Hello,

I really doubt that one accent can give you a master key for other accents. As a spanish speaker I still found it hard to understand other regions until after a while of hearing them.

Many people say that Colombian spanish is a very good source as it is more neutral than in other parts. However that is still a wide generalization because there you also have multiple accents.

Best way is to hear as much people as possible I guess.

Saludos,

Laura

Why learning American English which its the easier accent of English makes easier to learn others? Its much easier understand and american or canadian than a irish person.

Even in Spain you have different accents. Some countries have more variations than others.

You can get used with other accents but sometimes even the natives from other region or country cant understand eachothers. That happen because the differences and / or because the lack of contact with other variations. 

Arjun: Exposure is the only solution. Even among natives, we sometimes have trouble understanding each other when we visit other places. But after some weeks or months we "tune in" to the new accent. And I say "places" instead of countries, because the accent differences within a country can be bigger than those between countries. 

So go out and make friends with people from different places. =)