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limking 2nd July 2001 02:12 PM

Hello all!

I'm planning to build a 3 way loudspeaker system and is wondering how to make the passive crossover in a system wired in series(2 woofers) and parallel(the tweeter).

I am planning on using two 6.5" woofers and a tweeter (all 8 ohms) crossed @ 300 hz and 5000 hz...

If I wired all the transducers in parallel, the overall impedance would be 2.67 ohms... which is too low for my amp. So the alternative is to wire the two woofers in series and the tweeter in parallel relative to the woofers, which would have a total impedance of 5.33 ohms, which is acceptable...

But then, In a parallel connection, each woofer/driver/tweeter has its own set of +/- wires to connect the filter components to, while in the series connection, both woofers only have one +/- wire to share with....

So I was wondering how to make the low/high/bandpass filter for the 2 woofers in series...

And I was wondering what Zobels are used for and should I use them????

Thanks for any info...

Super 2nd July 2001 11:31 PM

This site was given to me in a previous post, and has a lot about passive crossovers. It all describes and gives crossover schematics for a zobel network.


GRollins 3rd July 2001 01:59 AM

It's a little unclear how you're laying all this out.
You're saying that it's a three way, but with two woofers and a tweeter. That's a two way system. A speaker is described as two way or three way (or four, or whatever) based on how many ways the crossover divides the frequency spectrum, not how many drivers are used.
Later, you say that you'd like to use crossover points at 300hZ & 5kHz. That describes a proper three way, but you've still only mentioned 6.5" woofers and a tweeter. If you try to run a 6.5" driver up to 5kHz, you'll have to listen with your head in a vise, as it will beam pretty badly. A 5kHz signal has a wavelength of something like 2.75", which coming from a 6.5" driver would be the sonic equivalent of a laser beam. (Proper dispersion of frequencies from a driver is a function of the wavelength you're trying to reproduce, vs. the size of the driver.)
What are you planning to use for a midrange?


Bill Fitzpatrick 3rd July 2001 03:52 AM

One of the most important things you can do is ignore the advise of the "Audio Elder" that says if you try to cross a 6.5" driver at 5KHz you'll need to listen with your head in a vise. Laser beam my foot.

I love being a critic. I think I'll stick around the DIY audio forum looking for and reporting errors.

I joined the forum some weeks ago and am amazed at some of the ******** I've read.

GRollins 3rd July 2001 04:30 AM

Just out of curiosity, have you ever tried using a driver that size for a frequency that high? 2kHz, sure. 3kHz maybe. 5kHz? Go ahead...try it.
Ever seen something called a polar diagram? It's a plot of dispersion of a driver at various frequencies. The main variable is the ratio of frequency to the driver diameter/width. On axis radiation is always strongest, but off axis radiation drops off rapidly with frequency. In the vernacular, that's called beaming. It means that you've got to sit in one place to hear the higher frequencies...move to one side, and the high frequencies drop off; the sound goes dead.
Electrostatic speakers have a justly deserved reputation for beaming. Why? Because the panel width is wider than the frequencies being recreated. Acoustat had a single panel wide model (the 1+1? I forget), but it beamed above about 2 or 3kHz. Ditto for the Stax F-81 (one of the best sounding electrostats ever made, but it took a 200W amp to make it even whisper).
Setting aside questions of dispersion (the math is trivial), there's also the mass to contend with--in other words, the transient response would be somewhat less than wonderful by the time you got up towards 4 or 5kHz.


P.S.: The whole Neophyte/Prophet/Elder/whatever thing isn't my doing. If you've got a problem with it, take it to Jason. It's his site. He did the coding.

Bill Fitzpatrick 3rd July 2001 04:21 PM

With a wavelength of 2.75" and a listening distance of 96" your head would have to shift laterally by about 16" before you would be at the center of the first cancellation null. This is nowhere near a situation that would require clamping ones head in a vise.

Additionally, the null wouldn't really be a null. The reduction in output would be on the order of 20-25db.

