Horns V. Vented Subwoofers

January 12, 2012

Which is better, Horn Subs or Vented Subs? Well, which is better, chocolate or vanilla? Your choice, in either case, will likely be based on your preference, your past experience, but not on empirical data. Let’s dig into the data…

During all my years in the business, I have been on a quest for the ultimate subwoofer. Horn-loaded subs were my preference and I started BASSBOSS originally based on the performance of the B-One and B-Zero horns. We developed a lot of horns over the years, and continue to do so, because horns have a number of desirable and beneficial properties compared to vented boxes. There was, however, just one thing I was always missing from the horn-loaded subs: Really DEEP bass!

Other than building individual horns that are absolutely massive, or building a segmented horn comprised of many separate elements that combine to make one massive horn, there was not a practical way to build a subwoofer horn that was portable and would reach a minimum frequency of 30Hz. I had to look for a more practical way to deliver the deep bass I wanted to incorporate into the horns.

Eventually I designed a hybrid box that incorporated a vented section with a long, partially folded horn-loaded section. It was 45″ square and 24″ tall. Although the box was also quite large, heavy and complicated to build, it was smaller and lighter and less complicated than the B-Zero… and it produced massively low bass compared to the B-Zeros. That particular design was really time-consuming to build, so it was impractical from a size and cost point of view. It did go low but the long horn and the vented section still left something to be desired. It didn’t have the dynamic impact that the B-Zeros did, and the box could have gone just as deep and been a lot smaller without the horn section.

What I then did was begin to develop a vented box to see what I could achieve with a highly optimized vented box. What I got was a really magnificent, musical and ruler-flat subwoofer with massive deep-bass output capabilities and virtually unlimited power handling. As good as it was, it still lacked the impact I loved about the horn-loaded boxes.

In order to deliver both impact and depth I started combining the two types of boxes and found it to be challenging to integrate the two types. I could get the super-deep bass I wanted from the vented boxes and I could get the massive impact from the horns but getting them to line up and do it together took a great deal of time, measurement and experimentation. When I finally got them to work together properly, it was magic! Massive shock impact with a thick, rich depth I’d never heard or experienced from any horn subs alone, especially since they had to at least fit through a door!

Not only do I understand and agree with the love for the impact of horns, I have improved upon it, to make it even more impactful. Think of it this way, if a 160 lb guy (80 kilogram) hit you in the chest with a solid punch, it would be a hard hit, but if that man was 320 lbs (160 kilograms) that hit would move you much farther! Why the reference? To go an octave lower requires four times (4x) the power, and displaces four times the air for the same sound pressure level. If you can extend the power behind that initial hit by an octave, then it effectively hits four times harder because it literally is four times the mass of air behind the hit.

This is effectively what we can do with the combination of the horns and vented boxes. The reason we do it with vented boxes is because to do it with horns would take up more than four times the space and that becomes impractical for both portability and for floor space in a nightclub.

In this case, for this purpose, I’m not using vented subs in the place of horn-loaded subs, I’m using vented subs to extend and improve the impact of the horn-loaded subs.

Done correctly, horns are awesome and wonderful things, but they have limits. There are three factors that essentially limit a horns performance. The first is its length. The horn’s low frequency limit is determined by how long it is, so its length, from driver to mouth, multiplied by 4 is the wavelength below which it is relatively ineffective. For a horn to be effective at 30Hz, it needs to be 112.5”, 9.375’ or 2.86m long. Some people say they have found ways to break that rule but any breaking of that rule involves compromises, and I’m not a fan of compromises.

Here’s why you need the length: The internal path length between the driver and the mouth must be long enough to support one-quarter wavelength of the lowest frequency that horn (or array of horns) needs to reproduce. If the horn isn’t long enough, the pressure wave will exit the mouth while the cone is still pushing forward and the “load” on the driver will fall off, losing efficiency and allowing the driver to hyperextend. Therefor, a horn must be long enough to support the expansion of the wave to the lowest frequency you need it to play. Assuming 30 Hz is your low frequency target, the horns you choose must be AT LEAST 2.85m long.

The second limitation is what’s know as the “flare constant”. This is the rate at which the area of the horn increases relative to the distance from the throat, or driver. As a general rule, the lower the target cut-off frequency, the slower the horn will flare (expand). The combination of the long horn and the slow flare that are necessary to create a quasi-portable horn with good low-frequency sensitivity and relatively flat response demands a lot of folds and a lot of wood. This makes their construction more complicated and more expensive to build, and makes the boxes heavier and larger. When designing a horn with a low frequency flare rate, one must choose on a continuum between efficiency and size. Most horns that are made in a reasonable size are NOT built with a low flare constant and a long enough path. One, the other or both are compromised. This leads to peaky response and “horn honk” and a total lack of depth in their performance. These are compromises I’m not willing to live with.

