Rational Acoustics

December 10th, 2014, 09:31 AM
I have a DSP power amplifier that I would to determine the transfer function, so that I can copy the preset to another DSP without the power amp. Can I do it with the transfer function mode of Smaart and my audio interface? How can I connect the output power of the amplifier to the input of the audio interface?

Thanks in advice

Arthur Skudra
December 10th, 2014, 04:56 PM
Depends on the audio interface you're using, you don't want to blow it up with excessive voltage on the input. I would think you either run the power amplifier at a very low output level and suffer with added noise floor in your measurement, or build yourself at least a 40 dB pad to be able to measure at higher output levels, maybe a 50 or 60 dB pad would be better. Here's an excellent resource for making your own pads:

December 11th, 2014, 01:27 PM
I would think measuring with the volume way down low would introduce the noise and poorer distortion that most amps exhibit at their lowest volumes. A "power resistor" across the amp output should also work as well as the pad approach, and then connect your analyzer interface. **But why measure the TF of the DSP inside the amp? Wouldn't what you're after be the result of the amp AND a speaker array in a room, as far as dialing in something usable on the second DSP unit? Not sure what the goal is, but I could be missing the point. Power resistors available at Radio Shack.

February 24th, 2015, 12:15 PM
You can't use a "power resistor" as the voltage will be the same as your amp output since the resistor will go in parallel to your input. I have a comercial available pad called VI Box (by linear X system) which I use among other things to get the TF out of DSP amps. It is a 40dB pad that have XLR outputs for you to connect to your interface.

The main use of it is to measure impedance loudspeaker's impedance curves, but if you only use the "voltage" output is simply a 40dB pad.

I hope this helps.


March 16th, 2016, 04:33 AM
Hi, Gluis

I read your posts carefully. I have a question.
I bought VI box recently. when you measure impedance , do you use [I] Current XLR output of VI box?