High Efficiency Speaker Asylum

Posted by tomservo (M) on September 07, 2024 at 07:05:31

In Reply to: RE: The Pros and Cons of Horn Speakers posted by cawson@onetel.com on August 21, 2024 at 05:19:58

I have hesitated to reply as this is a big subject.

Number one, a horn is a band limited device, more so than an average direct radiator.
It normally has a "non-flat" frequency response raw, because it has both directivty and gain both of which are horn size and shape and driver.
That being the case, the on axis sensitivity reflects BOTH the directivity and efficiency.
The are mostly a "minimum phase" device so making the response flat also corrects the phase response.

HF Horns with curved walls generally need less eq to be flat on axis, that is because as the frequency climbs, the radiation pattern gets narrower and narrower. IF your listening only on axis, some horns are even flat without eq. These can be very narrow at the top end.

Horns that have straight walls tend to be closer to "constant directivity" where the radiation angle is a fixed number over a wide bandwidth.
For multiple seats, this is an advantage because for some angle off axis, the frequency response stays the same instead of the hf progressively rolling off off axis. This EQ is often called "CD" compensation to compensate for the drivers falling acoustic power and no narrowing.

If you ever heard an altec A-7 in a living room, one can observe that outside the pattern in the room, the sound is dark, no hf.. That dark spectrum is the acoustic power radiated while on axis, its sound right because the hf gets very narrow vertically to off set the falling power.

A typical 1 inch compression driver's acoustic power rolls off starting about 1-3Khz depending.
IF one had a truly constant directivity source (like an omni), then the room sound spectrum is nearly the same as sitting in the sweet spot. IF these were far enough away from side walls (and you were closer), these can give a very good stereo image.

We also hear aspects of how sound is radiated and here is where a multi-way horn systems have issues, you have to be father away before they are not obviously separate sources.

At the opposite end of being able to localize the speaker as the source, here is where a single small full range driver used properly, makes a jaw dropping stereo image.

Here is a way to make one that does this.

IF your a diy'r like my background, try this and report back.
Obtain 2 of these amazing little drivers, don't substitute;

https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=401000100

Make a flat baffle, about 18 inches to 2 feet square with a hole in the middle to mount the rear of the driver through. This insures there is no discontinuity and re-radiation within a good distance and blocks energy going to the rear above about 300Hz at 18 inches.

Cover the baffle with 1/2 inch of foam padding and make a hole in it at the center.
Mount the driver from the front through the foam which makes a nice radius at the driver edge. make a small back volume for the driver,, if your game, take the T&S parameters and figure out a vented box with a nice low response shape.

This full range driver is small enough to radiate as a simple point source up to pretty high and so, it has very little spatial identity and can disappear making a stunning stereo / phantom image .

If you listen at a reasonable distance, you will be impressed, the only thing they don't do is low bass and they do narrow some up high.

Tom Danley