Hi Helge,
I think your measurement setup makes sense. You could leave out the initial delay and level adjustments, and just set SMAART delay finder using an on-axis measurement of the deepest driver - usually the horn. Then delay and level adjustments can be done in FIR Designer M as part of the overall preset design, after averaging.
Regarding averaging, I tend to not time align all the measurements to the reference, and then I do a complex averaging for each driver, but I generally work within modest coverage angles (+-45 degrees). It's worked for me in the past but might not work as well for wider angles. Re normalisation, I usually apply a common gain to all measurements across all drivers, so that the bulk level differences between drivers are maintained for FIR Designer's "Gain/Polarity/Delay" tab.
(For horn reflection correction, I'd suggest time aligning all to reference and then doing a complex average. This averaging should tend towards isolating complex, angle-invariant aspects of the horn.)
I think Mark's approach with SMAART - if delay finder is adjusted for each measurement - is analogous to time aligning all to the reference in averaging.
I'd recommend taking a look at FIR Designer M's "supplementary responses." Here sets of measurements for each driver can be loaded, matched and plotted with all gain/polarity/delay/IIR/FIR processing applied. The combined response, across all drivers, is also shown. With this feature you can work on the tuning with on-axis driver measurements, and simultaneously view the processed, combined response for many off-axis directions.
Related this, I'm working on another tool that shows polar and balloon plots of the acoustic sum of the driver measurements with processing applied. With this it's possible to see how the processing/crossover works across many angles and check the average of the combined acoustic response (with processing). I can't say when it will be ready.
Best,
Michael
Hola!
I’ve just gotten a copy of FIR Designer to start playing with FIR options for a 3-way line system I’m working on. I have a couple of questions.
Firstly, reading this thread, am I right in thinking that I should leave the relative driver levels and timing differences intact, and address these while making the preset?
If this is true, what’s the best practice for capturing measurements using Smaart? The big uncertainty is whether I should be capturing using impulses or transfer functions!
Using transfer functions, I only get good phase data if the delay finder is precisely set. However, I’m not sure how to approach this.
If I use Smaart’s delay finder for my initial 1m, on axis measurement, then moving the mic away for further measurements messes up the phase as acoustic group delay increases and isn’t accounted for.. Does this mean I should reset the delay finder for each listening position?
Should I use delay finder on the earliest arriving driver (in this case my HF driver), and leave it untouched when measuring MF and LF, so I’m capturing the relative timing and the phase rotation the longer paths cause?
In the quoted post you suggest measuring to the longest path, but this seems counter-intuitive to me as my shorter HF paths will then arrive early! Maybe this is just about the way the graph looks and doesn’t really matter?
Is there any guidance on using the moving mic method in a way that doesn’t get messy as the distance to the driver causes changing delay times? I don’t see an obvious way to move closer or further from the speaker without the transfer function getting messy. Is it necessary to move in an arc with consistent distance from mic to driver, but changing on or off axis?
