Subwoofers are a great addition to any stereo or home cinema system. They enhance the lower frequency sounds of other speakers to provide richer and fuller audio. This allows the standard speakers to be smaller, which is a big advantage in home stereo systems.
Choosing Used Subwoofers on eBay
Subwoofers, also known as subs, are speakers that reproduce bass sounds. There are various designs, and two basic types - active and passive. Subwoofers aimed at home users are typically contained in an enclosure, though in some cases they are sold separately.
The size of subwoofer speaker drivers varies from around 20 cm to around 50 cm, though both smaller and larger speaker drivers for subwoofers exist. The size of the speaker driver can affect the level of frequencies that can be reproduced as well as the level of interference. Subwoofer size may be a limiting factor in small rooms, but whether it is acceptable to sacrifice sound quality for space is largely an individual concern.
Power and Resistance
Power, expressed in watts, affects the volume and quality of the sound that can be projected. However, it is not always easy to determine how this works in practice just from looking at specifications. Reading reviews from trusted sources can often give a better indication.
RMS and PMPO
When it comes to the specifications, there are two basic ways in which the power of speakers is expressed. The first is watts root mean square (RMS). This is the sustained maximum level at which the speaker can deliver sound. The second is watts peak music peak output (PMPO). This is the maximum level that is produced during peaks. Watts RMS is therefore the rating that is generally considered most beneficial at indicating the subwoofer's power.
Resistance, or impedance, is the extent to which the subwoofer limits the amount of current from the source device or amplifier. Speakers with a higher impedance have a lower power output. Impedance is expressed in ohms. Most home stereo speakers have a rating of 8 ohms, and this is the standard level at which power outputs are measured. However, there are also some ratings, for example 4 and 6 ohm rated speakers, so always check. If the subwoofer does not have an 8 ohm rating other components, such as an amplifier, may not be compatible with it.
The frequency response is the range of frequencies that the subwoofer can reproduce. This is measured in hertz (Hz). The typical range of frequencies that consumer subwoofers cover is around 20 to 200 Hz.
Active and Passive Subwoofers
Active subwoofers have an integral amplifier, while passive subwoofers do not. Most subwoofers sold separately and aimed at consumers are active subwoofers, so there is no need to purchase an extra amplifier. However, this should always be checked.
Active subwoofers do have several advantages over passive subwoofers. The quality of the bass is often superior, at least with home systems. They also often have good equalisation controls, which enables the sounds of the subwoofer and main speakers to be matched more easily and pleasingly.
If buying a passive subwoofer, buy the sub first then the amplifier so that the amp will be compatible. Passive subwoofers are more commonly sold in all-in-one home cinema packages.
Localisation and Crossover Circuitry
Localisation is something to be avoided where possible. It occurs when the main speakers do not reproduce bass sounds at all, even relatively high frequencies. Higher frequencies are more easily picked up and localised - pinpointed by location - by the human ear than lower frequencies. The effect of all this is that bass sounds produced by the subwoofer become annoyingly noticeable rather than spread inconspicuously throughout the room. Localisation is more common with lower quality systems. These may be badly designed with regards to crossovers, the electronic filters that split the audio signal into different frequencies before it is passed to different speakers. It is worth looking at the crossover system of a subwoofer before committing to purchase, and reading reviews to check how well it can be expected to work with an existing home stereo or home cinema system. Subwoofers aimed at home use will typically contain crossover circuitry to enable this process.
Crossovers and Low Pass Filters
Crossovers can be adjusted on some active subwoofers, using a control on the rear panel. The point at which the dial should be set depends on the level to which other speakers can deliver sound at, but 80 Hz is a typical recommendation. This control is also known as a low pass filter, as it blocks out higher frequencies completely. Having some overlap is desirable for more streamlined sound.
High Pass Filters
High pass filters are also sometimes included in the crossover circuitry. High pass filters, like low pass filters, prevent certain frequencies coming through, but with high pass filters it is lower frequencies rather than higher frequencies that are blocked. This is because very low frequencies are unsafe and can damage the speaker.
Phase control is used to alter the polarity of the subwoofer's sound waves to keep them in phase with the other speakers, and to prevent disturbance at the level at which they cross over. The circuit used may be a switch which just reverses the polarity or it may be a continuously variable control.
A typical subwoofer has various connections for hooking it up to the home stereo system. A cinch input is for transmitting the line level signal. Sometimes it is possible to connect other subwoofers for bigger bass sounds - if this is a possibility in the future look out for a sub with this capability.
Subwoofers are often placed off centre, to the back of the room or seating area. Usually just one subwoofer is required for smaller rooms. Because they are often larger than standard speakers, it is often preferred to place them in a relatively inconspicuous area. One of the deciding factors, therefore, is likely to be convenience as well as where the subwoofer sounds best. However, there are some definite points about where a subwoofer should be placed for optimal sound quality. Room corners tend to be good spots, and it is generally recommended to keep them away from openings such as doors, as well as keeping them fairly near to the listener.
Buying Used Subwoofers
Used subwoofers can be a great bargain compared to buying the same, or similar, products new. There are, however, a few things to look out for and be aware of.
While it is ideal to listen to the subwoofer before committing to a purchase, this may not always be possible or practical, especially if buying online. In these cases it is sometimes necessary to depend on the seller's reputation and any comments or reviews left by previous customers. Always check to see if goods are returnable if there are any problems.
Photographs can be useful as they can show the general condition of the subwoofer, and if it has any damage such as tears and dents. Dents could mean the speakers have been dropped at some point. Always read the product description carefully and if there are areas for concern or further enquiries raise them with the seller before a purchase.
Find Used Subwoofers on eBay
To find used subwoofers on eBay, go to the homepage and either use the categories or the search bar. To use the categories, begin at the left hand side tabs under Shop by Category. Open the relevant tab, in this case the Electronics & Technology tab, and select the Sound & Vision option. Then scroll down and select Home Audio & HiFi Separates followed by Speakers & Subwoofers. For subwoofers, select Single Subwoofer under the heading Configuration. Used subwoofers can be specified under the heading Condition. To use the search bar, begin at the top of the page and use the field marked Search. Type in general terms such as 'used subwoofer' or include the brand or other criteria if necessary.
Used subwoofers can typically be found far more cheaply than new subwoofers and can be a good bargain. However, buying used products, especially electrical and audio equipment, can have its pitfalls so it is important to buy from trusted sellers and to check out reviews and feedback before committing to purchase. When it comes to the general features of subwoofers, check out the power, expressed in watts RMS, as well as the impedance and frequency response. Also check if it is an active or passive subwoofer, and the controls and connections, including filters and phase control. Integrating a subwoofer into an existing system may involve some tampering with the controls as well as experimentation when it comes to positioning the speakers in the room.