OT/Speaker impedance mismatch

[Rob11966]

Hi Folks,

With respect to OT and speaker impedance matching, I understand why you might damage your OT with a speaker impedance rated higher than the OT i.e. a 16 ohm speaker connected to a 8 ohm tap but is the reverse a problem?

For example, can running a speaker with a lower impedance rating than the OT (say a 8 ohm speaker on a 16 ohm tap) damage the amplifier, specifically the OT?

This is a question in theory only. I am asking because a friend at work put the question to me and I could not give a really conclusive answer. An internet search seems to indicate probably not but I was wondering if anyone has any definitive response?

Rob

[Tom Bavis]

You won't cause any damage with a 2:1 mismatch in either direction. But you will have less undistorted power output. The damping factor will change with speaker impedance, which may affect the sound with some speakers.

[DF96]

Damage is only likely if the load is much higher impedance than it should be. This can cause excessive voltage at the anodes.

It is also just about possible that a heavily capacitive load could make the amplifier oscillate - depends on how near instability it is anyway.

[ChrisA]

Originally Posted by Rob11966

..
For example, can running a speaker with a lower impedance rating than the OT (say a 8 ohm speaker on a 16 ohm tap) damage the amplifier, specifically the OT?...

a mismatch by a factor of two is not a big deal. Speakers are never running at their nominal impedance and a 8 ohm speaker might be 20 ohms at 4,000 Hz.

No speaker connected at all is an infinite impedance and this can damage the amp, but some amps can take it, others will smoke.