The Importance of Cleanliness in Direct Field Acoustic Testing (DFAT®)

In the realm of (mechanical) testing in the space industry, especially for sensitive equipment like spacecraft and satellites, cleanliness is not just a preference—it's a necessity. And of course, acoustic testing is included. At MSI DFAT, we understand that the integrity of a testing environment directly influences the accuracy and reliability of our customers’ test results and the operation of their hardware. This article delves into our meticulous approach to maintaining clean rooms and equipment for direct field acoustic testing, ensuring optimal environmental conditions for each project.

Cleanroom Classes for Spacecraft Testing

For spacecraft testing, cleanrooms are classified based on the maximum allowable number of particles per cubic meter. The most common classifications are Class 100, Class 1,000, Class 10,000, and Class 100,000, with Class 10,000 being one of the strictest environments for spacecraft with optics. Many components are assembled in cleaner environments.

Class 10,000 (ISO 7) Cleanrooms: These facilities allow a maximum of 10,000 particles (0.1um or larger) per cubic meter of air. This level of cleanliness is essential for assembly, integration and testing of spacecraft with optical components that require high degree of protection from contamination. For these spacecrafts there is an allowable exposure time to be in less strict environments, but programs do not like to push these limits. Companies operating Class 10K cleanrooms employ advanced filtration systems, strict gowning procedures, and highly controlled access to maintain the integrity of the environment. When the area the spacecraft needs to go is not Class 10K, the whole spacecraft is “bagged” and a nitrogen purge is applied for a slight positive pressure inside.

Class 100,000 (ISO 8) Cleanrooms: These environments allow a maximum of 100,000 particles per cubic meter. While still providing a high level of cleanliness, Class 100,000 environments are the most commonly used facilities for assembly, integration and testing (AI&T). Many components are assembled in cleaner environments. All commercial communication satellites are assembled and tested in 100K facilities even with small optical instruments. These smaller components and optical systems are individually protected with covers or bags. These covers are removed during TVAC and dynamic testing. MSI DFAT routinely tests various spacecraft and satellites in Class 100,000 cleanroom environments, even those with 10K requirements.

These specialized facilities are essential for testing components of spacecraft, including propulsion systems, electronics, mirrors and delicate sensors. The goal is to ensure that no contaminants interfere with the spacecraft's performance, especially during critical phases of development and testing.

Cleanliness Measurement: Parts Per Million (PPM)

Class	>0.1 um	>0.2 um	>0.3 um	>0.5 um	>1 um	>5 um	FED STD 209E equivalent
ISO 1	10	2
ISO 2	100	24	10	4
ISO 3	1,000	237	102	35	8		Class 1
ISO 4	10,000	2,370	1,020	352	83		Class 10
ISO 5	100,000	23,700	10,200	3,520	832	29	Class 100
ISO 6	1,000,000	237,000	102,000	35,200	8,320	293	Class 1,000
ISO 7				352,000	83,200	2,930	Class 10,000
ISO 8				3,520,000	832,000	29,300	Class 100,000
ISO 9				35,200,000	8,320,000	293,000	Room Air

To quantify cleanliness in these environments, many companies use Parts Per Million (PPM) as a measurement method. PPM refers to the number of contaminants found in a million parts of air or material. In cleanrooms, achieving low PPM levels is crucial, as even minor amounts of contamination can significantly impact the functionality of sensitive equipment.

Controlled Separation of Equipment

One of our key strategies at MSI DFAT is the deliberate separation of our acoustic testing equipment from our off-the-shelf concert speakers. Our custom-designed and purpose-built MP series of loudspeakers for DFAT® are stored in a completely separate facility from the commercial-off-the-shelf (COTS) loudspeakers used for concerts and live sound events.

These two types of loudspeakers are managed and stored independently, minimizing the risk of contamination and allowing us to maintain stringent cleanliness standards. Our dedicated acoustic testing speakers and equipment are handled in specialized storage rooms designed to prevent exposure to dust, debris, and other potential contaminants.

Controlled In-House Logistics

To further enhance our cleanliness protocols, we employ dedicated trucks for transporting direct field acoustic testing equipment. Each truck is equipped to minimize contamination during transit, ensuring that our speakers, amplifiers, and cables arrive at the testing site in pristine condition. Our team follows strict procedures to clean and sanitize all equipment before and after each acoustic testing event, including wiping down surfaces and using appropriate cleaning agents. This process is a routine step in our preparation efforts for each acoustic test event.

