Luigi from California, is one of a growing number of people who have a quality bass system, direct radiator or folded horn, upgrading to a horn loaded top end.

A substantial improvement can be made by adding an AH! horn, and the DBX PA electronic speaker management system.








Hello,

I am writing this letter to help whoever is considering buying AH! Horns and is not sure about what he will eventually get.

Before telling you about my system and the impressions from my listening experience with the AH! 700 horns, I would like to spend few words about Bill Woods for those of you who don’t know him yet.

Bill has been a researcher in the field of sound for many years and he developed different solutions in the field of PA: his technical expertise is deep and his passion for music is a clear complement to that; I consider this very important, because very often in this field you find people who love to listen to a system rather than music [ I am quoting my wife…]. Besides his outstanding technical expertise, Bill is a real gentleman who is not in the business merely to make money: he certainly does need to sustain his activity, but obviously for him giving you the ability to listen music at its best takes precedence over everything else. He will spend countless hours to find the best arrangement for your system and he will be open to all sort of technologies: if you just listen to digital formats and you use solid state amps, he won’t treat you with snobbery [ which is something you easily find with other people].

Said this, let me now describe my setup: as sources I have an old Sansui tuner, a Jolida CD player and a VPI turntable; as preamps I have a solid-state Bryston and a tube Audio Research; as power amps I have solid-state Bryston monoblocks and tube Luxman and Quicksilver monoblocks. Before getting the AH!700 horns, I had two pairs of B&W 801, one series 80 and one Matrix Mk2. I decided to keep the woofer section from one pair of them and to use Bill’s horns, driven by B&C de900 compression driver, to replace the mid and the tweeter. Given the difference in efficiencies of the drivers we went for bi-amping set-up with electronic crossovers [dbx].

As for the type of music we [me and my family] listen, it is mainly symphonic music, piano concerts, baroque music and some opera; since a couple of years we started to listen to quite some jazz as well, with preference for female vocals and trumpets players.
Last but not least, we also enjoy a variety of singers, as Bob Dylan, Johnny Cash and Tom Waits – to name a few.

Well, the horns improved the sound clarity, detail and depth of all kind of music.
Simply said, we are enjoying more listening to the same music.
It is not just my impression: it has been also my wife’s statement. She is always very critic of whatever investment I make on the stereo system, but after listening to them she approved the AH! Horns without reserve. The improvement is not apparent.

I can wholeheartedly recommend them to anybody loving music.

I’m often asked how horns differ from one another, and also how different types of horns differ in sound and design, such as exponential, tractrix, and new versions of these which carry the names of their designers. I’ve put together some observations, backed up by actual frequency response curves and measurements, so that people can decide for themselves what types of horns would work best for them.

For the past 30 years I have designed loud speakers for professional applications and more recently for home HiFi. While designing at Yorkville Sound and in the course of my career, have built and tested numerous exponential and tractrix horns. This includes hybrid profiles using a tractrix and a conical which were created to fulfill specific tasks. In professional audio, horns have to work as intended. They cannot be of unlimited size - in fact, there exists an obvious commercial advantage to building the smallest horn to do a given job well. Tractrix or exponential horns are rarely used in professional applications where clarity and coverage are an issue.

In the early 80's I built a four sided conical prototype to be converted to a bi-radial design. I was astounded by how good it sounded so I measured and tested it. This opened the door to the study of conical horns. Some of the characteristics of conical horns are….

Good directivity or power response - the hallmark of the conical horn.
Conicals keep the sound wave at 90 degrees to the wall of the horn at all times as the wave exits the horn.


...After Hughes (Peavey, Also Morse)

(this defines a conical.) The sound wave is not disrupted by the walls of the horn. For these reasons, conical horns have the best sound of any horns for home HiFi Use.

The accidental conical horn

The tractrix profile has been used in commercial products and in DIY. All exponential, and tractrix horns tend to beam as they go higher in frequency due to the squeezing of the side wall of the horn. This results in a "honky" sound and some of the high frequency information is lost, when listening off axis. This is the case no mater what type of mouth correction you might use. The tractrix profile itself is a form of mouth correction.


My first tractrix in production 1989


I have experimented extensively with all types of horns, using absorbing materials, mouth geometry, adding a foam ring at the horn’s mouth, cutting slots, and also with acoustical lenses. (see photo) I have discovered that these devices have, at best, an ameliorating effect, often redistributing the anomalies they try to correct to other places in the passband instead of eliminating them. The acoustic lens holds the most promise.



It is interesting to note that RCA acoustic laboratories analyzed the conical horn flare and mouth termination issues in the 1950's. I am lucky to be in possession of the very lab sample test horns, of which my work is based. See picture.




In listening tests, the rollback using pink noise is very slight. Few individuals have the time, money, space, and technical ability to build and compare using state of the art hardware and software. (I use a TEF analyzer, ATB B&K ,AKABAK, AJ horn software, etc).

I can, however, suggest a simple way to make some experiments for yourself, to see how horns differ from each other in a very rudimentary way. Choose a compression driver, and make a number of very short horns of only 4-5 inches in length ---really horn adapters-- for your driver.
The most critical part of a horn is the first few inches. This is often over looked. Start with a section of straight pipe. Listen to that. It will be very loud, and very colored. Next, try an exponential horn of the same length, then a tractrix - they will be progressively less colored. Finally, try the conical section. It will be the most natural sounding and uncolored.
Musical instruments such as trumpets and trombones are not conical. They are designed to produce harmonics, the very thing we try to avoid in a sound reproducing device. The more the horn is squeezed, the more the harmonics. On the other hand, voice producing devices such as megaphones are always conical.



Horn design is always a game of balancing the factors of length, angle, directivity, low frequency cutoff. There are many ways to tweak a horn’s response. One is to add an exponential throat adapter to a conical horn. This colors the sound, but improves the measurements. Another is to add a secondary flare to a conical to deal with the internal reflection issues.

One other area which deserves discussion is the crucial issue of the beginning of the horn- the throat- and the drivers being used. Compression drivers all have a horn beginning within the driver which you cannot see. The internal geometry of the driver and its phase plug has a direct relationship with the horn.
Sometimes a small exponential throat will be of benefit, sometime it will not. Once again it is a question of degree, and audibility.
If a driver has an exit a half inch, you will likely get to 12kHz, but a driver with a 2 inch opening will be lucky to reach 8kHz. Directivity decreases as the throat diameter increases. Also, if a 2 inch exit diameter driver is being used on a horn expected to go up high, the issue of mouth reflections coming back into the horn pales compared to the very real problem of high frequencies getting “stuck” across the 2 inch throat opening of the horn

As you can see, designing horns is actually a very complex equation involving parameters that all need to be addressed so that an optimal design results. There is no such thing as an “ideal” horn. But certain basic flare profiles work vastly better than others if the best sound quality is the most desired result.

Some general horn examples under test.
I have hundreds of pictures, hundreds of horns, but this is enough for now.







AH 700 with and without flare and throat...it's not as though I missed it somehow...



Itawa horn, and odd drivers I use to cover a complete range of drivers when testing a horn
Also A multiple flare horn after Olson

We stand on the shoulders of giants...

Olson
Holland and Newell



I built the Holland horn soon after his paper came out. the gray one was cut down from a 24" mouth version

Morse
Geddes


Here is 90 deg conical with and without rollback. Also a tractrix, and a tractrix mouth coupled to a conical throat

Danley
Keele
RCA
Western Electric
The US Navy



A battle annonce speaker with special articulation drivers. 119dB 1w/1m!

...and many others.