Coaxial woofer-subwoofer

hello everyone.
are there coaxial subwoofer-woofers that cover frequencies from 20Hz up to medium frequencies?.
I'm not talking about those that cover the entire frequency range up to 20khz which actually don't even get there.
if they exist, how do they compare to woofers and subwoofers?.
Thank you .
 
There is no significant technical advantage at low frequencies to a coaxial arrangement because of the long wavelengths. In fact for frequencies below 80 Hz the technical advantages are with distributing the sources around the room never mind coaxial with the mains! Nonetheless there can be marketing appeal in doing it. ME Geithain and Cabasse spring to mind but I am sure there are others. In the pro world there are plenty of large coaxials and even some 3 ways but the motivation is a bit different to home audio.
 
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the much acclaimed point source at what frequency does it begin to manifest?.

Unless you are sitting on top of the speaker the primary benefit of a coaxial is the improved quality of the reflected sound field. Below the Schroeder frequency the perceived sound quality is increasingly due to the room rather than the radiation pattern of the speakers reducing any potential benefits of a coaxial arrangement. At 80 Hz or so we largely lose the ability to perceive direction and the difference in path length due to an offset driver is negligible in comparison with the wavelength so the benefit here is effectively zero. So somewhere between 80 Hz and the Schroeder frequency depending on how picky you are.
 
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I asked at what frequency the point source begins to manifest itself
Yes but what is a point source.. and what is the benefit? Is it more than one thing? You can have two separately placed drivers on a baffle acting in a generally point source manner and you can have a coax acting in a non-point source way.

As Andy mentions, there are lobing issues, source direction, room mode differences. Each has a varying importance which usually become much less at various lower frequencies.
 
it could look cool - say on the cheap side a Goldwood GW1858 18" plus some small woofer which could fit in front of the 18" speaker
 

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GM

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Joined 2003
I asked at what frequency the point source begins to manifest itself
A point source driver's BW is from Fs - VC diameter's frequency, so if a 3" dia. VC, then ~13543/pi/3 = ~1437 Hz. Above this point it has TL modes (the flexing you see in slow motion video where the same frequency can be emanating at different locations on the diaphragm) with the dustcap filling out the extreme HF beginning around ~13543/3 = ~4514 Hz for 3".

Swag the dustcap for a second driver and this 'coax' still has the same VC cutoff.
 
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