Sennheiser Headphones SH350 User Manual

HMEC 350/352/355  
355-C/356/372/450  
HMDC 372  
Instructions for use  
 
The HMEC 350, HMEC 352, HMEC 355, HMEC 355-C, HMEC 356, HMEC 372, HMEC 450 and  
HMDC 372 are pilot headsets with closed ear protector headphones and NoiseGard™  
active noise compensation for use in helicopters, propeller and turboprop aircraft.  
Safety tips  
With the NoiseGard™ active noise compensation turned on, typical aircraft sounds  
(for example, those from engines, propellers, warning alarms, etc.) may sound  
different to you. Before operating any aircraft, make sure that, with NoiseGard™  
turned on, you can hear and recognize these sounds. Set the volume to safe levels  
that do not interfere with your ability to hear informational sounds and warning  
alarms.  
Do not attempt to repair the headset yourself. If problems occur, contact your  
Sennheiser agent for assistance.  
Only replace parts of the headset whose replacement is described in this manual. All  
other parts of the headset must be replaced by your Sennheiser agent.  
Do not immerse the headset in water! For information on how to clean the headset,  
contact your Sennheiser agent.  
3
 
Headset features  
HMEC 350 NoiseGard™ headset  
New active headset with effective attenuation of external noise across the entire  
frequency spectrum due to NoiseGard™ active noise compensation  
NoiseGard™ active noise compensation provides clear communications even in the  
noisiest environment  
Improved acoustic properties: The frequency response of the headphones has been  
optimised in the 1 to 4 kHz region to give significantly increased speech intelligibility  
over the HMEC 300 series  
Excellent comfort due to very low weight, soft ear cushions and padded headband as  
well as best possible freedom of movement due to unilateral connecting cable  
Foldable headband for easy and space-saving storage  
Clear communications due to MKE 45-1 pre-polarized condenser microphone with  
adjustable sensitivity  
Microphone can be easily positioned and worn on either left or right side due to  
flexible microphone boom with quick-fixing device  
Integrated volume control  
Adaption to the aircraft intercom system via Mono/Stereo switch  
4
 
With the NoiseGard™ active noise compensation turned off, the headset can be used  
as a conventional headset  
Power supply for NoiseGard™ is provided via on-board power supply system,  
cigarette lighter socket or battery pack  
Fail safe operation in case of power failure  
Supply voltage for the NoiseGard™ system is processed by the in-line electronics in  
the connecting cable  
Made in Germany, 5-year warranty (HMEC 450: 10-year warranty)  
Product variants  
HMEC 352 NoiseGard™ headset  
The HMEC 352 differs from the HMEC 350 in the following features:  
Connection of microphone and NoiseGard™ electronics via PJ-068 plug  
HMEC 355 NoiseGard™ headset  
The HMEC 355 differs from the HMEC 350 in the following features:  
No Mono/Stereo switch  
Connection of headphones, microphone and NoiseGard™ electronics to the on-board  
power supply system (12–35 V DC) via XLR-5 plug  
5
 
HMEC 355-C NoiseGard™ headset  
The HMEC 355-C differs from the HMEC 350 in the following features:  
No Mono/Stereo switch  
Connection of headphones and microphone via XLR-5 plug  
Connection of NoiseGard™ electronics via XLR-3 plug  
HMEC 356 NoiseGard™ headset  
The HMEC 356 differs from the HMEC 350 in the following features:  
Connection of headphones, microphone and NoiseGard™ electronics to the on-board  
power supply system (12–35 V DC) via 6-pin Redel plug  
HMEC 372 NoiseGard™ headset  
The HMEC 372 differs from the HMEC 350 in the following features:  
No Mono/Stereo switch  
Coiled cable  
Connection of headphones and microphone via U-174/U jack plug to a high impedance  
interface in the helicopter  
6
 
HMEC 450 NoiseGard™ headset  
The HMEC 450 differs from the HMEC 350 in the following features:  
Stylish silver design  
Leatherette ear cushions  
Headband padding can be buttoned  
HMDC 372 NoiseGard™ headset  
The HMDC 372 differs from the HMEC 350 in the following features:  
No Mono/Stereo switch  
Coiled cable  
M-87/AIC dynamic microphone and low impedance headphones  
Connection of headphones and microphone via U-174/U jack plug to a low impedance  
interface in the helicopter  
7
 
