Many ignorant music lovers buy a particular brand of speaker systems which is very well-known for making small satellite "cube" speakers coupled with a floor-standing subwoofer. These speaker systems have a brand image of top quality among the non-technical buyer community, primarily because their marketing department, like Microsoft in the software world, has done an excellent job of brand building, product positioning and advertising.
At current prices, you can often get better speakers for the same money, if you are not a sucker for advertisements and status symbols. I want to explain why this is the case, giving reasons.
As you will see, my reasoning applies to many other brands and models which are similar in design.
The sat-sub dream
These sat-sub speakers sell a dream. They position themselves as "lifestyle" products, not just functional speakers. The sat-sub design appeals to those customers who do not want to fill their rooms with large enclosures.
In the audio system world, "lifestyle" products focus more on appearance than raw sound quality. Very rarely is a top-quality sound reproduction machine advertised as a "lifestyle" product. There is nothing wrong with a product labelling itself as a "lifestyle" product if it does not compromise performance. Do these sat-sub systems compromise performance?
My comments will apply to all brands and models which have similar dimensions. My article is really not about any one brand of speakers.
I have never taken apart any of these sat-sub speaker systems. I have not measured their frequency response or other parameters. My "analysis" is based on an understanding of theory, plus comments and writeups I have read. Besides, four of my friends have these sat-sub speakers made by the most popular brand in this category. I have heard a lot of music through their speakers.
The satellites
Most of these satellite speakers contain one small 2" driver which reproduces the entire frequency spectrum from the highest frequencies to fairly low down, leaving the lowest end to the subwoofer. These satellites are also referred to as "cubes" because they have the shape of small black (or white) cubes about 3" a side.
Internally, these satellites are quite simple because they do not need to contain any crossover circuits: they are single-driver speakers. The enclosures are quite well-made, and do not resonate. This is easy to achieve given their small size.
Variants of this satellite design include two "cubes" mounted one on top of the other on swivelling mounts, so that one of the cubes from each channel can be made to face the listener directly while the other can create a more dispersed soundfield.
The subwoofer
The subwoofer in these systems is a box placed on the floor, about eight inches wide, and perhaps 18" long and 18" tall. This contains one driver, which is about 6" in size. It is mounted in a specially designed enclosure which has a fourth-order bandpass alignment. More on fourth-order bandpass later.
The crossover circuits which split the signal between satellite and subwoofer are usually kept inside the subwoofer enclosure.
The usual product claim with such sat-sub systems is that the subwoofer is acoustically not localisable, i.e. the listener can hear the sound coming out of the subwoofer but won't know where the sound is coming from. Therefore, he can keep the subwoofer in some unobtrusive corner of the room and avoid clutter. The satellites are small enough to be kept at appropriate locations without taking up space. I have often found that customers who have bought these speakers have used small brackets to mount the satellites on walls, or kept them on top of cupboards, sometimes well above head height.
What's wrong with the satellites
These satellites have two serious problems. One affects midrange reproduction, and the second affects the high frequencies.
The first problem with the satellites is that the drivers are too small to do justice to midrange. This is clearly audible when you listen to the popular sat-sub speaker models... the male voices have no punch, no depth. Do not even think of listening to Nat King Cole, Bhimsen Joshi, or Harry Bellafonte on these speakers, you will wonder where their energy has gone.
The physics behind this is very simple. When a speaker driver is trying to reproduce a particular frequency, its cone has to vibrate in that frequency. The distance through which it has to vibrate -- the peak-to-peak movement of the cone -- is inversely proportional to the frequency. If a driver has to reproduce a 1KHz sound, and can vibrate forward and backward through a 1 millimetre peak-to-peak distance, then to reproduce 500Hz equally loudly, it will have to vibrate through a 2 mm peak-to-peak distance. For 250Hz, it will have to vibrate through 4 mm peak-to-peak. And for 125 Hz, it will have to vibrate through 8 mm peak-to-peak.
Also, if a driver's cone is 2" in diameter and it's vibrating through 4 mm peak-to-peak to generate sound at a particular loudness level, then a 4" diameter cone will have to vibrate through one-fourth the peak-to-peak distance, i.e. 1mm. The reason is that two driver cones generating the same sound at the same volume level have to move the same volume of air. Therefore, when you move from a 2" speaker cone to a 4" speaker cone, you are increasing the cone surface area four times. Hence the distance through which the cone has to move to generate a sound of similar loudness can now be one-fourth.
