Hook 'em Horns!

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You've probably noticed at recent CES and CEDIA trade shows that a number of horn-loaded speakers are popping up. It may come as a surprise, too, because horns are typically considered (at least in the U.S.) to be fodder for Lo-Fi professional applications where the primary goal is volume and lots of it. Unfortunately, that stereotype has led many people to overlook horns as a legitimate and beneficial element of speaker design.

To a certain degree, horns deserve their bad reputation. Back in the middle of the last century, horns were used to increase the output capability of sound systems at a time when amplifier power was limited. Those horns also happened to sound pretty bad, but not because the theory was bad. They were simply bad horns. These days, horns are much improved, thanks to significant technological advancements in the last 50 years.

Now that horns are suddenly all the rage, you should know some of the benefits that they provide. First, obviously, is higher sensitivity and increased output through the processes of compression and impedance matching. The horn acts as an impedance transformer, improving energy transfer between the two drivers diaphragm and the air molecules. Given the same amount of power, a horn-loaded speaker will therefore play louder than a similar speaker without horns. Since todays power amplifiers are titans compared with their ancestors, horns may no longer appear to be required for adequate output levels in many applications. Im sure, for example, that you can find a plethora of non-horn-loaded speakers that play plenty loud in your living room. However, for larger home theaters, like 30-feet by 20-feet rooms, you will find that high-output designs become necessary if you want to reproduce all of the impact of action films. You need speakers with sensitivity ratings in excess of 94dB, and a horn-loaded design is definitely the easiest way to get there.

Second, horns shape the dispersion pattern of a speaker. They capture all of the sound energy produced by the transducers and aim itas opposed to letting it randomly propagate out according to the inherent dispersion character of the individual transducers.

Most of the time you want a speaker to cover the entire audience but not spray the whole room with stray sound energy. Its virtually impossible to accomplish this without a horn or waveguide of some kind to focus the speakers dispersion. Transducers in a bafflecalled a speaker cabinetwant to radiate most frequencies in a spherical (bass) or hemispherical (mids and highs) pattern. Unless the audience is on both the ceiling and the floor, 180-degree horizontal and vertical dispersion is a bit too broad.

Interestingly, horns do not always narrow the dispersion of a speaker. For example, a two-inch tweeter will produce an extremely narrow beam of sound at very high frequencies compared with a three-quarter inch tweeter. However, if the right kind of horn with a three-quarter-inch throat is placed in front of a two-inch transducer, its high-frequency dispersion suddenly becomes like a three-quarter-inch transducer but with the output capability of a two-inch. The additional output of the two-inch tweeter is harnessed without sacrificing the ideal dispersion character of a three-quarter-inch tweeter.

Third, horns can provide constant directivity, which is a fancy way of saying that the dispersion does not vary with frequencythe dispersion at 5 kHz is the same as the dispersion at 15 kHz. Notice I said can. Horns are not always constant directivity. In fact, the older horns that sounded like megaphones were not. They were, rather, collapsing directivity, meaning that the dispersion pattern narrowed, or collapsed, at higher frequencies. Modern horns are constant directivity. Their response is smooth and consistent both on- and off-axis. Listeners spread across a room all hear a similar response, and the reflected sound energy has the proper balance of lows, mids, and highs. Research has proven that constant directivity is one characteristic shared by all speakers that sound good to a wide range of listeners in a variety of rooms.

Understand that speakers with constant directivity can have different dispersion patterns. Some have narrow patterns while others are wide. In the professional world, you can tell whether a speaker is narrow or wide by looking at its Directivity Index specification. Sadly, the Directivity Index, like many professional audio innovations, has not caught on in the consumer market.

Horns arent a panacea, but they make it easier to get good sound in certain applications, such as large and/or high-performance systems. If you use horns properly, you can tailor the coverage pattern of each speaker to match the audience even in a large home theater. The pattern must be wide enough to include listeners on the extreme edges, but not so wide that strong reflections from surrounding wall and ceiling surfaces degrade imaging and frequency response. Horns also come in handy for non-dedicated media spaces that may be open to other parts of the house, lack an effective means of acoustic treatment, and require extremely broad horizontal dispersion. Again, horns will focus the speakers sound energy into a smooth response across the audience and eliminate unwanted reflections.

As I said earlier, it's becoming easy to find high-quality, horn-loaded speakers. JBLs Synthesis line has been around for a while, and they recently released the new Array series. Custom installation giant Triad also makes a couple of speakers, the Platinum and Classic Gold LCRs, with what they call dispersion control lenses. You will also find horns in Paul Hales Professional Home Cinema (PHC) line. Klipsch, one of the worldwide leaders in horns for commercial cinemas, uses horns in all of their speakers, including the relatively new THX Ultra2-certified models. These are just a few of the brands that are implementing horn technology in their speakers to improve the sound quality of home audio systems. Give them a try.

Anthony Grimani is president of Performance Media Industries in Fairfax, California.