Delivery includes  
HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 headsets  
Headset  
3-pin XLR socket for aircraft panel mounting (power supply via the on-board system)  
Padded carry and storage bag with shoulder strap for headset and accessories  
Wind screen for microphone (except HMDC 372)  
MZQ 2002-1 cable clip (Cat. No. 044740)  
HMEC 352, HMEC 355 and HMEC 356 headsets  
Headset  
Padded carry and storage bag with shoulder strap for headset and accessories  
Wind screen for microphone  
MZQ 2002-1 cable clip (Cat. No. 044740)  
8
 
Recommended accessories  
Replaceable gel ear cushions (Cat. No. 092807)  
BP-04 battery pack (Cat. No. 500357) (except for HMEC 352, HMEC 355 and HMEC 356)  
Battery pack with XLR-3 socket for powering the NoiseGard™ electronics of the  
HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 headsets. Four 1.5 V AA  
size alkaline manganese batteries (IEC LR 6) ensure approx. 15 hours of reliable  
operation (batteries are not included in the delivery). Length of connecting cable: 0.9 m.  
Adapter cables (except for HMEC 352, HMEC 355 and HMEC 356)  
Sennheiser offers special adapter cables for connecting the NoiseGard™ electronics of  
the HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 headsets to the on-  
board power supply via the cigarette lighter socket:  
ACX-2  
ACX-1  
ACX-1 adapter cable for powering one headset via the cigarette lighter socket  
ACX-2 adapter cable for powering two headsets via the cigarette lighter socket  
The adapter cables are also available with a right-angled jack plug featuring a 7.5 A fuse  
and a green LED operation indicator:  
ACX-11 adapter cable for powering one headset via the cigarette lighter socket  
ACX-11  
ACX-22  
ACX-22 adapter cable for powering two headsets via the cigarette lighter socket  
9
 
Connecting the headsets  
Connecting cables for headsets  
HMEC 350 and HMEC 450 headsets:  
1
1
1
¼” (6.35 mm) stereo jack plug for connecting the headphones  
PJ-068 jack plug for connecting the microphone  
XLR-3 plug for connecting the power supply for the NoiseGard™ electronics  
Connecting cable for  
HMEC 350 and HMEC 450  
HMEC 352 headset:  
1
1
¼” (6.35 mm) stereo jack plug for connecting the headphones  
PJ-068 jack plug for connecting the microphone and the power supply for the  
NoiseGard™ electronics  
Connecting cable for  
HMEC 352  
HMEC 355 headset:  
1
XLR-5 plug for connecting the headphones, the microphone and the power supply for  
the NoiseGard™ electronics  
Connecting cable for  
HMEC 355  
10  
 
HMEC 355-C headset:  
1
1
XLR-5 plug for connecting the headphones and the microphone  
XLR-3 plug for connecting the power supply for the NoiseGard™ electronics  
Connecting cable for  
HMEC 355-C  
HMEC 356 headset:  
1
6-pin Redel plug for connecting the headphones, the microphone and the power  
supply for the NoiseGard™ electronics  
Connecting cable for  
HMEC 356  
HMEC 372 and HMDC 372 headsets:  
1
1
U-174/U jack plug for connecting the headphones and the microphone  
XLR-3 plug for connecting the power supply for the NoiseGard™ electronics  
Connecting cable for  
HMEC 372 and HMDC 372  
11  
 
Connector assignment  
Redel connector (NoiseGard™)  
XLR-3 connector (NoiseGard™)  
XLR-5 connector  
1
2
3
4
5
6
Power supply NoiseGard™ (DC+) 1 Power supply NoiseGard™ (DC+) HMEC 355  
HMEC 355-C  
Audio Lo / DC –  
Audio Hi left  
2
3
Ground  
– *  
1
2
3
4
5
Audio Hi  
1
2
3
4
Audio Hi  
Audio Lo  
Microphone Hi  
Microphone Lo  
Audio Lo / DC –  
Microphone Hi  
Microphone Lo  
Audio Hi right  
Microphone Hi  
Microphone Lo  
Power supply NoiseGard™ (DC+) 5 Not assigned!  
¼” (6.35 mm) stereo jack plug  
U174/U jack plug  
PJ-068 jack plug  
1
2
3
Audio Hi left  
Audio Hi right  
Audio Lo  
1
2
3
4
Microphone Lo  
Audio Hi  
Microphone Hi  
Audio Lo  
HMEC 352  
HMEC 350  
1
2
3
Power supply NoiseGard™ (DC+) 1 Not assigned!  
Microphone Hi  
Microphone Lo / DC –  
2
3
Microphone Hi  
Microphone Lo  
* Note: Battery powering for the NoiseGard™ system of HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 only via BP-04 battery pack  
12  
 
