Streaming audio over WiFi for House of Worship (HOW) assistive listening is the new thing for the hard of hearing, for overflow areas and for multilingual events. Here we’ll compare WiFi audio to loop, RF and IR systems. We examine Android and iOS devices as receivers, discuss interfacing WiFi audio systems with hearing aids and look at the advantages gained in areas such as social media.
For several decades, the assistive listening technology landscape has been dominated by three 20th century analog technologies: inductive loop, RF (usually FM), and infrared (IR).
Inductive loop works like an electrical transformer, where the primary loop is the loop around the venue and the secondary loop is the telecoil, or T-coil, in the hearing aid. Another important example of a primary loop is the telecoil in a telephone (that is where the “tele” comes from). All telephones have these.
A third example of a primary loop is a neck loop, which is just what its name implies. It is a loop hung around the user’s neck that captures the signal from an audio device such as a streamer or phone and, as with the others, couples to the T-coil in the hearing aid. Neck loops can be either amplified (e.g., the CLA7 from Clearsounds) or passive (Williams Sound and Listen Technologies both offer these).
Millions of telecoil-equipped hearing aids are already in use, which has to be considered when looking at new technologies. Indeed, roughly 80% of new hearing aids in the US have T-coils. The big advantage of loop systems is that the user does not require any other device in order to hear the programming. On the other hand, loop systems are expensive, often inconvenient to install (one might need to pull up the carpet, for instance), and can have leakage and crosstalk among neighboring systems.
Some of these issues are mitigated in more modern models, but they are still expensive and challenging to install. In many cases, one can either loop the main service or the alternative or breakout service, but not both, unless relatively expensive phased low-leakage loops are used. Also, many houses of worship have movable walls, which complicates the problem.
In other congregations, it is the overflow that is a problem. These people are not necessarily hard of hearing; they were just late. Some congregations have video streamed to the overflow room, but many of those who can’t or won’t squeeze into the sanctuary do not get the full benefit of the service. With audio over WiFi, they can hear anywhere in the building that the WiFi reaches (the kitchen or the cry room, for example), and thus everyone is able to follow the service. The other challenge with overflow areas is that they are usually cacophonous. Smartphones with ear buds give people a chance to hear the service over the din.
FM Radio Frequency (RF)
Next are radio frequency FM systems. Like the loop, these have good broadcast capabilities. The disadvantage is that the users need FM receivers, and hearing-challenged users have to connect from the receiver to their ear or hearing aid. There is a wide range of receiver prices, but a per-unit pricetag of around $100 is not uncommon. Interference and leakage are problems, but for locations where a loop cannot be installed easily, these systems have significant advantages.
FM systems are quite popular. FM has also been the system of choice, until now, for multilingual events because those participants generally do not have hearing aids. Often, however, multilingual congregations cannot afford enough receivers for all attendees. Also, receivers have a tendency to “walk off” in the pockets of preoccupied attendees.
The signals from IR transmitters and receivers can be generally kept from leaking out of venue, so they are the preferred method when privacy is critical. On the other hand, all the problems that light has with shadows and dead zones are present with IR systems too, because infrared is just invisible light. To combat this, most installations require multiple transmitters and, just like with FM, receivers have to be provided to users. These factors drive up costs.
WiFi Streaming Audio
Compelling mass-market numbers are driving the emergence of WiFi audio as the up-and-coming technology. Every year, 1.4 billion smartphones are sold; indeed, smartphones are more ubiquitous than flush toilets. Also, more than $15B worth of WiFi equipment is sold every year. These numbers completely dwarf the entire assistive listening system market and lead to unmatchable economies of scale.
These economies of scale have lead to the BYOD (bring your own device) trend. Those devices are mostly smartphones powered either by the Android or iOS operating systems. Figure 1 shows the percentage of people in the US who have smartphones, nearly 70% [Pew Research Center, Oct 2015].
Of course, this chart shows the percentages for all adults, not necessarily for those who need assistive listening devices, a challenge we will address later. Figure 2 shows the percentage of phones that support each operating system [Gartner, Feb 2016]. Because of their popularity, most WiFi assistive listening systems support both Android and iOS.
Streaming WiFi offers an alternative to the older technologies, and there are, of course, pros and cons. Streaming WiFi audio works by converting the audio source to a digital stream, compressing it and streaming the bits over a local area network (LAN) to a WiFi wireless access point (WAP or AP). From the access point, the encoded data is streamed wirelessly to personal devices such as smartphones or tablets. An app on the phone receives the signals and decodes them for the user.
Figure 3 is a block diagram of the system. The core of the system is the appliance that converts the (usually analog) inputs to data packets. Some systems integrate the WiFi, as well.
Table 1 compares digital WiFi audio with the incumbent technologies.
Installed total system cost has many variables depending on the venue. Both IR and FM technologies require special receivers, which adds to costs. Indeed, we have seen demand for hybrid systems where existing FM receivers are provided for the more technically challenged visitors, while the majority of the visitors use their own smartphone. This can yield huge cost savings when large crowds are involved.
For IR systems, a second challenge is that, just like one experiences with visible light, most venues have infrared shadows, so multiple transmitters are generally required in order to get good coverage with few dead spots. RF/FM and WiFi systems experience this issue to a much lesser degree.
On the other hand, there is a constant challenge to find clear frequencies with RF systems, and crosstalk can be an issue when multiple systems are used. Note that there are many other systems that might be sharing the radio band, such as wireless microphones or wireless telephones. That said, WiFi is itself a microwave radio-based system, albeit usually at a slightly higher frequency, so radio interference is also a challenge with WiFi. The advantage WiFi has is that billions of dollars of research have gone into algorithms and software to make it maximally robust and flexible.