Specialized Test Article Protection

To protect particularly sensitive components, such as satellites and other delicate instruments, some customers utilize specialized protective bags and containment systems. This additional layer of protection ensures that particles, particulates, dust, and foreign object debris (FOD) are kept away from critical equipment during testing, while minimizing mass-loading effects on the Unit Under Test (UUT). In some cases, the whole satellite is wrapped on Mylar sheets, other facilities have dropped a tent of the top of the satellite, including the locations for the microphones controlling the test. This requires MSI personnel entering the tent to place and calibrate the microphones to wear extensive cleanroom suits. All equipment is wiped down before entering the tent.

Example of a bagged and protected satellite.

Adherence to Cleanliness Protocols

We recognize that our customers often have their own environmental cleanliness protocols and standards, and cleanliness requirements widely vary according to the individual needs of any spacecraft program. At MSI DFAT, we fully adhere to these requirements, collaborating closely with our clients and their environmental cleanliness teams.

This partnership ensures that our testing processes align with their expectations, fostering a mutual understanding of the importance of cleanliness in achieving reliable results. Any company employing the direct field acoustic testing approach should adopt similar methods and practices to maintain cleanroom environments. We invite anyone to examine our loudspeakers and related equipment for dust using a white glove at any time.

Our Team in Action

To further illustrate our commitment to cleanliness, take a look at these photo examples of our test technicians, engineers, and operators dressed in cleanroom gowns and hairnets for 100K facilities, When testing in 10K environment, the garb includes hood, booties and gloves taped to the gown to prevent any particles from escaping. Their dedication to maintaining a clean and safe testing environment is evident in every aspect of our operations. 

The MSI DFAT team in fully gowned for an acoustic test.

Invitation to Customers

We invite our customers to tour our facilities and witness firsthand our effective methods of maintaining cleanliness. Seeing our practices in action will provide you with confidence in our commitment to quality and reliability.

Cleanliness is a cornerstone of our approach to direct field acoustic testing at MSI DFAT. Through the separation of equipment, dedicated logistics, cleanroom environments, specialized protection measures, and strict adherence to protocols, we ensure that our testing conditions meet the highest standards. This commitment not only enhances the accuracy of our tests but also builds trust with our clients, reinforcing our reputation as a leader in the field of acoustic testing for sensitive equipment. By prioritizing cleanliness, we are better equipped to deliver precise, reliable results that our customers can depend on.

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Applying Aerospace Quality Standards to DFAT

In Direct Field Acoustic Testing (DFAT), it’s crucial to recognize the depth and breadth of experience that shapes best practices in our industry. While some may claim that DFAN testing has its roots solely in concert audio, this is a grossly overgeneralized and subjective viewpoint that inherently diminishes the credibility of DFAT as an empirical testing method. Rather, cross-pollination of diverse acoustical expertise can only further enhance the art and science of DFAN testing. A well-rounded yet focused approach combines decades of both aerospace and acoustic expertise. We at MSI DFAT know because we blew up millions of dollars of concert speakers while inventing DFAT back in the 90’s. Since then, we innovated by improving on the technology to the current purpose-built DFAT speakers available on the market today (see https://www.msidfat.com/patents for a few examples of our IP).

It is a false dichotomy to differentiate between being an "aerospace company with audio expertise" versus a "concert company with aerospace experience". This oversimplifies the complexities of either industry and incorrectly assumes that a company cannot successfully integrate or apply valuable know-how across both domains. Rather, at MSI DFAT, we have more specialized experience in both live concerts and aerospace environmental testing than any other company on the planet. We’ve played on both sides of the Dark Side of the Moon – from Pink Floyd to Artemis. With over 230 DFATs successfully completed—and counting—our experience is quantitatively unmatched.

Consider the parallels between concert events and the aerospace industry. High-stakes live audio events, such as presidential inaugurations or the ball-drop in Times Square, demand flawless performance and execution. Imagine the disruption and embarrassment if an audio signal were to drop during a speech by the President of the United States or if the audio cut out at the critical moment of the ball-drop countdown on live TV. Fortunately, our reputation is validated by our valued customers who entrust us with such important projects.

