A standard Y cable (stereo headphone plug to dual headphone jacks) will double the headphone outputs. Headphone outputs on home and professional audio equipment can probably drive two headphones to full volume. If the headphones are not the same model, the volume levels will be different. However, headphone outputs on portable stereos often have barely enough power for one set of phones, let alone two. This arrangement will present the amplifier with half of the normal load (assuming that the two headphones are the same model), which most amps should be able to handle. Distortion or inadequate volume are indications that the amplifier is being stressed. For more information about headphone adapter cables, see A Quick Guide To Headphone Accessories.

What is the best way to monitor and mix with headphones?

Performers gain many benefits by monitoring with headphones: true stereo mix, clearer sound and hearing conservation among them. But this question always starts a lengthy debate with recording engineers as to whether headphones should be used in mixing and how they should be used. The quality of a mix done with headphones depends on how well the engineer is able to correlate headphone sound fields with loudspeaker sound fields. A spatial processor can make the job easier by simulating an acoustic space. For an in-depth look at this subject, see The Art of Monitoring and Mixing With Headphones.

Can listening with headphones result in hearing damage?

Listening to any loud sounds can result in hearing damage - so the answer is yes. Headphone listening has a greater potential for causing hearing damage, because the transducers are positioned very close to the eardrums. For information about how to listen with headphones safely, see Preventing Hearing Damage When Listening With Headphones.

Is it legal to wear headphones while driving or biking?

In many places, the answer is no. In other places, the answer is yes or maybe (for example, some laws permit wearing headphones, if one earcup remains off the ear). If an accident occurs, the party wearing headphones may have trouble collecting insurance payments. The only way to know for sure is to check the local laws. Laws banning the use of headphones while driving or biking assume that headphones will block out important background sounds such as horns and sirens and that such use is unsafe. For an opposing view about headphone laws, see A Bicyclist's Sense of Hearing: How Important?.

What are the best computer sound cards for headphone listening?

Sad to say, most computer sound cards have unremarkable sound (often noisy, with an uneven frequency response and easily overloaded). They are built to be utilitarian and cost effective, and such design goals not always compatible with high fidelity. To make matters worse, it is rare (if not impossible) to find a computer store with its selection of sound cards installed and ready for auditioning. Trying out different sound cards on one's own PC is an exercise in frustration - it is difficult enough to configure a machine for one sound card, never mind a couple of them. Computers with the sound circuitry built into the motherboard may not be able to accept add-in boards. Professional sound magazines are publishing sound card reviews, and consumer audio magazines are beginning to evaluate them as serious audio equipment as well.

A discussion of criteria for selecting sound cards is beyond the scope of this FAQ, but here is a short list of suggestions. While the heart of sound card performance typically lies in the onboard D/A and A/D converters, the ability to drive headphones is dependent on the audio amplifier. Most consumer sound cards have a separate audio input (often used to amplify the audio output of the CD-ROM) which is a good means of testing the audio amplifier. In general, if a sound card has both speaker and line outputs, the speaker output is likely to be noisier than the line output (any hiss and hum will be more noticeable in headphones) . Unfortunately, the line output will probably have inadequate current drive for all but the most efficient headphones (look for models with sensitivity ratings of 100dB or higher). If available, compare the sound card's audio specifications with those of good headphone amplifiers. To improve sound quality or for more volume, consider adding a headphone amplifier to the line outputs. Some computers radiate RF frequencies that can cause a headphone amplifier to hum, so try to select one with good RF shielding.

Software-based acoustic simulators and audio equalizers, such as the Graphic Equalizer Pro from Anwida Soft, require sound cards with quality AD/DA converters that support full duplexing and have low latency times. Multimedia cards now commonly have built-in acoustic simulation algorithms that support 3D audio playback in headphones. Again, the quality of the DA/AD converters and the audio amplifiers will determine sound quality. For more information about headphones and headphone specifications, see A Quick Guide To Headphones. For more information about headphone amplifiers and equalizers, see A Quick Guide To Headphone Accessories. For information on the differences between 3D sound processing for stereo loudspeakers and stereo headphones, see Virtual Audio For Headphones.

Where can I find monaural/communications headphones?

