Time Alignment

[Al Klappenberge]

Alskinner,

I am going to modify what I said earlier. After some private message discussion with Mr Widget, I got to thinking. The time alignment is necessary if more than one driver is making a sound at the same time. Unless you have extreme-slope networks to see to it that only one at a time is sounding, you will need to time align with such a long horn! My thinking is getting biased by the extreme-slope idea and I forget about the vast majority of systems using networks with only 6, 12 or 18 dB / ocate slopes!

Al K.

[alskinner]

I am grateful for all input into the system I am proposing to put together. It becomes a lot more difficult to put drivers together in a configuration that has probably not existed before. The good thing is there is a good bit of information from JBL on the 2445J/2360 combination and the Altec A7 bass horn. Getting them to play together nicely takes a lot (at least on my part) of research and planning. Having said that right now I am not sure if I will keep the 416 drivers in the A7 or opt for one of the JBL woofers such as a 2225 which will bring about another variable. The time alignment issue just popped in my mind as one of the first things to work out because of the midrange horn and the other drivers.

It was somewhat easier to modify the 4345 using the 2397/2441 based on the known cabinet dimensions and the excellent posts on building the 4345 from Ian Mackenzie and others. Also using a good quaility electronic crossover like the ASHLY 4001 helped eliminate the construction of a passive crossover. Even with that it took a lot of amp juggling to get in place the best amp/driver combination out of what I could afford and already had.

Al
I am glad to see people like you working with the classic Klipsch designs. I have heard some great Kliipsch speakers in my time. I think a lot of Klipsch bashing comes from people not being able to set them up properly and some of the design characteristics that need updating. One of my fondest memories of Paul Klipsch is a picture of him creating some of the first designs out of plywood in the garage of his home. Don't have the picture now, but I remember saying to myself, this guy has got the guts to follow what he believes in.

As far as the Altec A7

I great theater speaker in it's day. However in a home setting most would agree the sound of the upper end is anything but HiFi. I know several people that have attempted to modify the existing system through crossovers and equalization and a lot of them ended up throwing their hands up. Even though the Bass Cab is only good down to 40-50Hz, it has unique sound that is hard to replicate in anything but a bass horn.

Thanks for letting me rant on. One thing I do know is a need to get some test equipment together to be more accurate in the questions that I am asking

Again thanks to all of you.

[Al Klappenberge]

Al,

I have been around the L-C filter design world for quite a few years and I
have never seen a passive filter that will give time delay on the order
necessary to time align even to a very small degree. I can easily design
group delay equalizers (all-pass filters) that can yield a big group delay
peak someplace, but that is useless! Group delay and time (propagation) delay
are two different things. All-pass networks will NOT do it! To really time
align you need a digital delay device and multiple amps. All this costs money
and you still can't get two drivers in alignment except at one spot in the
room. This cuts down the multipath "smearing" but can't do much for the
"lobeing". An extreme-slope passive network, though expensive because of its
parts count, will make the time alignment problem a moot point and will allow
you to do away with the active crossover, delay circuits and multiple amps.
You would need a calculator to add up all the equipment costs to figure which way would cost less!

I would like to do a set of extreme-slope networks that could be used in a
classic Altec speaker, like the A7, just to illustrate the point. I would be
happy to do the design just for the fun of it if I can get together with
someone who has a set he wants to modify. If your project is using drivers
that are common to a lot of the Altec speakers, it might be a good candidate.
The most important consideration is the woofer driver. I like to design the
woofer / squawker crossover to incorporate the woofer voice coil inductance
right into the woofer filter. That makes the network woofer-specific to some
degree.

Al K.

[alskinner]

Found a pretty good site for the layperson or those just beginning in electroacoustical theory.

http://www.lenardaudio.com/education/06_x-over.html

Although not real technical it does give a pretty good explanation of basic crossover theory and time alignment. as pointed out on the site one of the original uses for time alignment was for auditoriums where alignment would have an effect on the overall sound.

Thanks
AL

[Al Klappenberge]

Alskinner,

I looked at your link briefly. Needless to say, I don't agree with their warnings against complexity. This is what I call "conventional wisdom". I believe it's derived from years of experinece by people who know speakers but have had no experience with complex filters. I believe Paul W. Klipsch is an example. A bad complex filter will yield bad results. This conventional wisdom comes from the days of "image parameter", "constant-K" and "m-derived" techniques. You can't make a good high order filter that way! I want to prove my point by actually building extreme-slope crossover netwroks and have people listen to them. So far every set I have built listeners have confirmed what I have been saying. Here's an example: http://forums.klipsch.com/idealbb/vi...4-622FBEB3365F}

AL K.

