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Sennheiser ActiveGard Technology: Your investment in Sound Safety

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Great sound, comfort and fit, excellent build quality, versatility, compatibility. These are just some of the many reasons for choosing a headset from Sennheiser.
Introduction 
Acoustic safety is another important factor, so it is reassuring to know that Sennheiser Contact Center and Office (CC&O) headsets are equipped with ActiveGard, one of the most advanced hearing protection technologies against acoustic injury caused by sudden sound bursts. This White Paper provides an overview of the technology, the regulatory background and the safety and benefits of ActiveGard. 
 
Sound safety 
Occasionally, heavy phone users may be exposed to potentially dangerous acoustic shock from unexpected and extremely loud sounds on the line. Sennheiser's patented ActiveGard technology protects headset users from any hearing loss or damage on the rare occasions where they experience this type of incident, so that the users feel protected and secure to perform their jobs. 

With the introduction of softphone-based telephony, the ActiveGard technology has been further adapted to provide users of Sennheiser's digital (USB and wireless) headsets the same security and sound safety. This means that regardless of the choice of professional headset, users can be sure that ActiveGard is always on duty to protect their hearing, ensuring that nothing unexpected gets in the way of important communications. 
 
About ActiveGard 
First designed for Sennheiser's wired headsets, ActiveGard is a sound compression system consisting of a sophisticated electrical circuit incorporated into analogue headsets manufactured by Sennheiser Communications. The patented system utilizes a compression technology to remove the energy from an excessive incoming signal transmitted through the telephone system, leaving the signal free of distortion. 
 
ActiveGard can be compared to an automatic and fast-working intelligent volume control. If an incoming signal rises to a level that is harmful to your hearing, it is instantly turns down considerably, to a more comfortable level. When the sound level returns to normal, the volume will be turned back to the original level after a short period of time as ActiveGard reverts to its stand-by surveillance mode. 
 
Compression not clipping 
In many traditional wired headsets the noise limiting function is achieved by using simple diode- or transistor circuits, which activate a peak-clipping function when the headset speaker signal reaches a certain voltage. Though it may fulfill the legislative requirements, the peak-clipping technology still leaves distortion of the signal and offers only a certain degree of protection for the headset user. 
 
Compared with a traditional system, Sennheiser ActiveGard offers some key benefits and productivity-enhancing advantages: 
 
1. The incoming signal is compressed in one controlled operation. ActiveGard detects an excessive signal and reacts by initiating a compression process that occurs in just a few milliseconds Ð faster than the human ear. 
2. Due to the compression method there is virtually no distortion of the signal. 
3. In contrast to peak-clipping circuits, ActiveGard removes the dangerous energy from the signal by means of this compression technique.  
4. The more powerful the incoming signal is, the more powerfully the system compresses.  
5. In contrast to peak-clipping circuits, ActiveGard keeps the volume at a comfortable level, even if the incoming signal is a sound burst well in excess of the limit which is generally considered to be harmful to hearing. 
 
Below is an illustration showing how ActiveGard technology works compared to the traditional systems. 
ActiveGard_systems.jpgThe regulatory background 
The EU, the United States and many other countries have set noise limits covering the use of headsets so it's reassuring to know that all Sennheiser Contact Center & Office (CC&O) headsets meet or exceed the requirements currently in force. 
 
The EU directive in brief 
The European Union's Noise at Work Directive(1) lays down rules for protecting hearing in the workplace. The Directive basically deals with two types of noise induced hearing damage: Acoustic shock, and excessive noise exposure throughout a working day. 
 
Safety and well being 
Because acoustic shock can cause either temporary or permanent traumatic damage to hearing, the Noise at Work Directive also deals with areas such as instantaneous noise exposures and sets a limit of 137dB(C)(2) for these types of sudden loud sounds comparable with standing next to an aircraft taking off. The Directive does not specify the duration of such impulsive noises but the International Telecommunication Union3 defines the limit of 137dB(C) for sound impulses with a duration of less than half a second. 
 
Protection against excessive noise 
The Directive defines two critical levels for noise exposure throughout a working day. For up to 80dB(A)(4) the employer has no obligations. Between 80dB(A) and 85dB(A) the employer should offer hearing protection and education. For levels exceeding 85dB(A), employees must be provided with, and wear, hearing protection equipment. The Sennheiser DW Series,  SD Series, UI 760, UI 765, UI 770 interface boxes and CEUL 31 and CEUL 32 interface cables are just some examples that comply with the Directive. 
 
There are a number of international telecommunication standards(5) which have traditionally used another maximum acoustic output level that is also based on the 85dB(A) noise exposure limit. These standards define a maximum limit of 118dB(A) for long duration disturbance (above half a second), measured at the ear entrance. Since the late 1980s, the European Telecommunication Standards Institute (ETSI)(6) has shown that this long duration disturbance limit has provided satisfactory protection against acoustic injury. All Sennheiser CC&O headsets fulfill this maximum limit of 118dB(A). 
 
In Summation
ActiveGard benefits: 
* ActiveGard patented technology 
* Protects users against acoustic injury caused by sudden sound bursts 
* Limits maximum sound pressure on all Sennheiser CC&O headsets to 
* International telecommunication standards of 118dB (SPL) 
* Keeps the volume of a sound peak at a safe and comfortable level 
* Allows safer and stress-free working when using a headset 

Bibliography. 
1. 86/188/EEC (European Council Directive) 
2. C-weighted: The sensitivity of the human ear varies with the sound level. At higher levels (100 dB SPL and above) the human ear's sensitivity is more equally distributed across the frequencies compared with lower levels where the human ear is less sensitive at low frequencies (A-weighting). 
3. International Telecommunication Union standard: ITU-T P.360. 
4. A-weighted: Most common weighting used in relation to noise measurements. This weighting accounts for the fact that the human ear is less sensitive to low audio frequencies. 
5. Examples include: ITU-T Recommendation P.360, I-ETS 300 245-2, I-ETS 300 677 and UL/CSA60950-1. 
6. ETSI EG 202 518 V1.2.1 (2008-08) (or the more recent: ETSI EG 202 518 V1.3.1 (2009-11). 
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