beQXZZ9-pAwYi3JtRSSDJryAP7TG87oB2c9DlVplTXJkcbf4DDb6Be2K3hJUxZLcoDwHzkSkSeDYsp0" alt="" class="fr-fic fr-dii"></figure>The box must be placed in a reflection-free space such as an anechoic chamber and pointed towards the microphone. Since no baffle is used in this setup and a back volume is introduced, the frequency response will be different from the results present on the Adap datasheet. Due to the missing baffle, the SPL will be ~6 dB lower below resonance frequency. The following graph compares the results obtained with the USound coupler adapter and with Carme&nbsp;Box.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box-1024x409.png" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box-1024x409.png 1024w, https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box-300x120.png 300w, https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box-768x307.png 768w, https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box-1536x614.png 1536w, https://www.usound.com/wp-content/uploads/2021/07/Adap-UT-P2019-SPL-measurement-in-the-Carme-speaker-box.png 2048w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="height: 300px;"><figcaption>Adap UT-P2019 SPL measurement in the Carme UJ-R1020 test box in free field</figcaption></figure><h4>Measurement with Carme Box in a&nbsp;coupler</h4>For coupler measurements, two setups are possible: with or without the earmould adapter. Therefore, the Carme UJ-R1020 box can be placed directly on the base part of the coupler or the earmould adapter, as shown in the following picture.&nbsp;<figure><img data-fr-image-pasted="true" src="https://lh4.googleusercontent.com/cW1VA3oRLSVzuCXuaaqTYz517VDH1PopwuEFtUNawEpoylpEmP7GkF3flRI7wmd1ptO-tgEIjBXap-lFYdmIcyO1_1njwZiwsStlFh9orP6DNuDWjewiBWte62oKzpxwD4WZtR2J" alt="" class="fr-fic fr-dii"></figure><figure><img data-fr-image-pasted="true" src="https://lh4.googleusercontent.com/iJ9Fsql8g_vE7FFd00DiJcy4zhFNG_TelJwJ5L79xjxKP_lA99pWIZ_1rv9uxcwK58lwGF_mtHWCZGEIgnG5L8MY-RKepYMYQ3ZzBQlYZcHrGkC6ZB5YCAKcELRQb6YyQ4DDF-Y1" alt="" class="fr-fic fr-dii"></figure>In both cases, to seal the air volume between the box and the coupler, it is necessary to apply sealing material (blu-tack, putty) between the two parts. Since the dimensions are not the same as with the USound coupler adapter, some differences will emerge.&nbsp;Recommended reading:&nbsp;<a href="https://www.wevolver.com/article/why-usound-mems-speakers-outperform-electrodynamic-and-balanced-armature-micro-speakers" rel="noopener noreferrer" target="_blank">Why USound MEMS speakers outperform electrodynamic and balanced armature micro speakers</a>Nevertheless, the results will also be relevant to assess the MEMS speaker&rsquo;s performance. A comparison between the results obtained from the two methods mentioned above and the setup with USound&rsquo;s coupler adapter is shown in the following graph.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/Achelous-UT-P2018-SPL-measurement-in-the-Carme-UJ-R1020.png" alt="Achelous UT-P2018 SPL measurement in the Carme UJ-R1020" srcset="https://www.usound.com/wp-content/uploads/2021/07/Achelous-UT-P2018-SPL-measurement-in-the-Carme-UJ-R1020.png 1003w, https://www.usound.com/wp-content/uploads/2021/07/Achelous-UT-P2018-SPL-measurement-in-the-Carme-UJ-R1020-300x124.png 300w, https://www.usound.com/wp-content/uploads/2021/07/Achelous-UT-P2018-SPL-measurement-in-the-Carme-UJ-R1020-768x316.png 768w" sizes="(max-width: 1003px) 100vw, 1003px" class="fr-fic fr-dii" style="height: 300px;"><figcaption>Achelous UT-P2018 SPL measurement in the Carme UJ-R1020 speaker-test box</figcaption></figure>

USound MEMS loudspeakers can be evaluated in both acoustic domains: baffle and coupler conditions. 

