Sennheiser HDC 451 User manual

GEBRAUCHSANLEITUNG
INSTRUCTIONS FOR USE
INSTRUCTIONS POUR L‘USAGE
ISTRUZIONI PER L‘USO
INSTRUCCIONES PARA EL USO
GEBRUIKSAANWIJZING
HDC 451

6
Noise - can we ever escape it?
At work, at home, in public transport, on ‘plane, train or bus journeys - noise is with
us wherever we go.
Studies have verified the negative effects of noise, and every one of us will have
noticed them at one time or another:
왘Nervousness
왘Lack of concentration
왘Irritability
These are only the obvious effects on the human organism. Noise also affects the
vegetative nervous system, and can permanently damage the hearing.
The sources of noise are many and diverse and, all too often, cannot simply be
turned off. So, in noisy places, personal protection is the only remedy.
With the NoiseGard® mobile system, Sennheiser have come up with an effective
solution. These instructions explain its functioning principle and operation.
Sound level of noise sources
140 dB Jet engine (at a distance of 82 ft)
130 dB Aircraft engine
120 dB Pneumatic drill
110 dB Forging hammer, concrete works
100 dB Metal die-casting machine
90 dB Metal works
80 dB Tractor
70 dB Office
60 dB Conversation
50 dB Environmental noise
40 dB Living room
30 dB Library
20 dB Bedroom
10 dB Forest, no wind
SOFT
LOUD
The unit of measurement is the decibel (dB). A noise reduction of 10 dB is generally perceived
as a halving of the noise level. If the noise is reduced by a further 10 dB, this is perceived as a
75% noise reduction, and so on.

7
Reduction of subjectively perceived noise level
NoiseGard® mobile are dynamic stereo headphones which, in addition to transmitting
an audio signal, also electronically compensate low-frequency noise. This active
noise compensation functions according to the physical principle that noise and
„anti-noise“ (exactly reversed in phase) cancel each other out.
So, now you can enjoy your music undisturbed, without having to turn the volume
up so high that surrounding noise is completely drowned out.
The NoiseGard®compensation electronics in the headphone requires its own power
supply. This is provided by the power supply unit which is fixed to the cable.
The headphone is connected in the usual manner by a 3.5-mm stereo jack plug, by
an adapter to two 3.5-mm mono jack plugs (in aircraft) or by means of a 6.3-mm
adapter (to the hi-fi unit at home). Both adapters are supplied.
Noise compensation with noisegard
100 200 500 1000 5000
2000 Frequency / Hz
0
10
Attenuation in dB Human speech
Warning Signal
20
Reduction of the
subjectively perceived
noise level with
Noisgard

9
ON/OFF
LED
NoiseGard® mobile HDC 451
The first „open-air“ stereo headphone with NoiseGard®active noise compensation
At just 110 g, this „open-air“ stereo headphone with active noise compensation is
extremely light and provides excellent wearer comfort. Sound coupling to the ear
is directly on the ear.
왘When you are wearing the NoiseGard® mobile HDC 451 you will still be able
to join in conversation - the voice of the person talking to you is scarcely
changed,sincethespeechfrequencyispracticallyunaffectedbycompensation.
왘Warning or emergency signals remain audible.
왘Understandingspeech is evenimproved by NoiseGard®,as „upward-masking“
by low-frequency sound is eliminated.
Switching on/off
ON/OFF switch for the power supply to the compensation electronics is situated
on the battery box. A green LED lights up as a check.
If the power supply is switched off or the batteries are worn out, the headphone
can still be used as a normal headphone without noise compensation.
Inserting the batteries in the power supply unit

9
Technical data Noisegard® mobile HDC 451
Acoustic principle dynamic, „open-air“
Frequency range 20 Hz - 18,000 Hz
Impedance 160 ohms
Total harmonic distortion < 1 %
Active compensation 10 dB + in a range of 400 to 1,000 Hz
Headband pressure approx. 1.6 N
Weight without cable approx. 110 g
Cable one-side only, total length 2 m
with 3.5 mm-stereo jack plug for audio signal
Power supply 2 x 1.5 V mignon (AA) alkaline-manganese
batteries or 2 x 1.2 V storage batteries
mignon (AA) 600 mAh
Operating time approx. 80 hrs. (batteries)
approx. 20 hrs. (storage batteries)
Display green LED as battery check
Scope of delivery 1 headphone HDC 451
1 adapter to double mono jack plug 3.5 mm
1 adapter to stereo jack plug 6.3 mm
NOTES NoiseGard® mobile helps to reduce
noise for greater comfort.
NoiseGard® mobile is not a noise protection
system for medical purposes!
Listening to loud music ? - No !
Listening to music via headphones tempts
into listening to louder music than loud-
speakers would. A high volume that affects
your ears for a longer period can cause
lasting hearing defects. Protect your sound
hearing; Sennheiser headphones are good
even for low volume musical enjoyment....

Sennheiser elektronic KG Telefon: [phone]
D-30900 Wedemark Telefax: 05130/6312
Printed in Germany Publ. 7/94 54526 / A02