What are CROS and BiCROS Hearing Aids and Who Needs Them?

How CROS / BiCROS systems help people with asymmetrical or unilateral hearing losses and single-sided deafness, as well as a guide to the currently available CROS and BiCROS systems

CROS stands for Contralateral Routing of Signals. This hearing aid configuration is designed for people who are deaf* in only one ear. A CROS system typically consists of two hearing aids—one to pick up sound from the deaf ear and send it to the better ear (i.e., a transmitter), and one to play back the sound received from the deaf ear. If the better ear has hearing loss, sound from both ears amplified by the receiving hearing aid. When amplification is provided, we refer to this as a BiCROS system.

* A CROS is typically recommended when you are unable to understand speech presented to the poorer-hearing ear, only. This often occurs with asymmetric or single-sided hearing loss, also referred to as unilateral hearing loss.

Cros

A CROS hearing aid system consists of a transmitter on the poorer-hearing ear which transmits sound to a hearing aid on the other better-hearing ear. In this way, you gain hearing on both sides of the head, which is important for conversation and environmental awareness. When amplification is needed in the better ear, then the hearing aid also amplifies sound on that side, making it a BiCROS system. Illustration courtesy of Oticon.

Who needs a CROS or BiCROS hearing aid?

The vast majority of people who wear hearing aids have nearly identical hearing in both ears. This is described clinically as symmetric hearing loss.  About 9.5% of people with hearing loss have different hearing between the ears, or asymmetric hearing loss.1

When you have a hearing test, the provider will measure how loud the sounds need to be for you to hear them (threshold of audibility) and how accurately you understand them (word recognition). If your asymmetry is only in the domain of audibility, your provider will likely recommend two traditional hearing aids that are wirelessly connected into a “binaural” pair. If, however, there is a significant difference in how accurately you understand speech (called word recognition or speech discrimination) between ears, a CROS or BiCROS may be a better solution. Notice that the word “significant” above is bolded and italicized. Let’s talk a little about why that’s important.

Frequently Asked Questions

No. The main benefit of a CROS transmitter is to make sounds on the side of the poorer ear available. A good example is driving in the car. If your left ear is much poorer than your right, you will have a great deal of difficulty being a passenger in a car with the steering wheel on the left. A CROS transmitter would allow you to “ride shotgun” and still hear the driver. Other common settings where CROS transmitters help are at dinner tables or when playing cards.

Not directly. However, many users can hear a very subtle difference in sounds quality or timing between sounds from the CROS side and learn to approximate the direction of sounds.

No, you can use the receiver side as a stand-alone hearing aid; however, you will miss out on the ability to hear sounds on the poorer side.

How are CROS and BiCROS hearing aids selected and fitted?

Back when this author was in graduate school (late 1980s), the standard idea was that if the between-ears word recognition scores were different by 20% or more, then the poorer ear would interfere with the better ear, so directly amplifying that ear might not be beneficial. This was based largely on anecdotal and patient reporting that the hearing aid on the poorer ear “didn’t sound right.”

Hearing Test Sound Booth 1200x675

For asymmetric hearing losses, hearing tests may take slightly longer because, among other things, the hearing care provider needs to use multiple word lists (e.g., 50 words or more) to identify the optimal solution.

One of the most extensive and careful investigations behind this was done by the researchers Thornton & Raffin in 1978. They documented the amount of difference needed between ears to be statistically significant. The statistical term for being significantly different is one “Standard Deviation.”  The researchers created a table showing the range of a Standard Deviation for different scores of word recognition. Using this data, we can look at not only the patient’s preference, but also at how likely the difference is to make a measurably negative impact on hearing and understanding.

Why is this important? If there is usable hearing in both ears—even if it’s different—the brain can use that information to better understand the direction of sounds. This improves safety and also provides valuable cues to help the brain focus on speech and ignore noise. Another reason to carefully determine the amount of benefit left in the poorer ear is that if a future intervention (eg, a cochlear implant) is possible, then it will be important to maintain stimulation to that ear and auditory nerve, avoiding auditory deprivation (the gradual loss of auditory pathways to the brain).

In clinical practice, I evaluate word recognition in each ear separately (using recorded, 25-word lists) and make sure that I have attained the best possible score. This is called “PBMax.” In order to measure this, it’s often necessary to complete 2 or 3 lists of words.2

This is where Thornton & Raffin come into play. If the best score for an ear is outside the Standard Deviation of 100% (100-84), then I test at other intensity levels until I get the best score, or one inside that range. This is called a Performance-Intensity (PI) Function.

Regardless of the individual ear score, I also test both ears together (binaurally). If the addition of the poorer ear does not decrease the PBMax of the better ear by more than one Standard Deviation per Thornton & Raffin, I recommend two hearing aids. We repeat this testing with the hearing aids as part of the hearing aid selection, and again at the fitting, and once again 3 weeks afterward (ie, within the return-for-credit window of the hearing aid).

