Tag Archive for: MEMS

100 Things #98: MEMS Speaker Measurements

MEMS speakers are one of the biggest innovations in speaker technology in recent years. Offering full range performance with compact size and low power, they are rapidly being adopted for use in devices such as earbuds, hearing aids, smart glasses and more. With SoundCheck you can make exactly the same MEMs speaker measurements as you can with conventional mechanical speakers. Watch this short video where we demonstrate frequency response, impedance, and distortion measurements on the xMEMS Montara MEMS speaker.

MEMS Speaker Measurements

 

We’d like to thank Michael Ricci, Sr. Director of Electroacoustic Engineering at xMEMS for the technical guidance on Piezo-MEMS transduction.

Learn More About SoundCheck’s Advanced Features

Read more about more measurement features in SoundCheck.

Learn more about the Normalized Distortion Measurement technique mentioned in the video – we have a short video explaining this, or a longer (but rather old) technical paper.

More information is also available in the  SoundCheck Manual.

 

Video Script: MEMS Speaker Measurements

SoundCheck is one of the most widely used loudspeaker and microspeaker measurement systems in the world, but did you know that it can also measure MEMS micro-speakers? MEMS micro-speakers are rapidly becoming popular for devices such as hearing aids, earbuds, smart glasses and more as they offer full range performance with compact size and low power, and they are also SMT reflowable. They’re constructed in an entirely different way to conventional miniature speakers – rather than using inductive coils and magnets, they use a voltage driven capacitive actuator to provide full range performance.

I’m going to demonstrate a MEMS micro-speaker test using the xMEMS ‘Montara Plus’ full-range Piezo-MEMS microspeaker, that uses a monolithic solid state fabrication. These devices are entirely manufactured with MEMS processes in a semiconductor wafer foundry. When you’re testing these devices, the xMEMS provided driver circuit delivers Voltage bias and boost converter to step up the voltage as piezo-MEMS devices have a very high input impedance and draw very low current.

Here, I’m going to use xMEMS’ own charge amplifier. You’re also going to need to build the speaker into an earbud or make your own test jig in order to test it. I’m going to demonstrate using this test jig, which is actually the one that xMEMS uses for their own measurements, and we’re going to put an ear simulator coupler on it to simulate an in-ear measurement. Aside from that, the test setup’s very similar to what we would use for any other speaker. We have an AudioConnect 2 interface which will power the coupler, and that’s connected to SoundCheck for analysis.

So we have a test sequence that will play the stimulus and analyze the response. You won’t hear it as it’s all in the coupler. And here we can see the results.

Let’s start with the frequency response. You can see it has a very flat response at low frequencies, and then in the higher frequencies you have a resonance due to the piezoelectric material and the resonance of the coupler.

We can also look at the impedance. You can see here that it’s a very different shape from a conventional loudspeaker impedance. The values are much higher but it’s very linear, which makes it easy to compensate for.

We can also look at distortion. The total harmonic distortion is also very linear right up to where we get into the ear canal response.

And while we’re on the subject of distortion, I just want to use the measurements on this device to highlight the importance of using frequency normalized distortion measurement.

With this conventional distortion measurement, you can see the second and third harmonics plotted at their actual measured frequencies, along with the fundamental.

Frequency Normalized distortion measurement compares the harmonic levels to the fundamental level at their measured frequency before their ratio is plotted, rather than the fundamental level at the excitation frequency. This removes the effect of the non-flat frequency response from the distortion and makes it easier to see the peaks in the distortion response independent of the peaks and dips in the fundamental response. Here, you can see both regular THD, the orange line, and normalized THD, the blue line. And as you can see, you have a high Q here at resonance, but apart from that there is very little distortion, so you can focus your efforts on planning around this peak. If you were going by conventional distortion, you could be wasting your time trying to solve resonances you don’t have with this second bump on the graph here.

So that’s piezo-MEMS speaker measurements in a nutshell. Check out our website for more information on testing MEMS speakers, or if you want to learn more about normalized distortion measurement.

 

 

100 Things #69: Testing MEMS Microphones In SoundCheck

Testing MEMS microphones and devices in SoundCheck is as simple as any microphone test. In fact, SoundCheck’s ability to work with different devices means MEMS setup is plug and play. Just like testing an analog microphone, SoundCheck can perform standard tests using microphone substitution or microphone subtraction. SoundCheck allows up to 64 channels of simultaneous acquisition, so daisy-chaining MEMS inputs easily expands the number of hardware inputs. Testing MEMS with SoundCheck is simple for both individual components and finished products.

Testing MEMS Microphones In SoundCheck

Try MEMS microphone measurements for yourself!

Our free test sequence includes not just one, but three pre-written test sequences for testing MEMS microphones including Frequency and Sensitivity, Microphone Substitution, and Power Supply Rejection.

Video Script:

As you know, SoundCheck offers unrivaled flexibility for testing different types of devices, and testing a MEMS microphone is as simple as adding a small, stand-alone MEMS interface to your test setup.

Let’s look at how we measure a digital MEMS- or micro-electromechanical- microphone in SoundCheck from component level to a finished product.

Testing digital MEMS microphones is identical to testing an analog microphone, we simply add a MEMS interface like the DCC-1448 to convert the digital PDM signal to PCM. This interface has 2 inputs, and  two interfaces can be daisy chained together for 4 discreet MEMS inputs. Performing the measurement is the same as with an analog mic. SoundCheck calibrates the source speaker by first measuring the speaker’s response and applying the reciprocal response to the speaker, effectively flattening the speaker. This removes the speaker’s influence on the MEMS microphone measurement [diagram.. Short video B-roll]. Alternatively, we can capture the response simultaneously though the MEMS mic and a calibrated reference mic, and subtract the reference mic’s response from the MEMS response, leaving the raw response of the MEMS microphone [diagram].

