event.rb

class Event < ActiveRecord::Base
  has_many :event_users
  has_many :producers, :through => :event_users, :source => :user
end

event_user.rb

class EventUser < ActiveRecord::Base
  belongs_to :user
  belongs_to :event
end

producer.rb

class Producer < EventUser
end

user.rb

class User < ActiveRecord::Base
  has_many :event_users
  has_many :events, :through => :event_users
end