Our team is your team
The North Orbit team brings decades of experience and a real passion for the field of acoustics to every project. Our owners are also the primary techs performing the testing with rare thoroughness and attention to detail.
Take advantage of the in-depth consults and testing only an owner-operated acoustic lab can offer. Not only hard data on sound-based questions from seasoned experts but input on the tests and personal analysis of the results.
Associations and memberships
THE results are in
INVESTIGATIVE TESTING
NOAL offered up some free investigative acoustic testing last fall. Thank you to everyone who submitted suggestions. The selected test was an ASTM C423 absorption test series on corrugated cardboard. This test series included five different tests: flat cardboard, cardboard assembled into open boxes right side up, empty boxes placed upside down, open boxes filled with material, closed boxes filled with material.
Q&A WITH LAB MANAGER/OWNER DAVE BERG
Q: Can you recap the testing process?
DB: Sure! In order to test sound absorption according to ASTM C423, we need to measure the sound decay rates in the empty room and then measure the decay with the specimen in place. Currently, the ASTM C423 method requires using interrupted random noise – typically pink noise – as the source and measuring more than 50 decays to get a good average decay in each band. The sound is created from multiple incoherent sound sources, feeding sets of amplifiers and loudspeakers. Several types of results are available from the test. The most common results people may be familiar with are the single-number ratings of Noise Reduction Coefficient (NRC) and Sound Absorption Average (SAA). These ratings are derived from measurements in many frequency bands and boiled down to a one-number rating. For acousticians and people who are more familiar with the test, the detailed frequency data will be far more interesting.
Q: What were the results and how can people access them?
DB: People can see some of the results here or on our LinkedIN page. They can also email us at info@northorbit.com and we will send full results.
Q: Were any of the results surprising? What did the results reveal?
DB: Unsurprisingly, the flattened boxes had the least absorption, and the open boxes with partial fill had the most absorption. However, in between, we had some interesting results suggesting that the boxes worked as tuned absorbers, as there were peaks around 160 Hz – 200 Hz in the absorption spectrum on several tests. The flattened and partially filled specimen had flatter, less peaky absorption results. The tuned absorption is undoubtedly related to the chambered cavities created by the walls of the array of boxes. Due to the details of the method and the rooms used to measure, ASTM C423 isn’t particularly well suited to measuring things such as tuned absorbers. We’d love to be part of any research into new and improved methods of measuring sound absorption in the laboratory.
Q: Who might be interested in the results of this test?
DB: The results will likely be interesting to curious acousticians and some musicians or people working with sound propagation or recording, whether in the studio or in a more traditional architectural setting. For instance, the absorptive properties of the open boxes filled with shirts may be helpful to designers working with retail spaces.
NORTH ORBIT NEWS
North Orbit Acoustic Laboratories Achieves Brag-Worthy Flanking Limit
Inside a nondescript warehouse in the shadow of the Minnesota State Capitol, the team at North Orbit Acoustic Laboratories quietly made some very loud noise. When testing their new acoustic laboratory’s flanking limit, they discovered they had one of the highest on the continent.
A flanking limit is a lab’s capacity to measure sound. If you are a baker, for instance, and have a two-cup measure, you can measure a cup and a half or two cups of water, but you can’t measure more than that. With a bigger, four-cup measure you can measure two and a half cups and beyond, all the way to your cup limit. The same is true with sound. If your flanking limit is low, and your lab can only “hold” a small amount of sound, you are limited in what you can measure. But if your lab can handle high decibel levels, like North Orbit, you expand your ability to measure.
North Orbit uses a two-room reverberation chamber to test the change in sound levels as sound waves travel through different materials. This type of test, referred to as Sound Transmission Loss or STL, expresses in decibels the difference in sound levels for all of the frequencies recorded. A single-number STC rating (Sound Transmission Class) is dervied from the STL and is the most commonly used expression of sound isolation. A typical drywall and stud assembly might achieve a 45 STC, a more robust wall might earn a 62. For special situations, like theater walls or industrial isolation, a wall might need to achieve an 82 or above. North Orbit’s remarkable flanking limit of 89 allows them to measure them all.
In order to find their flanking limit, the team at North Orbit created over 120 decibels of sound in the chamber’s source room then measured the transmission loss through a test specimen into the receive room. At the point that sound escapes the chamber through a path that is not intended, you have found your flanking limit. The chamber construction performs so well that the limit they achieved is bounded more by their ability to make a sound loud enough (they are already at nearly jet-engine levels) than by what the chamber can hold.
This news will be of particular interest to manufacturers and engineers who use highly rated sound walls in their industrial or military settings. In mixed-use structures, architects or designers might need to specify high STC values where one tenant requires quiet and a neighboring tenant does not (imagine a workout facility next to a therapist). Highly rated walls are also used in high-performance theaters or where industrial sound isolation is required.
The design and construction of the reverberation chambers at North Orbit’s St. Paul location was an in-house accomplishment. Elliott Dick, North Orbit Acoustical Scientist, says, “I don’t feel like I can separate my role from the team because there was so much give-and-take in developing the chamber design and the specimen opening. It was all of us working together, trying to figure out what is buildable and what will achieve our needs.”.
“It’s an advantage to have so many highly skilled staff members on a project like this. We didn’t have to go outside for the expertise. Achieving this very high flanking limit, and actually, the construction of the whole lab, has been a passion project for our whole crew,” said North Orbit President Dave Berg. With this feather firmly in their cap, the crew at North Orbit will turn their capable attention to designing and building a hemi-anechoic chamber on site. North Orbit is an A2LA accredited acoustic laboratory with facilities in St. Paul, MN, and Dyersville, IA.
