# How to Make Them Horns Smaller



## Patrick Bateman (Sep 11, 2006)

In this forum I see the same question come up -
*How can I make my compression driver play lower and higher?*

I found myself answering this in another thread, so I thought I'd dedicate a thread to shrinking your horn.

The reason you might consider doing this is that *the bandwidth of a horn is tied to the depth, height, and width.*


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## Patrick Bateman (Sep 11, 2006)

_Here's the post I wrote in another thread, which sums up why you might chop a horn down to size:_



cheebs said:


> are all of the car hlcd the same basic shape and size ? what are the other shapes and sizes if any?


It's pretty easy to build your own waveguides.
Waveguides generally have straight or close to straight side walls.
Due to the simple geometry, one can build one in about an hour.

It's a great way to learn how horns and waveguides work, and I'm surprised more people don't do it.

In particular, when you build your own you can get rid of the 90 degree bend that exists in the Veritas, Image Dynamics, and USD horns.

Another option, if you don't want to build your own, is to buy a commercial horn and chop it down to size. Here's why this is easy/effective:

1) A horn provides directivity and gain for a compression driver.
2) high frequencies are very short. For instance, 10khz is 3.4cm long.
3) Because high frequencies are so short, you can remove as much as half of a horn body and it will still work. In fact, you may reduce the bandwidth by only 20%.









For instance, the horn in the middle is about 15cm deep.
If you cut it in half, it will be 7.5cm deep.
You'd think that would cut it's bandwidth in half, but it doesn't, because frequencies get longer as we go lower in frequency.
Due to that, the 'stock' horn, at 15cm deep, is good to about 566hz.
Chop the horn in half, and it's good to 1133hz.

*So even though the horn is now half as deep, and even though the volume of the horn is about 75% smaller, the bandwidth of the horn has only been reduced by one octave. It's gone from 5.5 octaves (500hz-20khz) to 4.5 octaves (1000hz-20khz).*

Even more impressive is that the *volume* of the horn has gone down by 75%, because it's expanding in two dimensions.

This 'trick' is especially effective if you push the horn into a corner.
There's a BMW with Image Dynamics horns that did this effect really well; basically the horn was almost flush with the firewall.


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## Patrick Bateman (Sep 11, 2006)

When you make a horn too small, a few things happen:

1) If you reduce the height or the width, the response starts to exhibit 'ripples'
2) If you reduce the depth, then the bandwidth of the horn suffers.

The good news is that the effect is fairly subtle; as noted above you can reduce the volume of the horn by as much as 75% and reduce the bandwidth by only 18%.










Here's a couple 'real world' measurements that show this.

1) The horn at the top is a Pyle PH612 ($14.) It's 6.4" x 11.9" x 4.4". That's a footprint of 335 square inches. (I'm too lazy to figure out the volume of the horn; when I say 'footprint' I mean a rectangle bounded by the dimensions of the horn.)
2) The waveguide in the second example is the 12" waveguide from the Gedlee Abbey. It's 12" wide by 12" tall by 6" deep. That's a footprint of 864 square inches, *or over two and a half times larger.*

In the measurement I've highlighted in red the areas where the ripples and the bandwidth reduction is most apparent. You can see that the small Pyle waveguide doesn't provided much gain below 1600hz. The larger waveguide from the Abbey goes almost an octave deeper, but it's also much much larger.

*Bottom line - If you're pressed for space, you might consider a much higher crossover point and a much smaller horn or waveguide.*

















^^^ This is the Pyle PH612









Here's the Abbey waveguide.

Note that you can get away with a really small waveguide if you're willing to raise that crossover point. Going from a 12" waveguide to a 6" waveguide only loses one octave of bandwidth, at the bottom end.


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## veleno (Sep 16, 2006)

Good Info, thanks!


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## veleno (Sep 16, 2006)

Patrick Bateman said:


> _Here's the post I wrote in another thread, which sums up why you might chop a horn down to size:_
> 
> 
> This 'trick' is especially effective if you push the horn into a corner.
> There's a BMW with Image Dynamics horns that did this effect really well; basically the horn was almost flush with the firewall.



Patrick, do you have a picture or diagram of this "trick" you speak of? Is it simply placing a horn at an angle facing center way under the dash?


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## turbo5upra (Oct 3, 2008)

Sub'd


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## minbari (Mar 3, 2011)

how does this effect directivity? With a home audio horn, you kinda want that uniformity. in a car you dont necessarily want uniform dispersion.

I assume that is why the horns designed for cars are the shape they are.


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## Eric Stevens (Dec 29, 2007)

minbari said:


> how does this effect directivity? With a home audio horn, you kinda want that uniformity. in a car you dont necessarily want uniform dispersion.
> 
> I assume that is why the horns designed for cars are the shape they are.




Minbari is correct here. Pattern control is one of the significant advantages to a HLCD in vehicles. Utilizing a horn with a dispersion pattern designed for sound reinforcement or studio monitoring is going to give that up. 

You can get a little bit of pattern control with angled mounting like doing kicks but its still not as effective and doing pattern control with the horn.

For example the trend in sound reinforcement is doing computer control arrays to create pattern control to improve the sound for the given environment. 

Eric

Eric


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## Patrick Bateman (Sep 11, 2006)

minbari said:


> how does this effect directivity? With a home audio horn, you kinda want that uniformity. in a car you dont necessarily want uniform dispersion.
> 
> I assume that is why the horns designed for cars are the shape they are.












The easiest way to understand the directivity thing is to picture a horn or a waveguide as a horn on top of a horn on top of a horn. (Literally infinite; you can subdivide it into two pieces or a million.)

Each segment is responsible for a fraction of the bandwidth. Highs at the throat, mids in the middle, lows at the mouth.

Once you understand that, then the directivity is simple. *The directivity is determined by the angle of the walls.*

That's why conical waveguides have nearly constant directivity, and horns have wide directivity at the low end of their bandwidth, and narrow directivity at the high end of their bandwidth.




























Maybe I'm missing something, but it looks to me that nearly all of the car audio horns have straight sidewalls, or close to it. The straight sidewalls should make the beamwidth constant up to a point.

The big difference that I see between the various models is where the *center* of the beam is pointed. In the deeper horns the center of the beam is pointed closer to the center of the car, while in the shallower horns (mini horns?) the center of the beam is crossfired at a steeper angle.

This will have a greater and greater effect as you go higher and higher in frequency, until you reach a point where only the compression driver is dictating beamwidth. For a 1" compression driver that point is 13,500hz, for a 1.4" it's 10,000hz.


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## Eric Stevens (Dec 29, 2007)

Patrick, 

The directivity or dispersion pattern is controlled by different parts of the horn in different frequency ranges. The throat area primarily affects higher frequencies, the mouth controls the lower frequencies. 

Just angling a horn designed for other uses will not accomplish what needs to be done.

Eric


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## Patrick Bateman (Sep 11, 2006)

Eric Stevens said:


> Patrick,
> 
> The directivity or dispersion pattern is controlled by different parts of the horn in different frequency ranges. The throat area primarily affects higher frequencies, the mouth controls the lower frequencies.
> 
> ...


Agreed. But be careful with your terminology; the mouth controls the lower frequencies _in the horns bandwidth._

"Each segment is responsible for a fraction of the bandwidth. Highs at the throat, mids in the middle, lows at the mouth.

Once you understand that, then the directivity is simple. The directivity is determined by the angle of the walls."


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