DIY Audio Speaker FAQ - Tutorial
Why build your own speakers? Basically, you can get great sounding speakers at a low price. Plus if you enjoy woodworking and some electronics, then it can be an enjoyable hobby. Granted, you probably won't achieve the quality of a $10,000 speaker unless you have some good measurement equipment and are able to go through several tries to perfect your design, but for a couple hundred dollars you can build speakers that will sound much better than anything you can buy at that price.
So what's the big deal? Build a box, cut a couple of holes, throw in some speakers, and wire them together. Well, it is almost that simple, but also much more complicated. You can make an ok sounding system by doing this and it could be done in less than a day. To do it right, you should spend some time with speaker selection, finding drivers that work well together. The box must be built to a specific size, possibly with multiple chambers. The box must be braced to the point that when the bass hits, the only thing in the room not vibrating is the speaker box. A well-designed crossover is also necessary so that each driver can perform optimally.
Should it be a 3-way speaker system? With your basic 2-way system, you have a tweeter and a mid-range speaker. A 2-way system will not produce very deep bass, although a good mid can provide more bass than you would expect. A 3 (or more) way system adds a woofer for full bass response. Before building, realize that there are many good 2-way systems on the market that you can get for about $200/pair, and it would be hard to beat that price & quality doing it yourself. PSB, Totem, & NHT are a few of the companies that make good 2-way bookshelf speakers. You really start to save money when building a 3-way speaker system. Any good system with a woofer will cost at least $400 due to the amount of wood and bracing required, shipping costs...
On the other hand, some high end drivers cost hundreds of drivers and there are bookshelf speakers on the market that cost more than $10,000. If you are an experienced builder with the right testing equipment using high end components, then a 2-way system might be right for you.
Build or buy the box & crossover? I have seen prebuilt 2-way boxes and premade crossovers that could make building a 2-way system very easy. The boxes were made of plywood, were stapled together, and were unfinished. Sometimes, cheaper wood is acceptable for a speaker system that doesn't have a powerful woofer. These speaker boxes ran for about $10. A cheap 1st order high & low crossover built into a binding post can run about $15. For $50 plus cost of drivers, you could have a cheap 2-way system. This could be the answer if you were looking for a cheap simple speaker, but then why are you building one at all? The problem is that the box and crossover haven't been specifically designed for your speakers. The box size and crossover point must match what the drivers are designed for. Attempting to use Off-The-Shelf parts like this will result in a speaker that sounds like crap. With China manufacturing bringing down the price of the low end market, it doesn't make sense to try to build your own very low end speaker anymore.
Use multiple speaker boxes, or one large box? Many people who do their own speaker projects separate the woofer from the rest of the system, putting it in its own box. Often, people also bi-amp the system, using a separate amplifier for the woofers. This greatly simplifies crossover construction and gives you more control over bass. The mid and tweeter should be at roughly the ear level of the listener (when sitting) so that the sound doesn't seem to come from above or below. You could build a box that was 4 feet tall. This just means more work and wood, but build the speaker you want. It is cheaper and simpler to build a large sub box, with a much smaller bookshelf sized speaker. Another option, which is becoming more and more popular with manufacturers, is to make a single, thin, deep box with a side firing woofer, as in the NHT 3.3 on the right. The front of the box is just wide enough to fit the mid and tweeter, and the box is just deep enough to fit the woofer on the side. The necessary volume for the woofer comes from the box's height, which is tall enough to allow the mid and tweeter to be at ear level. Since the box is thin, there is no wasted area (or wood) in the box. NHT, Klipsch, and Definitive Technologies are a few of the companies that design speakers like this.
The problem with this method is that it ignores the phase shift that occurs when the speakers are not aligned properly. The back of each cone (where the dust cap is) should be aligned on the same axis. Otherwise, the high notes will reach the listener before the low notes. There are also possible problems with cancellation. There are two ways to solve this problem. The first is once again to use multiple boxes, and position each box so that the rear of the cones align, as in the Von Schweikert VR-8 on the left. The other method is to slope the front of the box slightly so that the drivers align. This makes construction more difficult, but it looks a lot nicer.