Powering options  
There are three options for powering the NoiseGard™ active noise compensation:  
1. Connection to the on-board system (12–35 V DC)  
2. Connection to the BP-04 battery pack  
(accessory, except for HMEC 352, HMEC 355 and HMEC 356)  
3. Connection to the cigarette ligther socket (12–35 V DC) via adapter cable  
(accessory, except for HMEC 352, HMEC 355 and HMEC 356)  
The supply voltage for the NoiseGard™ system is processed by the in-line electronics in  
the connecting cable.  
Danger of short circuit!  
Before turning on NoiseGard™, ensure that the on-board power supply system is  
protected by a 1 A fuse.  
13  
 
1. Connecting the headset to the on-board system  
The NoiseGard™ electronics can be connected to on-board power supply systems with  
operating voltages between 12–35 V DC.  
Danger of short circuit!  
Before turning on NoiseGard™, ensure that the on-board power supply system is  
protected by a 1 A fuse.  
The HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 headsets are supplied  
with an XLR-3 socket for panel mounting in the aircraft. The XLR-3 socket must be  
mounted by a technician qualified to perform this type of installation.  
Power supply for  
NoiseGard™  
Ground  
Do not connect !  
XLR-3 socket  
HMEC 350 and HMEC 450 headsets:  
̈ Connect the ¼” (6.35 mm) stereo jack plug for the headphones and the PJ-068 jack  
plug for the microphone to the corresponding jack sockets of your intercom.  
̈ Connect the XLR-3 plug to the XLR-3 socket.  
14  
 
HMEC 352 headset:  
̈ Connect the ¼” (6.35 mm) stereo jack plug for the headphones and the PJ-068 jack  
plug for the microphone to the corresponding jack sockets of your intercom.  
HMEC 355 headset:  
̈ Connect the XLR-5 plug to the aircraft’s XLR-5 socket.  
HMEC 355-C headset:  
̈ Connect the XLR-5 plug for the headphones and the microphone to the aircraft’s XLR-5  
socket.  
̈ Connect the XLR-3 plug to the XLR-3 socket.  
HMEC 356 headset:  
̈ Connect the 6-pin Redel plug to the corresponding socket in the aircraft.  
HMEC 372 and HMDC 372 headsets:  
̈ Connect the U-174/U jack plug for the headphones and the microphone to the U-174/U  
socket of your intercom.  
̈ Connect the XLR-3 plug to the XLR-3 socket.  
15  
 
2. Connecting the headset to the battery pack  
(except HMEC 352, HMEC 355 and HMEC 356)  
The NoiseGard™ electronics of the HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and  
HMDC 372 headsets can also be powered via the BP-04 battery pack (see  
“Recommended accessories” on page 9). The battery pack can be operated either on  
standard or rechargeable batteries (not included in the delivery). However, to ensure a  
longer operating time, we would recommend using standard AA size alkaline  
manganese batteries (IEC LR 6) or NiMH rechargeable batteries.  
Inserting / replacing the the batteries  
̈ Open the cover of the battery compartment.  
̈ Insert four AA size alkaline-manganese batteries (IEC LR 6). Observe correct polarity  
when inserting the batteries.  
̈ Close the cover of the battery compartment.  
LED operation and battery status indication  
The battery pack has two control LEDs.  
Yellow LED: The battery pack is turned on and the battery capacity is sufficient.  
Red LED:  
The batteries are low. Replace the batteries.  
16  
 
