Ok gurus,
I have a 1x12 with horn (not tweeter) cab that is 8 ohm.
I happened across another 12 driver that is same spec but 4 ohm.
I would like to switch them to get the full wattage out of my nano head.
How will the passive crossover (no horn pad or control) be affected,
if at all, by this change?
Thanks
To hear a noticeable difference you need to increase SPL by 3dB. You get a 3dB increase by doubling the power.
Usually amps do not double power when you switch the load from 8 to 4 ohms. Some do, but it's rare.
Often 4 ohm drivers are slightly less efficient than 8 ohm drivers, so you may not gain any perceivable SPL from the switch, even if the amp doubles it output when you change the load to 4 ohms.
Better to get a second matching cab. Then you get the benefit of extracting the max power from the head and also the benefit of mutual coupling between the cabs.
If you have two identical speakers playing at the same volume you get near perfect coupling in the frequency range in which cone spacing is within approximately 1/4 wavelength. This results in an SPL bump of approximately 6dB across in the low end.
Keep in mind the power is split evenly between the two speakers. If the amp power remains the same when you connect the second speaker, the SPL of the first speaker will drop 3dB because the power being shared equally. The SPL of the second speaker will match the first speaker. Then the SPL will be boosted +6dB in the low end from mutual coupling. This basically means you will get at least +3dB when you add the second speaker.
If the amp can make more power due to the lower impedance, you also factor in the dB change that results from the extra power.
If you have one of those special amps that can double the power when the load changes from 8 to 4 ohms, then you get the full +6dB. Basically when you connect the second speaker the power is doubled and then split evenly between both cabs. Since the first cab continues receiving the same level of power it continues putting out the same SPL and the second cab will match the first. Then you will get approximately +6dB in the low end from mutual coupling.
Here's the Rule for Speaker Doubling.
With tube amps the max output is always the same as long as the amp sees the expected load (I.E. no impedance mismatch). Adding a second matching speaker gives you +3dB
Solid state amps may make anywhere from the same, to double the max output when you add a matching cab. Adding a second matching speaker gives you +3 to +6dB. Avoid connecting a load that is below the minimum that the amp is rated for or it will most likely damage the amp or cause it to go into protection mode.
One final thing to consider. If you change your speaker to the minimum impedance you amp can drive, you can no longer use an extension speaker.
