Display MorePilotltd quoted the Mesa CabClone manual as saying:
It may be "acceptable" from a "you won't blow anything up" standpoint. It doesn't necessarily mean you will get a good profile if you cut this corner.
Consider that if it doesn't change the interaction between the amp and cabinet, why not just make one Cabclone with 16 or 8 ohm specs, and a second with 8 or 4 ohm specs. Why bother making a 4 ohm unit? Somehow, it seems that there must be a difference. Or is the end user supposed to expect that using a 16 ohm Cabclone with an 8 ohm cab will give the exact same result as using an 8 ohm Cabclone with an 8 ohm cabinet?
My Mesa 20/20 amp comes with outputs for all three standard nominal impedance specs. I know that I can plug a 4 ohm cab into an 8 ohm output. It will not sound the same as using the 4 ohm output with the 4 ohm cab.
If I'm going to the trouble of doing Direct Amp profiling, I don't want to chance altering the result by cutting corners. I'm no expert. This is just my take on the subject of this form of profiling.
Scratch17
http://www.leo.ne.kr/data//101…705_active+direct+box.gif
look at above picture - you have untouched part of the signal going from the amp to the cab. What is you take is only Ac voltage from the connection of this two(Input to output).
There is a pot - you can regulate a Ac signal amplitude with this. So basically 22k resistor and 1k Pot is a voltage divider. So it is no matter how many watts you deliver to the cab you can set by this divider desired signal amplitude from the DI output.
From what you are writing you do not understand that when your cab has lower impedance then the output impedance of the amp you have lower signal in Volts so you can't destroy a DI. But if you connect larger impedance to the low impedance output your signal become larger and can destroy the DI IC's. I think such Di is bad projecting example.
You can always protect IC from over-voltages by Zener diodes.