​Rapid iteration of geometries resulted in a finalized design that would ensure compliance with P.51.

​The mouth prototype was built and compared to limits and simulation at both nearfield and farfield locations.

​Calibration at the mouth reference point (MRP) verified frequency response (FR) and total harmonic distortion (THD):

Outcomes: Bandwidth Gains with Trade-Offs
The prototype mouth achieved improved high-frequency bandwidth with no change in low-frequency performance. A limiting factor was the Helmholtz resonance near 2 kHz, caused by the mouth opening interacting with the front volume. This resonance is difficult to apply damping to reduce the peak, or EQ. The nearfield performance targets limit the size of the enclosure and opening.
 
Next Steps: Optimize for Far-Field Applications
Future goals include:

• Improving bandwidth and overall response flatness.
• Enlarging the front opening to eliminate the 2 kHz peak and boost high-frequency output
• Increasing enclosure volume to enhance low-frequency response

 
For far-field-only designs, new challenges arise

• If the mouth cannot be calibrated at MRP, what becomes the reference point?
• What off-axis directivity target should be used?

 
The IAR Mouth Source V1 proves that a high-performance, standards-compliant acoustic source can be made using 3D printing and off-the-shelf components. While there are limitations, the design offers a strong platform for future development and upcoming iterations. As a sneak preview- we know we can extend the bandwidth with the "big mouth" design shown below, if we are ok being slightly out-of-spec on the P.51 near-field directivity. And since most interfering talkers are in the >0.5  meter distance, this seems like an acceptable tradeoff. 

IAR is thrilled to introduce a significant enhancement to our prototyping capabilities: the Form 4 SLA Printer. This cutting-edge technology vastly improves our ability to swiftly address detailed acoustic queries such as "what happens when I change XYZ...?"

​IAR has prototyped plastic parts using a Fused Deposition Method (FDM) printer (Prusa), supplemented by a large-format resin printer (Peopoly L) added three years ago. While FDM remains ideal for economical and rapid fixturing solutions, its melted plastic lines and occasional air gaps between layers act acoustically like a highly resistive porous wall, necessitating epoxy coating of thin enclosure walls for transducer applications—a labor-intensive process.

A commercially available smart glasses product has two ports for the speaker in the stem near the ear:

​The dipole speaker design of the smart glasses provides greater than 10dB improvement in level below 300Hz at short distances, even after adjusting for expected level shift due to distance. This is the observed proximity effect.  This is identical to how a gradient microphone also has proximity effect when used in the nearfield:

This port stretching is done easily in simulation by magically entering a larger distance between the speaker outlets. ​However, this is not physically realizable without making the internal ports to the front and back of the speaker proportionally longer.   When port dimensions are allowed to stretch with increased spacing, high-frequency response will be affected.

 ​The need for open ear speaker designs has presented challenges to achieve comparable performance to traditional earphones.  A dipole speaker design can solve several issues with acoustic performance and comfort, but requires careful consideration of design constraints.  Innovative design solutions continue to push the boundaries of what these speakers can offer in terms of comfort, privacy, and audio quality.

IAR was interviewed by Note Magazine on our design involvement with Headphones for the Fall 2021 edition.
Check it out here: https://issuu.com/classicalmusicindy/docs/note-fall2021issue-v04-101821web
 

Within Comsol Multiphysics is the ability to create room acoustics simulations.  This can be extremely helpful in shaping the sonic picture of any space.  For example, when designing a classroom, if the room is large and has a lot of reflective surfaces, a high reverberation time and low clarity can cause students sitting in the back to have trouble understanding the speaker.  By using a simulation, you can test out many acoustic configurations of a room before anything is physically built, saving both time and money, and creating an auditory experience tailored to the needs of the space.

Users build out geometry of the room, adding in carpets, panels, and all other objects.  Next, users define absorption coefficients of all materials across frequency bands and map them to different surfaces in the room.  After this, the Sabine reverb equation can be calculated as a parametric sweep is simulated.
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The room being designed in this case is a room-within-a-room.  This will be useful for testing consumer devices in a setting that replicates actual use scenarios. After doing RT60 measurements in Soundcheck 19, it was decided corner bass traps would be a beneficial addition to the room.  In Comsol, multiple different bass traps were simulated in different positions to determine best material, placement, and volume to reduce sound reflections in low frequencies with minimal impact in high frequencies.   

By: Shannon McConnell

Whether you’re in a teleconference, a live music setting, or simply working in an office, noise and room reverberation time can affect your ability to pleasurably listen.  With our new Noise Files Comparison Tool, you can hear and easily compare different kinds of noise to aid in self diagnosing issues quickly and efficiently.  For example, you can toggle between 60Hz, Bluetooth, GSM, and Wi-Fi noise interferences to help find the source of unwanted sounds.  Also included are different types of broadband and background noise such as pink noise, white noise, city traffic, and a crowded pub.
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Additionally, recordings of the in-house Head and Torso Simulator (HATS) playing back an IEEE standard speech file were taken in an anechoic chamber, an acoustically treated room, and a highly reverberant non-acoustically treated room. These can be compared to highlight the impact partial and full acoustic treatment has on speech intelligibility.  

We can also use this tool to create custom recordings of your product in different noise conditions, tuning configurations, or other impairments- for subjective evaluation without a trip to our lab. For dB-accurate reproduction we ship you a DAC and Reference Headphones with Comparison Tool files corrected for both the headphone response and binaural HATS Head Related Transfer Function (HRTF).
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By: Shannon McConnell

Indy Acoustic Research collaborated with Listen, Inc. to bring the data behind the article "How to Measure Free-Field Speaker Response without an Anechoic Chamber" featured in the March 2021 Voice Coil article, linked below!

The hybrid splice method of loudspeaker frequency response measurement compares well with an anechoic chamber for a single loudspeaker if the splice frequency can be determined. However, complex devices require the greater flexibility in setup conditions and off-angle measurements afforded by a full chamber.