Free shipping in the U.S. — Click here for details .
Sign in Join now
Lightspeed AviationLightspeed AviationLightspeed AviationLightspeed Aviation
    0
  •   was successfully added to your cart.
  • Shop
    • All Products
    • Headsets
    • ANR for Helmets
    • Flight Bags
    • Accessories
    • Survival
    • Lightspeed App
    • FlightLink App
    • Authorized Dealers
    • Trade Up Program
  • About
    • About Lightspeed
    • Programs
    • Delta Zulu Saves Lives
    • Awards and Accolades
    • Patents
    • Lightspeed Foundation
    • Careers
    • Associations
  • Community
    • All Posts
    • Blog Posts
    • Events
    • News
    • Sponsorships
  • Support
    • Customer Support
    • Repair Request
    • Frequently Asked Questions
    • Shipping and Return Policies
    • PFX Firmware Update – PC
    • PFX Firmware Update – Mac
  • Contact
    • Contact Lightspeed
    • Authorized Dealers
    • Donation Requests
    • Media Kit
Sign in / Create Account

ANR 101: Section 2 – Acoustic Issues 

    Home ANR ANR 101: Section 2 – Acoustic Issues 
    NextPrevious

    ANR 101: Section 2 – Acoustic Issues 

    By Lightspeed Aviation | ANR, ANR 101, Blog Posts | 0 comment | 11 August, 1999 | 0

    Section 2: Acoustic Issues 

    Understanding and comparing cancellation specifications 

    Section 1 of this series dealt with the variables and complexity involved in canceling the repetitive and random aspects of airplane noise. It explained that although the basic elements of all active noise reduction systems are pretty much the same, the details of how they are designed and implemented has everything to do with the results you’ll experience. 

    The focus of this session is on the ways of measuring noise cancellation and determining comparative performance. Many claims are made about the amount of cancellation a given headset will provide. As we’ve said all along, the very best way to choose an ANR headset is to actually try out various headset models in the aircraft you usually fly. No chart, graph, or product review is as effective in determining your best choice of headsets as actually flying with them. Unfortunately, that is often not feasible, so you’re left to make a purchase decision based on the information you get from the manufacturers, the product reviews you read in the aviation press, and word-of-mouth recommendations from other pilots. 

    Our goal in this section, then, is to give you the knowledge you need to ask better questions and make a more critical analysis of the active and passive cancellation you can expect from a particular ANR headset model. 

    The cancellation profile 

    All active headsets have a profile of sound they are able to cancel. The profile can be graphed to chart the amount of cancellation and where in the noise frequency spectrum that cancellation occurs. The measurement process is relatively simple but requires fairly sophisticated laboratory equipment and techniques. The testing is done inside a closed, controlled acoustic chamber. The headset is mounted on a fixture that has a microphone located inside an artificial “ear” whose purpose is to sense or “hear” what you would hear. The headset is then swept with a tone from 10 hz to 10,000 hz…with the “ear” recording what was heard. The sweep is done twice, once with the ANR circuitry turned off and another with it turned on. The difference between the first and second sweeps indicates what was incrementally cancelled when the active system was engaged. The results are then usually plotted in the form of a graph, with frequency in Hertz (Hz) on the horizontal axis and cancellation in negative deciBels (dB) on the vertical axis: 

     

    Of course, different headsets provide different results based on how well they have managed the variables we learned about in Section 1 of this series. Before we begin to do any comparisons, let’s first talk about the attributes of this cancellation curve that will be present in every active headset. They include: 

    • Depth: how deep is the cancellation at its deepest point?  
    • Breadth: how wide is the cancellation frequency spectrum?  
    • Position: at what frequency the cancellation profile is centered?  
    • Boosting: places in the cancellation spectrum where ANR actually does more harm than good (i.e., noise is amplified rather than cancelled).  

    Each attribute tells us something about the effectiveness you can expect to hear from the cancellation. 

    Depth 

    The depth of the curve tells us the maximum amount of cancellation you would generally expect. Normally this is the active cancellation number that a manufacturer will advertise. Typically a range of 2-4 dB is given since variations in mic sensitivity, calibration, and even specific ergonomics of the pilot will have some modest effect on the final cancellation. It’s important to make sure you know how the cancellation measurements were made. Some manufacturers publish noise reduction figures that were not measured at the “ear” but at the headset’s ANR sensing mic instead. Recall from Section 1 of this series that the best ANR systems position the sensing mic to provide optimal correlation to the ear canal position, but correlation is never perfect. For example, headset “T” in the above graph claims 14-16 dB of cancellation but only measured about 11dB at the ear. Since every 3 dB represents roughly a doubling of sound pressure, that discrepancy is quite large and is probably explained by that different measurement technique. 

