Matching dispersion between ribbon and woofer - diyAudio
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Old 10th June 2009, 11:23 PM   #1
Defo is offline Defo  Norway
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Default Matching dispersion between ribbon and woofer

I'm curious about how you all match dispersion between your ribbons and a woofer with a size over 6,5 inch, considering their wide horizonal dispersion and the need for a high crossover point? I see some of the LCY ribbons have something that looks like a small waveguide, for example LCY 130. What is the dispersion of a unit like this?

And how about the Mundorf AMT2340?

Seems like most commersial speakers does nothing to match dispersion, as far as I can see.

What are your thoughts?
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Old 11th June 2009, 01:22 PM   #2
Defo is offline Defo  Norway
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Old 11th June 2009, 03:39 PM   #3
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I think it depends most on crossover.
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Old 11th June 2009, 06:44 PM   #4
doug20 is offline doug20  United States
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Im not an expert but I do believe its all based on the crossovers.

You have to know where your 6.5" drivers will start falling on the off-axis and crossover below that.
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Old 11th June 2009, 07:29 PM   #5
Defo is offline Defo  Norway
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Quote:
Originally posted by doug20
Im not an expert but I do believe its all based on the crossovers.

You have to know where your 6.5" drivers will start falling on the off-axis and crossover below that.
A regular 6,5 inch woofer beams 90 degrees at 2,2hz. A regular ribbon has a horizontal dipsersion of 120 degrees as far as I know. That means the crossover point would have to be lower then 2khz to match dispersion, which is way to low for most of the ribbons out there.

Thats where the dilemma lies. I guess a possible sollution would be a waveguide of some sort, but I cant think of any commersial speaker using one..
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Old 11th June 2009, 07:33 PM   #6
doug20 is offline doug20  United States
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Quote:
Originally posted by Defo


A regular 6,5 inch woofer beams 90 degrees at 2,2hz. A regular ribbon has a horizontal dipsersion of 120 degrees as far as I know. That means the crossover point would have to be lower then 2khz to match dispersion, which is way to low for most of the ribbons out there.

Thats where the dilemma lies. I guess a possible sollution would be a waveguide of some sort, but I cant think of any commersial speaker using one..

Hey, good point...I said I wasnt not an expert.

I have PHL1120 6.5 drivers crossover @ 2KHz with Neopro5i ribbons.

Dispersion is not equal.

Im building waveguides with larger drivers (12") to match each other.
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Old 11th June 2009, 08:01 PM   #7
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Why match dispersion at all?

Unless you have a very live room with extreme nearby reflections the energy out there is fairly meaningless - except for possible diffraction off the cabinet edges or similar.

I'd be much more concerned about the on axis response and the transition between drivers being smooth (not simple to do), and the overall sound of the system. The +/-15deg response is of interest as well...

There is an inherent problem in all speakers that have a crossover (especially two ways) in the 300 - 3000 Hz. range, and maybe an octave above the higher end as well. The issue is one of harmonic spectra. Consider what the spectra of a note that lies say above a 1.5kHz. xover point looks like - it reflects the ribbon only. Whereas a note that is one octave lower reflects the spectra of the woofer (midrange) + the spectra of the ribbon. Since this is not an identity and there is inherently some other energy/time related issues, and audible variation is there.

Which is one reason that many prefer wide range drivers like ESLs and "full range" dynamics, or wide bandwidth horns...

Adding a "waveguide" is a non trivial problem no matter what the driver. The addition of a waveguide at minimum raises the output in the range where the wavguide works, rendering a non flat response, if there was one to start with. That's just the start of the problems. If you make the waveguide so that it tries to work below the normal free-air drop off of the ribbon, you are potentially running the ribbon in a range where it is literally out of headroom (excursion) and/or power handling.

Imho, one is probably better off trying to absorb excess HF energy that is dispersed at a high angle than attempting to engineer an aftermarket waveguide solution by the seat-of-the-pants.

It's probably best to try to use a LF driver that simply does not narrow so much by the time you are crossing it over...

Ymmv.

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Old 11th June 2009, 11:28 PM   #8
badman is online now badman  United States
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Quote:
Originally posted by bear
Why match dispersion at all?

Because a ton of what we hear is from the reverberant field.
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Old 12th June 2009, 01:29 AM   #9
tinitus is offline tinitus  Europe
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All the music and mythic sonics etc is coming from in between the speakers, and nowhere else
But the reverb, ambience, air, breathing etc, or whatever its all called, all of what really makes the actual sound/music from between the speakers more interesting, is really whats happening beyond the speakers
And to my ears, its not delayed reflections from walls or anything else
I have no doubts that its solely controlled by the crossover, and nothing else
But in the end the sound comes directly from the speakers
You just dont hear the speakers
Aint that just nice, as I have no clew why it works, but it does
But sometimes I wonder whether explanations are facts proven, or in the end only what people believes in
Sometimes I tend to believe that noone knows why it works really, they just think they do
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