This thread applies to the roll-your-own crossover / DSP / LMS situation for bi-amp wedge owners. In my case, I picked up some used 15" units from a nearby regional provider.
I'm looking for comments on measurement mic placement, and am interested in comparing the relative merits of placing the measurement mic:
- where the performer's head would be, as contrasted with
- alternate arrangements whereby the meas. mic is placed on the floor / ground.
Topics which I'm hoping to see in this discussion of wedges as the D.U.T. (Device Under Test), are covered in Mark Frink's article
- Half-Space coupling of the wedge with the floor. (160 Hz area)
- Baffle loading & directionality of LO driver (300 Hz area)
- Use of wedges in pairs (1000 Hz area)
Also, it'd be great to see comments touching on:
- Quasi-Anechoic technique of time-windowing, as it applies to a D.U.T. so close to a nearby reflecting surface, that it's touching it (namely, the floor), and
- the obvious "weirdness" of elevating a floor wedge to an "above floor" position - done merely to achieve a measurement setup in which the meas. mic is placed on the floor / ground, and/or the D.U.T. is far enough away from a nearby surface such that quasi-anechoic time-windowing makes clearer sense.
So far, I've only conducted T.F. measurements by placing the wedge in the "as-used" position on the floor, and the meas. mic was at performer's head height, aiming down at the grill.
Propagation delay found, based on the HF driver (muting the LO), and used for T.F. measurements, I ran another impulse measurement on the LO to obtain an initial delay value to employ in the MiniDrive LO band.
I proceeded to apply gains, and some filtering, in both bands, to achieve a magnitude response picture suitable for identifying the acoustic crossover point.
Moving to the goal of achieving phase alignment through the crossover region, I captured a new T.F. trace of the (now) EQ'd HF driver, and proceeded to dial-in / fine-tune the LO delay by lining up the phase traces at f=acoustic x-over.
A 0.417 ms delay applied to the LO did the trick.
- Electronic X-Over: f = 1.14 kHz (L-R 24)
- Acoustic X-Over: f = 1.4 kHz
With both bands un-muted, it was very satisfying to sanity-check matters by reversing the polarity on one band, and observe a deep valley in the magnitude response at the crossover point.
P.S. Kudos to Rational Acoustics; I'm enjoying the demo version of Smaart v7.4. (... 3 cheers for Object-Oriented Programming!)