    Breadth 

    Here we’re looking at the overall frequency band that is cancelled by the electronics. Given the measurement deviation and sensitivity of our ears to small changes in dB, cancellation greater than 5 dB would begin to be of value in comparisons. When combined with “depth,” these two measurements constitute the “total” cancellation the electronics can deliver. 

     

    Position 

    You’ll notice in the graph that one headset cancels more low frequency than the other. While every plane has its own unique noise signature, it turns out there are some common things we can say about most single-engine piston planes:  

    1. The loudest part of the noise spectrum is generated by the resonant frequency of the propeller. For direct-drive engines red-lined at 2400-2700 RPM, that will occur at 80-90 Hz for two-bladed props and 120-130 Hz for three-bladed ones. That is the specific point in the spectrum where the noise is loudest. 
    2. The overall noise envelope in the cabin of these airplanes is loudest from about 40 Hz to 250 Hz, so this is the range where cancellation is most important. Noise levels at even 500 Hz are typically down at least 10dB from those at 100 Hz.  

    Section 3 of this series deals in depth with airplane noise spectrums and how they “overlay” with active and passive performance. For now, it’s sufficient to understand simply that the loudest noises are at the lower frequencies. So a cancellation profile “position” that is centered between 85 and 130 Hz will probably be the most effective in the typical piston-powered airplane. 

     

    Boosting 

    This is the last characteristic evident in all ANR cancellation profiles, and perhaps the least understood by most prospective purchasers of ANR headsets. Boosting is actually amplified, out-of-phase noise created by the ANR electronics that is not cancelled by existing ambient noise. Simply put, it represents the “overshoot” of the electronic “anti-noise” signal introduced into the acoustic chamber. It is present to some extent in virtually all active headsets, and here’s why. (Refer to the cancellation profile graph above to follow this). 

    The physics of sound waves and the acoustic cavity makes significant cancellation much more difficult as frequencies increase. This is due to the shorter wavelengths of sound at higher frequencies, in relation to the physical distance between the sensing microphone and the anti-noise speaker. The graph above shows this phenomenon on various headsets, all of which have declining cancellation at frequencies above 300 Hz. The deeper the 100 Hz cancellation, typically the steeper the profile drops off between 300 and 600 Hz. The steeper the drop-off, the harder it is to avoid some “overshoot” of uncancelled noise. 

    Is boosting a bad thing? 

    While not disastrous, we’d always like to have less. Like so many things, tradeoffs have to be made between the amount of boosting and the overall system cancellation. Unfortunately, greater overall cancellation generally means higher levels of boosting. This explains why the best canceling headsets often have the largest boosting effects. All things considered, the additional cancellation is generally worth it for at least two reasons: 

    1. Typically the boosted dB levels are relatively low (3-6 dB) while the additional cancellation at low frequencies are much larger. The actual amount of boosted noise (shaded area under the curve) is quite small compared to the total noise cancelled.  
    2. The boosting generally occurs at higher frequencies around 1 kHz where headsets typically have significant passive attenuation, and where most airplanes have relatively low noise to begin with. The net effect is still significant noise reduction at those higher frequencies…just a little less!  

    The one exception is low-frequency boosting like that shown for Headset “C” in the graph. While only 3-5 dB, the headset might provide less than 5 dB of protection passive at 40 Hz, so the additional noise introduced by the ANR circuitry could be more noticeable at those frequencies. 

    Congratulations! You now know more about interpreting cancellation profiles of ANR headsets than 99% of the pilot population (not to mention most so-called avionics experts). Of course, you can only use this data to compare the performance of different ANR headsets accurately if the data for the various headsets was derived using similar testing methods. Testing variables such as mic placement, sensitivity, and fixture design will substantially change the measured results. Again, the absolute best test data comes from your own ears…comparing different headsets in different planes and with different people! 