How to measure USound MEMS loudspeakers

Most consumer electronics nowadays use traditional electrodynamic speakers. They consist of a magnet, a voice coil, a diaphragm and a support structure/enclosure. This working principle limits the minimum height that can be achieved with such a loudspeaker. The diaphragm’s suspension solely controls the mechanical behaviour, as electrodynamic microspeakers typically lack the centering spider of larger&nbsp;loudspeakers.In this article we will demonstrate how MEMS-based microspeakers outperform the traditional voice coil-based microspeakers, and how manufacturers can benefit from a more reliable component to build more ergonomic and unique audio devices.&nbsp;The trend in MEMS sensors and transducers is to replace the complete system with a silicone equivalent. While this is a viable solution for many applications, the physics of generating sound demands a more sensible approach. To generate sound, an important factor is the effective radiating area – the higher the area, the more sound is produced. Silicon processes scale inversely with size, however, and MEMS technology gets cheaper the smaller the silicon elements are. A second factor is the movement of the radiating area: The more the area moves, the more sound is being produced. With silicon being a stiff material with inherently high resonance frequencies, this works fine for ultrasonic applications but is difficult to apply towards audio&nbsp;frequencies.USound’s innovation is to separate the radiating area and the driving elements into two components: the diaphragm and the MEMS motor. This allows to make the MEMS motor small, reaping all the cost benefits of smaller silicon elements while not sacrificing effective radiating surface area. It also allows optimization of the MEMS elements for force as opposed to large surface&nbsp;area.Combining the advantages of semiconductor processes with larger surface areas is the reason why USound MEMS loudspeakers outperform other comparable concepts: the use of a diaphragm allows for smaller MEMS elements while retaining a larger acoustically effective area to produce&nbsp;sound.Comparing MEMS speakers to traditional electrodynamic voice-coil or balanced armature loudspeakers, USound’s speakers are superior in three categories:<h3 id="isPasted">SYSTEM&nbsp;INTEGRATION</h3>Specific versions of USound MEMS loudspeakers can be used with reflow soldering. This allows integration into fully automated SMT assembly lines and many other&nbsp;environments.MEMS loudspeakers are capacitive in nature, which means that the energy is not dissipated as heat. MEMS loudspeakers heat up significantly less than electrodynamic loudspeakers during use, which means that surrounding sensors are less&nbsp;affected.<h3>FORM&nbsp;FACTOR</h3>Silicon processes result in inherently thin systems. The MEMS motor in USound loudspeakers is less than half a millimeter thick, an order of magnitude thinner than electrodynamic loudspeakers. The fact that neither a heavy voice coil nor a heavy magnet are used results in a much lower weight of the loudspeaker as&nbsp;well.The image below shows how much less space a MEMS loudspeaker (right) takes up compared to a traditional 6 mm dynamic loudspeaker (left) commonly used in modern TWS&nbsp;earbuds.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/03/USound-MEMS-speaker-solution-for-TWS-vs-voice-coil-solution-for-tws-2.png" alt="" class="fr-fic fr-dii" style="width: 500px;"></figure><h3>SOUND&nbsp;QUALITY</h3>Compared to voice-coil-base electrodynamic microspeakers, USound MEMS loudspeakers benefit from the stabilizing effect of the piezo motor, which not only provides the driving force but also acts similar to the centering spider of larger loudspeakers, keeping the movement more linear and controlled. The speed and precision of a linear actuator such as a MEMS piezo element are higher than a voice coil, which allows for&nbsp;<a href="https://www.usound.com/usounds-mems-speakers-extreme-bandwidth-technology/" target="_blank">higher bandwidth</a> and more accurate reproduction of high frequencies. At the same time, the bass can be tuned from linear (preferred by many audiophiles) to a significant boost (preferred by some people and anything in between. This means that a single MEMS loudspeaker can be used for the whole audible frequency range instead of using multiple&nbsp;speakers.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/03/USound-MEMS-speakers-Bass-boost.png" alt="" class="fr-fic fr-dii" style="width: 700px;"></figure>

In this article, we will demonstrate how MEMS-based microspeakers outperform the traditional voice coil-based microspeakers, and how manufacturers can benefit from a more reliable component to build more ergonomic and unique audio devices. 

Why USound MEMS speakers outperform electrodynamic and balanced armature micro speakers

