Big BenD Bass Horn: Driver Update

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This update is actually long overdue, and related to a project at Celestion I wasn't able to finish: a cone driver specifically designed for bass horns. It follows the ideas I outlined under My Approach to Bass Horn Design, and is a 12" driver designed for a compression ratio of about 1:2. As I wanted it to be easy for Celestion to put it into production, I used as many standard parts as possible, either directly or something that could be easily machined from standard parts. But I also added a feature that aren't easy to find in modern drivers: an underhung edge-wound voice coil. 

Here are a some of the features of this driver:

  • Underhung 3" edge-wound voice coil
  • Copper sleve on pole piece
  • Focused magnetic gap
  • Low moving mass
  • Vented pole piece and back plate
  • 250W power handling
  • Large ferrite magnet
  • Inverted dustcap to allow for phase plugs if desired

And for those who worry about the high power rating being detrimental to other qualities important for horn speakers, rest assured: this power rating was a result of the voice coil size and venting, not of "beefing up" the driver (which typically makes the moving assembly lighter) to take higher temperatures and forces. 

Here's a side view of the driver, without the front segments. It's built on a Celestion FTR chassis. 

New driver

The magnet system:

bigBendDrivers3

The gap flux is slightly above 1Tesla, which is quite good for a gap this size. It takes a substantial amount of magnet to produce that, especially when you lose gap width to a copper cap. 

Comparisons with old DIY driver

Below are a couple of photos comparing the new driver to a DIY project I used to begin with, referred to as 12" DIY driver in the performance measurements. The DIY driver used the motor system from a pair of Celestion NTR08-2009D 8" woofers I found in the bin. They had the cones cut out, but the motor was salvageable (even the voice coil), and I used them to build a pair of 12" drivers using available parts. I used the lightest 12" by 2" cones I could find, and a fairly soft spider. They turned out to be quite good, with the BL^2/Re being a good match for my bass horns. But the new drivers are more robust, and also give a very good performance and produces very clean bass in the Big BenD horns. 

Comparision with old DIY driver

Comparision with old DIY driver (back)

 Parameter  Old DIY driver  New driver
 Re [Ohms]  4.46  5.8
 Le [mH]  0.065  0.086
 BL [N/A]  12.3  17.0
 Mms [g]  39.2  64.5
 Rms  [Ns/m]  3.4  0.63
 Cms [m/N]  4.36e-4

 1.88e-4

     
 

Now I just hope Celestion will finialize this project and put the drivers into production, as I think this would be a good driver for bass and midbass horn use, especially for domestic use.

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