Thoroughly confused building an active crossover


2019-09-19 7:29 pm
I would like to try making my Klipsch LaScala speakers both time and phase aligned by replacing their passive crossover with an active digital crossover running in a computer.

Here are the components I already have that I would like to use:
1) Klipsch La Scalas (2 speakers, each 3 way)
2) A Mac mini, ideally running OSX, but also willing to run Linux, and reluctantly willing to run Windows.

I am planning on getting a cheap second hand MOTU firewire interface, that would give me an 8 channel DAC.

I'm usually pretty good at googling stuff, but this topic leads to so many old and obscure pieces of hardware and software that I have no idea where to start.

Here are some questions:

1) Which is the most sensible calibrated microphone to buy to measure the frequency response, time alignment & phase alignment of my drivers? Should it be a USB microphone plugged into the computer, or an analogue microphone plugged into the MOTU?

2) Which is the most sensible software to use to:
- Predict & test crossover settings?
- Gather the info needed to time align my drivers?
- Gather the info needed to phase align my drivers?
- Perhaps even gather info needed to do room correction?

3) Which is the most sensible software to use to perform the crossover/time & phase alignment/perhaps room correction in real time over 6 channels?
- Do I create a static convolution file that a program like HQplayer uses?
- Do I run my audio through a piece of software that does all the DSP and outputs 6 digital channels to the MOTU?

4) How do I convert the measurements gathered in step 2 into settings used in step 3?

5) I know quite a bit about good stereo amps, but I don't know much about the most sensible, most bang-for-buck way to tri-amp my speakers
- 6 identical mono amps? Which ones?
- 3 identical stereo amps? Which ones?
- A bigger amp for my woofers, smaller for my mids and tweeters? Which ones?
- A single multi-channel amp? Which one?

Any suggestions on where to start would be much appreciated!
Hello ebrandon,

There are a couple of commercial software packages that allow you to create digital XO's, time align drivers, optionally driver linearization, and room correction (i.e. global eq and excess phase correction). These are Acourate and Audiolense. I have used both to tri-amp systems with some walkthroughs on how to do it:

Advanced Acourate Digital XO Time Alignment Driver Linearization Walkthrough - CA Academy - Audiophile Style

Integrating Subwoofers with Stereo Mains using Audiolense

There is a non commercial product that works with REW called rePhase: rePhase - Official Site - Free FIR filtering tool

Yes, you would host a convolution file on your PC that convolves the music in real time with the static FIR filter and output 6 DAC channels to 6 channels of amplification.

Note the software packages for designing the FIR filters are PC based. However, the generated FIR filters can be hosted in a standalone VST convolver or music players with convolution on both Mac and PC or BruteFIR on Linux.

Make sure the measurement microphone is calibrated like: Cross·Spectrum Labs - Sound | Vibration | Engineering
USB is more convenient, and the aforementioned software will work with it, with a few hoops to go through to take care of the two clock problem. If your Motu has a mic preamp, then I would go this route and avoid any timing issues, especially if you want to time align the drivers. Which for the La Scala's (beautiful!) is going to make a big difference given the z offest of the drivers involved.

Amps - higher power on the bass, low power and low noise for the mid and tweet compression drivers. Some thoughts here on low power amps: Low Wattage, Low Noise Amplifiers

Lot's of reading there should get you started. And yah, totally worth it :)