Most components in consumer electronics are silicon-based. The last component that is still manufactured traditionally is the loudspeaker — until now. USound is leading the revolution of the global speaker market, being the first company to introduce MEMS loudspeakers to the mass market. The thin form factor and wide bandwidth of USound MEMS speakers enable miniaturization of the audio module in wearables, hearables, smartphones, and smart devices in general. With traditional technology, this would be impossible without compromising the audio&nbsp;quality.So what are the inherent advantages of USound MEMS loudspeakers compared to conventional electrodynamic and balanced armature&nbsp;speakers? <h3>SMALLER&nbsp;SIZE</h3><figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/article.jpg" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/07/article.jpg 1024w, https://www.usound.com/wp-content/uploads/2021/07/article-300x132.jpg 300w, https://www.usound.com/wp-content/uploads/2021/07/article-768x338.jpg 768w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="width: 800px;"></figure>The main size advantage from USound MEMS loudspeakers comes from the thickness or lack thereof. In traditional electrodynamic loudspeakers, there is a lower limit to the size of the voice coil and magnet assembly. And while rare-earth magnets (especially neodymium magnets) allow the use of smaller magnets while retaining the same sound pressure level output, they still dominate the geometry and impose a lower limit to the size of the loudspeaker. Simply put: traditional microspeakers consist mostly of the magnet. They can not be miniaturized further, as the magnet can not shrink without losing sound&nbsp;output.Replacing the voice coil + magnet assembly with a MEMS motor removes this limit. The thickness of a MEMS motor is essentially zero compared to a coil + magnet. In the case of MEMS loudspeakers, the loudspeaker thickness is limited only by how far the motor needs to excurse. This allows USound MEMS loudspeakers to be as thin as 1.3&nbsp;millimeters.This reduced thickness frees up more real estate for other components, such&nbsp;as<ul><li>A larger battery (higher battery life)</li><li>Accelerometers (headtracking)</li><li>Additional microphones (beamforming, noise cancelling)</li><li>UHF sensor (“find my device”)</li><li>Infrared-sensors (ear detection)</li><li>Pulse-oximeter (health sensoring)</li></ul> <h3>PCB-BASED</h3>Since USound MEMS loudspeakers are PCB-based, they can easily be combined with additional SMD components to form an audio module. They can be mounted to a PCB via reflow soldering or conductive glue. This allows for easy outsourcing of acoustic design, rapid prototyping, and evaluation and, thus, a faster time to market.&nbsp; <h3>NON-FERROMAGNETIC&nbsp;MATERIALS</h3><figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/MEMS-speakers-1.jpg" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/07/MEMS-speakers-1.jpg 1024w, https://www.usound.com/wp-content/uploads/2021/07/MEMS-speakers-1-300x103.jpg 300w, https://www.usound.com/wp-content/uploads/2021/07/MEMS-speakers-1-768x263.jpg 768w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="width: 800px;"></figure>On request, USound MEMS speakers can be manufactured without ferromagnetic materials with zero tradeoffs in acoustic performance. This allows the use of these loudspeakers in areas with strong magnetic fields, i.e., to communicate with the patient inside an MRI&nbsp;machine. <h3>SMALLER MOVING MASS, THEREFORE LOWER&nbsp;VIBRATIONS</h3><figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/article3.jpg" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/07/article3.jpg 1024w, https://www.usound.com/wp-content/uploads/2021/07/article3-300x132.jpg 300w, https://www.usound.com/wp-content/uploads/2021/07/article3-768x338.jpg 768w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="width: 800px;"></figure>Ideally, the only part of the loudspeaker that moves should be the diaphragm; if the ratio of diaphragm mass vs. total mass is too high, the casing of the loudspeaker will vibrate as well. These unwanted mechanical vibrations can cause solid-borne sound to enter microphones in the immediate vicinity. If the signal of these microphones is used to feed the loudspeaker (e.g., in an earphone in transparency mode or in a hearing aid), this will cause a feedback loop, typically audible as a highly irritating, screeching sound. Due to the absence of a heavy voice coil, USound MEMS speakers are much lighter and produce significantly fewer mechanical vibrations. This is important not only for hearing aids but also for modern TWS earphones with “transparency”/”hearthrough” mode, where the recording of the microphone is being played through the loudspeaker on the same&nbsp;device. <h3>NO ELECTROMAGNETIC&nbsp;RADIATION</h3>Conventional speakers rely on the Lorentz force, where a change in the electric field, by applying a voltage to the coil while it is suspended in a magnetic field, imposes a force on said coil and causes it to move. The induced change in the electromagnetic field is a form of electromagnetic radiation, which will radiate into the surrounding. Some types of sensors can easily be disturbed by this unwanted electromagnetic pollution. USound MEMS loudspeakers, on the other hand, rely on the piezoelectric principle, which causes no electromagnetic radiation. This eliminates the need for any magnetic shielding in mobile devices between speakers and other sensitive parts (like&nbsp;sensors). <h3>NO HEAT&nbsp;GENERATION</h3><figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/07/low-heat-generation-2.jpg" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/07/low-heat-generation-2.jpg 1024w, https://www.usound.com/wp-content/uploads/2021/07/low-heat-generation-2-300x103.jpg 300w, https://www.usound.com/wp-content/uploads/2021/07/low-heat-generation-2-768x263.jpg 768w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="width: 800px;"></figure>While the electric impedance of conventional microspeakers has a reactive component caused by the coil, the impedance of the whole system is normally dominated by the resistive component of the length of wire that forms said coil. This means that the electrical energy is mostly converted into thermal energy as it dissipates across the ohmic resistance. In typical mobile phone speakers, the coil heats up to over 70&nbsp;°C.However, in USound MEMS loudspeakers, the electric impedance is determined solely by the capacity between the two electrodes of the MEMS element. The impedance is therefore purely capacitive and has virtually no resistive component, meaning that the energy does not dissipate, and a much smaller percentage is converted to thermal energy. This means that less heat is generated. Typically the temperature of the hottest part of a USound MEMS loudspeaker is not significantly above room temperature. Like the reduced EMI, this causes less disturbance for surrounding sensors (especially infrared sensors) and also reduces the wear and tear of other components that are sensitive to temperature (e.g., batteries). The electric impedance being purely capacitive also means that the electric energy can be “reused” by pulling it back out of the loudspeaker, so to speak. This lowers the total power consumption of the&nbsp;loudspeaker. <h3>SUMMARY</h3>USound MEMS loudspeakers offer many benefits over conventional&nbsp;loudspeakers.<ul><li>Smaller size</li><li>Easier integration</li><li>Easier modularization</li><li>Direct PCB mounting</li><li>No ferromagnetic materials</li><li>Less unwanted vibrations</li><li>No EMI</li><li>No heat generation</li></ul>And all these benefits come while still fulfilling the requirements for audio performance. There is no need to make a tradeoff in the actual sound — but you can now build high-end audio products with additional functionalities.

