Advantages and Disadvantages of Different Full Range Enclosure Types In Particular Situations
Read all 6 design types in order
1. The Direct Radiator, Cone Woofer
This design of cabinet has a cone woofer and dome tweeter. It's a non-horn loaded speaker. You will find this type of cabinet in Hi-Fi applications or recording studio control rooms. The direct radiator is basically a point-source reproducer and made to have as wide of coverage angle as possible. Because this type of speaker fires sound as wide as possible, it has a very good near field listening area. However, it needs to be in a fairly dead (acoustically absorbent), non-reflecting environment to sound good. Because this speaker design shoots 98% of its sound in areas where you are not in, this type of speaker would sound unintelligible in an acoustically poor, reverberant room. In reverberant rooms, very little of the original music program will reach your ears and most will end up on the floor, walls, and ceiling and thus will simply bounce back and fourth. Other speaker design types are made to deal with the problems caused by reverberant environments, this one isn't.
2. The Direct Radiator Woofer with High Frequency Horn
The most widely used PA speaker in the world is probably a 12" or 15" woofer with a high frequency horn mounted above it. When we refer to a "horn" we are talking about a horn loaded projection device with a high frequency driver mounted on the rear of the unit. Click for a picture of a cabinet that uses a horn.
The ability of your speaker to shoot a portion of its output in a smaller, more defined area is called 'pattern control.' The first step in improving the pattern control of your speaker is to use a high frequency horn. This is an improvement in your ability to focus the upper mid's and high's to where your audience is and nowhere else.
If your budget is limited to one box per side, a 15" with a 90º x 40º dispersion high-frequency horn would be a good first choice. For example, our 15-2-SS, and 15-X-SS series is designed for this purpose. This 15" with a 90º x 40 º dispersion high-frequency horn box design is not too large to be unmanageable and has a wide enough dispersion to cover most smaller-sized events. The next step up from this would be to have two of these boxes per side with a more narrow horn dispersion angle like 60º x 40º.
3. Cone Woofer with Horn Loaded Mid-Bass & High Frequency Horn
Let's say you start doing more shows, your system is growing in size, and you decide to tackle larger rooms. It costs a lot of money to acoustically treat an auditorium or gymnasium. Chances are you are going to find yourself in a large room with a reverb time of 2 to 5 seconds before the sound quiets down. You can get a ball park idea by clapping your hands once loudly and counting the seconds until the sound quiets. Your going to find out that the wider dispersion system you have won't perform to your expectations.
The next step in improving the directivity of your system is to use a speaker cabinet that horn loads the lower mid's as well as the high frequencies. Tremendous improvements can be heard in auditorium or gymnasium if you can add control in the 400 Hz to 1 kHz range. Pattern control in these frequencies not only helps in overall sound reproduction, but also helps with mid-bass feed back problems that arise in highly reverberant environments.
The only downside of this speaker design is the fact that the size of the enclosure will be larger and more expensive with the addition of a mid-bass horn section. If you don't horn load the woofer section, this design can be an effective trade off in box size, portability, versatility, and price.
4. Fully Horn Loaded Full Range Speakers
One step better than mid-bass and high-frequency horn loaded system is the horn loading of every component in the box. Not only do you get an improvement in pattern control, but also efficiency. With proper design, horn loaded bass and mid-range cone transducers can be as much as 6 - 10 dB louder than direct radiator type speaker designs at the same amplifier output! That's like having an amp that's four to eight times more powerful.
As discussed in the previous section, the lower we can go with good pattern control, the better. A fully horn loaded enclosure can put even more of the audio spectrum where your audience is and less where they aren't, which is where you don't want it. The narrower the dispersion of the horn, the more direct it will be and the further it will throw its projected sound. Remember, you are taking the same amount of energy and focusing it in a smaller area. It's like adjusting a hose nozzle from a wide misty spray to a straighter stream. It's the same amount of water, just focused better. You increase distance and accuracy.
By combining four or more of these speakers properly and flying them in the air you can achieve enough low frequency control to crossover to your ground loaded subwoofer section in the 80 to 90 Hz area. This gives the impression that the system in the air is producing the bulk of the sound, producing a more pleasing sound system.
There is always the Size vs. Portability Tradeoff in the pattern control of bass and mid bass horns. In order to respond and properly load to a particular frequency, the length around the perimeter of the mouth of the horn needs to be close to the length of the lowest wavelength you wish to reproduce with power. However, if you desire real effective pattern control, the length of just one side of the same horn needs to be close to the length of the same lowest frequency you wish to have control of.
Once again, you can see this results in a trade off between what you need and what you can economically transport. This leaves these really large horns to large, permanent install applications where they work well. To keep good coverage without having to transport massive boxes, you can combine four or more smaller speakers together to get improved pattern control and be more economically transportable.
So if the solution is really a setting up and combining a large number of full range boxes and getting really even pattern control, what's the best way to do it? Line arrays.
5. Line Arrays
Line array systems are a calculated combination of a large number specially designed full-range boxes that achieve even pattern control in all frequencies. Line array boxes get their upper-mid and high-frequency pattern control by having a wide horizontal pattern angle and an extremely narrow vertical pattern. Then, to get their mid-bass and low-frequency control they rely on the vertical combination of enough boxes to equal the length of the lowest note you want to control. This translates to approximately 2 meters to get down to 200 Hz and 4 meters to get down to 100 Hz.
Line arrays have a very unique acoustical property. Their output drops off at only 3 dB every time the distance from the array is doubled. Other speaker system designs fall off at 6 dB per distance doubling. That translates to line array systems going at least twice as far at the same level. Remember though, this phenomenon only occurs if you have enough vertical height in your array like we discussed earlier.
This unique acoustical property of line arrays allows you to achieve better levels at the rear of your listening area without being as loud to those up front. That's what we mean by even pattern control.
Line array systems do have some disadvantages. They usually end up being a more expensive box to purchase because of the larger number of loudspeaker components in each box. This results in more amplifiers to operate the line array system along with more cabling and expensive fly hardware. However, you end up with a system that has greater acoustic output and excellent versatility for its size. Check out our line array system and see how it's exactly what we are talking about.
6. Asymetrical Horn Loaded Enclosures
We left this last section out of our progressive explanation because this type of enclosure is usually used in permanent installations. If you are considering an installation in a square or rectangular listening area, this is an enclosure you should consider using.
The asymmetrical horn has a narrow dispersion at the top and a wider dispersion at the bottom. Just so you can see what we are talking about, here is a picture of one of our cabinets that use this horn type.
When you tilt a standard horn forward and fly it in the air , it projects a trapezoid-shaped sound pattern onto the ground with a narrow coverage up front and wider coverage in the rear. This is the exact opposite of what you really need. The asymmetrical horn corrects this phenomenon. It also has another unique quality. Because the asymmetrical horn has narrow dispersion at the top, the sensitivity is increased with distance, performing better than a non-asymmetrical horn flown the same way. This increase in sensitivity over distance results in less of a drop in sound level as you walk back to the rear of the room. This is the same 'even pattern control' concept we talked about previously. Another benefit that comes from this increase in pattern control is that you end up placing less direct sound on the side and rear walls of your installation, decreasing reverb problems and increasing sound quality perceived by your audience. If you are considering an installation in a square or rectangular listening area, this is an enclosure you should consider using.
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