For recording and live performance a common practice is to place a microphone very close to a guitar speaker cabinet and connect the output of the microphone to a recording device or a mixer.  This approach has several problems.  First, it requires using large and heavy speaker cabs.  Also, the results can be somewhat unpredictable due to technique and bleed-through from other instruments.

 

A speaker emulator DI load box can be used instead of a speaker cab and microphone to take the speaker-level signal directly from an amplifier and output a signal than closely mimics the sound of the closed-miced cab.

 

I purchased several speaker emulators and found that they all had some limitations.  All of them either didn't sound like a speaker cab or had too little control over the sound.  Also, the ones with an internal dummy speaker load required the purchase of a different unit for each impedance (4, 8 or 16 ohms).

 

I designed a filter circuit that  matches the frequency response of a typical 12" guitar speaker.  I also  designed a dummy load that matches the impedance vs. frequency characteristics of a typical guitar speaker.

 

Finally I added two controls to provide control of the tone.

 

I think the result is a speaker emulator load box that can replace a speaker cab and microphone without sacrificing tone.  I hope you agree.

 

Kim Hardee