If the patient dislikes the sound quality AND the binaural score is MORE than one Standard Deviation worse than the better ear’s PBMax, I exchange the poorer ear’s hearing aid for a CROS transmitter. If, however, the binaural score remains within one standard deviation of the better ear, I continue to work with the client to adapt to the binaural hearing aids—emphasizing the benefit of maintaining neural stimulation in both ears for as long as possible.

Cros P Illustration

An example of a CROS hearing aid system is the Phonak CROS P, illustrated here. Courtesy of Phonak.

Considerations for CROS / BiCROS Hearing Aids

Let’s assume that all the above was done and you still have poor enough hearing in the worse ear that a BiCROS or CROS is needed. How do you pick the best one?

Fortunately, all the major hearing aid manufacturers offer at least a few CROS / BiCROS options, so you can select the hearing aid for your better ear that best matches your hearing and lifestyle needs, then just add the appropriate CROS transmitter. If your hearing loss has progressed over the years, check with your hearing care professional about how long he/she thinks a CROS transmitter might be compatible with future upgraded hearing aids. While this isn’t a deal breaker, since CROS transmitters are generally less expensive than the matched hearing aid, it’s a good idea to get the most current version that may be usable for future models as well.

Progress in CROS / BiCROS technology

The first CROS hearing aids were built into eyeglasses and later behind-the-ear (BTE) instruments with a wire connecting the two components. In the 1980s, Telex developed a line of CROS devices using low-powered AM radios that allowed for wireless CROS, BiCROS, and a flexible “Multi CROS” system. This was very helpful in cases of asymmetric hearing loss where feedback—the annoying whistling caused by the receiver re-amplifying sound from the microphone—was an issue. The MultiCROS would pick up sound on the right, and deliver it to the left, and vice versa. Since the amplified sound was on the opposite side of the head relative to the microphone, the head prevented most feedback.

Modern hearing aids have digital feedback controls to stop the devices from whistling, and most also have the added capabilities of wireless streaming of sound. For many hearing aid models, Bluetooth and wireless connectivity not only helps you on the phone, but also means CROS / BiCROS systems can be paired with a wide range of accessories, including remote microphones or TV listening systems.

What companies make CROS hearing aids?

Currently, CROS and BiCROS hearing aids are available in BTE, receiver-in-the-canal (RIC) and in-the-ear (ITE) hearing aid styles. There are even CROS transmitters available for some cochlear implant systems. The HearingTracker staff has assembled the following CROS / BiCROS hearing aid options from the major global hearing aid manufacturers:

Oticon CROS hearing aids

Oticon hearing aids include its CROS and CROS PX solutions and offer a choice of a rechargeable Oticon CROS PX miniRITE R or non-rechargeable Oticon CROS miniRITE T (telecoil) transmitter. They are compatible with Oticon Intent, Oticon Real, More, Opn S, Opn Play, Play PX, Xceed, Xceed Play, Zircon, and Ruby models (but not compatible in Opn S 3 and Opn Play 2 models).

However, note that even though the new Oticon Intent is compatible with the CROS system, there are notable differences in the two hearing aid's style, appearance, push-buttons—they'll require two different chargers. That's why some hearing care providers are currently recommending the use of previous-generation technologies for Oticon CROS systems.

Oticon CROS hearing aids feature TwinLink technology, making it possible to use audio devices that employ 2.4 GHz Bluetooth® Low Energy (LE), while simultaneously receiving sound transmission via Near‑Field Magnetic Induction (NFMI) from the transmitter. This enables you to watch television or listen to music while carrying on a conversation with someone positioned on their poorer-ear side.

CROS PX

CROS PX

The new Oticon CROS PX is rechargeable and offers TwinLink™ dual streaming technology, which provides access to more sounds in challenging listening environments and handles wireless streaming at the same time.

Phonak CROS hearing aids

The Phonak CROS portfolio offers both the Lumity CROS L-R and the Paradise CROS P.

The Lumity CROS L-R is a rechargeable Receiver-in-Canal (RIC) hearing aid that uses the Recharger Ease recharging case and provides all the advanced features found in the Lumity hearing aid family. Lumity CROS/BiCROS hearing aids can work with Audéo L-R, Audéo L-RT, Naida L-PR, and Sky L-PR hearing aids.

Lumity CROS L-R is compatible with the MyPhonak app and the myPhonak Junior app—the industry's only dedicated app for dual control by kids and their parents. In late-March 2023, Phonak also made CROS P compatible with the MyPhonak app, although some of the functions for the aids are not available for CROS aids (see Phonak website for details). Both CROS L and CROS P offer universal connectivity to smartphones, TV, Roger™ microphones, and more.

Phonak also provides some earlier CROS II models: CROS BTE, CROS H2O (water and dust resistant version), and the custom CROS 13 and 312 ITE models. These work with the DECT CP1 home phone, Roger Pen, and ComPilot & TVLink S accessories.

