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Discussion in 'Amps and Cabs [BG]' started by Davidoc, Mar 11, 2003.
What do they do?
Using a horn makes a loudspeaker more efficient. The horn has to be the right size for the frequencies it will be augmenting however. For bass, this means big. To fit the proper length in a speaker-shaped box, the horn can be "folded", like most brass instruments aren't straight tubes.
Another of the reasons that folded horns were (are?) popular for bass is that the fold creates a longer path, allowing the fundamental more room to unfold. Some low notes actually require many feet for the actual (ie: not the harmonic) wave to be produced. I'll let the experts debate this as I am uncertain, but I seem to recall that a low B requires something like 18 feet... on the other hand I may just be a victim of the Acoustic 370 marketing blurb.
I used a pair of folded horns back in the late 80's for the bottom end of a bass rig. They provided good long throw bass but not very much stage volume close up (which is a good thing as Bass tends to be boomy on stage). Folded horns tend to have the Driver inside the cabinet, so high frequencies tend to get lost. The shape and "folds" of the cabinet affect the way the sound is projected.
Most Outdoor concerts I have been to use Folded Horns. Large indoor concerts (such as arenas) that I have attended almost always use folded horns.
They were very popular in clubs in the Late 80s and Early 90s but I don't see them as often anymore (in clubs).
I have found that front loaded subs tend to drop off quicker (and much louder on stage) than folded horns. I have also found that front loaded subs tend to have more hot spots and dead spots than Folded horns. Next time you are in a club, walk around and see if the Bass sounds good in some areas but weak in others. I did not have that problem with folded horns.
The biggest downside to Folded horns is weight and size. An efficient Folded horn has to be large and have several folds (adding weight) inside the cabinet.
Here is a link to some Folded horn designs:
oddio - You're info is certainly something I understand as a layman, (lord knows, I don't know acoustical physics or electrical engineering at all).
But I used an EMC B450 for a long time in the late 70's ("Electronic Music Corp of Cleveland" 3x15" in a reverse-W enclosure with 30 ft. of folded horn). As the owner's manual said, you couldn't really hear the thing until you were at least 18ft. away. I didn't have a 5-string until long after I stopped using that amp..........but the point of "sonic convergence" was at least 18 ft. away from the speaker enclosure Either way, I'm sure it's why I have severe tinnitus in my right ear.
I suspect 60+ Hz is about as low these horns will go before significant roll off occurs. To reach full performance, the horn's air column length and mouth diameter measurements must be at least as much as the wave length of the lowest produced frequency.
18 feet is the wave length for a 62 Hz note. An 18 foot mouth diameter is approximately 25 square feet. A mouth size less than a 5' x 5' opening will degrade the performance. A full blown bass horn operating down to 31 Hz will be 36 feet long, with a mouth diameter of 11.58 feet, or 10.25 feet square.
Even degraded, the horn acts as a significant wave guide, making the cabinet into a "long throw" device. Even a modest horn like the ones above will "throw" much farther than a direct radiator cabinet. I've noticed that one full wavelength distance from the source is required to clearly hear the bloom.
From one layman to another...
Your comment on the minimum distance is the way I remember it too, which is prolly why 18 feet sticks in my head. I still have my old Traynor Custom Special head with an 8x10 and folded horn 18. It was the first amp I purchased "brand new" (in '71), and boy does it sound great if you're back a few car-lengths. Too heavy to lug, so I don't know why it's still here... hmmmm
It was the years I spent next to a Hammond B3 w/ Leslie rotor horns that did my hearing in (tinnitus).
BGavin - that's excellent info! Thanks for adding the "facts".
I love folded horn PA subs. I don't know that I'd ever use it for bass though unless the stage is huge, and even then probably not.
One of the things I like about Eden cabs is their porting which kinda overlaps a bit with folded horn theory. The speakers are front loaded but the air has to travel quite a distance before it leaves the cab, giving them a nice "throw" characteristic. I wouldn't call them a folded horn, and it was probably not even part of the intended design, but they throw nicely (ie not too much, not too little).
One of these days I'm gonna make a PA sub that has one front loaded speaker and one folded horn. The trick is making it small enough to fit in a van.........'
mmmmmmmm. . . I won't dispute your experience, but I don't think that's the reason. The "flare" is a very important part of what makes a horn a horn. And it's not about how far the air travels - remember, it oscillates, and it doesn't go very far. A horn is an impedance matcher - it helps smooth the transition between what's going on around the speaker (a little air moving a lot) and what's going on in the room (a lot of air hardly moving). And anyway, the distance from the speaker back and through the port isn't very far at all as far as bass is concerned.
Please do question my experience. I'm far from a guru, but I'm learning. So please pull me up if I say something silly.......
As a part time sound guy, the folded horn subs I've used have all had a fairly long passage of travel before the sound even reaches the flare. Some have such a long passage that it is necessary to put a slight delay on the mid-high speakers in order to get them firing the sound at the same time.
As you correctly point out, the eden does not have a flare so is therefore not a horn. But can you see where I'm comming from?
Oh when you say a horn is an impdeance matcher, would it be correct to say then that any ported speaker also an impedance matcher?
Oops, I didn't mean to imply that horns don't have a long sound travel - I was talking about the air. I'll just come right out and say though, that a simple ported box behaves nowhere near a bass horn. Front, rear, port, whatever.
A ported box is not an impedance matcher. A ported box is a resonator, which changes the system from second-order to fourth-order. The port, and driver, are still fairly mis-matched to the room air.
Some horn designs use horns only for the port, some only for the driver, you can also do both (with the same, or separate, horns). The horn part is distinct from the tuned box part though - it's a combination of the two systems.
One thing needs to be mentioned about horns. They are dependent on where they are in space. (what?) a speaker in mid-air (like a flown box) is in full space, on the floor is in half space, on the floor with a wall behind is 1/4, and in a corner, 1/8 space. So depending on where you put a horn (folded or not) you get a lower cutoff. The less space you are in the more bass. That's why a Klipschorn in a corner can go down to 38 hz and it's maybe 3' high and 2' wide with an effective mouth area of about .85 sq. meters. (what's that in sq. feet?)
Also, the upper limit of frequency can be extended quite a bit by curving a horn instead of folding it with sharp corners. Not necessarily easy to do, but it can be done.
Stay Low, no matter how you get there.
The Klipschorn uses the walls of the room as the extended walls and mouth of the horn. The effective air column length and mouth diameter are much larger than the physical dimensions of the box itself.
A Klipschorn will not operate at all unless it is in a corner.