Why are Speakers Concave (CBT**2 With Inverted Domes?)

[TheWalkman]

Virtually all speaker drivers are more or less concave (ok, Magnapans, Ohm F’s, tweeter arrays, excluded.)

I was just reading the thread on CBTs and line array design/ theory and how they work.

Constant Beamwidth Transducer (CBT) Speakers

Not sure how many members have CBT speakers, but I know a few have shown interest. Since there have been scattered ongoing discussions, am creating this thread to give it a home. If you are wondering what CBTs are, they are the work of former JBL and Audio Artistry engineer Don Keele. Edit...

www.audiosciencereview.com

and Don Keele’s video series:

Based on this information, like the large CBT array, wouldn‘t a convex speaker cone act as a miniature CBT and, similarly, radiate a much broader waveform across the working frequency band than a concave speaker cone?

Take this to the next level: wouldn‘t placing convex drivers in a line array reinforce the sound radiation pattern further (creating, in effect, ”recursive“ sound beams - (sort of an audio Mandelbrot function?)) with an even broader and more evenly dispersed sound?

What am I missing and more importantly, why don’t we see (hear) convex speakers on the market?

 

[TheWalkman]

1) Convex drivers would have the magnet and electrical connections on the outside. Would you care to electrocute a curious child?
2) The magnet assembly and spokes would interfere with the sound wave ..... and you thought edges caused diffraction!
3) A simple flat screen protects concave drivers. How would you protect convex drivers?
4) After a certain frequency all drivers, concave, convex or flat, will beam.

Jim,

If you extended the voice coil on a tube connected to the back of a convex shaped cone - just like a concave cone- the connections are still on the inside of the speaker, protecting users from electrical shocks. I’m sure this would require a very stiff tube to avoid distortion.

Granted, there might be a greater chance of physical damage to the cone if it stuck out from the front face of the speaker. However, many of the CBTs seem to have very small (2” to 4” drivers) so I’m guessing an inverted cone would stand out a fraction of an inch at most. By simply extending the front face of the speaker a bit to the sides and having a lip at the edge, it seems you could protect the cone while minimizing any side interference (directing/ reflecting) the sound wave coming off the edge of the driver cone.

Then again, a simple wire mesh, “cage” could be placed over the driver cone, to protect it from physical damage.

Just as you have with virtually all speakers, by adding a convex dust cone to the now convex driver, it seems like we would have another level of the recursive sound radiation, reinforcing the benefits of the CBT concept at yet another level: this design would result in a spherical dust cone within a spherical (convex) driver cone within a spherical line array.

This is way over my technical level of audio design theory, but intuitively, this all seems consistent with the spherical driver design philosophy to me. Where is the gotcha?

 

[Doodski]

What am I missing and more importantly, why don’t we see (hear) convex speakers on the market?

The Infinity Kappa Series had convex drivers and they worked wonderfully. very nice speakers.