When connecting a 4 ohm amplifier to an 8 ohm cabinet, the amplifier will work harder to produce the same amount of power as it would if it were connected to a 4 ohm load.
This can cause the amplifier to overheat and become damaged. Additionally, there may be a decrease in sound quality and power handling, as the amplifier is not designed to work with an 8 ohm load.
It is generally recommended to use an amplifier and cabinet with the same impedance rating or to use an impedance-matching device to ensure that the amplifier and cabinet are properly matched.
However, it is possible to connect a 4 ohm amplifier to an 8 ohm cabinet, but it’s not recommended for long-term use, because it can cause damage to the amplifier.
If you have to use it temporarily, you should be aware that the volume and power handling will be lower, and you should also be prepared to keep an eye on the amp temperature to avoid damage.