▁have ▁a ▁limited ▁range , ▁usually ▁a ▁nin th . ▁While ▁it ▁is ▁theoret ically ▁possible ▁to ▁get ▁the ▁re ed ▁to ▁over b low ▁a ▁tw elf th ▁above ▁the ▁fundamental ▁note , ▁this ▁is ▁extremely ▁difficult ▁because ▁the ▁re ed ▁is ▁not ▁held ▁in ▁the ▁mouth ▁( and ▁even ▁if ▁done ▁would ▁result ▁in ▁a ▁gap ▁of ▁two ▁notes ▁in ▁the ▁scale ▁on ▁historical ▁instruments ), ▁and ▁in ▁practice ▁all ▁playing ▁is ▁conf ined ▁to ▁the ▁fundamental ▁series . ▁Some ▁larger ▁instruments ▁have ▁their ▁range ▁extended ▁down wards ▁by ▁means ▁of ▁additional ▁holes , ▁keys ▁and ▁sl iders , ▁and ▁the ▁pitch ▁of ▁the ▁instrument ▁can ▁be ▁lower ed ▁a ▁perfect ▁fifth ▁by ▁dro pping ▁the ▁breath ▁pressure ▁( called ▁" under b low ing "). ▁Some ▁modern ▁instruments ▁have ▁their ▁range ▁extended ▁up wards ▁to ▁an ▁ele vent h ▁by ▁two ▁keys . ▁C rum horn s ▁can ▁be ▁chrom atically ▁played ▁by ▁using ▁cross - f inger ings , ▁except ▁for ▁the ▁minor ▁second ▁above ▁the ▁lowest ▁note . ▁ ▁D ifferent ▁sizes ▁Because ▁of ▁the ▁limited ▁range , ▁music ▁for ▁cr um horn s ▁is ▁usually ▁played ▁by ▁a ▁group ▁of ▁instruments ▁of ▁different ▁sizes ▁and ▁hence ▁at ▁different ▁pitch es . ▁ ▁Such ▁a ▁group ▁is ▁known ▁as ▁a ▁cons ort ▁of ▁cr um horn s . ▁C rum horn s ▁are ▁built ▁in ▁im itation ▁of ▁the ▁vocal ▁quart et ▁with ▁sop rano , ▁alto , ▁ten or ▁and ▁bass ▁as ▁a ▁family , ▁as ▁was