As a space program manager tasked with finding a partner for DFAT, you face a critical decision: should you take a chance on a new, uncertain startup for a mission-critical acoustic test? What if they run out of money before they can show up onsite for the test?

Another simple risk that is often overlooked is that large-scale tests (requiring more inventory of loudspeakers) could lead to significant delays due to manufacturing lead times. With the previous years of shipping issues and port congestion, and recent weeks of even more port strikes, this is not a gamble that any aerospace supply chain team or spacecraft program manager should be willing to take. In contrast, MSI DFAT boasts a ready-to-go immediate inventory of over 700 (and counting) purpose-built DFAT speakers immediately available, allowing us to support large-scale acoustic tests, right away. We could even support two simultaneous acoustic test events over 60 feet tall—concurrently. This capability is unmatched and is not something you would want to gamble on with an unproven, risky startup company.

We prioritize immediate test support, significantly enhancing testing efficiency for our customers. Our extensive ready-to-go inventory means large-scale tests can proceed without the delays often associated with manufacturing, which is crucial in today’s high-stakes environments of launching on-time and under-budget. And, rather than manufacturing our loudspeakers overseas with cheap labor and poor quality controls, we manufacture our state-of-the-art loudspeakers right here in the United States in Baltimore, Maryland at our own facility.

Additionally, our commitment to rigorous Quality Management Systems and continuous improvement principles—such as ISO 9001 and AS 9100 certifications—underscores our dedication to excellence. Our focus is not on flashy marketing but on delivering real results grounded in scientific methodology and proven engineering practices. Instead of investing in a sleek website design or hyper-polished gimmicky PowerPoint sales presentations, we allocate our resources to hiring and retaining top industry talent and advancing R&D for DFAT technology. Since our inception, we have integrated Kaizen principles of continuous improvement into our technology, people, and processes, constantly refining our approach.

The logistical complexities of testing—similar to those faced in high-profile live concert events like the presidential inaugurations—require not only technical expertise but also operational insight gained from years of experience in both aerospace and live event management. This unique combination fosters an unparalleled level of preparedness.

We are not merely a concert speaker company. We are not merely an aerospace testing company. We are both! Our background in the concert industry gives us irreplaceable knowledge in managing complex logistics and live testing events with the precision of an F1 mechanics team. Our ongoing R&D initiatives in DFAT for specialized and custom speaker models reflect our forward-thinking approach, ensuring that our products are tailored specifically for the demands of DFAN testing.

Ultimately, our goal is to enhance the safety of personnel and flight hardware. Everyone at MSI DFAT is committed to delivering a quality product and service. Every decision we make is grounded in expertise and quality, prioritizing safety and reliability above all.

Launching things into space?

👉 info@msidfat.com

One Size Does Not Fit All

One size loudspeaker model does not fit all acoustic test requirements!

Tailored, Scalable DFAT Systems

While we own our own in-house manufacturing and production processes - and therefore we could easily choose to design and manufacture a single loudspeaker for DFAT - our Matthew Polk ("MP") lineup of speakers are instead purposefully designed to be separated out by frequency ranges. This results in tailored, scalable, and modular test setups that can precisely meet a target test spectrum.

Wait... Why Separate Transducers by Frequency Ranges? 🤔

A single cabinet design attempting to cover the full acoustic test spectrum can lead to inefficiencies and sub-optimal performance. Simply adding identical speaker cabinets into a bigger stack assumes consistent, uniform test conditions. However, this overlooks the varying frequency responses of different components, which may need specialized frequency emphasis.

MSI DFAT provides frequency-specific, scalable loudspeakers for DFAT.

Optimized Performance: Our cabinets are optimized for low, mid, high, and ultra-high frequencies, enhancing acoustic performance and test accuracy.

Proven Results: Specialized configurations with frequency-specific loudspeaker cabinets can result in better test outcomes, particularly in high-precision tests involving complex satellite systems and large-scale tests.

Efficient Inventory Management: Maintaining separated speaker design models is simple and straightforward.

Cost-Effectiveness: Specialized configurations can reduce costs by optimizing power usage and minimizing over-provisioning, avoiding unnecessary expenses for unneeded frequency ranges.

Space-Savings: A large, clunky single-cabinet design requires more space and is harder to maneuver, setup, and fit inside a room.

Acoustic experts understand the importance of separating out transducers according to their frequency ranges.

That's all for now folks!

Launching things into space?

👉 info@msidfat.com