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
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
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.
It's a valid method in theory.
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
www.gattiweb.com
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
www.gattiweb.com
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
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
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.
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.
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.
Went down this road a while back and here's the thread.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=29159&highlight=
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
http://www.diyaudio.com/forums/showthread.php?s=&threadid=29159&highlight=
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
Thanks David and everyone, that makes everything much clearer. The off axis performance consideration of the tweeter is probably why it's crossover point is around 1600hz, which is pretty darn low for a first-order design!
I'm surprised more manufacturers don't do the inverted driver array thing for time alignment considering having a flat baffle maintains aesthetics a bit better. I guess you do need drivers that can handle the off axis dispersion and wide-banding... which I guess is where Dynaudio has an edge since they can design their own drivers.
As a side thought, would it be possible to have another woofer below the tweeter, i.e. an MTM configuration (or an MTTM configuration like Dynaudios speakers further up the chain) and still maintain time-alignment? Would you have to roll-off the bottom woofer differently?
(Audibly, there probably isn't much difference with a phase-coherent time-aligned design as opposed to a phase-coherent non-time-aligned design but it's fun to discuss
Sincerely,
Mal
I'm surprised more manufacturers don't do the inverted driver array thing for time alignment considering having a flat baffle maintains aesthetics a bit better. I guess you do need drivers that can handle the off axis dispersion and wide-banding... which I guess is where Dynaudio has an edge since they can design their own drivers.
As a side thought, would it be possible to have another woofer below the tweeter, i.e. an MTM configuration (or an MTTM configuration like Dynaudios speakers further up the chain) and still maintain time-alignment? Would you have to roll-off the bottom woofer differently?
(Audibly, there probably isn't much difference with a phase-coherent time-aligned design as opposed to a phase-coherent non-time-aligned design but it's fun to discuss
Sincerely,
Mal
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