High Efficiency Speaker Asylum

Posted by Mark Seaton on April 05, 2001 at 12:34:14

In Reply to: Very Strange..... hmmmmmmm.. posted by Mike Bates on April 04, 2001 at 23:11:59:

Ummmm... I presume you are reffering to the Unity horn implementation since you didn't specify. Below is a link to the Proffesional products that use the technology and the company Tom Danley works for(Servodrive is the same people).

I am by no means an expert on horns, so I'll do my best to explain the basic idea, recalling from my chatting with Tom Danley and an explanation he made to the BASS list a long while back. First, the Unity horn is not really a single product per-se, but rather a type of implementation of a multi-way, common horn, co-axial design.

As a little background, the idea came from a joking comment made to Tom about making a speaker out of a pyramid, as he had just been sent out to the great pyramids to perform measurements of their acoustic properties for a documentary. Well, if you put a Constant Directivity (CD) horn on it's face, it looks like a pyramid :-). As Tom explained to me, CD horns generally sound quite good, yet they only load a driver for a limited bandwidth due to their increasing rate of expansion. From this fact, you see most CD horns for tweeters with limited bandwidth. What Tom essentially did with the Unity was to "stack" multiple CD horns. Each section of the horn further from the throat is used to load the frequencies which it's profile suits. The tweeter is a compression driver which loads conventionally into the throat of the horn. Then, a few inches from the throat, the 4 midrange drivers are compression loaded into the horn through 8 critically placed holes. The profile of the horn from this point out to the 16.5" square mouth loads the midrange driver allowing response down to ~300Hz.

The use of 4 midrange drivers makes for a midrange system of about 110dB/1W when passively corrected, and a power handling of 100W RMS. As you can see with the various iterations available in kit form, the compression driver is the limit of the system efficiency above 300Hz. Since the midrange is not loaded all the way from the throat of the horn, this configuration also greatly reduces throat SPL levels which in some horns can get high enough to cause distortion from the non-linearities of air. Likewise, the 2 sources are phase and time aligned when an appropriate crossover is used. The point source nature of the horn also has some serious benefits in the axial response, which I have seen measured as near perfect over a 25 deg. window, and tightly controlled within a 60 deg. window. Like other horns, you can imagine the lack of early reflections has a great effect on the sound in a room.

I wish I had more time to talk about this concept which I am so fond of, but back to work for me...

More later,

Mark Seaton

• Sound Physics Labs