Cool XR57 bi-amp feature?

[Lindahl]

I recently started the Zaph ZP5 thread, because I want a slim floorstander with good bass extension, but didn't want the tweeter he had chosen. Finding out how complicated it was to design a good crossover, I thanked everyone for the advice and began what I thought would be a long stint of reading.

So I was doing some research and found this nice link that provided a good primer on LR crossovers. Basically, saying that a LR4 crossover provides an ideal crossover, providing you can time align the HF and LF drivers. It was then that I vaguely remembered about a bi-amp feature of the Panasonic XR57: time delay. Basically, you tell the receiver the distance between the LF and HF drivers, entered in .5" increments, and it applies the proper time delay to get a phase correct response. Any thoughts about how useful this is? Is .5" increments enough? The older XR55 provides .36" increments, if that helps. Granted, I'd have to measure it, but theoretically? The XR57 obviously allows you to balance the SPL between the HF and LF, so I shouldn't need to add attenuation filters, either.

So basically, can I take a LR4 crossover at a good frequency for my drivers, add the right delay and LF/HF balance using the XR57, add the right Zobel filter for the LF, set up a decent baffle and then, build it, measure the response, and then correct the rest with notch filters, as necessary?

Also, another question. I was thinking about routing a inverted radius into the tweeter face plate to reduce the distance between the tweeter and woofer. This allows me to get a better vertical off-axis response at the crossover point, right?

Oh, one more question, how do you find the final nominal and minimum impedance of the speaker? Any way other than a measurement? I assume it's not a normal parallel impedance calculation, because that completely disregards the crossover network and would mean 2.6 ohms. :E

Here's a snapshot of the XR57 manual, describing the bi-amp options:

[cjd]

So basically, can I take a LR4 crossover at a good frequency for my drivers, add the right delay and LF/HF balance using the XR57, add the right Zobel filter for the LF, set up a decent baffle and then, build it, measure the response, and then correct the rest with notch filters, as necessary?

You can do whatever you want. Delay is not usually a problem to integrate into the crossover - in fact, it's there inherently in the measurements when they're done right. And, as for the rest of the process you describe, still yes... if you feel like it. No guarantees on results.

Far simpler to figure out baffle (use the modeling tools to get box size and diffraction - you'll need to have some understanding of what kind of series impedance you're likely to need to get box volume *just* right but...), build it, measure it, work up a crossover in a modeling tool and adjust.

Also, another question. I was thinking about routing a inverted radius into the tweeter face plate to reduce the distance between the tweeter and woofer. This allows me to get a better vertical off-axis response at the crossover point, right?

It allows you to cross higher/shallower without center to center troubles.

Oh, one more question, how do you find the final nominal and minimum impedance of the speaker?

Measure it. However, for a quick notion you look at the driver or drivers on each leg of a crossover - the lowest sum is likely to be close to the nominal impedance. So, 2 8ohm mid-woofers and an 8ohm tweeter, parallel the MW's for 4ohm, my nominal is 4ohm.

C

[Lindahl]

You can do whatever you want. Delay is not usually a problem to integrate into the crossover - in fact, it's there inherently in the measurements when they're done right.

Hmm, from the reading I've been doing, I haven't found a single source that had decent info on delays in crossovers. The rest of crossover design has been very straight-forward, so that was the only real mystery left. Can you recommend any links talking about this?

[cjd]

It shows up in phase

However, you can do ladder circuits to tweak time delay as well I believe.

C

[Lindahl]

However, you can do ladder circuits to tweak time delay as well I believe.

Also, I have read about (and seen) how time-corrected/phase-aligned circuits do so only at the crossover frequency, and they drift apart the farther you get from the crossover frequency. Is the result the same for a time-delay applied in the processing stage (i.e.. XR57 bi-amp delay)? Or does this align the phases across the entire frequency range?

[cjd]

Phase relationship is a complex subject. The phase of each driver MUST wander, at least in a minimum phase model, as it is a function of frequency response.

Digital signal processing can do all sorts of funky cool stuff. I would NEVER design a speaker that relied on a piece of electronics that wasn't a permanent part of the design - so, phase? Make it a digital crossover OR built it into a more traditional active filter OR passive... but dependent on a specific amp? It may work, but that's asking for trouble IMHO. A one-off effort at best. So absolutely something you can pursue, and it may well be quite an interesting effort. Experiment with it at the very least just to LEARN what it changes.

C

[Lindahl]

Phase relationship is a complex subject. The phase of each driver MUST wander, at least in a minimum phase model, as it is a function of frequency response.

What is a minimum phase model and how come the phase must wander with frequency response? I thought only the period was required to wander (obviously). Rather than you explaining it, links that I could follow up to explore this would be great. I just haven't been able to find much information on this subject.

...dependent on a specific amp?...

I hear what you're saying. It's more of an exploration, for me. Allows me to test different phase offsets and LF/HF balance to see how the differences affect the plots and the sound. When the electronics fail and no replacement exists, I assume that I could always spend some time adding to the crossover to get something sounding comparative.

Thanks!