SoundCheck also tests MEMS sub-assemblies like a hands free microphone array. These sub-assemblies usually have multiple MEMS microphones and onboard D/A. Since SoundCheck easily supports multiple channels and multichannel audio hardware like our own AmpConnect 621, scaling for testing 4 or 6 channel MEMS sub-assemblies is a snap.

Of course, once the MEMS sub-assembly is installed into the finished product, we can measure that too. Here’s a test setup of SoundCheck testing the hands free MEMS microphones installed in a vehicle. SoundCheck plays a test stimulus through the mouth simulator and captures the response through the on-board microphones. The microphone response is transferred to SoundCheck via a BTC-4149 Bluetooth interface paired to the vehicle’s head unit, then analyzed. 

Aside from basic audio quality tests using sine waves, SoundCheck can also measure MEMS microphones with real world signals like pink noise, speech, music and more for all types of tests including communications, voice activation and more.

Check out our website for more information and free test sequences for measuring MEMS microphone sensitivity, frequency response and power supply rejection.

100 Things #50: Soundcheck Supports Multiple Interfaces for Ultimate Flexibility

SoundCheck is built on flexibility, and it’s hardware compatibility is no exception. SoundCheck supports multiple audio interfaces and devices, all simultaneously. Freely combine and measure with analog and digital interfaces together. Use a Listen interface like AmpConnect 621, and pair it with an A2B, I2S, or Bluetooth interface for highly customizable tests.

Audio Interface Options in SoundCheck

Learn more about SoundCheck’s Interface & Device Options

Listen’s Audio Interfaces.

Why did we design our own hardware: A look into why our in-house designed and manufactured audio interfaces offer advantages over off-the-shelf products.

Audio over IP with Dante interfaces.

Testing Automotive Audio Via A2B Interfaces.

Testing MEMS Devices with a MEMS Interface.

Using Bluetooth Interfaces with SoundCheck.

 

Video Script: Soundcheck Supports Multiple Interfaces for Ultimate Flexibility

Since 1995, SoundCheck has supported the use of external sound cards and audio interfaces. But did you know that SoundCheck can support multiple audio interfaces and other audio devices simultaneously giving you ultimate flexibility for a wide range of audio test applications?

Here are some examples of test applications that take advantage of this flexibility:

Add additional audio interfaces to expand your channel input and output count, for up to 64 channels of input and output

For example, add Bluetooth, Digital MEMS, I2S, A2B interfaces and even Dante to test these devices

Directly connect a USB audio device like a USB headset, microphone or speaker to test these devices

On Windows OS, SoundCheck supports a wide range of audio drivers including WDM/MME, ASIO, WASAPI, NiDAQ (if using National Instruments hardware) and even Dante. On MacOS, SoundCheck supports CoreAudio. As long as your audio device has an input or output path through a compatible audio driver in SoundCheck, it can be used as an audio source or destination for testing in SoundCheck. Furthermore, SoundCheck can easily support mixed analog and digital signals simultaneously as well as  hardware with different sampling rates.

Let’s look at a hardware setup window in SoundCheck fully exploiting this capability. In my hardware setup you can see a Listen multi channel AmpConnect 621, a BQC-4149 Bluetooth interface, an A2B interface and a USB headset all peacefully coexisting. Note: these devices use different audio drivers, mixed analog and digital signals and even different sampling rates.

With SoundCheck’s auto-delay algorithm, we can even account for latency differences outputting from one hardware device and inputting from another. For example, delays from transmitting a test stimulus to a Bluetooth device like a speaker or headphone.

SoundCheck also has resample and frequency shift post-processing steps to correct for sample rate mismatch and/or hardware clock phase differences as a result of inputting and outputting from different hardware interfaces. This means we can resample and phase align the test stimulus and response prior to analysis to assure accurate measurements.

If you’d like to verify if your device can be used with SoundCheck,  please give us a shout and we’ll check it out!

 

Measuring Digital MEMS Microphones: Frequency, Sensitivity and Power Supply Rejection (PSR) Performance

seq_dig_mic_final_display_substitution_methodThis test suite contains 3 sequences to enable comprehensive testing of digital MEMS microphones.

The first measures the frequency and sensitivity and displays two graphs: absolute level in dBFS, and the same response curve but normalized to 0 dB at 1 kHz.

The second sequence uses the substitution method to test a digital MEMS microphone frequency response with a source speaker that is not or cannot be equalized. The MEMS microphone is simultaneously measuring with a reference microphone , and by subtracting the response of the reference microphone from the DUT microphone the response and sensitivity of the device under test is revealed.

Measuring Digital Microphone PSR (Power Supply Rejection)
The third sequence demonstrates a method for measuring a digital MEMS microphone’s power supply rejection performance (PSR). This sequence measures PSR at 217 Hz (the 217 Hz GSM TDM pulse often of concern) but is easy to modify to test at any frequency. A DC supply with a calibrated AC signal, simulating electrical interference is applied to the MEMS microphone. SoundCheck then records the audio from the DUT, analyzes it with a spectrum analyzer and extracts the RMS energy at the specific frequency of the simulated electrical interference and returns the PSR value. The setting of frequency, waveform type and amplitude of the simulated electrical interference is controlled entirely from within SoundCheck.

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