Other computer slow when downloading on another

This is something that I have noticed after getting a new internet service.

My internet speed is a 10MB down and 1MB up connection.

When I am downloading a file, avg ~200kbps from work, the internet is really slow on other computers in the house. I ran a speed test on a second computer while first computer was downloading at ~200kbps and my speedtest was around 1MB.

I have a Comtrend AR-5381u modem from my service provider which I cannot log into.

Is there any reason that when I am actively downloading with one computer when it is not anywhere near the 10MB connection speed that my internet would almost completely stop for other computers until my download is done?