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Multi-Way Conventional loudspeakers with crossovers

What do you think of passive crossovers?
What do you think of passive crossovers?
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Old 29th September 2011, 11:02 PM   #101
planet10 is offline planet10  Canada
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What do you think of passive crossovers?
Quote:
Originally Posted by Pano View Post
I don't want no stinkin' active crossovers in my surround speakers. Ha!
No crossovers at all in mine

dave
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Old 29th September 2011, 11:03 PM   #102
rob g is offline rob g
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Right on brother, right on. You rock.
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Old 29th September 2011, 11:11 PM   #103
Pano is offline Pano  United States
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What do you think of passive crossovers?
Very much possible, yes.



Dave, you are truly a misfit.
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Old 29th September 2011, 11:16 PM   #104
rob g is offline rob g
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Dave, you are truly a misfit.
Which paradoxically means he is perfect for diy audio.
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Old 30th September 2011, 12:32 AM   #105
AllenB is online now AllenB  Australia
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Quote:
Originally Posted by dirkwright View Post
didn't respond as I thought it would to a Zobel network. The rising impedance curve turned into a sine wave instead of a flat line as expected.
Larger cap?

Quote:
going active may be a better choice.
...and over the weeks it will take me to get moving on this, I'll be starting out passive then evolving from there. I have some active sections in mind. Good luck with yours...
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Old 30th September 2011, 12:53 AM   #106
dirkwright is offline dirkwright  United States
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Quote:
Originally Posted by AllenB View Post
Larger cap?


...and over the weeks it will take me to get moving on this, I'll be starting out passive then evolving from there. I have some active sections in mind. Good luck with yours...
OK, so you're offering help again? Man, you are a champ! I used the standard formula for Zobel networks based I think on the actual measured values from WT2. Let me look at it again and get some files together for you...
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Old 30th September 2011, 01:30 AM   #107
AllenB is online now AllenB  Australia
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I only wish I was as ready to pick up a saw and make sawdust.
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Old 30th September 2011, 03:24 PM   #108
dirkwright is offline dirkwright  United States
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Originally Posted by AllenB View Post
I only wish I was as ready to pick up a saw and make sawdust.
Well, if I was nearby, I'd certainly be willing to help out with that. I'm just about done with the cabinets on the other project that you helped me on. I posted a couple of photos up in the projects thread.
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Old 30th September 2011, 05:19 PM   #109
Tom Danley is offline Tom Danley  United States
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Steph tsf said;
“If you target a perfect acoustic wave reconstruction, you need a linear phase.
If you target a wide and smooth directivity, you need zero relative phase shifts in the transition band.
Analog crossovers (passive or active) can't deliver both. With passive crossovers, even if it is possible to get a linear phase, you still get a relative phase shift in the transition band, something like 90 degrees.”

Actually with the right combination of acoustic relationships one can have cake and eat it too.
One can have a high order crossover where the summation has no apparent phase shift and the resulting radiation remains a constant beam width with a high degree of angular “confinement”.

In defense of passive filters I would offer the up side. When a driver is driven by an intended source impedance, one finds that is several ways it is not quite the same as actively driven. For example, in the case where a source is driven directly, one finds all of the effects of power compression and parameter alteration are large for a given temperature rise than when driven by a higher source impedance. At the extreme, when driven by a current source (high source impedance) power compression is non-existent up to the point of letting out the magic smoke. Keep in mind too that us poor designers are often faced with the situation of “say, we need a passive box to do X with”.

The down sides would be that one is usually dealing with loudspeaker drivers and not resistors. Drivers only add like resistors (unilaterally in all directions) when they are acoustically very close.
At a spacing of larger than about 1/3 wavelength, drivers begin to produce an interference pattern instead of adding coherently. While the spacing is say less than ¼ wavelength apart, inverting one of two sources results is a near complete cancelation of the energy, when you invert one of two
sources at a large spacing, one only re-arranges the interference patterns pattern of lobes and nulls to even the idea of “speakers adding” only happens in specific conditions.
Once one has an interference pattern, then one is concerned with where the lobe (s) and nulls are relative to where the people are.
Driver placement and interaction is then an X, Y and Z issue.

As if dealing with how drivers add or cancel spatially, the next problem is the two fold issue that the drivers are not simple resistive loads and in a horn system, each range has it’s own magnitude and phase response before adding filtering and one has to equalize the response in addition to providing a crossover. Here, in addition to the crossover part, one usually has to add 3 parts (R,L,C) to address a single bump.
Clearly, the only way to design crossovers like this is using measurements and a computer program, there is no way to design a proper crossover for real drivers even in a simple cabinet by look up tables and tweaking as was the practice in the old days.

Attached is a measurement for a 3 way full range horn I was working on some years ago. This was an SH-50 synergy horn measured on a tower about 25 feet off the ground with the mic at two meters using a TEF-20 at 1/20th octave smoothing. The crossover frequencies are around 250Hz and 1200Hz. The phase rise in the upper part is due to where the TEF places “time =0” which here is about 5/16 inch late relative to actual, otherwise, it looks like one driver instead of 7. It is a 3 way system and can reproduce a square wave from fair to very good looking on an oscilloscope, from about 260Hz to about 2900Hz and has no nulls or outside lobes in it’s pattern.

For what we do, the concern about having everything add up into one source is because for large spaces one needs a lot of acoustic power, for that one needs a lot of drivers. The down side of “a lot of drivers” is those systems usually radiate a complex interference pattern such that if the wind blows even a small amount or if you move around, there are audible changes. Also the large interference arrays that are so popular now, produce a difference spectrum at every seat and distance. With a constant directivity point source like this, the sound spectrum is the same essentially everywhere in the pattern and only gets quieter with distance.

It is hard to describe how large a difference reducing or eliminating the self interference makes in large scale sound but it really is large. We have been selling a lot of speakers for stadium sound upgrades.

If you have headphones hooked up to your computer, try this video Mike from the shop took at a stadium demo Tuesday. Listen to the sound as he walks around and keep in mind, this is all coming from the three speakers (one aimed right, one left and one forward) are the little black blob under the scoreboard.

Danley Sound Labs, Inc.'s Videos | Facebook
That system is active as the power levels add an entirely new layer of issues to passive crossover design, active is so much easier.
Best,
Tom Danley.
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Old 30th September 2011, 06:26 PM   #110
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Hey Tom

My alma mater!
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