    “Total” Cancellation: an “apples and oranges” comparison 

    We can’t leave the subject of cancellation measurement and comparison without dealing with a very misleading notion: “Total” cancellation. What we’re talking about here is the practice of adding some measurements or claims of passive cancellation to the ANR cancellation profiles we discussed above. While often done in advertisements, this practice is inaccurate and quite misleading for several reasons. To understand why, you must first understand the “NRR” measurements that are normally used to quantify passive hearing protection systems, and how this relates to aircraft noise. 

    Passive attenuation (NRR) measurements 

    There is still considerable debate about how well this “standard” fits the aircraft environment. The NRR measurements were developed for industrial safety hearing applications where the noise spectrum is higher in frequency, and intermittent or impact based (e.g., the noise in a machine shop). The way the noise was measured affects the relative importance of the frequencies in the weighting of the noise effect on your hearing. The graph below shows the “equivalent effect” curves for different scales of noise. 

     

    Hearing protectors (including headsets) were measured and rated based on “A” weighted noise curve. As you can see, the ratings are heavily weighted to the 1 to 4 kHz noise spectrum for protection based on hearing protection needs of our ears. Because of the way God designed our ears, we can tolerate about 20 dB more 100 Hz noise without hearing damage than we can 1,000 Hz noise. (That’s why the “A” scale curve crosses the 100 Hz line at about -20 dB.) “A” weighted NRR measurements “discount” the 100 Hz noise by 20 dB in the calculations of hearing protection. 

    The problem for pilots is that we don’t fly machine shops, and our cockpits have lots of 100 Hz noise…often 25-30 dB more there than at 1,000 Hz!! While it’s true that we are more susceptible to hearing damage from higher frequencies, the dB levels we’re exposed to at low frequencies often contribute significantly to the hearing loss that pilots who fly without hearing protection often suffer. Those excessive levels of low-frequency noise also have a noticeable effect on speech intelligibility and human physiology…which we’ll cover more in Section 3 and Section 4 of this series. Consequently, “A” weighted NRR measurements are really not the best standard for judging the protection your headset will provide in your single engine airplane 

    Real NRR data for active headsets 

    Even if NRR could be used as a reference (by using a weighting more appropriate to the cockpit noise spectrum), there is a problem with using such figures for active headsets. We’re not aware of a single manufacturer who publishes actual NRR measurements for their active headset models 

    When passive headsets are “converted” by adding active noise reduction circuitry, sales literature often “implies” that the active cancellation is in addition to the headset’s original passive NRR. However, the fundamental laws of acoustics dictate that passive attenuation will go down when active circuitry is inserted and cavity space is consumed in the active version. Recent product reviews of ANR insert kits make this point quite clear. 

    The NRR and active cancellation “numbers” don’t add up! 

    Passive attenuation NRR is an accumulated measure of cancellation taken at eight frequencies from 125 Hz to 8,000 Hz. Those numbers typically range from about -10 dB to well over -30 dB…a very wide range! The NRR (which is a single figure) is intended to provide a summary measure of cancellation over a very broad spectrum of noise (weighted for hearing protection as discussed above). By contrast, the active cancellation dB numbers that are normally quoted refer to “peak” attenuation at one frequency where active noise cancellation is at a maximum. When you add the broad spectrum-weighted NRR to the single-frequency active cancellation figure, you get nonsense! The figures simply cannot be added with any validity. 

    So how can you judge which ANR headset is most effective? 

    If you’ve read this far, you already know the answer. Compare the active cancellation profiles of headsets, provided they were derived using comparable measurement techniques. Look for the depth, breadth, and position of the ANR spectrum. Look also for areas where boosting occurs, particularly at the low-frequency end of the spectrum, where it’s likely to be noticeable. Then once you’ve developed your “short list” of headset candidates, try to actually fly with them so you can truly evaluate the performance, comfort and convenience features of each one. After all, the ultimate laboratory test fixture is your own head in the cockpit of your own airplane! 