Off-the-shelf mono headphones are more likely to be found in office and radio supply stores than audio outlets. Often sold as communications headphones (also referred to as headsets), they are used in business equipment such as telephone and speech recognition systems, as well as amateur and broadcast radio. Unlike stereo headphones, communications headsets are designed for intelligibility of speech and may have a limited frequency response (between 300 and 3kHz). Although the audio signal is monaural, they may have one or two earpieces ("binaural" headsets feed the mono signal to both ears) and accessories such as keypads and microphones or voice tubes. They are available in a variety of headphone technologies such as cordless and noise cancellation and wear styles such as in-ear and supra-aural earpieces, under-chin headbands.

The Commercial Links page lists communications headphone makers and retailers. However, be forewarned that communications headphones tend to be expensive (at least more so than average stereo sets). If that is the case and an integrated microphone or other headset accessory is not needed, consider buying stereo headphones and using a mono adapter (such as Radio Shack part no. 274-368) to split the signal to both earpieces. Adapters are not a good idea if the cord will be subject to constant tugging and there is no way to anchor the cord to prevent the adapter from being pulled loose. Also, since stereo headphones have an extended frequency response, a low pass filter can improve speech intelligibility. For more information about mono headphones, see A Quick Guide To Headphone Accessories.

Where can I find old-style high-impedance (2,000 ohms or more) headphones?

By modern standards, the term "high impedance" when applied to headphones usually means anything between 100 and 600 ohms, but in the not too distant past, headsets of 2,000 ohms or more were in common use. These old-style hi-Z headsets have steel or mica diaphragms and are very efficient, achieving high volume with only millivolts of input. They are especially prized by Xtal radio owners, many of whom prefer to build their sets with "authentic" parts (Xtal or "crystal" radios do not use any transistors or batteries).



Antique and surplus electronics stores may carry old stock - brands such as Western Electric and Baldwin. The Xtal Set Society, which is dedicated to crystal radio building, occasionally has antique headsets in inventory. Antique Electronic Supply sells new hi-Z headsets. DIYers can try making a pair of ultra-high impedance headphones by using two old telephone receivers. Modern low impedance headphones (choose models with very high sensitivity) coupled to an audio output transformer (such as Radio Shack #273-1380) as an impedance converter, may also work. For more information, see High Impedance Headsets for Crystal Radios.

Where can I find water-resistant/underwater headphones?

Several companies, such as Sony and Panasonic, make water-resistant ("sports-style") headphones which can survive the occasional splash of water or brief submersion. Water-resistant headphones are not waterproof and prolonged exposure will damage them. The lightweight sports-style electronics (mostly radios and some media players) are worn with headbands, neckbands, arm-bands or wrist-bands (like wrist-watches) or are sometimes integrated with the headphones (all-in-one). Water-resistant headphones are either in-ear types (earbuds or vertical) or supra-aural (now in the popular neckband style). Water-resistant supra-aural headphones have hard rubber-like ear cushions. Swimmers and other water-sports enthusiasts will often use water-resistant headphones with regular portable stereos packed in protective plastic bags with water-tight seals such as ZipLoc bags or sealed with waterproof tape.

True underwater headphones (also called submersible headphones) are completely waterproof. They are available in closed-back or in-ear designs that are specially calibrated to compensate for hearing differences underwater. The closed-back versions can often be found at dealers of underwater metal detectors. Common features include heavy-duty construction and cords, large ear-cushions that provide superior coupling and isolation from ambient noise, and standard underwater-equipment bulkhead connectors. They are generally monaural and not high fidelity - with a frequency response to about 3kHz at best. The transducers and the headphone frame should be both waterproof and corrosion-proof.

Waterproof in-ear headphones (canal-type headphones) are sold in some specialty sports equipment outlets. The transducers are embedded in waterproof earplugs instead the typical foam surround. Speedo (of swim gear fame) makes this product with a waterproof radio (worn around head or wrist) or a waterproof belt pack for use with regular portable stereos. While fine for use in swimming pools, they should not be worn in deep water. Jim Lee writes:

These systems are often used by lap swimmers to play music or motivational tapes while they work out. I am a little concerned that someone might assume that these devices are not only waterproof but suitable for diving or even snorkeling. Not so. Plugs that completely block the ear canal can cause serious injury because they create a space that cannot be pressure equalized. Any hearing devices suitable for diving would have to allow the relatively free flow of water into and out of the outer ear canal.

c. 1998, 1999, 2000, 2001 Chu Moy.