Today, I’m going to get down to the basics, as I need to cover a few fundamentals before we move on to our next topic. In this article, I’m going to briefly discuss the basic differences between the types of speaker drivers commonly available; tweeters, mids, woofers, subwoofers, and full-range drivers. Each of these serves a specific purpose in reproducing parts of the frequency range.
This article will focus on the drivers you will typically run into. This is not intended to be a comprehensive list of all drivers of each of these types, but a general beginner’s guide to understanding speaker drivers and their purposes.
Tweeters are high frequency drivers that are designed to reproduce the highest octaves of the frequency spectrum. Typically, this is from 2,000Hz to 20,000Hz, while some tweeters will reproduce frequencies as low as 1500Hz. These drivers are smaller and usually dome-shaped. The membrane on dome tweeters usually measures 0.5″-1.25″ in diameter. There are several other different types of tweeters that are used, including ribbon tweeters, planar tweeters, horn loaded tweeters, and so forth, all of which have a slightly different sound. Dome tweeters are the most popular, and come in a variety of materials, including poly (such as mylar), silk (and other treated fabrics), aluminum, and ceramic. Each of these also has a different sound but hey generally serve the same purpose. Due to limited size and very limited excursion, tweeters cannot play frequencies below their frequency range without sounding fatigued, distorted, or harsh.
Midrange drivers are designed to reproduce frequencies between a woofer and a tweeter. However, not all speaker systems have them, as they are often not required. Mids will pick up where the woofer drops off, and drop off where the tweeter picks up. This frequency range is typically from 500Hz to 2000Hz. These are typically 3″-6″ in diameter, and are most commonly typical cones, although some dome midrange drivers do exist.
Woofers are drivers that are designed to reproduce a variety of frequency ranges. In a 3-way system with a midrange, they will play below what the midrange plays, but in a 2-way system, they will play below what the tweeter plays. This depends heavily on the design and purpose of a given woofer. These are sometimes also known as midwoofers or midbass drivers. How high and low in the frequency range a woofer will play depends heavily on the design and material used. Some woofers are capable of playing down to as low as 30hz musically, effectively eliminating the need for a subwoofer where high output isn’t needed. These are typically between 5″ and 15″ in size, with the larger varieties found in pro audio applications.
Subwoofers are specifically designed to reproduce bass frequencies. This is typically between 20Hz and 125Hz. Due to their size and design, they are rarely able to play above midbass frequencies, with some exceptions existing in pro audio. Subwoofers are designed with higher excursion capabilities in order to create enough sound pressure and move enough air to reproduce frequencies down to 20hz.
Full Range Speaker Drivers
Full range drivers are drivers that are designed to reproduce a large frequency range, although their ability to reproduce a wide range of frequencies is very compromised. These range from anywhere between 8″ and 3″ in diameter. Their ability to reproduce high frequency sound is often lacking, and many of them suffer from a “beaming” effect. While dome tweeters are able to reproduce high frequencies (which are very directional) over a significant area, full range drivers function more like a flashlight that focuses the frequency response of that beam directly at the area they are pointing to. For you as the listener, this means that you need to be sitting in a specific location and have the speakers pointed directly at you in order to get the best sound you can, while 2-way and 3-way speaker systems are much more forgiving.
To highlight some of the above, I’ll provide a few examples. The following speakers are my “Florians” design. These feature a 1″ silk dome tweeter and a 5″ Tang Band poly woofer. The woofer is an extended range woofer that has the ability to play up to the 2500Hz crossover point that I have set for these speakers. In their ported cabinets, they are able to play down to 45hz musically, although their bass output begins to fall off below 52Hz.
The below speakers are based on the Overnight Sensations MTM design. These feature a 3/4″ silk dome tweeter, and two 4″ HiVi extended range aluminum drivers. The HiVi drivers are able to cross over to the tweeter at 3500Hz on these specific tweeters, and can play down to 50hz musically, although their bass output begins to drop below 55Hz.
The below speakers are my “Starfish” design. They are a low-budget design ($40 in parts total), using a 3/4″ Mylar tweeter and a 3.5″ extended range poly driver. The crossover point for these is at around 3,500Hz, but due to their small size, they can only play down to about 70Hz musically, with output significantly dropping below 80Hz.
The below speaker based on the Statement Monitors design. While the above speakers have been 2-way designs, these are a 3-way design. These feature a Fountek ribbon tweeter, a 4″ Tang Band titanium midrange, and a 7″ Dayton Reference series aluminum woofer. These speakers are able to play down to 32hz musically, with bass output beginning to drop below 40hz. They are considered high-end speakers, with a parts cost for materials and drivers coming in at no less than $650.
As noted earlier, this article is intended to be part of the Audio-100 series discussing the basics of audio. My hope is that this article has outlined the general function of different kinds of speaker drivers. There are often many ways to achieve a given objective, and this is certainly the case with speakers. It is important to understand what each speaker is intended to do in order to design a good speaker system for either home or car audio.
Keep an eye out for the next article in the series on crossovers!
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