Time Alignment

[boputnam]

...I got to thinking. The time alignment is necessary if more than one driver is making a sound at the same time.

This is a most interesting discussion...

Per the above, I cannot think of a time when that is NOT occurring. Even a single note will have harmonics octaves above the primary tone, and those harmonics will almost certainly emanate from an other element in a multi-element cabinet.

[sfogg]

Al,

Thats cool that it can be done actively too.

The sub crossovers in my pre-pro are done via DSP. So literally for Lexicon to implement a very high order crossover would be for them to write the code to do that assuming they have the DSP cycles and such needed.

Shawn

[sfogg]

"Per the above, I cannot think of a time when that is NOT occurring."

I think Al meant when two drivers were reproducing the same frequency sound. With Al's crossovers the harmonics would still be nearly entirely reproduced by one of the drivers unless the sound was right at the crossover point.

My ES crossover cross at about 600hz. There is only about a 50hz band where the drivers aren't more then 10dB down relative to each other.

Shawn

[Al Klappenberge]

Bo,

Shawn is right. The harmonics are simply the componenets of a complex waveform. The crossover will simply direct them to the appropriate driver and ONLY that driver.

Al K.

[Mr. Widget]

I think we all agree that having all drivers reproducing part of a note (a note being a group of frequencies made up of a tone and it's harmonics) will be best if time aligned. Just how audible this may be is certainly up for debate.

Here is an excellent example of what Al is talking about. It is from recent work we have been doing with Project May. In this example we are changing the configuration below the crossover point. The crossover is a low order passive design at 800Hz. As you can see changes in the woofer configuration cause changes in the frequency response as high as 3200Hz! The significance of this is that for every frequency on either side of 800Hz (for at least 2 octaves on either side of the crossover frequency) both drivers are reproducing the same frequencies.


Blue is MTM.
Red upper woofer disconnected and replaced with resistor.
Green lower woofer disconnected and replaced with resistor.

[sfogg]

"The significance of this is that for every frequency on either side of 800Hz (for at least 2 octaves on either side of the crossover frequency) both drivers are reproducing the same frequencies."

Another test a person can do to hear this is to play pink noise on their system.

Then standing fairly close to a vertically aligned speaker stand up and squat down. As your position changes you will hear the interaction between the drivers as changes in how the pink noise sounds.

When you do the same thing with Al's ES network the sound hardly changes at all until you get out of the dispersion of the horns.

This is signifigant as the sound the listener hears at their normal listening position is a composite of the on axis and off axis sound from reflections within the room.

Shawn

[alskinner]

Thanks Guys

I think I finally understand what Al is saying, although there is some interaction between drivers the 120db/octave keeps the interaction between the same frequencies going to different drivers are kept to a minimum resulting in a a lot more coherent system without the smearing and phase shifts associated with lower order crossovers. Am I close?

Also it is certainly nice to have a thread where differing viewpoints can be discussed with civil discourse.

Cheers
AL

[Mr. Widget]

I think I finally understand what Al is saying, although there is some interaction between drivers the 120db/octave keeps the interaction between the same frequencies going to different drivers are kept to a minimum resulting in a a lot more coherent system without the smearing and phase shifts associated with lower order crossovers. Am I close?

By George, I think he's got it.

... nice to have a thread where differing viewpoints can be discussed with civil discourse.

Don't push it.

[Al Klappenberge]

YEP! He's got it!

Al K

[Al Klappenberge]

Guys,

Here's an accoustic plot of the actual network that Shawn is using (600 Hz) being tested in my speaker. It's a Belle Klipsch woofer, JBL 2426h driving an Altec 811b horn. The two plots show the driver wired in and out of phase. My "ES" networks acts just like 2nd order Butterworth networks in that the outputs of the two channels are exactly 180 degrees out of phase at the crossover.

Al K.

[Tim Rinkerman]

Man, I was really getting into this thread,thinking I was really learning something out of the box, and indeed I agree with all that was said...and then I went to view your home system,Al,....and please tell me that those Rane EQ's are a mis-print,or you modified(gutted) them to not make that "RAIN" sound when you insert them into the signal path!

[Al Klappenberge]

Tim,

It seems that equalizers are like cats. You either love 'em or you hate 'em! Believe me, I use them very sparingly! They are both set exactly alike and are only being used to remove a room resonance that was making the system sound boomy. They are set to mostly cut and only to boost a db or two when all else fails! I think I have two of the five sections bypassed. I learned the hard way what an incorrectly adjusted equalizer can do to you. They can drive you up the wall !

Al K.

[scott fitlin]

That would be Ed Long. He definitely broke new ground. His ideas about time alignment while ground breaking were more conventional than his "Live End Dead End" studio control room designs.

I agree with Al Klappenberge, that the use of extreme slope filters does lessen the need for time alignment significantly, but with some of the new technologies becoming available we will be able to have our cake and eat it too.

Widget

The crossovers that were used at Studio 54 were built and designed by Alan Fierstein for Richard Long in the 70,s! They did state in their brochures they had implemented " linear phase " technology in their crossovers and that it was the first time this technology had ever been used for disco playback sound systems!

I have and use these crossovers, and I can tell you his units have the clearest imaging I have heard on just about anything!

They had indeed broke new ground and succesfully outdid everytrhing else available at the time, and it still outdoes many things more modern, made today!

Of course, I might be willing to try the DEQX based on what some I respect have been telling me of the unit, and its linear phase filters!

[Al Klappenberge]

Scott,

As soon as somebody starts talking linear phase a big red flag goes up in my head! Linear phase is very easy to do in an all-pole lowpass, somewhat difficult to do in a narrow bandwidth bandpass, VERY difficult in a wide bandwidth bandpass and totally impossible to do in a highpass filter! Many desingers simply "invert" and scale out a linear phase (Bessel) lowpass into a highpass. This is what the text book Bessel crossover are. The results retain the very slopy attenuation of the lowpass but none of it linear phase properties. They are a waste of parts! The easiest wideband linear phase bandpass is called a "Blinchnicoff / Zverev" filter. I have the software to synthesize it singly terminated (which you need for a crossover) but I really doubt may other people have it! Besides, like I said, the human ear is deaf to phase relationships of components of a complex wavefore anyhow. Like I showed earlier, the linearity of the netwrok is overwhelmed by the "excess phase" contributed by the propagation delay. So I wouldn't believe any of the claims unless they were proven to me!

Al K.

[Tim Rinkerman]

OK,Al..I'll let you off this time I was a live sound guy for a long,long time and any time I came into a place that had Rane equipment in the rack,I knew I was in for a long day....I guess I mostly ran into their 1/3 octaves and eek!ametric paralizers, but when I pushed the insert button on any of them,even with no boost or cut at unity gain,it was like somebody leaked in a pink noise generator.

And I do understand what you're saying about x-over points and slopes and couldn't agree more!