Most components in consumer electronics are silicon-based. The last component that is still manufactured traditionally is the loudspeaker — until now.  Loudspeakers using USound MEMS technology offer a multitude of inherent advantages, compared to traditional ED or BA speakers.

Inherent characteristics of USound MEMS speakers

When we discuss what makes a headphone or earphone sound “good” and “bad”, we inevitably need to ask the question, well how should a headphone&nbsp;sound?Is there an objective way to answer this? Or does it all depend on personal&nbsp;preference?The truth, as so often, is somewhere in the&nbsp;middle.The first question we need to answer is: “what should a speaker sound&nbsp;like?”&nbsp;The short answer is (after decades of&nbsp;research):<ol><li>A speaker should produce a flat frequency response in an anechoic room.&nbsp;</li><li>The loudspeaker should be designed such that its directivity (how the sound is radiated to directions other than to the front) makes it so that when the same speaker is placed in a “normal” (slightly reverberant) room, the frequency response will be a little tilted – about 4 dB more bass, and about 2 dB less treble.</li></ol>The debate about this is&nbsp;basically over, the&nbsp;<a href="https://books.google.at/books/about/Sound_Reproduction.html?id=sGmz0yONYFcC&redir_esc=y" target="_blank">question has been answered</a>, and indeed, virtually all “good” speakers show this behavior (flat on-axis, controlled sound power&nbsp;output).<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/04/room-target-curves-1024x683.png" alt="" srcset="https://www.usound.com/wp-content/uploads/2021/04/room-target-curves-1024x683.png 1024w, https://www.usound.com/wp-content/uploads/2021/04/room-target-curves-300x200.png 300w, https://www.usound.com/wp-content/uploads/2021/04/room-target-curves-768x512.png 768w, https://www.usound.com/wp-content/uploads/2021/04/room-target-curves.png 1200w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="height: 480px;"></figure>And since recording studios use good speakers (studio monitors) to record, monitor, and mix the music that consumers listen to later, it makes intuitive sense to listen to the music on similarly performing speakers – because that is what the music is supposed to sound like, this is what the artist and recording engineers decided “sounded good”. So the&nbsp;target for speakers is Flat on-axis, controlled sound power output (smooth&nbsp;directivity).Now, the same question can be asked for headphones: “what should a headphone sound like?” (in terms of: What is the ideal frequency response of a headphone”), and the short answer is: “it’s not that&nbsp;simple”.The answer is simple for speakers (not that simple really, but it has been answered), but for headphones, it is much more&nbsp;difficult.The first difficulty is “how do you measure it?”. It’s easy with speakers – put a calibrated microphone at a standardized distance, in a standardized room (e.g. anechoic). With headphones, this isn’t possible, because much of the sound depends on the shape of the head. The general consensus is to measure headphones on artificial heads, with artificial ears and artificial ear canals. The problem with this is, that head shape, ear shape, and ear canal has a significant influence on the acoustics, most prominently a 10-20 dB boost in the upper midrange / treble part of the spectrum, depending on the angle of&nbsp;incidence:<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/04/ear-resonance-1024x683.png" alt="Influences on measured ear resonance" srcset="https://www.usound.com/wp-content/uploads/2021/04/ear-resonance-1024x683.png 1024w, https://www.usound.com/wp-content/uploads/2021/04/ear-resonance-300x200.png 300w, https://www.usound.com/wp-content/uploads/2021/04/ear-resonance-768x512.png 768w, https://www.usound.com/wp-content/uploads/2021/04/ear-resonance.png 1200w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="height: 480px;"></figure>The important thing is: We “hear” this boost even when listening to speakers – because our ears are&nbsp;always there. When the artificial head measurement shows a high boost at 3 kHz, this