[Argus25]

One really easy and effective way to get back around the issue with radios with high impedance speaker outputs, is just get a donor transformer with a 1/2 inch square core cross section or a 3/4 square section (something out of an old plug pack/wall wart is fine or some other speakers transformer) and rewind it to be an autotransformer, around 500 turns total and simply put a tap on it to suit your speaker remembering the impedance ratio is the square of the turns ratio. Typically the wire diameter would be in the range of 0.25 to 0.35mm.

This way you get the impedance match correct and you won't have any issues with the frequency response and it will be flat. I did this to match a 32 R speaker to a 100R output on a Zc1 radio