Connecting the headset, turning on the battery pack  
̈ Connect the XLR-3 plug of the headset connecting cable to the XLR-3 socket on the  
connecting cable of the battery pack.  
̈ HMEC 350 and HMEC 450 headsets: Connect the ¼” (6.35 mm) stereo jack plug for  
the headphones and the PJ-068 jack plug for the microphone to the corresponding  
jack sockets of your intercom.  
HMEC 355-C headset: Connect the XLR-5 plug for the headphones and the  
microphone to the aircraft’s XLR-5 socket.  
HMEC 372 and HMDC 372 headsets: Connect the U-174/U jack plug for the  
headphones and the microphone to the U-174/U socket of your intercom.  
̈ Turn on the battery pack by setting the ON/OFF switch to ON. The yello LED power  
indicator lights up.  
Note:  
When using the battery pack, the ON/OFF switch integrated into the headset  
connecting cable is out of operation.  
Attaching the battery pack to clothing  
The battery pack can be attached to clothing by means of the supplied attachment clip,  
Velcro tape is also supplied.  
17  
 
3. Connecting the headset via a cigarette lighter adapter cable  
(except HMEC 352, HMEC 355 and HMEC 356)  
Sennheiser offers special adapter cables with XLR-3 socket for connecting the NoiseGard™  
electronics of the HMEC 350, HMEC 355-C, HMEC 372, HMEC 450 and HMDC 372 headsets  
to the on-board power supply via the cigarette lighter socket:  
ACX-1 adapter cable for powering one headset via the cigarette lighter socket  
ACX-1  
ACX-2  
ACX-2 adapter cable for powering two headsets via the cigarette lighter socket  
The adapter cables are also available with a right-angled jack plug featuring a 7.5 A fuse  
and a green LED operation indicator:  
ACX-11 adapter cable for powering one headset via the cigarette lighter socket  
ACX-22 adapter cable for powering two headsets via the cigarette lighter socket  
ACX-11  
ACX-22  
Connecting the headset  
̈ Connect the XLR-3 plug of the headset connecting cable to the XLR-3 socket of the  
adapter cable.  
̈ Connect the plug or right-angled jack plug of the adapter cable to the cigarette  
lighter socket.  
18  
 
Preparing the headsets for use  
Adjusting the headband  
For good noise attenuation and best possible comfort, the headband has to be adjusted  
to properly fit your head:  
̈ Wear the headset so that the headband runs over the top of your head.  
̈ Adjust the length of the headband so that  
• your ears are completely inside the ear cushions,  
• you feel even, gentle pressure around your ears,  
• a snug fit is ensured.  
Note:  
Make sure not to squeeze any connecting cable when adjusting the headband.  
Squeezing can damage the connecting cables.  
̈ Turn on the NoiseGard™ active noise compensation by setting the ON/OFF switch to  
“ON” (see “Turning NoiseGard™ on/off” on page 22).  
̈ Final adjustment is best made in a noisy environment.  
19  
 
Positioning the microphone  
Relocating the microphone boom  
The microphone boom can be worn on either side of the mouth.  
̈ Loosen the quick-fixing device.  
̈ Rotate the microphone boom by 180°.  
̈ Tighten the quick-fixing device.  
Positioning the microphone towards the corner of the mouth  
The HMEC 350, HMEC 352, HMEC 355, HMEC 355-C, HMEC 356, HMEC 372 and HMEC 450  
headsets feature a flexible microphone boom. Bend the microphone boom so that the  
microphone is placed at the corner of the mouth. Maintain a distance of approx. 2 cm  
between microphone and mouth.  
20  
 
For positioning the microphone of the HMDC 372 headset, proceed as follows:  
̈ Adjust the length of the microphone boom so that the microphone is placed at the  
corner of the mouth. To do so, loosen the quick-fixing device and adjust the  
microphone boom in length.  
̈ Pull the middle part of the microphone boom towards the mouth so that the distance  
between microphone and mouth is approx. 2 cm.  
̈ Tilt the microphone for final positioning.  
21  
 
Using the headsets  
Turning NoiseGard™ on/off  
With the NoiseGard™ active noise compensation turned off, the headset can be used as  
a conventional headset.  
Turn on the NoiseGard™ active noise compensation by setting the ON/OFF switch to  
“ON”. When using the BP-04 battery pack, set the NoiseGard™ ON/OFF switch to “ON”  
and use the ON/OFF switch on the battery pack.  
Mono/Stereo selection (except HMEC 355, HMEC 355-C, HMEC 372 and HMDC 372)  
In general, you’ll receive a mono sound source so that the Mono/Stereo switch can  
remain set to “Mono”. When using a stereo intercom system, set the Mono/Stereo  
switch to “Stereo”.  
Adjusting the volume  
Exposure to loud sounds can cause hearing damage!  
Set the volume control to a medium value. Make sure that you can hear critical sounds  
such as warning alarms.  
22  
 