What is the best shape for the box? Internal reflections in the box combined with the vibration of the box itself can cause spikes in the frequency response of the system. Different box shapes have a different effect, with perfect cubes being the worst and spherical or egg shaped boxes being the best. Although spheres have advantages, it is very difficult to create a spherical speaker box that is as strong as a typical rectangular box. One good example of a spherical speaker is the Gallo Nucleus Solo, on the right, which is made of rolled steel or brass. An even better design is the sphere/tube concept by B&W shown on the left. This design gets the benefits of a spherical design, but also adds a tapered tube at the back to eliminate all internal resonances.
|Beveled Cube||+-1.5 db|
|Beveled Rectangle||+-1.5 db|
This is not something you would likely build yourself. The general rule is stay away from perfect cubes, and use a rectangle box with beveled edges on the front. Sharp edges on the front of the speaker box will cause distortion, so rounding the edges can make a world of difference.
Why Individual Chambers? The mid and woofer both need their own separate chambers in the box. Both the mid and woofer are designed to work in an enclosure of a specific size. If they are both in the same chamber, like most cheap speaker systems, then the enclosure size for the mid will be too large and performance will be lost. Also, the sound waves from the woofer can overpower the mid and distort it. The tweeter is independently sealed and doesn't need it's own chamber.
Sealed or Ported? Each driver is different, so this isn't a yes or no question. The advantage to a ported box is that is can be louder (about 3db), but this increase in db will only be at certain frequencies, depending on how the port tunes the box. If tuned at the right frequency, then this bump in sound level can counteract the normal roll-off of the woofer at the low end and actually help to create a flatter response curve. A standard sealed box improves the power handling of the driver, produces a smoother low end roll off, and basically sounds tighter, but you don't get the extra bump at the end. Sealed boxes also allow more room for error in design.
In the end, the driver itself should determine if it is best suited to a sealed or ported enclosure. If the Efficiency Bandwidth Product (EBP) is less than 50, then a sealed enclosure is better. If the EBP is greater than 100, then an ported enclosure is better. Between 50 & 100 either sealed or ported will work. Again, these are only rough guidelines. The EPB can be calculated with this formula EPB = Fs/Qes. These numbers will be provided by the speaker manufacturer.
What testing equipment do I need? You technically don't need any testing equipment to build a speaker. Typical testing equipment involves a microphone plus computer software to analyze the response of your speaker system. Basically, the software generates tones at 20-20K Hz, records the actual speaker levels at those frequencies, and then presents the data to the user. A calibrated microphone will cost more than $100. There are some free / open source software projects for measuring speaker response, but they are not as good as the professional software. Search online to see what the latest recommended products are.
The manufacturer specifications for drivers can only help so much in determining speaker box volume and crossover design for your system. For professionals, these values are a starting point in designing a speaker. Every system is different and even small changes in box shape (even if the volume is identical) have have a dramatic impact on the system as a whole. Testing allows you to tweak the design to achieve a better, flatter response curve. Without access to a lab filled with different crossover components, your ability to tweak will be limited to what you have available. You can make some simple changes without testing equipment by simply making the change and then seeing if it sounds better.
What can I do to tweak a speaker without expensive testing equipment? Some simple changes you can make are:
- Reversing polarity of the speakers - Some phase problems can be solved by simply inverting the signal to one of the speakers
- Adding/removing poly-fill stuffing
- Changing box volume - In old (decades ago) cheap systems, sometimes putting a brick in the speaker made it sound better. The brick would effectively decrease the box volume. Today, you can experiment by adding wood to the speaker to see if it sounds better. If it does, then add that wood to the speaker in the form of permanent bracing. No reason to start over and change your box design to decrease the volume of a chamber by a couple of square inches when you can keep the current box and make it stronger in the process.
- Changing port length - Technically, if you have purchased expensive flared ports, then you can only make them shorter. If the change makes them sound worse, then there isn't much you can do to make them longer again.