Someone please help me with transistors because I’m going crazy

I want a simple circuit I have 9v going into the transtor and when it detects 3.5v from arduino it powers a speaker with 9v. I tried pnp and npn I used chat gpt and google and it’s not working. Right now I’m trying a bc547b npn transistor.

I have the emitor connected to gnd shared with arduino and 9v battery gnd

My base is a pin 7 that outputs pwm(it works without the transistor)

My colector is connected to the negative speaker terminal

My positive speaker terminal is connected to the + of 9v battery

My multimeter measures that On collector it’s 6v and not 9v