Attaching the cable clip  
The headphone cable can be fixed by means of the cable clip. Guide the headphone cable  
through the metal cable clip as shown in the illustration on the left. Attach the cable clip  
to your clothing and then loop the cable through the clip so that the headphone cable  
doesn‘t disturb you.  
Folding up the headphones  
For easy and space-saving transportation, the earcups can be folded up and tucked  
between the headband.  
Unfold the headphones by grasping both earcups and pulling them down and away from  
the headband.  
23  
 
Spare parts  
The following spare parts are available from your Sennheiser agent:  
Wind screen for MKE 45-1  
Cat. No. 075823  
Cat. No. 077966  
Cat. No. 085764  
Cat. No. 089382  
Cat. No. 086628  
Cat. No. 044740  
Cat. No. 078366  
Ear cushions for all variants except HMEC 450  
Ear cushions for HMEC 450  
Soft ear cushions for HMEC 450  
Headband padding  
MZQ 2002-1 cable clip  
Carry and storage bag with shoulder strap  
Replacing the wind screen  
If the wind screen shows signs of wear such as tears or holes, replace the wind screen.  
Pull the wind screen from the microphone. Gently slide-on the new wind screen and  
ensure that it fits securely over the microphone.  
Replacing the ear cushions  
Replace the ear cushions if they are damaged. Grasp behind the ear cushions and pull  
them up and away from the earcups. Fix the new self-adhesive ear cushions to the  
earcups. For best results replace the ear cushions after 100 hours of use or two years.  
24  
 
Replacing the headband padding  
Replace the headband padding if it is damaged.  
̈ Pull the Ziploc type fastening strips of the headband padding apart and remove the  
worn headband padding.  
̈ Put the new headband padding around the headband.  
̈ Pull the two edges of the headband padding together so that the fastening strips  
slightly overlap.  
̈ Join the fastening strips.  
Replacing the headband padding of the HMEC 450 headset  
Replace the headband padding if it is damaged.  
̈ Open the snaps on the headband padding and remove the worn headband padding.  
̈ Put the new headband padding around the headband.  
̈ Pull the two edges of the headband padding together and close the snaps.  
25  
 
Valuable information on NoiseGard™  
The NoiseGard™ principle  
One of the greatest stress factors today is noise. Research has shown that noise affects  
the nervous system, and can cause tiredness, poor concentration, irritability and tension.  
Of even greater concern is the permanent damage to hearing that can result from noise  
at high levels.  
This problem concerns pilots in particular. Cockpit noise amounts to about 80 dB(A) in  
jets and to 90 up to 97 dB(A) in turboprops. During takeoff and landing, the noise level  
is even higher. To be able to understand radio traffic in spite of the noisy environment,  
the ATC signal level must be set to at least 95 dB(A). Permanent hearing loss caused by  
the continuous noise in aircrafts is the reason why many pilots became prematurely  
disabled or lost their pilot´s license.  
Circumaural communication headsets provide noise attenuating properties and are  
commonly used to address this problem. However, the noise attenuation of these  
headsets is uneven. High frequencies are reduced considerably, but low frequency wind  
and engine noise, the most prominent noise in many of today's aircrafts, is attenuated  
very little. In response to these problems, Sennheiser has developed an active noise  
compensation system – NoiseGard™ – which, combined with a high-quality passive  
hearing protector, provides consistent noise attenuation over the entire audio range.  
The overall noise level is reduced so that the radio volume can be turned down but  
enough noise still remains for the pilot to safely monitor the aircraft engines.  
26  
 
NoiseGard™ active noise compensation is achieved by generating a signal identical in  
sound pressure level but exactly reversed in phase to the noise signal, the effect being  
that the out-of-phase signal cancels most of the noise signal.  
Active noise compensation is accomplished in the following manner: Each earcup  
includes a microphone, a feedback control circuit, and a transducer to reproduce both  
the communication and the noise cancelling signal. The feedback control microphones  
sense the total sound pressure within each earcup resulting from both the desired radio  
signal from the receiver and the undesired noise that has come through the earcup. The  
microphone signal is amplified and the radio signal is subtracted from it. The remaining  
signal (noise) is then filtered and inverted and the radio signal is added back in.  
Eventually, the entire signal is amplified and fed back to the transducer in each earcup.  
Since the noise component of the signal is inverted, it cancels the noise signal coming  
through the earcup. The radio signal remains unaffected, as it was not processed  
through the cancellation circuits.  
The diagram on the left shows noise compensation with NoiseGard™: Passive hearing  
protectors effectively attenuate noise from the middle and upper frequency range, the  
effect decreasing sharply in the lower range. However, active noise compensation with  
NoiseGard™ combined with passive hearing protectors results in a reduction of noise of  
approx. 25 dB in the 25–500 Hz frequency range. The total attenuation resulting from  
active and passive noise compensation is about 30 dB over the entire audio range.  
A 10 dB reduction in noise is perceived subjectively as a halving in volume. A further  
reduction in noise of 10 dB again results in a decrease in unwanted noise by 50 %.  
27  
 
