Shopping Tips for iPod Speakers

There are many things to watch out for when buying a set of wireless speakers. However, you don't have to be an expert to be able to pick your ideal speaker. I will offer some advice to help you avoid unpleasant surprises when picking your wireless speakers.

Running the wires to set up a new pair of speakers is often a hassle. If your home is not prewired for audio you may end up drilling holes and doing a big cabling project. Wireless speakers promise to eliminate the speaker wires. Regular speakers require an external audio amplifier to be driven. On the other hand, wireless speakers have their own built-in power amplifier. For medium to high audio power amplifiers, these speakers typically have to be plugged into a power outlet. This means that these speakers can only be placed in locations that have power. This typically is not much of a problem if you plan on putting speakers in another room of your house. However, to eliminate the power cord, some wireless speakers are powered by internal rechargeable batteries. Speakers with moderate audio power, however, require fairly heavy batteries which makes logging the speakers to a place where the batteries can be recharged somewhat of a hassle. In addition batteries will age over time and need to be replaced.

Depending on your application, you want to select speakers with the correct audio power that is sufficient for your environment. Depending on whether you are planning to use the speaker indoors or outdoors, you may want to go with a speaker that is waterproof or at least water resistant.

Next, make sure the transmitter offers the correct audio inputs for your audio equipment. First check what type of audio outputs are available. Then check that your transmitter can connect properly. Obviously if the transmitter has more than just one type of input, you will have more flexibility in case your audio equipment changes down the road. Some more sophisticated transmitters also come with an iPod cradle. This cradle allows streaming of music directly from an iPod or iPhone and also acts as a recharger base. However, if you have another MP3 player, you can still stream your music by connecting to the transmitter through a standard line audio input which almost every transmitter has. Some transmitters have an audio input with a volume control. This allows the transmitter to adjust to virtually any audio device, regardless of the audio output level.

Wireless speakers typically employ either analog or digital wireless audio transmission. Analog transmission typically at 900 MHz uses a method which is similar to FM radio. Digital wireless speakers use a transmission which is more similar to sending the contents of a CD as data and normally transmit at 2.4 GHz or 5.8 GHz. By transmitting audio as data, noise and distortion which are common problems of analog audio transmission are eliminated. With the growing number of wireless gadgets, there is more and more wireless interference. Modern wireless speakers typically utilize some sort of error correction scheme. This method allows the speakers to be able to tolerate interference without audio dropouts.

If possible, try to arrange a listening test. Be aware though that the sound quality also depends on your listening environment. Some wireless speakers have adjustable treble or base. If you cannot part with your existing speakers or cannot find a wireless speaker that sounds just right, you can go with a wireless speaker kit. These kits come with a transmitter and one or several wireless receivers. These receivers incorporate an audio amplifier and can connect directly to your existing speakers.

You can find additional information regarding iPod speaker systems as well as iPod docking stations at Amphony's web site.

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Are Wireless Speakers Dependable In Real-World Conditions?

I will investigate how modern audio transmission technologies which are used in today's wireless speakers and wireless headphones work in real-world environments with a large amount of interference from other wireless devices.

The most popular frequency bands which are used by cordless gadgets are the 900 MHz, 2.4 GHz and 5.8 GHz frequency band. Mostly the 900 MHz and 2.4 GHz frequency bands have started to become clogged by the ever increasing number of gadgets such as wireless networks (WLANs), cordless phones etc.

The least expensive transmitters typically transmit at 900 MHz. They operate similar to FM radios. Since the FM signal has a small bandwidth and thus only occupies a small fraction of the available frequency space, interference can be avoided by changing to another channel. Digital audio transmission is usually employed by more modern audio products. Digital transmitters usually work at 2.4 GHz or 5.8 GHz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high.

Frequency hopping devices, however, will still cause problems since they will disrupt even transmitters using transmit channels. Real-time audio has fairly strict requirements regarding reliability and low latency. In order to offer these, other mechanisms are required.

An often used method is forward error correction in which the transmitter sends additional data along with the audio. From this additional information, the receiver can recover the original data even if the signal was corrupted to a certain extent. FEC is unidirectional. The receiver does not send back any information to the transmitter. Thus it is often used for products like radio receivers where the number of receivers is large.

Another method uses receivers which transmit data packets back to the transmitter. The data packets include a checksum from which each receiver can determine if a packet was received correctly and acknowledge proper receipt to the transmitter. Since lost packets will have to be resent, the transmitter and receivers need to store data packets in a buffer. This buffer causes an audio delay which depends on the buffer size with a larger buffer increasing the robustness of the transmission. A large latency can be a problem for certain applications however. Especially if video is present, the audio should be in sync with the video. Also, in surround sound applications where some speakers are wireless, the wireless speakers should be in sync with the corded speakers. Systems which incorporate this mechanism, however, are limited to transmitting to a small number of receivers and the receivers consume more power.

To avoid crowded frequency channels, some transmitters monitor clear channels and can switch to a clean channel as soon as the current channel becomes occupied by another transmitter. This method is also known as adaptive frequency hopping.

Get additional information about wireless speakers from Amphony's website.

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