I came across this reply from Tom Danley regarding crossover design and I thought you might find this interesting:
Joined: July 4, 2002
I can explain a bit more about this.
When you model any passive crossover and you sum the high and low outputs to get the result, the ideal is flat response.
If one looks farther into it, one also finds that the phase of that sum appears NOT to be one new output as if one source but to be that of an all – pass filter. An all pass filter has flat magnitude response BUT is not minimum phase, that is, there is a change in phase which is independent of a change in amplitude as a minimum phase relation has.
If one examines that phase as Group delay plot (the difference in time of one groups of frequencies vs another), one finds the low pass part of the filter is always behind the high pass in time.
All conventional crossovers above first order, cause the hf and lf portions to be separated in time, that is normal operation and is one reason why most multi-way loudspeakers do not preserve the harmonic time relationships or are able to reproduce a wide band waveform like a square wave in more than one location or frequency.
What I was explaining was that for all of our Synergy horns at work, I have been able to devise filters which take advantage of the fact that the drivers are not conventionally aligned, the tweeter is rear most and woofers most forward. That physical location allows a passive filter that sums without the all pass response and so looks like one single driver in time instead.
An indicator of preserving time is that one like the SH-50, can reproduce a square wave over a decade wide bandwidth spanning both crossovers and not just in one special spot. It’s not quite as good in time as the Manger driver I measured but it goes about >+40dB louder.
Anyway, I was suggesting to Freddyi that he look for those drivers because the hf driver is already behind the woofer AND there is only a small acoustic discontinuity where the hf horn couples to the cone as the horn. About 8 years ago I had designed a number of speakers for work that used it because one can make it sum into one source in time.
As the crossover in a real speaker has to not just sum properly but to sum it’s magnitude and phase plus the individual responses and phases of each driver and that fixed delay cause by location, it is not a text book job or filter.
Fwiw, if you’re interested in this stuff, you can look up “the man” who discovered the time aspect and developed a way to measure and describe it. He unfortunately passed away more than 25 years ago but his writings, his measurement system and my one single meeting with him have changed my audio life. Look up Richard Heyser and his work on loudspeaker arrival time and so on.
While we don’t sell any hifi speakers (I have been unable to interest my partner in that market in light of the growth of the sports stadium area) but when you can make a single source in time and space with constant directivty on a large scale, it sounds very different and much better than concert arrays and you can even hear that on an hand held camera video.
Here is a camcorder video of the first public demo of a J-3, used in large installations like the Michigan state football stadium (which uses 3 per side).
Its hard to tell how loud it was until you scale the volume when the operator walks up and talks to the guy holding the camera. As this was for a bunch of stadium sound people, at one point you can see them standing out in the field at about 400 feet.
There is a nice video of the first installation those were used in, taken from 700 feet. If you have ever head a large stadium sound system, even with headphones you can hear the difference. There are three of them per side and only at one end of the stadium. Normally the wind and sound quality both would be a huge problem with the array system, here the wind is hardly detectable.
Some places these new Synergy horns have already been installed (all replacing well known concert sound style pa’s and gear);
Anyway, my partner might be willing to let me supply a synergy style crossover for the B&C driver.
I will ask him today if he’s around.
Danley Sound Labs