LEVEL LIMITED HEADPHONES AND HEADSETS
Canford has considerable experience in the design of headphone limiters and their use in the operational environment. Whilst virtually any headphone or headset can have a limiter fitted, using one of the seven types of standard multipurpose limiter circuits, this usually has to be in an in-line housing. By designing type-specific circuits for individual ear loudspeakers, these can be made small enough and appropriately shaped to enable them to be built into the earcup housing. Adding a limiter circuit to a headphone alters the input impedance.
The Sennheiser HD480 type headphone is an open back type headphone with 1700 ohm capsules. In order to distinguish these headphones from standard non-protected versions, they are distinctively marked. Limiting level is fixed at 88dBA or 93dBA (note 1). Standard connector options are available, and because the limiter is within the capsule, it is possible to use spare or replacement leads, as for standard versions.
All types have interwoven copper/Kevlar cables for extra strength. As with in-line limiters, each headphone is individually calibrated, and as each capsule has its own individually calibrated limiter, spare limited capsules are available.
Single-sided cables connect to the left earpiece, with a loop over the headband to the right earpiece; a fixing kit is supplied to hold the cable onto the headband. Note that in these versions, the earpieces are mounted onto the headband the opposite way up (connector at the top).
The headphones are available as standard in eleven terminated versions:
||1200 ohms per earpiece
||91dB for 1mW
Beyerdynamic DT231 and DT234
The DT231 is a lightweight closed headphone, impedance 32 ohms, with a 2.5m straight or coiled cable terminated with a 3.5mm 3-pole jack plug with 6.35mm A-gauge plug adapter, or coiled cable terminated with a Neutrik A-gauge jack plug. The DT234 is the headset version of the DT231, suitable for multimedia applications, and has a noise-cancelling electret microphone fitted to a 150mm boom. The microphone output is unbalanced and requires a supply voltage 1.5-9VDC. The headset is terminated with two 3.5 mm 3-pole jack plugs on a 1 metre Y-cable.
A professional monitoring headphone with great comfort for extended wearing. Supplied with 2.5m coiled cable, 3.5mm jack plug with 6.35mm adapter.
Beyerdynamic DT280 and DT290
Headsets with an extremely low visual profile for improved 'in-shot' appearance, and great comfort for extended wearing. Dual muff (DT290) or single muff (DT280), hypercardioid dynamic mic. 'XJ' suffix denotes supplied fitted with Neutrik NC3MX XLR 3-pin male for mic and NPC3C 3-pole A-gauge jack. 'XLR5M' suffix denotes supplied with Neutrik NC5MXX 5-pin male (mic pins 1 & 2, common pin 3, ear left pin 4, ear right pin 5).
As DT290 but with cardioid pattern condenser mic. Supplied fitted with Neutrik NC3MX XLR 3-pin male for mic and NPC3C 3-pole A-gauge jack.
Closed ear design, incorporating Beyerdynamic’s bass reflex system, combines articulate low end response with a lightweight diaphragm. Frequency response equalised to the diffuse sound field. Fitted with 3.5mm jack with 6.35mm adapter.
Beyerdynamic DT100 and DT109
The closed back DT100 headphones and DT109 headsets both have 400 ohm capsules, the DT109 has a 200 ohm dynamic microphone. Units are available in the black shell version, with distinctive marking to distinguish them from standard non-protected versions. Limiting level is fixed at 93dBA (note 1). As with in-line limiters, each headphone is individually calibrated. Standard connector options are available, and because the limiter is within the earshell, it is possible to use spare or replacement leads, as for standard versions. Due to the method of construction, it is not possible for replacement ear loudspeakers to be user-fitted in these types, units requiring repair must be returned to Canford. For the same reason, replacement limited ear loudspeaker units are not available as spare parts.
The DT100 level-limited headphones are available as standard in five versions - four terminated and one without cable:
The DT109 level-limited headsets are available in four versions - two terminated, one unterminated and one without cable (XLR wiring is compatible with Tecpro and RTS intercom systems, see Tecpro Communication System - Headsets product group for details of the wiring conventions):
||Straight cable, wired mono, terminated with XLR 4-pin female
||Straight cable, wired stereo, terminated with XLR 5-pin female
||Straight cable, unterminated
||Without cable (for users requiring to use coiled cables
||500 ohms per earpiece, nominal
||90dB for 1mW @ 1000Hz, nominal
||350g (excluding cable)
Heavy duty ‘closed ear’ general purpose or studio headphones. Very robust construction, hidden fixings hinder tampering whilst allowing easy repairs. 2 metre cable with steel conductors, fitted with robust Neutrik 3 pole A-gauge or B-gauge plug. Impedance 2 x 400 ohms.
Rugged closed ear design and wide frequency response for reliability and accuracy (note 2). 3 metre coiled OFC cable, fitted with gold 3.5mm 3-pole mini jack with 6.35mm 3-pole jack adapter.
Shure SRH440 and SRH840
Closed-back, circumaural headphones designed for recording and programme monitoring, with 3 metre straight cables. Both types are available with 3.5mm plugs with 6.35mm A-gauge adapters. The SRH440 is additionally available wired stereo with a Neutrik B-gauge plug with black cover.
- 1) The quoted limit level of 93dBA and 88dBA is for measurement using dummy head (or mannequin) systems. For measurements using flat plate calibrators the level will differ. Health and Safety authorities are more inclined to use the dummy head type measurement.
- 2) Due to the enclosed circuitry, the sensitivity and presented impedance of these headphones is different from standard versions.