Hi,and welcome to my speaker page.One of many.I hope you find the info helpful. As you can see, there's still a lot to be done ,but for starters we'll go over the basics.
One of the main advantages with the ported box is the extended bass range. Small speakers perform quite well in vented boxes if the enclosure is the correct volume and tuning frequency for that particular driver. Some models,however have the port on the back of the box. Correct placement is a major factor in getting a good bass response as the port air has a tendency to interact with the wall, or preferably corner of the room. Most speakers are designed to be placed in corners by the way.
One of a less obvious disadvantage is the tendency of the port to unload the driver at subsonic frequencies. This can be a problem, especially if the system is used at high power levels. An infrasonic filter is a good idea in this case and should be considered if you have this senario and are buying a new amplifier.
Vented boxes need more thought when being designed as well. Correct tuning of the box for a specific driver is critical for optimum performance.Vented enclosures, if properly designed, can have a flat response curve till cutoff. Sealed enclosures on the other hand, roll off smoothly as the frequency decreases. Vented boxes can also sound a bit 'peaky' at some frequencies while on the other hand sealed enclosures sound much smoother in their bass range.
This provides a cleaner bass response over the range of frequencies that particular system has to cover. Sealed boxes also have better control over the speaker at subsonics. They are also easier to design and build when it comes to the crunch.However, to get a good bass response from a closed box a long throw woofer or high compliance woofer should be used. These woofers "grab" more air with a resultant better bass output. This may be a must, especially if just a pair of stereo speakers is driven by themselves without a subwoofer.
Even if one of the above enclosures could be proven as better, it would not necessarily become a universal choice. There are, of course, other types of enclosures than the ones mentioned here. One is the transmission line enclosure and the other the horn. The two types just talked other however are certainly the most common.
As far as I can see, it comes down to two factors:
-You might have your mind set on a price range, and therefore a particular driver. The parameters of that driver would then determine the type of enclosure,persuming you are designing the system properly.
-Matter of taste.
The best way, I reckon, to build a speaker system, is to choose a driver, then an enclosure type to suit, and then design the enclosure within the parameters of the driver. If you are dead set on an enclosure type (i.e. It's gotta be Bass Reflex), then there is one important factor to consider before you deside on a driver: the Q of the speaker.
It shouldn't be above 0.4 for vented boxes, or ideally under 0.4 for sealed enclosures. A Q of 0.35 is about the minimum for sealed boxes.
If you have a vented box in mind and its Q is above 0.4, then give vented boxes a miss.
In my opinion, 18 mm wood should be the minimum thickness to aim for. You know then, especially if the box is only 10 litres or so, that it will be rigid enough. Obviously as the box size increases, material thickness should increase.
Another useful thing (and this can be done with any box) is to brace it internally by tying the opposite walls together with a piece of timber. It doesn't need to be thick because as the walls try to move, it will try to stretch and compress the wood, which is basically impossible.When designing a box,DO NOT make it a cube. It is one of the worse shapes you can have for speaker box, and I don't mean just looks. Theoretically speaking it is the worst shape. I heard a set of speakers a while back (an 8 or 10 inch woofer it was) that was built like a cube. The guy that planned to buy them (they looked like a home made job, by the way) was put off simply because they lacked bass. On top of that they sounded shocking anyway.
Try to keep the dimensions apart, however don't make a dimension more than three times of any other or you might get a "resonant pipe" effect. A good ratio is 0.6:1:1.62. Now you will walk through your local stereo shop, look at the four foot high,skinny fronted speaker boxes and say "What a hypocrite". Thing is, a partition is probably placed a third of the way down to seperate the two compartments, giving you, in effect, a small speaker box.There are many different sized drivers around and it can be confusing to match what with what. I'll name a few of my preferences....
There are two common sized tweeters, 3/4" (19mm) and 1" (25.4mm).
If you are building a 3 way system with seperate tweeter,midrange and woofer units, then the 3/4" tweeter might be considered. As far as I'm concerned though, the 1" textile soft dome tweeter is the best way to go. These tweeters have a soft sound, unlike piezo tweeters, or cone tweeters. (I don't recommend piezos or cones for HI FI).
Also, these sized tweeters have a frequency range that extends into the upper midrange, providing better midrange performance.
A 6.5" woofer pairing up with a 1" tweeter is about the largest size you'd want in a two way. Any bigger and a three way must be considered. Big woofers (8" and up) will simply not produce enough midrange, even if you do use a 1" dome tweeter. As midrange is easily detected when missing,(speakers sound dull and flat) it is critcal that these frequencies are reproduced properly.
Many people (including myself) are turning and have turned to the small two way plus subwoofer combination for added bass.
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