[alskinner]

Al

I agree with you on the part about the site being filled with "convential techniques" as I meant it as a link for just basic understanding. After all the creator of the site is also a speaker system designer and I am sure some of his bias is because of the products he designs and sells. People like yourself, Mr Widget, Earl K, Giskard and Ian Mackezie and a host of others on the forum are way beyond the basic theories , just thought it would be a good starting point with people with no or very little experiance. Thinking outside the norm is what makes for new innovation and techniques. After all crossovers wether passive or active qre one of the main things make or break a great speaker system. Complexity shouldn't be an issue if the results desired are reached. I can't remember the guys name but he built a lot of the crossovers for places like Studio 54 and people will pay thousands of dollars for a set of them, comming as far away as Japan. I am sure he was another guy that went against the theories of the day


Cheers
AL

[Mr. Widget]

I can't remember the guys name but he built a lot of the crossovers for places like Studio 54 and people will pay thousands of dollars for a set of them, comming as far away as Japan. I am sure he was another guy that went against the theories of the day

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

[Ian Mackenzie]

Wasn't it one of the Sheffield Lab owners that offer'd new crossovers for the 604-8G Altec Duplex?

Ian

[Mr. Widget]

Doug Sax, founder of Sheffield, started the ball rolling.

[sfogg]

"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. "

Sure, the DEQX box would let someone cross over as steep as 300 db/octave AND allow time alignment between drivers along with other processing but that is a $3k box and of course you need more amps with that too. And for those of us with three speakers up front we would need two of them. Gets very expensive.

I'd love to use the DEQX box but Al's crossovers worked out very well in my setup using an Altec 902/511B on a LaScala bass horn.

Shawn

[Mr. Widget]

....but Al's crossovers worked out very well in my setup using an Altec 902/511B on a LaScala bass horn.

Hard to argue with that.

I intentionally didn't mention DEQX in my post because I expect there will be many other products in the coming years that will also take care of these issues. In the mean time, going passively is certainly one solution.

Widget

[Al Klappenberge]

Guys,

I never thought about speaker system problems for applications like nite clubs and such. I would have to assume there is a long list of "gotchas" involved there! Shawn is one of my first users of extreme-slope networks. He seems to be happy with them.

I suppose if you had a way to time align along with extreme slope crossovers you would be having the best of everyhting. There is a small band of frequencies right at the crossover where adjacent drivers can still interfere with each other and aligning them might help with that. It's a small problem compared to the overlap you get with conventional crossovers though.

The link Al gave is a good overview of the job a crossover does and following its advise certainly wouldn't get you into any trouble. I guess I'm just a rebel!

Al K.

[sfogg]

I am sure you are correct that there will be more options as time goes by.

This could do it too:

http://dias.umist.ac.uk/PAG/signalwizard.htm

Though you would one board per channel. Probably will be more options when/if Tact or Behringer implement much higher slopes into some of their products too. A very high slope crossover option in the DCX2496 would be fantastic IMO.

Shawn

[sfogg]

Al,

"Shawn is one of my first users of extreme-slope netwroks. He seems to be happy with them. "

Yup, I have been very happy with them. They are what really made the speakers sing.

Now I just wish Lexicon would implement very high slope crossovers in my pre-pro to cross from the mains to my Sub1500 subwoofers. Fourth order is just so slow.

Shawn

[Al Klappenberge]

Shawn,

The idea of an extreme-slope active crossover for subwoofers has crossed my mind. The other filter software I sell (Dr George Szentirmai's S/FILSYN) will design pole-placed or elliptic active filters that could be used for a crossover at subwoofer frequencies. It is someting I may consider doing someday. I just hate getting into PC boards! I am getting stuck with that now anyhow though. The switched tweeter L-pads I am putting in my ES5800 squawker / tweeter networks is becoming a pain to wire and the switch I have sellected is not what I had hoped. Good switches cost in the range of $25 each! I am working on replacing it with a PC board having a movable plug to replace the switch and a small transformer to replace the resistors. A PC board for an active extreme-slope subwoofer crossover would be a MAJOR undertaking! All I can say is: SOMEDAY!

Al K.