The logistic requirements of providing receivers should not be underestimated. The receivers must be available. Working. Charged. And one must ensure that they are returned, e.g., by taking the user’s license or passport hostage.
In terms of receiver cost, inductive loop is the lowest for people who already have T-coils in their expensive hearing aids, and know how to use them. With that said, inductive loop systems can be quite expensive to install. Many systems are available at different price points, from simple loops to complex multiloop systems with phasing among the loops. If two loop systems are near each other, the user may hear both signals unless the phasing is excellent. For this reason, WiFi audio systems are often tasked to work in conjunction with installed loop systems because it is practical and cost-effective to add assistive listening to a room adjacent to an existing loop system.
In Table 1, we list WiFi audio as low cost under the assumption that the venue already has an existing WiFi infrastructure and most people bring their own smartphones. In terms of quality, WiFi can also have its challenges. For example, in every system, one will occasionally hear the hiccup from a lost data packet or two.
We also see a quality difference between 2.4GHz band systems and 5GHz band systems, with the newer 5GHz band generally being higher quality. The 2.4GHz band is crowded and it has interference from garage door openers, microwave ovens, wireless phones and so forth. Older smartphones, or very low-priced ones, may only work on the 2.4GHz band. Also, 2.4GHz generally penetrates walls better and can have better range. Flip phones, which many seniors still use, generally do not work with audio over WiFi.
WiFi is a general wireless networking technology already used for social connectivity. Thus, as much of this capability as one wants can be added to the assistive listening app on the phone, such as fundraising banners, weekly bulletins and other notifications.
Are there any negatives to WiFi audio? There are always tradeoffs. For WiFi audio, the first tradeoff is that WiFi audio has more audio delay than RF, IR or loop. In a test, hard-of-hearing people who lipread to augment their limited hearing experimented with one system. In tests with about a dozen people at a convention, what people found was that the tested system, which has between 45 and 55ms of end-to-end latency with an iPhone, was low enough latency that lipreading was effective. On the other hand, the Android phone we had, which had about 80ms of latency, was not as effective. Most of the delay was in the phone and, happily, that was improved over time.
The WiFi standard also has an idiosyncrasy that makes it difficult to broadcast the same audio to many people at once. The solution to this is to make every connection to each phone its own data stream, which creates challenges scaling to thousands of users at one time. The sweet spot for WiFi audio is fewer than 500 simultaneous listeners, although larger systems have been built.
Another challenge is that many seniors do not have smartphones, nor are they facile with them. Having some phones preset with the app and simple controls helps this situation. What we tell houses of worship is that they should take up a collection of older iPhones (generation 5 and above), from those congregants who always upgrade to the newest Apple offering, wipe their data and preset them for the seniors. Offering training in the use of these devices could even be a reason for teens and young adults to work with seniors.
Another alternative is to acquire devices specifically for this purpose, such as the iPod Touch. Any iPod Touch that has a Lightning connector is good enough for this purpose. Android phones can be procured more cheaply than Apple devices, but must be tested for efficacy. Some seniors have difficulty pressing the correct buttons and staying in the app. Apple has a “guided access mode” that can help solve this problem, and Android has something similar.
And there is the simple question of whether the house of worship wants to allow people to use their smartphones during services. It is possible to prevent them from using the WiFi to access the internet, but past that, the problem is not really “solvable.”
Multipath issues are important in cases where one is using electronic speakers in addition to a WiFi audio system. If the audio volumes of the systems are such that one hears both paths at about the same level, they need to be well synchronized; that is, within about 15 or 20ms, which is nearly impossible. To make this work, the WiFi listener would have to either crank up the phone volume to drown out the through-the-air path or wear headphones that block most of the through-the-air sound. Of course, if the person is 20 meters from the electronic speaker, the delays would about cancel out, but that is not the usual case.
How Do You Hear With It?
We have focused on getting from a primary audio source to someone’s smartphone, but what about from the phone to the ear? What we tell people is that, “However they listen to their smartphone today, that is how they should do it with WiFi streaming audio.” There is quite a large variation, including wires to in-ear buds, over-the-ear buds (appropriate for use with hearing aids) and headphones. Then there are T-coil-type systems that connect to a hearing aid or cochlear implant.
To connect to the T-coil, one can use the telecoil built into the smartphone or, more practically, a neck loop. (Our experience with trying to connect a T-coil to an iPhone 5 or 6 was not very successful.) There are low-power Bluetooth systems, again for hearing aids or cochlear implants, for instance, so-called “made for iPhone” hearing aids. It should be noted that Bluetooth itself has latency, which varies from manufacturer to manufacturer, that adds to any other latencies in the system.
And then there is the world of streamers, which are external devices that couple the phone to the hearing aid, often with a proprietary RF link. Figure 4 shows some examples. It can be very confusing, but the key is, however people make this connection today, that is what they should use with WiFi audio.
Streaming WiFi audio is excellent for multilingual applications where one or more simultaneous interpreters are speaking in alternate languages for specific populations. Many houses of worship in the US and around the world have events in two or more languages going on at the same time. Because of digital technology, the appropriate alphabet can be used on the smartphone to communicate with the listener, as shown in the Figure 4.
An increasing number of venues are using streaming WiFi audio for assistive listening applications, either as their only solution or in conjunction with other technologies. There are numerous advantages to these systems. For instance, hard-of-hearing people are understandably sensitive about what they put in their ears, especially ear buds of unknown providence, and using their own devices are thus appealing to them. Another subtle advantage is that when the loop goes down in a venue, only a few people care. When the WiFi goes down, everyone cares.
We are at the beginning of the WiFi audio age, and adoption growth rates are accelerating as people experience its benefits. Assistive listening, overflow listening and multilingual applications are now part of those benefits.