CROS Lumity

CROS Lumity

A CROS hearing aid is a system designed for individuals with unilateral hearing loss, where a microphone on the unaidable side transmits sound to a hearing aid on the better-hearing side.

Functions

  • CROS System
CROS P-R

CROS P-R

CROS P is fit with a Audéo Paradise to help people with unilateral hearing loss hear speech from their worse hearing side.

Functions

  • CROS System

Compatible Aids

Phonak's sister company, Advanced Bionics, also offers a CROS for their Naída Q implant sound processors called the NaídaLink CROS.

Starkey CROS hearing aids

Starkey provides CROS systems for both RIC rechargeable (R) and disposable-battery size 13 or 312 models, as well as a BTE 13 model.

The company offers CROS transmitters for their Genesis AI, Evolve AI and Livia AI hearing systems. Starkey Genesis AI CROS is compatible with the Genesis AI RIC RT rechargeable hearing aid.

Evolv AI provides CROS transmitters that work with Evolv AI RIC R, RIC 312, and the BTE 13 models. All come standard with a telecoil, feature both 2.4 GHz and NFMI streaming technology, and offer the company’s Full Acuity Immersion Directionality on the transmitter.

Starkey’s Livio line also provides CROS systems for Livio Edge AI, Livio AI, and Livio RIC R, RIC 312, and BTE 13 styles in all but the 1000 technology (basic) level. The devices are compatible with the company’s remote and mini-remote microphones, table microphone, and TV streamer.

CROS

CROS

CROS system for Starkey Genesis AI.

Functions

  • CROS System

Compatible Aids

Signia CROS hearing aids

Additionally, the newest Signia CROS IX (Integrated Xperience) models released in October 2023 include Pure Charge&Go IX and TIX CROS, and Silk Charge&Go IX CROS which are rechargeable Receiver-in-Canal (RIC) and Completely-in-Canal (CIC) hearing aids, respectively. The latter, Silk IX CROS, is the only instant-fit rechargeable CIC on the market—a unique and discreet hearing aid with a flexible ready-to-wear silicon click sleeve. However, to allow for their tiny size, these hearing aids sacrifice the advanced Bluetooth LE audio streaming found in the rest of the IX line. Pure TIX CROS differs from Pure IX CROS because it has a telecoil (T-coil) and longer battery life.

Signia also offers CROS AX and CROS Pure transmitters, with each having three corresponding hearing aids to choose from. In the CROS AX line, CROS Styletto AX is Signia’s rechargeable Slim-RIC, the CROS Pure Charge&GO T AX is Signia’s smallest rechargeable RIC, while the CROS Pure 312 AX RIC is powered by traditional size 312 batteries.

All CROS IX and CROS AX models include Bluetooth® connectivity for Android and iPhone. In the CROS Pure X product line, the CROS Pure Charge&Go X and CROS Pure 312 X RICs offer Bluetooth® connectivity and acoustic-motion sensor technology designed to adjust to your personal listening environment while you’re moving. Like the CROS IX, the CROS Silk X is a CIC-style system.

CROS Pure 312 AX

CROS Pure 312 AX

A non-rechargeable CROS solution for Signia's Augmented Xperience platform.

Functions

  • CROS System

Compatible Aids

ReSound CROS Hearing Aids

For several years, ReSound did not offer a CROS solution—perhaps the only real hole in this global hearing aid giant's product offerings. That all changed with the September 2023 launch of its new Nexia hearing aids and the Nexia Micro RIE CROS, which at this writing is the smallest available CROS system in a Receiver-in-Ear (RIE) form factor (i.e., same as RIC or RITE styles).

Nexia Micro RIE CROS offers improved hearing-in-noise and runs on the latest Bluetooth® LE audio streaming standard, allowing for reception of Auracast™ broadcast audio technology—a first for hearing aids—which give people new streaming and communication opportunities in public places such as theaters, airports, restaurants, and arenas (however, it does not currently offer a telecoil option).

Resound Nexia Micro Rie Size Comparison

ReSound Nexia Micro RIE CROS is 25% smaller than the company's standard RIE and is Bluetooth LE Auracast-ready.

Widex CROS hearing aids

Widex has an extensive complement of CROS systems for its Evoke, Beyond, Unique, and Dream product lines, but the company has no updated website for its MOMENT or MOMENT SHEER CROS options. Please consult with your hearing care provider for more information on these product lines.

References

  1. Suen JJ, Betz J, Reed NS, Deal JA, Lin FR, Goman AM. Prevalence of asymmetric hearing among adults in the United States. Otol Neurotol. 2021 Feb 1;42(2):e111-e113. Available at: https://pubmed.ncbi.nlm.nih.gov/33332857/
  2. Mueller HG, Hornsby BWY. 20Q: Word recognition testing - Let's just agree to do it right! February 17, 2020. Available at: https://www.audiologyonline.com/articles/20q-word-recognition-testing-let-26478