In case of difficulty  
If problems occur that are not listed in the below table, please contact your Sennheiser  
agent.  
Problem  
Possible cause and what to do  
Clear communication but no  
active noise compensation  
The NoiseGard™ electronics are turned off.  
̈ Check to see if the ON/OFF switch is set to “ON”.  
The XLR-3 plug has been pulled out of the power source.  
̈ Check to see if the XLR-3 plug is correctly connected to the power source.  
If aircraft powered: The aircraft fuse is defective.  
̈ Check the aircraft fuse.  
If battery powered (except HMEC 352, HMEC 355 and HMEC 356): The batteries are low.  
̈ Check to see if the yellow LED on the battery pack is lit. If the red LED is lit, replace  
the batteries.  
28  
 
Problem  
Possible cause and what to do  
Active noise compensation but  
very low volume communication  
The volume control is set too low.  
̈ Check the volume setting of the headset.  
The headphone connection has been pulled out (except HMEC 355, HMEC 355-C and  
HMEC 356).  
̈ Check to see if the headphone jack plug is correctly connected.  
Active noise compensation but  
reduced intelligibility  
The microphone connection has been pulled out (except HMEC 355, HMEC 355-C and  
HMEC 356).  
̈ Check to see if the microphone jack plug is correctly connected.  
Communications in one ear only  
(only HMEC 350, HMEC 352,  
HMEC 356 and HMEC 356)  
You are using a stereo intercom system but the headset is set to mono operation.  
̈ Set the Mono/Stereo switch to “Stereo”.  
You are receiving a mono source but the headset is set to stereo operation.  
̈ Set the Mono/Stereo switch to “Mono”.  
29  
 
Technical data  
HMEC 350  
HMEC 352  
HMEC 356  
HMEC 450  
Headphones  
Transducer principle  
dynamic  
Ear coupling  
circumaural, closed  
45–15,000 Hz  
Frequency response  
Nominal impedance active/passive  
300/150 , mono  
600/300 , stereo  
Attenuation (active and passive)  
Max. sound pressure level  
Contact pressure  
> 25–40 dB  
120 dB ( 5 %)  
approx. 10 N  
Microphone incl. preamplifier  
Transducer principle  
pre-polarized condenser mic capsule, noise-compensated, MKE 45-1  
Frequency response  
Sensitivity  
300–5,000 Hz  
Max. sound pressure level  
Min. terminating impedance  
Output voltage  
120 dB  
150 Ω  
400 mV 3 dB at 114 dB (as per RTCA/DO 214)  
typ. 16 V DC (8–16 V DC, approx. 8–25 mA, as per RTCA/DO 214)  
Supply voltage  
30  
 
HMEC 350  
HMEC 352  
HMEC 356  
HMEC 450  
General data  
Connecting cable  
1.5 m, unilateral  
370 g  
Weight without cable  
Power supply for NoiseGard™  
Current consumption  
Fuse  
12–35 V DC  
27 mA (zero signal current), max. 80 mA  
500 mA thermo fuse  
Connectors  
6.35 mm stereo jack plug 6.35 mm stereo jack plug 6-pin Redel plug for  
6.35 mm stereo jack plug  
for headphones,  
PJ-068 jack plug for  
microphone,  
for headphones,  
PJ-068 jack plug for  
microphone and  
NoiseGard™  
headphones, microphone for headphones,  
and NoiseGard™  
PJ-068 jack plug for  
microphone,  
XLR-3 for NoiseGard™  
XLR-3 for NoiseGard™  
Controls  
Mono/Stereo switch  
On/off switch for NoiseGard™  
Volume control for headphones  
Temperature range  
Operation  
Storage  
–15 °C ... +55 °C  
–55 °C ... +55 °C  
Operating time of battery pack  
(except HMEC 352 and HMEC 356)  
with batteries (four 1.5 V AA size alkaline-manganese batteries): approx. 15 hours  
with NiMH rechargeable batteries: approx. 15 hours  
31  
 
