Re: Dual Channel FFT
Hi,
I will go through the procedure for dual FFT when I use Praxis.
We will measure a 2-way box with a passive crossover.
Praxis comes with two “Probes”. This is a cable with a high impedance resistor in the cable. For convenience the ends have mini-alligator clips.
For our first input attach one probe to the speaker cable at the back of the power amp.
This will be the “reference” signal.
The other input of our “DUAL FFT” is from our measurement microphone.
So whatever comes out of the power amp gives us a reference, be it pink noise, chirp, or music from the band.
The limitation when using live music is if there are no bottom frequencies because the only thing playing is a flute, you cannot measure there.
It has been found that you can add some pink noise to the music at a very low level and get a valid measurement.
Note you can buy or build “Probes” and use them with any dual FFT, such as Smaart.
They are handy cables to have around.
Another way you can use Praxis and LspCAD at the same time.
You need two computers with good soundcards.
LspCAD can let you hear your speaker with the crossover you have designed even though you have not built a physical crossover with caps and coils. It is called “emulation”.
From the sound card that Praxis is using feed the test signal from Praxis (Chirp?) into the sound card you are using for LspCAD.
Here is the tricky part.
We have a 2-way speaker with two drivers. In the model add a third driver that is just a flat line. Adds or takes away nothing.
This is our reference point.
What it does for us is it goes through exactly the same digital latency as all the other drivers go through. So we have a measurement that is correct for flat delay and phase.
Hi,
I will go through the procedure for dual FFT when I use Praxis.
We will measure a 2-way box with a passive crossover.
Praxis comes with two “Probes”. This is a cable with a high impedance resistor in the cable. For convenience the ends have mini-alligator clips.
For our first input attach one probe to the speaker cable at the back of the power amp.
This will be the “reference” signal.
The other input of our “DUAL FFT” is from our measurement microphone.
So whatever comes out of the power amp gives us a reference, be it pink noise, chirp, or music from the band.
The limitation when using live music is if there are no bottom frequencies because the only thing playing is a flute, you cannot measure there.
It has been found that you can add some pink noise to the music at a very low level and get a valid measurement.
Note you can buy or build “Probes” and use them with any dual FFT, such as Smaart.
They are handy cables to have around.
Another way you can use Praxis and LspCAD at the same time.
You need two computers with good soundcards.
LspCAD can let you hear your speaker with the crossover you have designed even though you have not built a physical crossover with caps and coils. It is called “emulation”.
From the sound card that Praxis is using feed the test signal from Praxis (Chirp?) into the sound card you are using for LspCAD.
Here is the tricky part.
We have a 2-way speaker with two drivers. In the model add a third driver that is just a flat line. Adds or takes away nothing.
This is our reference point.
What it does for us is it goes through exactly the same digital latency as all the other drivers go through. So we have a measurement that is correct for flat delay and phase.
