Exploration Intent

At Chemeketa we have challenges capturing adequate quality audio from the physical classroom environment so that students online can participate effectively in class discussions and activities. Recent advancements in audio conferencing technologies now offer potential opportunities for cost effective solutions that could address these issues.

This project seeks to explore new innovative solutions in audio conferencing technology that could provide cost effective, portable, and easy to use solution for instructors teaching live synchronous hybrid courses.

We wanted to test the MXL AC-360-Z microphone to see how well it could perform in various size classrooms. We also wanted to explore Zoom Rooms to evaluate how the audio is individually processed and optimized as well as support for linking multiple mics together to accommodate larger room sizes.

Our hope is to offer instructors easy-to-use solutions that can transform any classroom into a collaborative workspace with high quality web and video conferencing capabilities.

Technology Evaluated

Setup & Implementation

Image above showing the iPad ethernet adapter from Red Park.

Connecting the AC-360-Z Microphone

The microphone was nicely packaged and included an AC power adapter and several USB-C cables. The mic included rubber feet for firm placement on a table surface. There were no instructions included on how to install or configure the mic. The USB-C cables provided with the mic were not long enough so we had to also purchase 15 ft extension cables for this project.

Connecting the mic to the computer for the first time was simple. Zoom Rooms was able to detect both AC-360-Z mics once we connected them all together. Once connected we had to manually adjust the microphone sensitivity input levels for each of the four microphones from the Sound Properties Control Panel on the computer.

After performing a few test recordings in Zoom Rooms we then had everything setup and configured to begin using the mic in the room.

Microphone Testing

During this project we performed a variety of tests with the MXL AC-360-Z microphone:

• Captured audio in various size classrooms
• Used the mic to conduct a hybrid class
• Recorded sample audio to analyze for quality of sound

Classroom Seating Sizes

Large Classroom (30+ seating)

We conducted testing in a very large classroom approx. 100ft x 50ft. This room had tile floors and lots of windows and hard surfaces.

Classroom Size Microphone Performance

After recording a variety of tests in each of these rooms I analyzed the audio using Adobe Audition.

The MXL mic performed best in smaller rooms when placed in close proximity to the speaker’s voices. The microphone proximity had more impact on my test results than the overall size of the room. The MXL mic did not perform well when placed further than 6 ft away from people speaking. Audio loudness or perceived volume was not adequate.

When reviewing the audio from the Hybrid Classroom the instructor’s voice was clear and with moderate volume/loudness. However, student’s voices were faint and difficult to hear. The instructor was sitting at approximately the same distance as students from the MXL mics in the room (+/- 6ft). 

In the Large Classroom the recording tests showed very similar results. This room has a hard surface floor with a large spread out seating arrangement. We connected two MXL AC-360-Z microphones together to cover this larger area. Once again the MXL mic needed to be within 6 ft or less from people speaking to capture adequate volume.

Comparing the MXL Microphone

We recorded audio samples using four different microphones to see how well the MXL Ac-360-Z was able to perform when compared to other microphones we had available to us. Below are the four microphones we tested.

Frequency Response

A microphone frequency response chart can tell us how a given microphone performs at certain frequencies. Analyzing a microphone’s frequency response can help us better understand how a microphone will sound to the human ear. A really low male voice can reach a frequency below 100 Hz while a female voice can often start at 200 Hz. Vowel sounds are captured near the lower mid frequencies (200 to 1,000 Hz) while consonants are recorded near the upper mid frequencies (2 kHz and up). Air and breathiness is captured near the high frequencies (10 kHz an up).

Shaped Response Curve

The shape of a frequency response is called the response curve starting at zero on the low end and dropping off to zero at the high end. The peaks and dips in the curve can tell us how well a microphone is suited for a certain application. 

A microphone intended for recording vocals will show a rise in its upper midrange that adds brightness and intelligibility to the voice. The high and low variations in a shaped response can be intentional by design allowing unwanted noise to drop off at very low frequencies or very high frequencies.

The frequency response chart above shows horizontal numbers with frequencies from 20 Hz to 20 kHz range. The vertical numbers represent amplitude or volume in dB (decibels). 

 The shaped response curve for the MXL mic above shows a higher amplitude under 2 kHz capturing more noise and boominess that is not really part of the human voice. There is also a significant drop off in amplitude from 2 kHz to 10 kHz where consonants occur.

A short recording of four different microphones using Adobe Audition.

The chart above is a visual representation of my ambient tests showing the perceived loudness in LUFS measured from various distances.

The video above is a comparision of audio quality from recordings captured with the MXL mic using in Adobe Audition vs. Zoom Rooms.

Lessons Learned

Bring Your Own Device

Zoom Rooms was originally designed for huddle and conference rooms. Most classrooms at Chemeketa include a single computer at the instructor podium connected to a projector or HDTV display. Using Zoom Rooms in a classroom is a major shift for instructors. Zoom Rooms requires a BYOD (Bring Your Own Device) approach which may not be practical for some faculty. 

Speaking Volume and Human Behavior

In most cases we found that students do not speak loud enough to capture good audio. Instructors are often accustomed to speaking louder and projecting their voices in the classroom. To address this challenge we can place microphones closer to students but this can also capture unwanted noise. We can try increasing microphone sensitivity or gain but this also introduces more noise in the audio. Passing around a handheld microphone in the classroom can provide improved audio quality but is not practical and can negatively affect student behavior in classroom discussions.

DIY vs. Professional 

Zoom Rooms offers Design Guides for both Do-It-Yourself (DIY) and Professional AV Installations. DIY designs are considered simple plug and play solutions and are limited to small to medium size rooms.

Professional AV designs require experts who are well versed in audio and microphone configurations and optimization for room conferencing systems. 

For the average size classroom (15 > people) you should consider a professional installation. There are several online guides and resources available to elevate your Zoom Rooms experience.

Here are some tips to elevate your Zoom Room audio:

Implement a Professional Audio Infrastructure

• Ceiling Microphones – upgrade to a microphone array with microphones strategically placed throughout the room.
• Digital Signal Processor – connect microphones to a DSP to process multiple mic inputs into a single digital output signal for improved audio (echo cancellation, noise reduction, equalization). 
• In-ceiling Speakers with Amplifier – use speakers with a wide dispersal to spread out the sound throughout the room. Connect the speakers to your in-room amplifier to boost volume output.

View the Zoom Rooms Design Guides for recommendations on DIY vs. Pro AV, considerations for various room sizes, equipment lists, microphone layouts and more.

Zoom Rooms with Dual Screens

Zoom Rooms can reduce screen clutter by providing Zoom meeting controls on a seperate touch device. To really take advantage of Zoom Rooms you should be using at least two displays. This allows the instructor to display content fullscreen on one of the monitors while displaying students on the second monitor. Zoom Rooms can support up to three monitors with the third displaying the instructor fullscreen. 

Next Steps

Ultimately the MXL AC-360-Z microphones did not support our goal of offering instructors an easy, portable solution for capturing high quality audio for hybrid courses in various classroom environments. However, through our testing we believe the MXL AC-404-USB microphone may be better suited for this purpose. We would like to collaborate with our college Media Services team to implement a dedicated Zoom Room on campus with a professional audio infrastructure installed.