sounds “flat, linear” to us, because this is what our ears hear. But how should this boost look exactly? What is the&nbsp;target frequency&nbsp;response?Enter a scientist named Sean Olive. His hypothesis was that the best way to come up with a target response for headphones was to place a pair of good speakers in a “regular” listening room similar to the control rooms of recording and mixing studios, and measuring the frequency response with an artificial head setup. Harman’s&nbsp;<a href="ttps://www.aes.org/e-lib/browse.cfm?elib=14873" target="_blank">reference listening room</a> is neither fully reverberant nor fully anechoic, it features a reverberation time of about 0.4 seconds, very similar to what professional recording and mixing studios&nbsp;use.Now if we measure a headphone using that same artificial head and the headphone was to have the same frequency response that we previously measured in the room, then this frequency response would be ideal, or so Sean Olive proposed. And further research proved that&nbsp;<a href="https://www.aes.org/e-lib/browse.cfm?elib=16768" target="_blank">he was right</a>, the majority of both trained and untrained listeners prefer this target curve over any other target&nbsp;curve.This allows us to escape the circle of confusion, and get closer to the ideal of hearing the same thing the artists, producers and engineers heard when creating the music that we listen to. But the topic does not end&nbsp;here!It’s important to understand that the result of this research is – contrary to popular belief – is not a single fixed frequency response curve that needs to be followed to the letter. In fact, the research confirmed what listeners had suspected for quite some time: The preferred amount of bass varies from person to&nbsp;person.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/04/bass-variation2-1024x683.png" alt="Preferred bass-response on in-ear headphones" srcset="https://www.usound.com/wp-content/uploads/2021/04/bass-variation2-1024x683.png 1024w, https://www.usound.com/wp-content/uploads/2021/04/bass-variation2-300x200.png 300w, https://www.usound.com/wp-content/uploads/2021/04/bass-variation2-768x512.png 768w, https://www.usound.com/wp-content/uploads/2021/04/bass-variation2.png 1200w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="height: 480px;"></figure>Additional research performed by&nbsp;<a href="https://iem.kug.ac.at/institut-fuer-elektronische-musik-und-akustik-iem.html" target="_blank">USound and IEM</a> showed that in the presence of background noise (such as distant traffic), listeners tend to prefer more bass and slightly less treble compared to the original Harman&nbsp;Target.For this reason, USound’s USOUND1V1 reference target was tuned by expert listeners to contain more bass energy below 300 Hz, at the same time exhibiting a more smooth and timbrally accurate reproduction of the upper midrange and treble response. This results in a warm and punchy sound without sacrificing clarity, which maintains the original timbre of&nbsp;voices.<figure><img data-fr-image-pasted="true" src="https://www.usound.com/wp-content/uploads/2021/04/target-curve-comparison2-1-1024x683.png" alt="Comparison of target frequency response curve." srcset="https://www.usound.com/wp-content/uploads/2021/04/target-curve-comparison2-1-1024x683.png 1024w, https://www.usound.com/wp-content/uploads/2021/04/target-curve-comparison2-1-300x200.png 300w, https://www.usound.com/wp-content/uploads/2021/04/target-curve-comparison2-1-768x512.png 768w, https://www.usound.com/wp-content/uploads/2021/04/target-curve-comparison2-1.png 1200w" sizes="(max-width: 1024px) 100vw, 1024px" class="fr-fic fr-dii" style="height: 480px;"></figure>The predictable and&nbsp;<a href="https://www.usound.com/usounds-mems-speakers-extreme-bandwidth-technology/" target="_blank">highly precise performance of MEMS loudspeakers</a> enables more accurate tuning with digital filters. The precision of the MEMS actuators makes them the ideal transducer for an acoustically optimized system and allows using more natural-sounding filters to achieve the target sound.

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