This is a ‘compound’ horn… a single driver, with a midrange front-horn and back-loaded with a bass-horn.
In my 13 April 2014 post, you can see the fibre-glass Tractrix Midrange Horn, which was designed for a ‘cut-off frequency’ Fc=140Hz.
The Bass-horn therefore needs to operate from 180-140Hz down to around around Fc=30Hz.
Now a 30Hz horn in ‘free-space’ would be huge!
A quick calculation…343/30 (speed of sound/freq) = 11.4m horn-mouth circumference!
So we must utilise room boundary loading (walls & floor) in order to have an acceptable sized horn. By using corner-loading, we can reduce the horn mouth area by 1/8.
Corner-loading also has other advantages:
- Bass output to match midrange horn in dB level and in LF extension, tonal balance.
- In my case, I do not want the loudspeaker to extend forward too much, occupying unnecessary room space. (Room size 6.1m x 3.6m x 3.3m height.)
- With multiple horns, the listening position needs to be relatively far away, for best sonic integration.
- Low frequency response is most uniform with corner placement – all of the room resonant modes are excited uniformly (see below):
Further reading – Best Placement of Sub-woofers (Sonic Design, Sweden).
Horn concept ideas:
This is the Yamamura Dionisio 27 – a nice ‘compound’, single driver horn, but the bass-horn does not utilise corner loading. And the front output is not properly horn-loaded.
Below, an early idea for corner-loaded bass-horns, built across the front wall – however this needs a separate midrange loudspeaker per channel:
Another corner-loaded bass-horn – ‘spiral’ horn folding, with 2 x 180° bends:
A corner bass-horn variation with a single 180° bend:
Below, is close to the final design – a single driver, with a rear, corner-loaded, folded, curved bass-horn, 4.0m long. Bass-horn design cut-off frequency Fc=30-34Hz: The Tractrix Midrange Horn attaches to the front.
(Part 2 to follow – detailed design using David McBean’s Hornresp and the horn construction.)