Hardware

Connectivity

Two iPod wall chargers, with FireWire (left) and USB (right) connectors, which allow iPods to charge without a computer.

Originally, a FireWire connection to the host computer was used to update songs or recharge the battery. The battery could also be charged with a power adapter that was included with the first four generations. The third generation began including a dock connector, allowing for FireWire or USB connectivity. This provided better compatibility with PCs, as most of them did not have FireWire ports at the time. The dock connector also brought opportunities to exchange data, sound and power with an iPod, which ultimately created a large market of accessories, manufactured by third parties such as Belkin and Griffin. The second generation iPod Shuffle uses a single 3.5 mm jack which acts as both a headphone jack and a data port for the dock.

Eventually Apple began shipping iPods with USB cables instead of FireWire, although the latter was available separately. As of the first generation iPod Nano and the fifth generation iPod Classic, Apple discontinued using FireWire for data transfer and made a full transition to USB 2.0 in an attempt to reduce cost and form factor. With these changes, FireWire could only be used for recharging.

iPod dock connector

Introduced in the third-generation iPod, a 30-pin dock connector allows iPods to be connected to a variety of accessories, which can range from televisions to speaker systems. Some peripherals utilize their own interface, while others use an iPod's own screen for access. Such accessories may be used for music, video, and photo playback. Because the dock connector is a proprietary interface, the implementation of the interface requires paying royalties to Apple.

Accessories

Many accessories have been made for the iPod line. A large number are made by third party companies, although many, such as the late iPod Hi-Fi, are made by Apple. This market is sometimes described as the iPod ecosystem. Some accessories add extra features that other music players have, such as sound recorders, FM radio tuners, wired remote controls, and audio/visual cables for TV connections. Other accessories offer unique features like the Nike+iPod pedometer and the iPod Camera Connector. Other notable accessories include external speakers, wireless remote controls, protective cases/films and wireless earphones. Among the first accessory manufacturers were Griffin Technology, Belkin, JBL, Bose, Monster Cable, and SendStation.

Two designs of iPod earphones. The current version is shown on the right.

The white earphones (or "earbuds") that ship with all iPods have become symbolic of the brand. Advertisements feature them prominently, often contrasting the white earphones (and cords) with people shown as dark silhouettes. The original earphones came with the first generation iPod. They were revised to be smaller after Apple received complaints of the earbuds being too large. The revised earphones were shipped with second through early fifth generation iPods, the iPod Mini, and the first generation Nanos. The earbuds were revised again in 2006, featuring an even smaller and more streamlined design. This third design was shipped with late fifth generation iPods and the second-generation nanos. All first generation iPod Shuffles and the second generation up until 30 January 2007 (when color models were introduced) were shipped with the second design; those that shipped after that date were destributed with the third design of the earbuds.

In 2005, New York's Metropolitan Transportation Authority placed advertisements on the subways warning passengers that "Earphones are a giveaway. Protect your device", after iPod thefts on the subway rose from zero in 2004 to 50 in the first three months of 2005.

BMW released the first iPod automobile interface, allowing drivers of newer BMW vehicles to control an iPod using either the built-in steering wheel controls or the radio head-unit buttons. Apple announced in 2005 that similar systems would be available for other vehicle brands, including Mercedes-Benz, Volvo, Nissan, Toyota, Alfa Romeo, Ferrari, Acura, Audi, Honda, Renault, Infiniti and Volkswagen. Scion offers standard iPod connectivity on all their cars.

Some independent stereo manufacturers including JVC, Pioneer, Kenwood, Alpine, Sony, and Harman Kardon also have iPod-specific integration solutions. Alternative connection methods include adaptor kits (that use the cassette deck or the CD changer port), audio input jacks, and FM transmitters such as the iTrip—although personal FM transmitters are illegal in some countries. Many car manufacturers have added audio input jacks as standard.

Beginning in mid-2007, four major airlines, United, Continental, Delta, and Emirates reached agreements to install iPod seat connections. The free service will allow passengers to power and charge an iPod, and view video and music libraries on individual seat-back displays. Originally KLM and Air France were reported to be part of the deal with Apple, but they later released statements explaining that they were only contemplating the possibility of incorporating such systems.

Bass response

The third generation iPod had a weak bass response, as shown in audio tests. The combination of the undersized DC-blocking capacitors and the typical low-impedance of most consumer headphones form a high-pass filter, which attenuates the low-frequency bass output. Similar capacitors were used in the fourth generation iPods. The problem is reduced when using high-impedance headphones and is completely masked when driving high-impedance (line level) loads, such as an external headphone amplifier. The first generation iPod Shuffle uses a dual-transistor output stage, rather than a single capacitor-coupled output, and does not exhibit reduced bass response for any load.