Why horns?

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Hi folks,

I have never heard horns. I have mainly played with BR and OB designs and found OB to be extremely appealing. I understand the adventages and disadvantages of bass reflex vs open baffle, but why would anyone build horns if open baffle does things so very well? Is it a case of finding a suitable cabinet for an exquisite driver (like Lowther)? Or do horn (BLH) speakers do something special that other designs can't do because of the enclosure design? I guess if I had an opportunity to actually hear a pair, it would be easier for me tounderstand, but since I haven't, I hope you can help me see the appeal of horns.

Thanks,

Rafal
 
I have not heard any Lowther-style BLH implementations, but I have heard three excellent horn-loaded systems: Bruce Edgar's, Steve Schell's, and Eric Overman's.

All three are horn-loaded from top to bottom. Schell's is a three-way, the other two four-way.

The overwhelming feeling is of speed, dynamics, effortlessness. In the sweet spot, they image really well, there is no feeling of multi-way. Horn-loaded bass is TANGIBLE, a good recording makes you feel that the string bass player is right there in the room with you. On microwatts, Overman's stereo sub-bass horns shake your gut.

A horn converts high-energy, low-amplitude signal at the driver to low-energy, high-amplitude signal in the room. The horn therefore limits excursion (hence the low Xmax of Lowthers works in horn-loading) and tends to be very "fast" and responsive.

I assume a good BLH implementation of Lowther shares some of the same attributes in the bass, while having the slightly more euphonic (?) sound of DR cone full-ranger.
 
I've had this discission many times with my non-horn loving speaker building friend. He thinks that since he had a pair of Voice of the Theatre in the 70s, and they were bad sounding, that all horns are just as flawed. Personally, I've never heard a good horn speaker that I wouldn't take over the same driver ina conventional enclosure. Lowthers are loaded into BLH enclosures to take advantage of their ability to reproduce some low bass, without running into the wall induced by their inability to move large amounts of air in a conventional enclosure.

Lowthers, and most high efficiency drivers, have very limited excursion, and the horn allows them to couple efficiently at low frequencies. Drivers designed to operate open baffle typically have much higher linear excursion, and higher Qts.

Front loaded horns typically operate over a higher frequency range, and allow very specialized, high pressure drivers to couple efficiently to the air. Low frequency horns exist, but very quickly, their size becomes excessively large. A 100Hz horn, without room boundary effects, has a mouth several feet in diameter. The Magico uses such a horn for low frequency reproduction, but hands over the truly low bass to a conventional subwoofer below 100Hz. Front horns have an upper frequency limit, beyond which, the horn begins to limit high frequency dispersion, or roll off, due to the effects of the long air column in the throat of the horn interacting with the volume of the compression chamber formed by the air space in front of the cone or dome. Oversimplified, but there you have it.
 
Horns produce high SPL with minimum cone displacement. In BLH enclosures, the bass (and low mid) is "amplified" while retaining the same minimum movement and maximum SPL.

No movement = no distortion (OK it's actually more complex) and high SPL with low wattage means high dynamics ability.

So, no distortion, high SPL and dynamics makes for very interesting bass quality (as in slam and impact and scale)
 
My experience with the CSS FR125s in a couple of different back horns and then into an open baffle, found the bass a bit weaker in the open, but much clearer, quicker and more melodic. The treble of this driver, when in the open, took on much more clarity, sweetness and harmonic life. It was especially the trebles harmonic life that confinced me that in the open a full range driver is most beautiful sounding. In a back loaded horn, like in any kind of enclosed box, some of the sound that bounces around, morphing and mutating, will come back out through the driver--some say that the small compression chamber of most back horns makes for more of this mutated sound coming back through the cone. A straight front horn will not have this problem (but will be colored by the horn chamber). Drivers especially designed for a horn loading are generally well damped and exhibit little movement, thus making for a lovely midrange from a larger driver. Every driver I've tried in the open has even a better midrange when in the open. Having made numerous backhorns, zHorns, for several Fostex drivers and other drivers, has led me to appreciate the bass benefits of a back horn and how it can be manipulated.
 
Why horns

after 8 years BR, CL
until 1982 i constructed a lot of horns:
http://www.hm-moreart.de/70.htm


Let me start by stating the obvious: when you call out something
to someone, you automatically form a funnel with your hands.
This is what makes the difference, in sound and size, between a
trumpet and a bass tuba.
A horn is an acoustic transducer which transforms the small
membrane area of the horn driver to the considerably larger
area of the hornmouth.
It can give a sound improvement of ten dezibel !
With horns, the best pulse performance, minimum distrotion and
maximum effectiveness are possible with a low level of membrane
movement.
 
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