A two way system which takes advantage of the mechanical roll-off of the woofer, omitting the low pass filter AND which properly integrates a tweeter will, for serious listening from your favorite seat, impose little or no penalty when the head is shifted from side to side by a reasonable amount.

None of this is helping limking with his speaker project and GRollins and I might best continue this thread as a new one. All I'm saying is that the situation is not nearly as dire as GRollins suggests. I have constructed systems which take advantage of the mechanical roll off of midranges and when done correctly they are very nice indeed.

limking, buy yourself a copy of the "Loudspeaker Design Cookbook". Read it and understand it. You will then be ready to get started. You will also save a great deal of time.

GRollins 6th July 2001 12:44 AM

With a 20-25dB drop at 16", what do you get at, say, 4-6"? 6dB, perhaps? That's a quarter as loud. I don't know about you, but I regard -6dB as pretty significant; to be avoided if at all possible. And 4-6" is pretty limiting, as far as seating arrangements. What if another person wants to listen? Their head will be 16" away, minimum, even if they're sitting shoulder-to-shoulder with the person in the sweet spot. You've just condemned them to a serious hole on the lower side of the 5kHz crossover point.
And there's still the mass to contend with. There's a *reason* that dedicated midranges are smaller and lighter than 6.5"
Now, you and I are in agreement as far as the mechanical rolloff trick...when it can be arranged. It takes a well behaved driver to get away with it--and we don't know what limking has on hand--but it's an elegant solution if the driver is up to it.


Bill Fitzpatrick 6th July 2001 02:17 AM

Hmmm. A 2 person, serious, listening session. That's a new one on me.

40 years in audio as an enthusiast and moderate to high end retailer and it's never happened. Am I missing something here?

Anyway, if these 2 listeners are not passionately in love there will probably be 36"+ between them. Even if the sweet spot was wide enough for both, what about the room; you know - standing waves and boundary reflections? An out of phase reflection can create a serious null too.

One room, one best spot. That's why people labor over speaker placement. If you want to give your guest a treat, you're supposed to give him/her your seat. You can then sit on the sidelines agonizing about room modes.

And the hits just keep on coming.

GRollins 6th July 2001 03:10 AM

Life sure must be different on the other coast, as people over here frequently have guests. I've got a buddy who regularly hosts Friday and/or Saturday night sessions with as many as four or five other people in addition to himself and his room mate. His sweet spot isn't a spot--it's about three or four feet wide. Two people easily, three if they're friendly. (His listening seat is a nice sofa, so people can scoot back and forth as the occasion demands.) The image is stable, and the frequency response stays balanced. It works.
There used to be an audio club here locally. They met once a month at each others' houses. Some systems were pretty tight, others were wider. I didn't attend often, as I wasn't an official member of the club, but I never saw less than eight or ten people at one of their meetings.
There were four people the day I visited the fellow with the Genesis 1.1s. The listening spot there was easily two people wide, and I felt that the system might be capable of more (in many ways) once it was tuned in some more.
My system is similar. I don't have guests often, as my schedule doesn't match well with others. Still, when I get a new piece of equipment bought/built, I have people over.
In my view, anyone who's putting up with less should at least be aware that it's possible.
So...yeah, you're missing something.


Bill Fitzpatrick 6th July 2001 04:09 AM

You're describing a social situation.

OK, so the difference is in our definition of "serious."

Here's serious to me.

A very well loved piece of music.

Sitting comfortable in THE chair.

The room is black - not dark but BLACK. Not even an LED showing. No visual distractions. No unwanted photons bouncing around.

Zero aural distractions. No talking, shuffling, throat clearing, mechanical noises or breathing. No air conditioning, heaters or refrigerators cranking away. No ice melting in a glass. The phone is unplugged and the neighbors have been warned.

Not an object in the room vibrates, rattles or otherwise responds to the sound of the music; except the speakers of course.

Attention to the music is rapt, almost trance like; a transportation into the very heart of the matter.

But, then, I like to party too.

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