In part 2 of this series we discussed the basics of picking the best speaker for your specific application. So you went to Amazon or Parts Express and found exactly what you were looking for, right? Well if not, then keep reading. As I mentioned before, it’s very hard for a single speaker to do everything well. Speaker designers know this so they actually build speakers with multiple speakers within them. These individual speakers are called drivers. When you look at a speaker without the grill on you will usually see 2 or more drivers. A speaker with 2 drivers has a woofer (to produce the bass) and a tweeter (to produce the treble). Some speakers add in a third driver called a mid-range driver (yes, to produce the mid-range), while others have even more.
Frequency Bands
Why would a speaker designer use more than one driver? Because each driver works best when it operates within a certain frequency band. The size of each driver is directly related to what frequencies it can produce well. Tweeters are small because they need to vibrate very quickly to produce sounds in the 1,000Hz-20,000Hz range. Woofers are large because they need to move a lot of air to produce audible sound waves down to 100Hz and below. These are a few examples of the primary frequency ranges from certain instruments or sounds:
- Bass guitar: 30Hz-400Hz
- Piano: 25Hz-3,000Hz
- Drum Cymbal: 2,000Hz-20,000Hz
- Cello: 150Hz-2,000Hz
- Singer: 300Hz-4000Hz
- Explosion: 10Hz-150Hz
Drivers
Here are a few standard speaker configurations, the drivers that they use, and the frequency ranges that the drivers operate in:
Full-Range
- Full-range – The little speakers built-in to your TV, computer, or iPod dock are likely full-range speakers. They have one driver that has to cover as much of the frequency band as possible. A typical full-range speaker will cover approx 300Hz-6KHz, resulting in decent sound for listing to talk radio, and that’s about it
2-Way
- Woofer – The size of the woofer will dictate the frequency band that it can cover well. A 5″ woofer can produce proper output from around 120Hz-4Khz. A 10″ woofer can operate down to 50Hz or less, but only sounds good up 1KHz or so.
- Tweeter – The woofer and tweeter have to work together at the crossover point (the frequency area in between the 2 bands), so the frequency band of the tweeter will need to complement that of the woofer. A system with a 5″ woofer might use a 3/4″ tweeter, which operates well from 3.5KHz-20KHz. A system with a 10″ woofer would have to use a 1-1/8″ tweeter (or larger) to be able to reproduce down close to 1KHz.
3-Way
- Woofer – A 3-way system adds a mid-range driver, which means that the other 2 drivers in the system can be more optimized for their specific frequency bands. A woofer in a 3-way system will usually be at least 8″, sometimes up to 15″. The frequency band covered will normally start around 20-40Hz and won’t go above 800Hz. The bass in a 3-way speaker will usually be much stronger than a 2-way speaker since the woofer can be optimized for loud, clean bass.
- Mid-range – The mid-range driver is very important in a 3-way system; it reproduces much of the sound that you hear, especially voices. If you want to hear clean vocals then a 3-way system can be helpful since it keeps the speaker crossover points outside of the main vocal frequency range. Typical sizes are 2″-5″. Most mid-range drivers, like this 2″ unit, will cover around 600Hz-5KHz.
- Tweeter – The tweeter in a 3-way will usually be 1″ or smaller, better able to cleanly reproduce the higher octaves. They only have to cover approx 4KHz-20KHz.
4-Way
- Sub-woofer – Most 4-way systems add a sub-woofer on to the low-end of the speaker. This takes gives the speaker some serious thump. Subwoofers usually cover the 20Hz-80Hz band. A 12″ subwoofer in a good enclosure can create very loud output all the way down to 20Hz. Subwoofers are also often used as stand-alone speakers, adding a 4th band to a 2-way or 3-way speaker system (e.g. the .1 in a 5.1 surround sound system).
- Woofer – Since the woofer doesn’t have to worry about creating sound below 80Hz it will be optimized for clean, distortion-free output in the 80Hz-600Hz band.
- Mid-range – This driver will be performing the same as it did in a 3-way model, although it may not be set up to go as low as it did, e.g. the crossover point between the woofer and mid-range may be 700Hz where it was 500Hz in a 3-way system.
- Tweeter – There will likely be little or no difference in the tweeter setup from the 3-way system. Some 4-way systems have a “super-tweeter” instead of a subwoofer as the 4th channel. They advertise frequency response to 50KHz+. These are mainly a marketing gimmick, but if you want your dog to be able to hear extra details in the music then you could consider this option.
Multiple Drivers, Same Band
You will see some speakers that have more than one driver that are the same size. This could be due to one of several reasons:
- It’s likely that the system is just using 2 of the same driver to produce double the output. Maybe the woofers are not as efficient as the tweeter, so the designer put 2 of them in to make up for it.
- The design might also be a 2.5-way or 3.5-way design, which is similar, but one of the woofers outputs the full band while the other only outputs a portion of the band, often to improve bass output. An example of this would be a 2.5 way system with two 8″ woofers, one of them operates in the full band from 50Hz-1000Hz, while the other just outputs from 50Hz-150Hz.
- One final reason you might see multiple drivers is if the speaker is a line-array, I’ll talk about what those are in another post in this series
Which One To Pick?
To decide which one to pick you’ll want to refer to the Applications post I wrote last time. If your application needs good low-frequency extension then you will want to either have 3-way or 4-way speakers, or have a system with a separate subwoofer. If you don’t need the low-frequency extension then a 2-way speaker can be a good choice to save money. A 2-way speaker can also be more accurate in some cases because there are usually fewer electronic components in the crossover, which might provide a more clear and clean sound. If size is a priority for you then you will likely want a 2-way speaker since the speaker boxes will be smaller.
My own speakers are used for surround home-theater and stereo music listening. They are currently 2-way units that I built, plus I have a subwoofer to make it a 3-way system. I plan to build 3-way speakers some time in the future to improve the bass response from my main left and right channels, enabling me to use the sub more as a LFE device instead of for bass-management.
Start making your wish-list of what speaker priorities and configurations you might want. In my next post in this speaker series I’ll share why speaker enclosures are so important, and the different types that you have to choose from. Come back on Thursday for part 4, Enclosures.
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