One way to determine whether channel overcrowding might be a problem is to go into your PC's Wi-Fi utility to detect networks that are in range. If you see more than half a dozen, chances are good that all of them are battling for bandwidth. You can download the free InSSIDer Wi-Fi scanning tool to get an easy readout of all your local Wi-Fi networks, including their channels and signal strength, so you can figure out which channels are less crowded.
Channel overcrowding is less of a problem on the 5GHz band, because it has many more channels and it isn't used as much as 2.4GHz is to begin with. In the Wi-Fi universe, only 802.11a devices used 5GHz in the past, and they were far outnumbered by 2.4GHz-based 802.11b and g devices.
However, manufacturers are starting to turn to 5GHz for streaming media. If you have a dual-band router, and you have devices that support a 5GHz network (for instance, we're starting to see connected TVs that support dual-band Wi-Fi), you should try setting your devices to use the 5GHz band. Note, however, that the 5GHz band doesn't support the range that 2.4GHz does, so you will want to check whether the 5GHz coverage is adequate where you need it.
Even if you have a router that doesn't support the 5GHz band--maybe you invested in a 2.4GHz 802.11n router before dual-band routers were widely available--you can add 5GHz support via an access point (which you would plug into an available ethernet point on your 2.4GHz router). Few vendors ever released 5GHz-only access points, but you should be able to pick up a dual-band access point--the D-Link DAP-1522, for example--for under $100 and run it in 5GHz mode.
Also, if you're shopping for an 802.11n router and you intend to use it for streaming media, check its antenna array. The speed and coverage of 802.11n depend a lot on the technology's ability to send and receive multiple data streams simultaneously, so the more antennas you have, the faster and farther the network should reach. The fastest 802.11n gear uses 3x3 (three transmitting and three receiving) antennas; gear with 2x2 antenna arrays is less expensive and not as powerful. The difference in antenna arrays is responsible for the varied top potential speeds you see on 802.11n packaging.
Try Hybrid Home Networking
If multimedia and coverage issues persist, consider adding a wired component to your network. Although I wouldn't ever want to give up the convenience of Wi-Fi for portable devices such as cell phones, tablets, and laptops, there's no compelling reason to prefer wireless connections for equipment that stays in place, such as home entertainment gear or a desktop PC.
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