High Efficiency Speaker Asylum: RE: One of the thougest question in acoustics by tomservo

Hi

Radiation into free space requires the energy to â€œgoâ€ somewhere and not come back.
Normally that job is accomplished by the sound radiating away from the source, with the result being that the acoustic load looks resistive or dissipative.

As one looks closer, one seeâ€™s this radiation resistance appears as a constant value above some source size and is a variable number below some source size (acoustic size, physical size relative to the wavelength).

When a radiator is acoustically small, then the act of placing a second driver at a distance which permits coherent addition, results in the radiation efficiency going up by two.
Thus, one woofer VS two identical woofers, one finds that the double unit has twice the power capacity, allowing it to handle twice the power AND the radiation efficiency is doubled. Now, one finds the double unit is 3dB more efficient AND handles 3 dB more power, it is 4 times louder than one.
There is an observed practical limit to this increase at around 25% efficiency (about 106dB 1W 1M) and this also stops when the drivers are more than about Â¼ wl center to center at the farthest point.

Now, in a Tapped horn, using a program like AKABAK, both sides are enclosed within the acoustic cavity so mutual radiation is not an issue here, pressure is modeled on both sides etc. Akabak is very good and I used it to model all of the Tapped horns including this â€œportableâ€ Tapped horn

http://www.danleysoundlabs.com/images/Matterhorn%20Finished.jpg
The construction video of it is kind of funny.
http://www.danleysoundlabs.com/matterhorn.htm

Best,

Tom Danley

party woofer (Open in New Window)