A guide for digital xo, driver alignment, etc?

[beanbag]

Hello folks,

In my other thread about what makes speakers sound "big" the issue of crossover phase response was bought up over and over again. So I figure now would be a good time for me to start on my active xo project.

I have Martin Logan electrostatic speakers. The panel crossover electronics I plan to leave it place since it has protections against transformer saturation, too much capacitance to the amplifier, etc. So lets just assume it is some kind of second order HP filter.

The woofer section has an inductor and capacitor to also act as a filter, but I plan to bypass those and drive the woofer directly. I would need to program my little MiniDSP device with some kind of a second order filter to match this. Here I assume that an active xo can beat the performance of the passive one.

While I am at it, may as well do driver time alignments too.

The equipment I have is:
MiniDSP nanodigi. That means I can do IIR filters only plus digital delays.

Umik-1 USB microphone AND
Radio Shack SPL meter which sorta acts like a microphone for lower frequencies. I read that you can't do driver alignment with a USB mic due to no loopback, but I have seen somebody do it by purposely delaying the woofer by 1ms, and then observing the gap. Or I could just use the Radio Shack meter with a kind of loopback configuration.

Anyway, does anybody know of a guide on the internet that gives a good overview of how to do these procedures with something like Room Equilization Wizard, or maybe HolmImpulse, or whatever. And especially with respect to how to choose and optimize filters, what features to look for, etc. Or you could help me here, but I have a lot to learn.

Also:
If I have a woofer and big electrostat panel, where am I supposed to place the mic?
Should I add extra orders to both HP and LP filters to make it steeper?

Thanks

 

[jtalden]

HolmImpulse is friendlier to use for phase alignment purposes than REW. Its interface controls makes the job easier. With its timing lock feature there is no need for the "loopback timing" necessary in REW. I haven't used it with a USB mic, but would expect it to work.

I would suggest the XO LPF be selected to provide the best; phase tracking, driver protection, and SPL smoothness rather than some specific type. The But12 may be a good choice but was chosen based on the constraints of the passive XO implementation. There may be a better choice or other good solutions that you can listen to and choose from.

I do not have a link to a step-by-step (maybe someone else does), but would be willing to help you with the process.

 

[Juhazi]

Here is rather good advice for REW, actually the best!

miniDSP tutorials

Start with "subwoofer integration" but please read all of them.

When you have accustomed to making measurements, make just one change at the time then measure and listen! This way you will learn what each change really does and you find your own way and preference. Then ask friends to come over listening too!

 

[Juhazi]

Here is a link to a thread about crossover phase integration, we see some well respected names... Third Order Transient Perfect Passive Crossover - Page 4

I still want to remind that we must look at the acoustic response of each driver first. Make them symmetrical. Then adjust crossover points so that individual slopes overlap by book. Then adjust delay by the inverted polarity method to set time alignment at your preferred point (be aware of reflections, this is best performed outdoors)

 

[jtalden]

...Also:
If I have a woofer and big electrostat panel, where am I supposed to place the mic?

If you use your normal speaker positions you can just place the mic at the LP.

Should I add extra orders to both HP and LP filters to make it steeper?

That is one of the options.