Saturday, July 26, 2014

"VoXConcentriC" - Beyma 12" high efficiency speakers





























I wanted to build a high efficiency speaker to work with my low power valve and SS amps. These Spanish designed and made 12" concentric drivers by Beyma (12XA30/Nd) filled the bill. The woofer section is 98db efficient and the tweeter section 105! Because these drivers have a very low Q only a 30ltr ported box is required but also a result of high efficiency and low Q there is not a lot of low bass. Sub-woofers or bass drivers are required if you like your low bass. The woofer cone is heavy and quite stiff the the domed concentric tweeter is titanium. The drivers and rated at 350W! The magnet assembly is extremely powerful and uses neodymium magnets.

The boxes are heavily braced inside and lined with bitumanised heavy Al tape and a layer of dampening. The external Xovers are very simple crossing from the woofer to the tweeter at 2KHz. There is a -6db slope on the woofer and -12db slope on the tweeter. The finish is one I have developed myself by using a roller to produce a very stippled, sonicly damp layer. Grills are magnetically attached. The overall sound of the speakers is detailed.

5 comments:

george said...

No wonder you don't have any low bass ! Cabinet volume needs to be 5x what you currently use

retro-thermionic said...

I used two different box calculators for these drivers and both came back with 30ltrs. What a lot of others don't understand is with these drivers is they have an extremely low Q (0.2 measured). When playing loud the cones barely move at all. If you were pushing 700W through them, as they are designed to handle, a bigger may be required.

Anonymous said...

Use the EBS alignment . That is the way to achieve deep bass from low Q drivers . Vas~Vb , tune the port to approx Fs . The only issue with this alignment is limited Xmax but for these drivers , you'll never go anywhere near Xmax due to the high sensitivity

maxlorenz said...

Dear M,

If you don't need bass (VG: have separate woofers) I would try open baffle.

The perfect cabinet, though, would be a big front and back loaded horn, รก la Tannoy Autograph, which would need good corners (>5m appart) and several months of work, but which would give you great overall performance and balance (it complements the climbing frequency response), and good bass until at least 40Hz (horn Hz) and even lower...
The 15" version of the coaxial is ideal.

Another tip: try Dammar varnish for the woofer. Dries in several weeks but lifts the performance a few steps.

Best wishes,
Maxlorenz.

retro-thermionic said...

maxlorenz, thanks for the comments. I 'tend to take the easy way out. Also I rely on my cabinet making friend to supply the raw boxes. I'm currently using the Beymas with 180W Tripath amp (Audiophile) and my Adiy 12" stereo subwoofers rolling in at 100Hz. So bottom end is covered. These speakers really grow on you.