Understanding Speaker Specifications
A buyer's guide to what makes a good audio speaker
Speaker specifications tell you a lot about a speaker's ability to deliver good sound. Having a true understanding of the different specs you would come across is therefore a prerequisite to avoid costly mistakes when selecting and buying audio speakers for a home theater set-up.
In this article, we explain the most important speaker specs you need to look into when researching home theater speakers. In the process, we also discuss speaker anatomy as this helps you make more sense of the actual speaker specs.
These 10-Inch 200W cont. powered subwoofers are capable of almost the same bass performance of a 12-inch subwoofer, yet they are significantly cheaper than a 12-inch model.
Features include Polk Room Optimizer to choose the best bass response for your room, multiple hook up options, and adjustable rubber/spike feet.
These subwoofers can be used in a down-firing or front-firing configuration, thus giving you further placement options, apart from enjoying either more accurate bass (front-firing) or better feel the shake (down-firng).
Both models come with the same specs; the only difference is that the Polk Audio DSW PRO 550WI include the convenience of wireless connectivity.
A Buyer's Guide to Speaker Specifications
Definitely, the best way to buy good speakers is to listen to a lot of them before you buy. But...
Let's face it, very few will have the possibility to listen to as many speakers they would like in an ideal non-echoing environment at their local retail store.
In these circumstances, a specs sheet can tell a lot about a speaker's ability to deliver good sound. In particular, online buyers need to have a good understanding of speakers specifications.
Even if you are buying from your local retail store, perusing an audio speaker specs sheet can help you get to know more about a speaker performance or its compatibility with the rest of your speaker system, than any sales rep would ever be able to tell you. It is true that for some, perusing technical specs can be frustrating if not confusing. After all, what matters for many in the market for audio speakers is simply pure, good quality sound.
However, perusing speaker specifications should not be that difficult. As we will further explain in this article, there are not that many numbers to look at when it comes to home theater speakers — at least when it comes to the most important specs like speaker size, power handling, driver type, enclosure construction, speaker sensitivity, and yes, speaker weight! The latter may sound strange but the overall weight of a complete speaker unit gives a pretty good indication about both the speaker buildup structure and its ability to deliver solid clear sound; a heavier speaker for the same driver size would normally deliver better overall sound.
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As indicated in our introduction, we first start this speaker guide by presenting an overview of speaker anatomy, more specifically of what constitutes a speaker. This is important as it helps you get a better understanding of how certain speaker specifications relate to the speaker build-up structure. In other words, a basic understanding of speaker anatomy puts you in a better position to visualize what speaker specifications are actually telling you about a speaker.
Speaker Anatomy Basics
A speaker unit can be defined as a sound driver or a set of multiple drivers contained within an enclosure. In other words, a speaker unit does not exist without its enclosure. The latter can be a dedicated wooden or plastic box in the case of free standing speakers, or the cavity created between a drywall and a concrete wall in the case of in-wall speakers.
The driver is the central element of any speaker system as it is that which converts the electrical energy from your amplifier into audible energy via internal driver movement. It can take various forms — from the common reinforced paper cone shape to a metal dome diaphragm; all is housed within a metal basket.
Picture Credit Infinitysystems.com
The driver diaphragm is fixed to the metal basket via a flexible surround at one end and a spider type acoustic suspension at the other. The whole assembly is rigidly connected to a voice coil suspended in a strong magnetic field created by a suitably shaped permanent magnet. The whole diaphragm/voice coil assembly is free to move in accordance with the movement created by the voice coil in response to the electric signal. This movement moves air in the room to create sound.
In the case of multiple drivers within the same enclosure, cross-over circuitry is used to determine which frequencies are directed to the individual speaker drivers. Two-way designs use a woofer and tweeter while three-way designs add a mid-range driver. Multiple-driver designs with a woofer less than 6 inches would not produce a solid enough bass and would therefore require a subwoofer to supplement the overall bass response. The ideal woofer size in full-size tower speakers is 8 inches.
Directly related to the speaker cross over circuitry are the cross-over frequency cut-off points; these determine which sound to route to the different speaker drivers. These vary depending on whether you will be using two-way or three way designs as well as on the size of the woofer speaker. With an 8- to 10-inch woofer, the woofer cut-off point for the cross over should be limited to less than 2KHz; a woofer of this size would not be able to produce clear sound above this frequency limit.
All elements constituting a speaker unit impact speaker performance, supported frequency range, and speaker tonality. The whole issue for one in the market for home theater speakers is to understand how speaker specifications relate to speaker performance. This is only possible if one is able to correctly interpret speaker specifications.
Speaker Specifications in detail
No speaker exist without its enclosure; the size of the enclosure determines the volume of air movement, and therefore the sound energy that such a speaker system can create in a given room. This implies that the volume 'or size' of a speaker enclosure should be related to the room size.
Do not just buy the biggest speaker you can afford. A speaker designed for a much bigger room will not sound good in a smaller room; the same holds true for the other way round.
Speaker enclosures come in various forms such as bass reflex or ported enclosures that have a hole in the front or back to leak more bass into the room. Others are completely sealed; well designed sealed enclosures tend to produce more accurate sound.
Well-made speaker enclosures use a reinforced structure — referred to in speaker specifications as a braced enclosure — to ensure that the enclosure vibrate as little as possible. Enclosure vibration adds undesirable coloration to sound especially at the resonant frequency of the enclosure; this tends to be closer to the upper bass frequencies.
