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Old 7th April 2005, 04:40 AM   #1
Mal P is offline Mal P  Australia
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Default Possible to emulate a sloped baffle?

Hello there,

I refer to the Dynaudio Confidence C1 speaker. This speaker has an inverted driver array, with the woofer on top, tweeter on the bottom. As a result, the technical description states that this driver configuration "creates an upward polar tilt due to the distance of the voice coils to the baffle, emulating the effect of a sloped baffle while providing a much larger sonic window than would otherwise be possible" and thus implies the speaker is time-aligned.

Basically, is this possible? If so, what are the technical reasons behind this? I do note that Dynaudio always uses 1st order crossovers in their speakers. I'm very curious.

Thank you,
Mal
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Old 7th April 2005, 05:56 AM   #2
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Basically, what's happening is that the woofer is now on the horizontal listening axis. Hence the woofer to listener distance is shorter than the tweeter to listener, and that compensates for the location of the woofer's voicecoil (which lies a cm or so behind the baffle).
It's a valid method in theory.
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Old 7th April 2005, 10:57 AM   #3
Mal P is offline Mal P  Australia
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Hi David,

Thanks for the reply! How does this work... why does swapping the drivers around make the woofer's acoustic centre shorter in distance to the listener? Since the frequencies produced by the tweeter still travel faster than those of the woofer?

Thanks,
Mal
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Old 7th April 2005, 12:28 PM   #4
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All frequencies travel at the same speed - 330 m/s.

A woofer has greater depth and it's voicecoil is usually located a cm or 2 behind the baffle (more in bigger woofers). A tweeter on the other hand has it's voicecoil very close to it's baffle surface.

The acoustic centre (apparent source of sound) is approx the voicecoil of the driver, hence sound from the woofer has to travel that little bit further than that from the tweeter., to reach the listener's ears.

So if you put the woofer directly on axis, and the tweeter 5-10 deg or so off axis, the tweeter is slightly further away and can compensate for it's shallower voicecoil.

Hope that's clearer.

David

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Old 7th April 2005, 12:47 PM   #5
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However the difference is quite small.

Using Phytagoras. If L is the distance of the listener to the baffle (with a 90 degree angle) and the center of woofer and tweeter (in the plain of the baffle) are d apart, than the difference in distance to the tweeter is

square root(L^2 + d^2) - L (in the plain of the baffle)

eg with L= 300 cm and d=15 cm the difference would be 0.375 cm.

So the woofer can have an acoustic center 0.375 cm deeper than the tweeter.

With a greater listening distance (eg 4 meter) the effect would be even more neglectable
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Old 7th April 2005, 12:56 PM   #6
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I think the real reason is that odd-order crossovers cause a (15 degree, if I remember for 3rd order) tilt in the polar axis due to the phase induced delay. This tilt is downwards for the usual driver configuration. By inverting the drivers and spacing them correctly you can compensate for the tilt in the crossover.
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Old 7th April 2005, 01:21 PM   #7
AuroraB is offline AuroraB  Norway
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The usual assumtion has been to assume the start of the wave to beappx 2/3 into the woofer cone, rather than at the voice coil.

More important though is the inherent time delay or phase shift that occurs in all high pass sections. Even using the socalled linear phase X-overs, ( or fill-in driver ) , this delay will be present in all the high pass sections used.
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Old 7th April 2005, 02:55 PM   #8
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First order crossover, phase shift etc., are O.K. But beware, unlike Dynaudio's designs, this configuration will not sound good with all drivers - reason - "Offaxis response" of tweeters are usually bad. Hence, imaging will suffer and your sweet spot becomes narrower.
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Old 7th April 2005, 07:02 PM   #9
rabbitz is offline rabbitz  Australia
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Went down this road a while back and here's the thread.

Time Alignment on a flat baffle.....

How much is an ego trip and how much is actually a sound improvement, who knows, but I'm happy with the results .

It is quite common for the inverted drivers to be used with odd order crossovers and there's a reference to that in the LSDCookbook.

Cheers
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Old 7th April 2005, 09:13 PM   #10
Bricolo is offline Bricolo  France
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Quote:
Originally posted by richie00boy
I think the real reason is that odd-order crossovers cause a (15 degree, if I remember for 3rd order) tilt in the polar axis due to the phase induced delay. This tilt is downwards for the usual driver configuration. By inverting the drivers and spacing them correctly you can compensate for the tilt in the crossover.

could you tell us more about this?
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