What is more powerful, woofer or subwoofer? What does it do?
Normal modern speakers that are manufactured today come with at least 2 drivers, the woofer and tweeter. The woofer produces bass (low frequency sounds) and the tweeter produces high frequency sounds (high-pitched sounds). This is the minimum standard in the hi-fi/stereo production industry, but computer speakers have the fewest features of them all, a single speaker with a port/vent, which you may call a 1-way speaker. Before we discuss the difference between a woofer and subwoofer, it’s important to understand the factors contributing to the efficiency of a speaker, and thus how much bass (low frequency ranges) it can produce. Basically, the lower the frequency, the deeper and richer the bass. Super bass systems are below 80Hz. Professional bass systems are below 100Hz and home consumer systems are below 200Hz. Most subwoofers (both commercial and consumer) have a minimum frequency rating of 20 or 25Hz. The maximum can be anywhere in an acceptable range depending on the manufacturer’s specifications, but anything that exceeds 200Hz going over 300Hz is not bass. You are approaching mid-range frequency.
The efficiency of a speaker at low frequency ranges is defined by Thiele/Small parameters, whereby:
ᵑ₀ = (4₀∏² F3 Vas)/ (c3 Qes) * 100%
ᵑ₀ = Acoustic reference efficiency
F3 = Resonant frequency of the speaker. Frequency at which the mass of the speaker (cone and voice coil) will start to vibrate naturally at its highest amplitude, causing it to shatter or break. It can also be described as the frequency at which the sound/acoustic frequency is equal to the natural frequency of the speaker or vibrating mass. The speaker will be unable to generate sound from the input signal as it approaches this point.
Vas = Equivalent internal volume of the speaker box in litres needed for compliance for a given speaker size/cone diameter (determinant of optimum box size).
Qes = Electrical damping or Amount of control from the speaker’s electrical suspension system (Voice coil and magnet)
C or Cas = Acoustic compliance of the speaker’s suspension.
What this equation tells you is that the efficiency of a speaker is directly related proportional to its Vas parameter, that is its cone diameter and optimum box volume.
Efficiency ~ Vas
E ~ Vas
The efficiency is also directly proportional to the resonant frequency F3 (F to the power 3)
Efficiency ~ F3
E ~ F3
But this is an exponential equation, we need to find out what F is proportional is to:
E = F3
Re-arranging the equation >>
F3 = E
Finding F by re-writing the equation >>
F = E⅓
We can see that F is proportional to E⅓
This means when we decrease the frequency further (extend the range in the lower end of the spectrum), the efficiency of the speaker will be reduced.
As seen in the above formulas and relationships, the size of the speaker matters. Generally for shopping purposes, the bass power of a speaker is represented by its cone diameter, this also applies to a subwoofer and woofer. The bigger the diameter of your subwoofer, the deeper the bass. Hi-fi/stereo Subwoofer speakers range from 20cm to 53cm in diameter, but they can exceed this size, a maximum size of 152cm has been made. Computers and small home theatres make use of smaller 10cm diameter subwoofers.
What Does a Subwoofer Do?
Previously, we noted that bass systems are in the low frequency ranges, and that 300Hz and below is where bass lies. The human hearing range is 20Hz to 20,000Hz. Anything outside this range is inaudible to the human ear, so the minimum low-frequency (deepest bass) you can hear is 20Hz.
We also said 2-way driver speakers are the most common standard in the Hi-fi and stereo market. Of course, we also have a lot of 3-way drivers and higher. Tower speakers can accommodate a lot of drivers. A 2-way speaker has a woofer and tweeter for low and high frequency ranges respectively, whereas a 3-way speaker has woofer, mid-range speaker and tweeter for low, medium and high frequency ranges respectively. A 4-way speaker has a woofer, squawker, tweeter and super-tweeter for low, medium, high and extremely high frequency ranges in order.
As you can see, a woofer is included in every modern speaker to cater for bass, but the question that you must ask as a Hi-fi/stereo consumer is what is the frequency rating of the speaker. All speakers have a frequency rating shown on the device as well as in the manufacturer’s specifications manual. Just to give you an example, here are screenshots of the frequency range of some speakers on sale:
LS50 Meta 2-way reflex bass speaker
Frequency range: 47Hz to 45KHz (45,000Hz)
XTRIKE-ME 2.0 stereo speaker with RGB backlight
Frequency range: 160Hz to 20KHz (20,000Hz)
BRAND 2×6.5 inch Big Power Wireless Party Speaker
Frequency range: 90Hz to 20KHz (20,000Hz)
2.0CH BT5.0 Hi-fi Bookshelf Studio Speakers
Frequency range: 60Hz to 20KHz (20,000Hz)
2.0 Bluetooth Computer Speaker
Frequency range: 200Hz to 20KHz (20,000Hz)
Audioengine A5+ Speakers
Frequency range: 50Hz to 22KHz (22,000Hz)
Crosley S100A-BK Bluetooth 2-Way Stereo Speakers
Frequency range: 50Hz to 20KHz (20,000Hz)
If you noticed above, a speaker like XTRIKE-ME 2.0 only supports the upper band of the bass frequency range. It doesn’t go lower than 160Hz, whereas a speaker like LS50 Meta covers a wider bass frequency range, going as low as 47Hz. This is a speaker you would like to buy if you are interested in a deeper bass. The lower the minimum the better.
A speaker like XTRIKE-ME 2.0 is fine if you don’t care about a richer/deeper bass. What if you bought this speaker and you want to improve its bass? This is where a subwoofer comes in. In this case, you must get a subwoofer that will go deeper than 160Hz to your preferred minimum for example 50Hz. Subwoofers can go deeper than 50Hz, down to a minimum of 25Hz or 20Hz which is the lower threshold of hearing.
How Does a Subwoofer Get to this Lowest Hz?
What Hz is required to increase bass? The answer lies in the previous formulas we discussed about the efficiency of a speaker. The bigger the size of the speaker (cone diameter), the better the bass. As you have realized, subwoofers often come as standalone speakers because they are too big to be integrated in compact speakers such as bookshelves. There is an economic limit at which the size of a speaker can be. It cannot be too big for packaging and transportation as this will drive up costs. Consumers also expect products that won’t take up too much space or stick out like a sore thumb. That’s the reason why most stereo speakers don’t have a built-in subwoofer as it takes up too much space.
To fire up the bass in your stereo, you have to connect it to a subwoofer. A subwoofer is often larger than your stereo, which shows you how much of bass power it packs. There are two types of subwoofers, the passive and active subwoofer. The former is powered by an external amplifier and the later is powered by an inbuilt amplifier. Active subwoofers have a more powerful and deeper bass.
At this point, if you have read through the article, you should know that a subwoofer is an optional/standalone item that is more powerful than the woofer on your 2 or 3-way stereo speaker.
When you are shopping for stereos and hi-fi systems, it’s important to know you have the following options:
- Buying a stereo speaker (e.g. bookshelf speaker). These are not sold with a subwoofer, you have to find one for yourself if you need it.
- Buying a hi-fi system with stereo speakers.
- Buying a hi-fi system with stereo speakers and subwoofer.