Many go through a speaker specifications list reading about the driver material without actually having an understanding of the implications of this spec.
The material used for the driver impacts speaker performance, in particular the speaker covered frequency range as it impinges on the speed with which the driver moves. Faster high quality drivers use either aluminum or titanium; these are mainly employed in high-end tweeters. However, cheaper materials such as reformed silk, paper and certain plastics also produce excellent sound and are often used to make speaker drivers.
Driver material also impacts speaker tonality as explained in our speaker timber matching discussion; hence it is essential to match the driver material when buying separate speakers as part of a multichannel home theater speaker set-up.
This is often defined in either nominal or continuous power (Watts RMS), and short-term peak input power a loudspeaker can handle before destroying the loudspeaker. However, a speaker driver may be destroyed as a result of overheating even with a lot less power than its peak rating if its continuous power handling capability is exceeded for a sufficient length of time.
Even driving an amplifier into clipping may destroy your speaker drivers, and especially the tweeters. In a similar manner, an amplifier struggling to drive a speaker may produce a high level of distortion which may also destroy your speakers. In either situation, more energy is passed onto the speaker especially at high frequencies which may easily damage a speaker driver unit.
This implies that: More amplifier power is better than less, and the cleaner the better!
Related with a speaker power handling capability is speaker impedance; this speaker specification is defined in Ohms. Typically, home theater speakers come with 8-Ohms but speaker impedances of 6-Ohms, 4-Ohms and 2-Ohms are also available. 2-Ohm impedance speakers are mostly used in low voltage supply applications such as in cars.
Impedance represents the resistance a speaker offers to the electrical signal; the lower the impedance, the more power a speaker will draw from the amplifier for a given output voltage. This means a 4-Ohm speaker will load more an amplifier for the same output signal level than an 8-Ohm one. Inexpensive amplifier systems would generally find it hard to drive speaker loads less than 6-Ohms.
So do not just buy speakers without taking into account your AV receiver or amplifier specifications.
One of the most critical speaker specifications often ignored in speaker choice is speaker sensitivity. This is specified in dB (decibels), using a one-watt test tone (a 2.83 rms volts into 8-Ohms) measured one meter away from the speaker. It is a measure of the sound pressure produced and will tell you how loud a speaker will play in a non-reverberant (i.e. non-echoing) environment.
A higher value implies a louder speaker for the same input signal, and therefore a 'more efficient' one. This means sensitivity affects how much power your system needs to perform well within your set-up. Average speaker sensitive stands at around 87 to 88 dB. Note that this measure is logarithmic, meaning a 3dB reduction in speaker sensitivity requires doubling of the amplifier power to produce the same sound volume in the room.
Some speaker manufactures define sensitivity at two or more frequency points, while others define sensitivity in terms of room efficiency by taking the average room environment rather than a non-reverberant environment. Doing so however would inflate the resultant efficiency measure by at least 2 to 3 dB over a non-echoing measure; it also makes it hard to compare speaker specs between different models and brands.
Speaker frequency response:
This speaker specification represents the speaker output over a frequency range for a constant input level varied across the specified frequency range. In view that speaker frequency response is not constant over the entire range, response is often specified within a variance limit - typically ±3dB. This ±3dB represents reasonable consistency; some manufactures also specify an extended frequency response at ±6dB but this in itself is meaningless as it would require up to four times the amplifier power for the lows in the speaker response to sound as loud as the highs within the range.
A speaker having a specified frequency response ranging from say 40Hz to 22kHz ±3dB can be considered to have pretty good coverage ranging from good bass to a high frequency that is just in excess of the average human hearing upper limit.
Speaker dispersion, or Directivity:
If speaker efficiency is one of those speaker specifications that are hardly considered by would-be buyers, speaker dispersion forms part of that category of speaker specifications that are hardly indicated by speaker manufactures. Yet this is a very important speaker specification to home theater designers as it enables for a more precise placement of home theater speakers.
Speaker dispersion specifies the speaker sound radiation pattern along different angles. It tells you how sound varies as one moves away from the speaker main axis. As such, it enables you to determine the best listening position, as well as how sound would vary across the different seating positions in a home theater. The best speakers are those that can maintain a uniform response for a more consistent sound as one moves around the room further away from the speaker main axis.
In a home theater set-up, speaker placement should be designed such that the best spot for your listening coincides with that of the best viewing position.
Magnetically shielded speakers:
This is one of those speaker specifications that are becoming less of interest to a wider segment of home owners as more are making use of LCD and plasma TVs for their home entertainment. Yet things are different with CRT TVs.
The permanent magnets used in speakers are extremely strong magnets that may interfere with the CRT TV electromagnetic field used to deflect the electron beam; the result is a distorted TV image when speakers are placed at close distance to the screen. Speakers intended for that purpose should use magnetic shielding.
Magnetically shielded speakers are more accurately referred to as 'negligible stray field' speakers. This means you can place such speakers as close as you want to a CRT TV or computer monitor, or even magnetic computer media without fear of distorting the image or corrupting the data. It is not possible to remove the resultant stray magnetic field completely; hence the term 'negligible' should not be taken to mean zero stray field. But it can still be taken to mean as such within the practical limits of how close you can move a speaker.
Magnetic shielding is carried out either through the use of a magnetically conductive assembly around the speaker driver magnet, or through the use of additional magnets that surround the driver magnet such as to cause the stray magnetic field to turn on itself. Some magnetically shielded speakers use both methods for a more effective shielding.
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