Horns, horns, who wants horns? Certainly not anyone concerned with high fidelity, right? They're fine in your PA if you're in a rock band but otherwise - Forget It!!! If that's what you believe then you should read on.

To be specific, SP Technology Loudspeakers Precision Monitoring Products do not use traditional horns associated with high power sound reinforcement applications. Rather, we employ and take advantage of "Waveguide" technology to achieve the high degree of accuracy and performance of our products. The difference between the two is considerable and is outlined in depth in the following text. Never-the-less, a waveguide is more like a horn than not. So what is(was) the problem with horns and why has the majority of the high fidelity community so overwhelmingly rejected them?

To begin, in 1967 pioneer Gerald R. Stanely of Crown international, Inc., designed the first commercially available high power, solid-state amplifier (the DC-300). This made it possible for speaker designers to abandon the use of horn technology in favor of direct radiator types. It was perceived that a horn's only major advantage was that of high efficiency. Prior to the DC-300, such efficiency was vital for achieving reasonably high sound pressure levels from the low powered vacuum tube amplifiers available at that time.

Horns had been (and still are) associated with a "honky" type of distortion that many find objectionable. This observation is accurate but misleading. Horn Theory suggested other advantages as well, but they were mostly overlooked due to the focus on efficiency. Once having abandoned horns, the "Hi-Fi" industry never really looked back (save a VERY small minority).

Conversely, an astute observer would have realized that horns are not inherently a source of distortion but rather a fundamental means of avoiding it. The "honk" associated with them is a by-product of over-zealous engineers attempting to squeeze out every last percent of efficiency. To be fair, we can understand their motivation. When a 10 watt amplifier is all you have, you do what you have to do.

Without getting too technical, we will attempt to explain why horns got their bad "rep." The efficiency of a horn is directly proportional to its "compression ratio." This is the ratio of the impedance (resistance) of the air load at the mouth (outlet) to the air load at the throat (inlet) where the driver is mounted. The higher the ratio (to a point), the greater the efficiency. A highly efficient horn can approach a 50% (the theoretical maximum) transfer of electrical input energy to acoustical output energy. A highly efficient horn will play quite loud while being driven with only 1 watt of electrical power. This also greatly reduces the demand on the driver, which is the "motor" of the horn. When being "pushed" hard by the amplifier, the driver is far less likely to reach its mechanical "excursion limits" and produce any abrupt increase in distortion.

So this is good right? You don't need a big amplifier and the driver doesn't distort. What a deal! Well…sort of. There's "no free lunch" as the saying goes and that truth applies here as well. Although the amplifier needed is not large and the driver is not driven to distortion, something else is…the very AIR itself! You see, air has a limit to which it can be "compressed." The absolute limit is when it is compressed from a gas into a liquid. That point is obviously well beyond the compression levels developed in the throat of a horn but the idea does serve to prove a point -- and the point being is that even the air has its limits.

Long before the air is ever compressed to the point of turning into a liquid it becomes what is called in engineering terms "non-linear." All that really means is that "for the amount of compressive force applied to the air by the motion of the driver diaphragm, the corresponding amount of actual compression that takes place is not equal to the amount that occurs when the applied compressive force is at a lower absolute level." Whew! Below is a simple graph showing a Non-Linear relationship (not to any scale).

The upshot is that the air itself "distorts" and in fact, produces "Harmonic Distortion" in the throat area of a conventional, high compression / high efficiency horn. This happens even when it is driven to low output levels. High drive levels are not required to produce this distortion as "transient" (short duration) signals are often 10 dB (10 times the acoustic power) or more louder than the average power. Such transients drive the air into its non-linear region quite often throughout the music. The problem is aggravated even further by the fact that the distortion percentage increases as the operating frequency increases. This occurs even though the volume level has not changed with respect to the volume at lower tones. The overall phenomenon is a function of the rate of change of molecular velocity or "acceleration" and beyond the scope of this text.

So…that's where the irritating "honk" and harshness comes from. The higher the efficiency and consequently the compression ratio, the sooner the onset of air non-linearity and distortion. Often the chosen compression ratio is high enough that even quite low drive levels produce distortion. That's why many horns produce that familiar, irritating "horn sound" at just about any level. That is also why audiophiles often shun any use of them.

There is another source of distortion horns can produce that is the result of poor mouth (outlet) termination. This distortion is often less severe than that outlined above but is never-the-less significant. It will be examined further in the next segment.

Horn Theory | Waveguide Theory | Bass Driver Tech | Enclosure Tech | Crossover Tech