    Go to Section 3 >> 

     

    active noise, ANR, ANR performance, attenuation, frequency, headset, noise cancellation, noise profile, NRR, passive, passive noise, spectrum

    Lightspeed Aviation

    Lightspeed Aviation is a leading manufacturer of premium aviation headsets and helmet products. Since the first product was introduced in 1996 at AirVenture in Oshkosh, WI., the company has established a reputation for leading innovation in the aviation headset marketplace with a number of “first to market” advances, technologies, and features. In 2022, the company launched a new category of aviation products called “Safety Wearables”. Layering life-saving technologies on top of their award-winning audio and ANR platform, Lightspeed ushered in a new era of aviation safety. With this, the company continues to live its mission of “creating products that protect and save lives”. Additionally, Lightspeed is a passionate supporter of initiatives to encourage the next generation of pilots through its support of programs like Young Eagles and Ray Scholars. The company is proud to have participated in helping countless young people experience everything from a discovery flight to getting a Pilot Certificate.

    More posts by Lightspeed Aviation

    Related Posts

    • ANR 101: Section 3 – Airplane Issues 

      By Lightspeed Aviation | 0 comment

      Section 3: Airplane Issues  Looking at actual cockpit noise profiles, and how well aviation headsets cope with it  In Section 2 of this series, you learned how engineers measure effectiveness of active noise canceling systemsRead more

    • ANR 101: Section 4 – Ergonomic and Interface Issues 

      By Lightspeed Aviation | 0 comment

      Section 4: Ergonomic and Interface Issues  In this section, we’ll be looking at the comfort and human-factors issues associated with ANR headsets. The ergonomics of the human head demand a wide range of adjustments toRead more

    • ANR 101: Section 1 – The Basics of ANR 

      By Lightspeed Aviation | 0 comment

      Section 1: The Basics of ANR  A good place to start is with one of the most-asked questions that we receive from pilots:  Don’t all active Pilot Headsets work the same way… or do theRead more

    • ANR 101: A Tutorial on Active Noise Reduction 

      By Lightspeed Aviation | 0 comment

      A Tutorial on Active Noise Reduction  by the technical staff of Lightspeed Aviation  This is a five-part series on Active Noise Reduction in General Aviation. It came about because hundreds and hundreds of you haveRead more

    • ANR for Helmets by SocialFlight’s T-51 Mustang Aircraft Build

      By Lightspeed Aviation | 0 comment

      Our friends over at SocialFlight have been hard at work with their T-51 Mustang Aircraft Build. So when they took a minute to discuss their helmets from FlightHelmet.com with the Zulu H-Mod installed, we took notice.Read more

    NextPrevious

    Recent Posts

    • Pilots N Paws Volunteer Takes Animal Rescue to New Heights
    • Angel Flight West Pilot Treasures the Human Connection
    • Delta Zulu gets a Warm Reception this Winter in Europe
    • CO and Aviation: A Deadly Mix
    • Flying with Hearing Aids – a Game Changer

    Join Our Newsletter




      Top Rated Products

      • Zulu 3 - Pilot Headset - LightspeedAviation.com Zulu 3 ANR Headset
        Rated 5.00 out of 5
        $899.00
      • Markham Flight Bag - LightspeedAviation.com Markham Flight Bag
        Rated 5.00 out of 5
        $249.00
      • Sierra® ANR Headset - Pilot Headsets - LightspeedAviation.com Sierra® ANR Headset
        Rated 4.75 out of 5
        $699.00

      Lightspeed Aviation, the leader in wearable ANR technology for pilots, operates with a simple strategy: know your customer well and remain committed to relentless product evolution. At Lightspeed, everything we do is in service to our customer and our products push performance to the edge of technological possibilities.

      Stay Updated – Sign Up Here




        Information

        • Contact
        • Support
        • Frequently Asked Questions
        • Privacy Policy
        • Home
        • Shop
        • About
        • Community
        • Support
        • Contact
        © Copyright 2022 | All Rights Reserved
        • Shop
          • All Products
          • Headsets
          • ANR for Helmets
          • Flight Bags
          • Accessories
          • Survival
          • Lightspeed App
          • FlightLink App
          • Authorized Dealers
          • Trade Up Program
        • About
          • About Lightspeed
          • Programs
          • Delta Zulu Saves Lives
          • Awards and Accolades
          • Patents
          • Lightspeed Foundation
          • Careers
          • Associations
        • Community
          • All Posts
          • Blog Posts
          • Events
          • News
          • Sponsorships
        • Support
          • Customer Support
          • Repair Request
          • Frequently Asked Questions
          • Shipping and Return Policies
          • PFX Firmware Update – PC
          • PFX Firmware Update – Mac
        • Contact
          • Contact Lightspeed
          • Authorized Dealers
          • Donation Requests
          • Media Kit
        Lightspeed Aviation
          0 items
        We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies.
        Do not sell my personal information.
        Cookie SettingsAccept
        Manage consent

