What is Bluetooth

Bluetooth is a set of standard wireless radio  protocols, or instructions that can be used for exchanging information.  It is governed by a central body SIG (Special Interest Group).  They implement the technology standards.  This is an non-profit organisation that aims to improve compatibilities of Bluetooth across all business sectors. There are around 30,000 members of SIG, including hearing aid  manufactures that use Bluetooth.  The concept is that by using accepted standard protocols, it will enable different systems to communicate with each other and to securely exchange information. 

Bluetooth was first developed by The US Military as a short range secure communications tool in the 1980s. It began to be used commercially by phone manufactures in 2000.  Since then the number of applications has increased exponentially. It is estimated that by 2021, there will be 16 billion Bluetooth devices on the planet (Ref Bluetooth Sig 2020)

Bluetooth is modular.  There are many different versions and each has been designed for specific task.  This could be for answering a phone, commonly used in Hands Free car kits, or in audio used for listing to music from a phone.  Increasingly, Bluetooth protocols are also being utilised in hearing instruments as this allows standardised connectivity to other devices.  

There are legal limitations as to the parameters such as power that can be used so theses various protocols and they are optimised by manufactures, for the specific tasks they need to perform.  Within a protocol there are layers, called “stacks”.  One stack may transfer audio and another may automatically switch a phone from music to a phone call. 

There are currently around 40 different protocols and within these, there are multiple different stacks optimised in many different ways.  This is why sometimes incompatibilities can occur as there are so may possible variances. 


How does it work

Bluetooth is a radio signal.  It transmits in the 2.4GHz (ISM Band).  In fact it does not operate on one frequency, but multiple frequencies from 2.402GHz to 2.480GHz in 79 different channels (40 for BT LE).  Whereas FM(UHF) frequencies are in the range or 169MHz to MHz 176MHz, Bluetooth is a thousand times faster.  This may seem high, but there are currently technologies that use frequencies up to 300GHz, so the frequencies Bluetooth utilise, in themselves do not bare any relationship to the quality of the signal.  They are merely a method of getting information wirelessly from one place to another.  

The Bluetooth band of frequencies is one of the, termed as “Licence Exempt” so anyone is free to develop technologies in this band and can broadcast, without the need for a license.  Hence many technologies use this band.  Such as microwave ovens, car alarms or other radio technologies such as Roger.  As a result of the heavy usage of the 2.4GHz band interference can occur.  Bluetooth attempts to mitigate this by randomly changing which channel it is using in the hope of avoiding interferences, approximately 1600 times per second. This happens so quickly that it is generally not perceivable but as with any wireless system,   is still technically possible.  You just need lots of devices operating at the same time! 

When you connect two Bluetooth devices together they must be “paired”.  This process is exchanging a code or key that allows these two devices to communicate and recognise each other.  Hence this only has to be performed at the initial pairing.  Then they should recognise each other automatically.     This key also exchanges stack information that controls the interactions between the devices such as: power management, security or behaviour.

Due to the ever increasing number of devices inevitably conflicts may occur even though the protocols are standardised. This may be simply a phone not switching to a call from, music or it may not even work with a specific hands free car kit.  There are so many complex interactions you can never have 100% compatibility and also you may find products that are not manufactured appropriately to the recognised standards. This can also create problems as the potential multiple sources are impossible to control.  Hence it is recommend to use recognised manufactures equipment as they will be SIG compliant and more importantly a safe design. Ultimately most of this equipment will probably have to be connected to the mains at some stage to charge, so it’s certainly worth considering if their design is compliant with necessary safety legislation prior to any on line purchase. 



Latency is essentially the time it takes for an electronic signal to pass from the input to the output, of a device.  Any electronic product will have some form of latency, but this will not be constant for all situations.  Latency in itself is not an issue.  It depends on the usage of the equipment. For example it does not matter if there is latency if you are communicating on a phone with someone in another part of the world. But it does if you are trying to lip read at the same time.  If it can be perceived by a user, then it is a problem. Figures vary but most people cannot detect latency of less than 40ms.  Hence if possible it’s good to keep latencies below 30ms.  

It may be the case that you are using multiple pieces of equipment together.  Hence the latency of one item may be low, but by using 2 or 3 pieces of equipment, the sum of all the individual latencies may cause a problem.

The type of Bluetooth protocol used can also effect the latency.  The more data you send then the more processing needs to be performed hence the greater the risk of latency.  For example high quality stereo music signals need increased processing but, this does not matter if you do not need to lip read.  Live speech, or lecturing in classroom needs to be synchronised so you may have to limit the amount of data that is sent to ensure this is acceptable.  This is why there are different Bluetooth protocols for differing situations.  


Bluetooth Safety

This is a complex topic and the effects are dependent on the radio frequency being used, the duration and power levels and the type of person, adult or child and exposure.   It must be emphasized that there a huge number of RF transmissions being used at any one time in any location and there is currently no evidence of negative health effects, for low power equipment such as Bluetooth.  There are some areas in military or scientific use cases that are potentially harmful, but these will restricted areas and not accessible to the general public. 

However even so there are strict regulations that any manufacture of a radio device must comply with. These  govern the power and exposure that they are allowed to produce.  In simpler terms, this is the amount of radio frequency (RF) energy, a person can be exposed to in  a certain time frame.  The unit of measurement is SAR value (Specific Absorption Rate) this is measured in Watts per Kilogram of body tissue.    They cover many aspects such as: the effects of frequency, power levels, different body types and physiology.  There have been extensive studies over the years and huge amounts of data generated on this topic.  The current general global consensus, is that a figure of 2 Watts per kilogram of body tissue is a safe limit.  There are still many non-scientific concerns regarding this, but no data exists to currently disprove these limits.     You can see these quoted limits, in manufactures data sheets and in user guides.  It slightly differs between countries but the average smart phone has a SAR value of approximately 1.6. Radio mics used in a school environment would be around 0.1.  Hence incredibly low. 

Regarding concerns, combining radio aids with other implantable devices such as Pacemakers. It’s always difficult to know the full medical history of a person, and there are many variables such as, location of the device,  or different models, so even though radio aid power levels are low it is always advisable to consult the medical professional for guidance prior to the use of any additional radio device.



Bluetooth and associated similar wireless technologies are incredibly useful and have enabled further integration with media within education.  However, they should be used appropriately and you need to consider what form of Bluetooth is the most beneficial to the situation you are trying to overcome.  For Audio transmission a, high quality audio profile should be used, with a high data rate.  For live speech you need to be cautious regarding latencies that could hinder lip reading with Low energy type devices. These are fine for remote control, but may not be optimal for speech understanding in noise.  There is not one Bluetooth that will satisfy all requirements and this was never the intention.  It is designed as a modular system and you choose which protocols are optimal for each situation.


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