Why is the enclosure so important? The Enclosure is the most important part of a low frequency musical speaker system, without a high quality and correctly made enclosure the woofer will not have the correct bass alignment and will not perform correctly as intended. A very high quality bass woofer in an incorrectly sized enclosure will not sound impressive at all, When an average woofer in a correctly and high quality enclosure will sound amazing and accurate in comparison, this shows very clearly how important the enclosure is for a bass alignment, they have to be designed as one system and not treated as separate parts. A metaphor I like to use is: you can have very big strong muscles but if you have no bones in your body you will not be able to use your muscle to there full potential. This is the same for a bass woofer, without the enclosure and the correct loading of air inside it, you will not have the correct springiness which will result in a sound quality that is flat, wobbly and empty. So why is this air so important? All woofers have a natural frequency or movement at which they will resonate with very little power, this is called the Fs. Bass woofers have very low frequencies, 30Hz for example, the lower the number the deeper the sound is typically from the woofer, at this frequency it will have a very large movement and the air space around it has a great influence on the movement of the speaker cone so this affects the sound we hear. Air is Springy A very small sealed box has very little air inside it, now air can be compressed but once it is compressed it will try and return to the original static air pressure, called atmospheric air pressure. If you have ever seen an action movie when people are in an aero plane and the door opens, you see people being seeming sucked out, this is not really what is happening, they are really been blown out! as the air pressure inside the plane is much higher than the very low pressure at such high altitudes. Another good example is: When you blow air into a balloon, you are forcing the air into the balloon with your flexible lungs ( Lungs are like the woofer cone moving the air) Now there is very little air space inside the small balloon ( the Balloon is like the Enclosure) plus the rubbery skin of the balloon is also trying to push the air back into your lungs to equal the pressure. The pressure is very high inside the balloon once you force the air inside it and you can feel the pressure in your mouth, as the air tries to equalise or escape! the very same can be said for a woofer in a sealed enclosure. When the speaker cone moves with the music this compresses the air inside the sealed box, if the box is very small there is very little air inside the box, so the air compress very quickly, this will push against the speakers cone very quickly and stops it natural resonance, hence it will not natural or sound powerful or accurate. The correct amount of air space is very important for a sealed low frequency bass woofer to allow it to perform to its full potential, giving its a natural deep sound and high power handling, this also helps protect the speaker as the air helps control the cone motion. How would your car handle without the springs in the suspension system? it would work and still go round corners but the quality and firmness would be lost as there would be no damping and this is the very same principals in a bass woofer. In the car we have the steel springs providing damping and in a bass speaker we have the air providing damping, if you get it right the bass will be tight and firm and controlled, get it wrong and it will be flat, sloppy and shallow. Ported or vented Enclosures and how they work The air is being let out the box so how could it provide damping to the cone? Ported and vented boxes work on a different principal from the sealed enclosure. Well the air is being let out the enclosure so there is less damping but there air inside the tube has mass, this is like a plunger when the bass woofer moves up and down it drags the air inside the port or vent backwards and forwards. This provides the damping we need for the speaker and can allow high volumes as there air can be equalized but there is a problem, the air inside the port will only provide damping down to a certain frequency after that point the port allows air to pass through it will very little or no resistance so there is no damping. The affect on the bass speaker is it has no real control on the speaker cone motion below that tuning frequency of the port, apart from that which is given to it from its surround and dampers. The result is the sound of the speaker can become muddled and the speaker is venerable at below the ports tuning frequencies as there is no real resistance, so given a very powerful signal from the amplifier deep musical signal below the ports tuning system provides not protection and the woofer can be damaged. Lucky for us we are not talking about average woofers, we are not talking about Shadow Works woofers, as all our bass woofers have protection against such damage in ported systems. The quality of the enclosure is very important. What difference does the enclosure make if I have the correct air space for the woofer? This is when things get picky, even if you have the correct air space and its very well made and strong, the quality of the materials makes a very large difference to the sound quality once again. If one use cheap MDF or chip board to make a speaker enclosure it can work, but not to the full potential of the woofer - it will not compare to a high quality and I stress high quality, MDF enclosure as there is a large difference between good and cheap MDF. Bare this in mind when choosing a material for an enclosure and when buying an enclosure as these poor enclosures have very little weight, typically under 5Kg per box. Plywood is also a very good strong material for making enclosures, these are natural fibres and will benefit from having bracing or ribs glued inside the enclosure, as they can flex under high pressure and this can create a box sound or coloration, remember to account for the bracing as this removes air space from the total volume of the enclosure. Examples of exotic box materials are: cast concrete, 22mm Marble, 22mm Granite, 25mm Slate or 18mm Glass. All have been known to be excellent materials for enclosures but can be costly and difficult to work with. However, some of our customers have told us about there excellent results with these materials and are extremely happy with the performance of their woofers. The Stuff or not to Stuff ? Isn't this important to stop resonance or standing waves? Well this is an old chestnut and misunderstood by many, the fact is adding stuffing, wadding, foam whatever you fancy, will not absorb standing waves as these bass wave lengths are very long, much longer than the interior of a sealed box with only a transmission line being the design exception. The reason for adding these materials is to reduce reverberations inside the box, the same thing that happens when you talk in an empty room, you don't have an echo but a reverb that is very quick and harsh. This happens inside the enclosures as well, stuffing reduces this effect and can help make the woofer sound taught and less hollow at times. People can add heavy damping materials like lead or bitumen as another means of removing vibration but this will not remove standing waves. On the whole stuffing is important for some reason but not the ones people typically believe, stuffing will have an affect on the MMs (the mass of the cone) this is not a well understood mechanism but the result is the higher the MMs the lower the resonance of the woofer becomes so the woofer sounds deeper as the Fs resonance will have changed because of the extra weight inside the box which is connected to the cone via the air load. Adding stuffing can reduce the air space if you have a enclosure that is to large, so on the whole its a good tool to have in the speaker building world. Should I Bracing the enclosure or not? Lots of people disagree on this point, I would say bracing on the whole is a good thing to have, but it more time consuming to make well and needs to be very precise to get the full benefits. Bracing reduce resonance of long or large panels of an enclosure and makes for a more solid and purposeful enclosure on the whole. If bracing is beyond your wood working skill then I would recommend adding simple strong ribbing to the walls and surfaces of your enclosure. This is a very effective technique , simply add stripes of wood that are glued down to the largest panels and these behave as ribs, just as in submarines and high pressure vessels that can withstand modern deep water cruising . The Ribs should not be boxy or square they should be rectangular in profile like this shape ? which has more strength than a simple box section like this shape ? and add lots of glue and clamp or weight or screw these down until the glue dries. This make a difference in the weight and strength of your enclosure and is a very cost effective method if done well over normal more complex bracing techniques The Conclusion What is best enclosure ported or sealed? Well this is a billion dollar questions and the answer is............... it depends on your woofer, the system and sound quality desired. There is no perfect answer and there is no perfect enclosure, each one has merits and down sides but they all work well as proven by many designers around the world. The sealed system is my personal favourite as the bass has a tension and quality that is very hard to attain with a vented system as there is not the same level of compression, on the other hand a ported system can have higher sound pressure levels even when the theory says it should not. I would say its apples and oranges. Whatever enclosure you choose, as long as it can provide adequate damping and control over the cone you will not be disappoint with the results The Infra Demon is a registered Trade Mark of Shadow Works Ltd and Shadow Laboratories.Registered in Scotland No SC 266946. Shadow Works Is an Equal Opportunities Employer.