When pressing for the above functions, you must do all the presses within a three second window.

The XM4 is equipped with switchable Bass Boost:

The XM4 is equipped with variable crossfeed. To use Crossfeed, the Crossfeed Enable switch must be in the IN position. Then, you can adjust the amount of crossfeed using the Crossfeed Adjuster potentiometer.

Why You Want Crossfeed: Most music is mixed to be listened to on loudspeakers. The studio technicians mixing the recording assume there will be alot of crosstalk, since, with speakers, the listener's left ear clearly hears the right speaker's output, and vice versa. Thus, most music is mixed with a very wide stereo soundstage.

With headphones, however, the left ear only hears the left channel, and the right ear only hears the right channel, with nearly zero crosstalk. This can, for many recordings, cause the soundstage to appear to be "in the center of your head". Further, some recordings (early Beatles' recordings are infamous for this) have each instrument and vocal track panned 100% to either left or right, which can almost immediately cause listener fatigue.

The XM4's CrossFeed feature feeds some of the left channel into the right channel, and vice versa. In order to properly simulate the forward soundstage of loudspeakers, the amount of crossfeed needs to vary with frequency, which the XM4 does. Low frequencies (bass) bend around corners (including the corners of your head - bass from the left speaker will bend around your head and enter your right ear) much better than higher treble frequencies (treble is more directional); thus more crossfeed must occur in the lower bass frequencies.

Further, the XM4 allows the user to adjust the overall level of crossfeed, from near-stereo to complete mono. This is adjusted using the crossfeed controller potentiometer inside the unit (don't forget to turn on the crossfeed with the CrossFeed Bypass Switch).

With the Main Volume knob at full volume, the overall gain for the XM4 is:

It is preferable to not use the gain boost (ie. It is preferable to remove the jumpers) unless you need it. "Need it" means your headphones are too quiet, even with the volume knob turned up to maximum. This is because too high a gain will result in a tendency to turn the volume down on your audio source (mp3 player, etc), and weak sources are more susceptible to noise.

Usually, only very high-impedance headphones (300Ω or above) require the gain boost.

Hint! When not using the jumpers, place the jumpers over one pin only, for storage, so you don't lose them. Your XM4 was shipped from the factory like this.

The XM4 was designed with ergonomics and portability in mind. The main volume, status LEDs, power button, and both input and output jacks are all located at one end of the unit, allowing the XM4 to be easily carried in a pocket.

The extruded aluminum case and internals are machined to give a snug fit, with no rattles or loose batteries, or risks of short circuits.

The unit has a "FlashLight" mode, which turns on both LEDs to full brightness. Not too useful for, say, spelunking, but the focussed LEDs are quite strong and very handy if you're fumbling for your keys in the dark, for example.

Finally, the XM4 weighs only 140 grams (4.9 oz), so it can be easily carried anywhere.

You have several options for powering your XM4:

1. Optional Lithium-Ion FastCharge^® System
2. Alkaline non-rechargeable battery. You may also use an external power supply, to save battery life when listening at home.
3. NiMH or NiCd rechargeable battery

1. Optional Lithium-Ion FastCharge^® System: If you ordered your XM4 with the Lithium-Ion FastCharge system, just plug in the external charger to charge the battery.
   
   
   • The battery will fully charge in approximately 1.5 to 2 hours. When charging is complete, the LED on the charger will turn from red to green.
   • The battery will charge even if the XM4 is turned on.
   • You can leave the charger connected indefinitely.
   • You can expect 30 to 40 hours of use per charge.
   • Your charger is a "World" charger - it will work with AC Mains voltages from 105 to 240 VAC, at 50 or 60Hz. If you are using the charger outside of North America, you may need a plug adapter (available from any local electronics store).
   
   
2. Alkaline non-rechargeable battery. You can expect approximately 50 hours of use from a single Alkaline battery. You may also plug an external power supply into the XM4, in order to save battery life while listening at home. An external power supply must conform to the following:
   
   
   • 6 to 15V DC
   • must have a "barrel"-type connector, which accepts a 1.3mm center pin.
   • the center pin must be positive polarity
   • The milliamp (mA) rating on the supply does not matter; any mA rating can be used
   • A suitable power supply is RadioShack PN#273-1773 (make sure you ask for Adaptaplug "H" PN#273-1711, which is included with the adapter).
   
   
3. NiMH or NiCd rechargeable battery A rechargeable NiMH or NiCd battery can be used instead of an alkaline, and you can use the built-in trickle charge and an external power supply to recharge it. The battery must be:
   
   
   • Nickel Metal-Hydride (NiMH), 8.4v or 9v, or,
   • Nickel-Cadmium (NiCad), 8.4v or 9v
   • An example of a suitable battery is RadioShack #23-529
   
   Using a 7.2v battery is not recommended, as overcharging may result if the external power is applied for too long. When using the internal trickle charger, the external power supply is the same as describe above in section 2, but must be Regulated 12VDC ? 5%. Again, a suitable supply is RadioShack PN#273-1773 with Adaptaplug "B" PN#273-1705.
   
   To enable the internal trickle charger, you must open the XM4 and install one jumper. See your User's Manual for details.
   
   Note that the ground of your external power supply will not be at the same potential as the XM4's metal case.
   

   Use of an external power adapter which is higher than the voltages shown above may cause battery overcharging, damage to the battery and/or the XM4, battery electrolyte leakage, or possibly even battery explosion. If in doubt, measure your power adapter with a voltmeter, or enquire at your local electronics store.