        Privacy Overview

        This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
        Necessary
        Always Enabled
        Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
        CookieDurationDescription
        __cfruidsessionCloudflare sets this cookie to identify trusted web traffic.
        __hssrcsessionThis cookie is set by Hubspot whenever it changes the session cookie. The __hssrc cookie set to 1 indicates that the user has restarted the browser, and if the cookie does not exist, it is assumed to be a new session.
        _GRECAPTCHA5 months 27 daysThis cookie is set by the Google recaptcha service to identify bots to protect the website against malicious spam attacks.
        ci_session2 hoursThis cookie is set as default session Cookie name in config.php in config folder in CodeIgniter.
        cookielawinfo-checkbox-advertisement1 yearSet by the GDPR Cookie Consent plugin, this cookie is used to record the user consent for the cookies in the "Advertisement" category .
        cookielawinfo-checkbox-analytics11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
        cookielawinfo-checkbox-functional11 monthsThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
        cookielawinfo-checkbox-necessary11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
        cookielawinfo-checkbox-others11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
        cookielawinfo-checkbox-performance11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
        JSESSIONIDsessionThe JSESSIONID cookie is used by New Relic to store a session identifier so that New Relic can monitor session counts for an application.
        PHPSESSIDsessionThis cookie is native to PHP applications. The cookie is used to store and identify a users' unique session ID for the purpose of managing user session on the website. The cookie is a session cookies and is deleted when all the browser windows are closed.
        viewed_cookie_policy11 monthsThe cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
        Functional
        Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
        CookieDurationDescription
        __cf_bm30 minutesThis cookie, set by Cloudflare, is used to support Cloudflare Bot Management.
        __hssc30 minutesHubSpot sets this cookie to keep track of sessions and to determine if HubSpot should increment the session number and timestamps in the __hstc cookie.
        Performance
        Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
        Analytics
        Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
        CookieDurationDescription
        __hstc1 year 24 daysThis is the main cookie set by Hubspot, for tracking visitors. It contains the domain, initial timestamp (first visit), last timestamp (last visit), current timestamp (this visit), and session number (increments for each subsequent session).
        _ga2 yearsThe _ga cookie, installed by Google Analytics, calculates visitor, session and campaign data and also keeps track of site usage for the site's analytics report. The cookie stores information anonymously and assigns a randomly generated number to recognize unique visitors.
        _gat_gtag_UA_28458117_11 minuteSet by Google to distinguish users.
        _gid1 dayInstalled by Google Analytics, _gid cookie stores information on how visitors use a website, while also creating an analytics report of the website's performance. Some of the data that are collected include the number of visitors, their source, and the pages they visit anonymously.
        CONSENT2 yearsYouTube sets this cookie via embedded youtube-videos and registers anonymous statistical data.
        hubspotutk1 year 24 daysHubSpot sets this cookie to keep track of the visitors to the website. This cookie is passed to HubSpot on form submission and used when deduplicating contacts.
        Advertisement
        Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
        CookieDurationDescription
        _fbp3 monthsThis cookie is set by Facebook to display advertisements when either on Facebook or on a digital platform powered by Facebook advertising, after visiting the website.
        fr3 monthsFacebook sets this cookie to show relevant advertisements to users by tracking user behaviour across the web, on sites that have Facebook pixel or Facebook social plugin.
        VISITOR_INFO1_LIVE5 months 27 daysA cookie set by YouTube to measure bandwidth that determines whether the user gets the new or old player interface.
        YSCsessionYSC cookie is set by Youtube and is used to track the views of embedded videos on Youtube pages.
        yt-remote-connected-devicesneverYouTube sets this cookie to store the video preferences of the user using embedded YouTube video.
        yt-remote-device-idneverYouTube sets this cookie to store the video preferences of the user using embedded YouTube video.
        yt.innertube::nextIdneverThis cookie, set by YouTube, registers a unique ID to store data on what videos from YouTube the user has seen.
        yt.innertube::requestsneverThis cookie, set by YouTube, registers a unique ID to store data on what videos from YouTube the user has seen.
        Others
        Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
        CookieDurationDescription
        ppwp_wp_session30 minutesNo description
        Save & Accept