|
There are 3 main types of enclosures used for subwoofer design. These are sealed, vented, and horn loaded designs. The rest are combinations of these three.
Sealed Boxes:
In professional sound applications, you don't see many sealed box subs. They are mostly used for mid-bass output in larger vented full range designs. They are more popular in home theater and car audio sound applications. Sealed boxes roll off in their low frequency limit curve at 12db per octave instead of 24 db like their vented box cousins. Cone excursion requirements are a lot higher in sealed boxes as the frequencies go lower. However, this is why they are slower to roll off below the cut off of their tuning frequency. Sealed boxes do not require as much air (cubic space inside the box) to go as low as vented boxes, but they are nowhere as efficient either.
Vented Boxes:
Vented box designs are by far the most popular box for subs in professional sound applications. Properly designed, vented boxes handle much more power in the lower frequency ranges. This is because the port actually produces most of the lowest notes, reducing cone movement tremendously. If you want high efficiency in your subwoofer with modest box size this is a good compromise. You should note that your box size will grow quickly if you want your box to go lower then 40 Hz. We at Ramsdell Pro Audio achieve better all around results in the pursuit of the low note by mutually coupling smaller, punchier subs than by larger boxes tuned lower. You may notice this in the design of our subwoofer products.
Horn Loaded and Bass Horn Subwoofers:
If you are a no compromise individual, or you need to be for a particular application, then this is the subwoofer design for you. When it comes to being able to extract the maximum capabilities of a low frequency transducer, the low frequency bass horn stands alone. Horn loaded speakers can be as much as 12 db louder on a watt by watt basis then their vented box cousins! Basically, a smaller group of horn loaded subs can outperform a much larger group of vented subs and do it with less amplifier power. This smaller grouping of subs will result in more even coverage with less peaks and dips in your low frequency levels. Also, voice coils of speakers in horn loaded boxes can run much cooler for the same acoustic output levels. This 'cool coil' property of horn-loaded subs results in a lot less power compression and reduction of long term output loss. Bass horns are finding a new lease on life in the professional sound world as one of the few types of boxes that can produce the output needed to keep up with today's line array systems. As the professional sound industry rushes to re-invent the past, we encourage you to consider this unparalleled enclosure design.
Low frequency notes travel more effortlessly through air than high frequencies, because they don't get absorbed by the air as fast as high frequencies do. Because of this property, they travel farther. In technical terms, air is not an acoustically linear medium. Over the years, we've had a number of our customers tell us that bass horns "throw better" then other types of subs. We have never been able to measure this with single units placed side by side and run at the same level. However, we have measured that properly designed bass horns couple better than vented types when placed in groups of four or eight units. Also, low frequency horns need to be allowed one wave length of the lowest frequency they are going to be called on to reproduce to fully develop. In the case of a 30 - 40 Hz note, this could be 40 - 50 feet from the box. This phenomenon probably contributes to the perceived increase in "throw" of the box design. On the flip side, this property makes bass horns more difficult to work with in smaller rooms. It seems to complicate this problem even worse if more than one location in the room is used for subwoofer placement. Vented box designs usually will work better when you encounter this type of problem in an installation.
<< Go to Back to the Beginning
- Choosing the Right Crossover Point
- General Rules to Follow to Get the Most Out of Your Subwoofer Investment
- What Type of Subwoofer Design Would be Best
View Full Article (Printable) www.RamsdellProAudio.com © 2004 Ramsdell Pro Audio. All Rights Reserved. |