Technical data  
HMEC 355  
HMEC 355-C  
HMEC 372  
HMDC 372  
Headphones  
Transducer principle  
dynamic  
Ear coupling  
circumaural, closed  
45–15,000 Hz  
300/150 , mono  
> 25–40 dB  
Frequency response  
Nominal impedance active/passive  
Attenuation (active and passive)  
Max. sound pressure level  
Contact pressure  
50/35 , mono  
120 dB ( 5 %)  
approx. 10 N  
Microphone incl. preamplifier  
Transducer principle  
pre-polarized condenser mic capsule, noise-compensated, MKE 45-1  
dynamic mic capsule,  
noise-compensated,  
M-87/AIC  
Frequency response  
Sensitivity  
300–5,000 Hz  
500–4,000 Hz  
1.8–4 µV / 74 dB at 5 Ω  
Max. sound pressure level  
Min. terminating impedance  
Output voltage  
120 dB  
–  
–  
–  
–  
150 Ω  
400 mV 3 dB at 114 dB (as per RTCA/DO 214)  
typ. 16 V DC (8–16 V DC, approx. 8–25 mA, as per RTCA/DO 214)  
Supply voltage  
32  
 
HMEC 355  
HMEC 355-C  
HMEC 372  
HMDC 372  
General data  
Connecting cable  
1.5 m, unilateral  
370 g  
coiled cable, unilateral  
Weight without cable  
Power supply for NoiseGard™  
Current consumption  
Fuse  
12–35 V DC  
27 mA (zero signal current), max. 80 mA  
500 mA thermo fuse  
Connectors  
XLR-5 for headphones,  
microphone and  
NoiseGard™  
XLR-5 for headphones  
and microphone,  
XLR-3 for NoiseGard™  
U-174/U jack plug for headphones and microphone,  
XLR-3 for NoiseGard™  
Controls  
On/off switch for NoiseGard™  
Volume control for headphones  
Temperature range  
Operation  
Storage  
–15 °C ... +55 °C  
–55 °C ... +55 °C  
Operating time of battery pack  
(except HMEC 355)  
with batteries (four 1.5 V AA size alkaline-manganese batteries): approx. 15 hours  
with NiMH rechargeable batteries: approx. 15 hours  
33  
 
Certificate of Conformity  
Sennheiser electronic GmbH & Co. KG declare that these devices conform to the basic requirements of EEC  
Directive 89/336/EEC and 73/23/EEC.  
Guarantee Certificate  
The guarantee period for this Sennheiser product is 5 years from the date of purchase. Excluded are accessory items,  
rechargeable or disposable batteries that are delivered with the product; due to their characteristics these products have a  
shorter service life that is principally dependent on the individual frequency of use.  
The guarantee period starts from the date of original purchase. For this reason, we recommend that the sales receipt be  
retained as proof of purchase. Without this proof (which is checked by the responsible Sennheiser service partner) you will  
not be reimbursed for any repairs that are carried out.  
Depending on our choice, guarantee service comprises, free of charge, the removal of material and manufacturing defects  
through repair or replacement of either individual parts or the entire device. Inappropriate usage (e.g. operating faults,  
mechanical damages, incorrect operating voltage), wear and tear, force majeure and defects which were known at the time  
of purchase are excluded from guarantee claims. The guarantee is void if the product is manipulated by non-authorised  
persons or repair stations.  
In the case of a claim under the terms of this guarantee, send the device, including accessories and sales receipt, to the  
responsible service partner. To minimise the risk of transport damage, we recommend that the original packaging is used.  
Your legal rights against the seller, resulting from the contract of sale, are not affected by this guarantee.  
The guarantee can be claimed in all countries outside the U.S. provided that no national law limits our terms of guarantee.  
34  
 
 
Sennheiser electronic GmbH & Co. KG  
30900 Wedemark, Germany  
Phone +49 (5130) 600 0  
Fax +49 (5130) 600 300  
Printed in Germany  
Publ. 04/05  
512743 / A04  
 

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