The third limitation is that a horn (or array of horns) must have a radiating area whose perimeter is at least one full wavelength of the lowest frequency to be reproduced. For 30Hz that would require the perimeter of the frontal area of the horn array to be 37.5 feet. That calculates to an array just over 6 feet high and 6 feet wide. (3m high by 3m wide) Anything less than that and the low-frequency response is compromised. Not only the lowest frequencies are lost, but the response again tends to become peaky, so you lose the smoothness of a flat system.

From this information you can gather that in order to install or transport a horn-only subwoofer system with flat frequency response to 30Hz would require a large amount of space, many cabinets and lots of money. But why bother? Low frequency response is NOT what people love about horns. It’s the impact and immediacy of their delivery. It’s the tight, punchy-ness and the tremendously dynamic transient response. Therefore, if you use the horns for THAT function and use direct radiators for the extended low frequency response, you can use smaller horns that are specifically designed for and perfectly suited to delivering the impact that people love about them!

While a single horn can’t achieve flat frequency response and low frequency extension in a reasonable size due to the limitations of low frequency horn-loading, a single vented box can reproduce extremely low frequencies. Not at the same efficiency, but in a smaller, lighter, often more cost-effective and portable sized enclosure. Power and power-handling become more significant factors with vented boxes, but they can do what horns cannot. It works both ways. Each is better than the other at what it does best.

If you want the best of both worlds, the trick is combining the right horn with the right box in the right way. The vented box you choose MUST offer low frequency extension, well below the horn, and must be capable of output sufficient to match that of the horn. Horns are naturally more efficient than vented boxes, so they require less power. Within their operating band, they convert more of the electrical energy into acoustical energy. Boxes are less efficient than horns, so in order to have a box (or boxes) able to match the output level of a horn an octave lower than the horn, that box must be able to handle a great deal of power. In essence, the trade-off between horns and boxes is size and complexity versus power demand. Vented boxes can invariably be built smaller and lighter than horns but they require more amplification to reach equivalent output.

The reason direct-radiating boxes can’t deliver the impact of horns is due to the limitation of coil/cone inertia. In most cases, the vented boxes can’t reach equivalency with horns before they reach either an excursion, thermal or distortion limit. In the past, the answer has been to add more vented boxes until there are enough drivers to match or beat the SPL of a horn-loaded array. Unfortunately, all those vented boxes might be able to match the output LEVEL of a horn-loaded array but not the transient dynamic response and impact of the horn-loaded array.

This is the point at which the Sub-Mergence system was developed. Its low-frequency component is the ZV28 subwoofer, which extends system response to 21Hz, and its horn component is called the Z5/D. This solution takes advantage of both technologies’ strengths to create a system that offers the benefits of both with the weaknesses of neither. The combination overcomes the limitations of both the boxes and the horns. In the Sub-Mergence system, the cabinets are properly aligned and integrated with each other, so the shocking impact of the horn combines with the extended depth of the boxes while keeping the size and the power requirements reasonable and affordable. The boxes weigh 220lbs each, are the same size and they interlock with each other.

So why is it called Sub-Mergence? Two reasons: The first is because we’re merging the benefits of two different loudspeaker technologies.

The second is the experience the system delivers. It’s the experience of being immersed in the music, submerged in it, swimming in it, being a part of it. It’s beyond hearing it. It turns the air into a liquid. It’s the transcendence that happens when you fully integrate the senses of hearing and feeling into the experience of music and dancing. For those who get it, it’s an instant addiction. It takes your breath away, modulates your voice, caresses your skin, moves your clothes, blows your hair and gives you warm chills…. It’s what happens when you hear a familiar song and realize there are layers in the music you’ve never heard before. Frequencies below the capability of what you’ve heard before, dynamics above it, textures behind it and subtleties within it.

Such a system will allow you to listen at very high levels and not be in pain. It sounds big and effortless and open. From barely on to dangerously loud, it will be crystal clear at any level and will keep the same character no matter how high you turn it up. It offers tremendous loudness with no compromise in quality. Its intelligently designed so that you have enough headroom that you never force it to strain and distort and compromise the experience of the audience.

With the Sub-Mergence system there is no need for you to have to choose tight over deep or deep over tight or make any compromise. BASSBOSS knows subwoofer systems better than anyone.

Now, if you want the best of both worlds fitted into a much smaller package, into one box in fact, now you know the path that led to the VS21. V for Vented, S for Short-horn, 21″ woofer. The merging of the depth and the impact characteristics everyone can agree are good but can’t decide which one they like better… Why choose? The VS21 is a deep-bass, punchy-bass swirl of chocolate vanilla and cool!

And there is also something very big on the horizon! It’s called B.O.S.S Concept and it’s the ultimate realization of the uncompromised subwoofer horn!

Music Made Physical