And this has an impact on the sound quality. If you make a cone move through large distances, it will either fail to do it properly at all, or it will do it inaccurately, thus distorting the sound. In general, a speaker driver of 4" will be able to reproduce midranges much better than a 2" driver, because the larger cone will have to move through much shorter distances, and will therefore be able to reproduce sound without much distortion. During the loud portions of the music, the larger cone will have a better chance of reproducing the sound by moving a bit more, whereas the smaller cone will probably simply run out of space to move, thus failing to reproduce the sound loudly enough. I strongly suspect that this is what happens with the popular 2" sat-sub speakers... they simply fail to reproduce the lower midrange sounds with any convincing degree of loudness or impact. This distorts the sound, and saps its life. This is very audible if you compare a popular sat-sub speaker with a good pair of conventional speakers side by side.
Almost all conventional high-quality speakers which have a separate driver for midrange reproduction use drivers which are at least 4" in diameter. This is not accidental; it's grounded in physics. In theory, it is possible to build a 2" driver which will have four times the excursion (i.e. the peak-to-peak cone movement) of a 4" midrange driver and do it with no compression or distortion. In practice, it's proved to be bloody difficult, and all the sat-sub speaker systems selling in the $500-$1000 price range seem to have failed to do this.
The next problem relates to the high frequencies. A 2" driver is too large to handle high frequencies well. Firstly, the extreme high frequencies needs an extremely light driver; a 2" driver is rarely light; a 1" or 0.75" driver is much better. Secondly, you need a small driver to allow the generated sound to disperse in all directions -- larger drivers tend to "beam", or focus the sound in a narrow cone in front, which makes the overall sound in the room less realistic. Good speaker designers try to use small tweeters where it's possible to have better dispersion and lighter diaphragms. Therefore, good designers usually prefer to use a separate midrange driver (to handle low midrange and human voices with very little excursion) and a small dome tweeter (for very light moving parts and good dispersion of the extreme high frequencies).
These problems affect all the popular satellite speaker systems that I have seen and heard.
Building a good satellite speaker
Does this mean that there is no way to do this right? Is there any way to have a single 2" driver reproduce all the frequencies from the extreme highs down to subwoofer frequencies convincingly? Apparently, there is, if you use very high quality and expensive drivers, and reduce the stress on each driver by using many of them together. A very good speaker design which takes this approach is the Nonesuch range from Seventh Veil. This design has four Bandor 2" drivers in each channel's enclosure. Each Bandor 2" driver is quite expensive; we have heard of prices of the order of $50 each, in retail quantities. They, together with the 2" drivers from E J Jordan, represent the cutting edge in 2" wide-range drivers, and none come cheap. This quality of technology is not possible to be incorporated in mass-market sat-sub systems selling for $500 a set. Remember, you'll need four of these drivers per side to generate high quality output.
Compare these prices with the price of mass-market sat-sub systems. The most popular brand of sat-sub systems used to have a two-channel speaker model which used to retail for $400 for two satellites plus one subwoofer. This means that the entire raw material cost for this product would not exceed $100, which probably means that the satellites will use raw drivers costing $5 or less, each. At these price points, there is no possibility of using cutting-edge 2" drivers in sufficient quantity to make a good speaker. Even assuming that wholesale OEM pricing for good wide-range 2" drivers will be half the retail prices (i.e. $25), you will still need eight of these for a stereo set, bringing the speaker driver cost for just these drivers to $200. If you are clocking up parts costs at this rate, your final system will probably carry a sticker price of $5,000 or more for a full system.
There is another way to build a reasonable quality satellite speaker pair which can be mated to a subwoofer. Just forget about tiny, sexy, 3" cubes which the marketing departments would love to sell. Just build realistic sized bookshelf speakers, maybe a foot tall, each with at least one midrange driver and one tweeter. Linkwitz, of Linkwitz-Riley fame, did it in 1980 with supposedly excellent results. In this sort of design, the 4" midrange handles the full mid frequencies with low distortion and convincing volume levels, and the small tweeter handles the high frequencies with good dispersion and accuracy. And the net result does not even have to be expensive.
The subwoofer's tale of woe
What's wrong with the subwoofer of most of these sat-sub systems, including the Most Popular Sat-Sub Brand Icon we all see all around us?
The poor subwoofer suffers on two counts. First of all, it's not a subwoofer at all, and secondly it's built to be inexpensive and inadequate. Only non-discriminating customers will accept such subwoofers.
Firstly, the subwoofer has to take over where the satellite speakers leave off. As we have seen above, the satellites using single 2" drivers per side can't go very low, i.e. they cannot reproduce low frequencies very well. And the term "subwoofer" actually refers to a speaker which restricts itself only to the lowest two octaves or so, so that its position cannot be localised when the listener listens to it. This means that it should not reproduce anything above about 100Hz. However, if the subwoofer of these under-designed sat-sub systems has to stop at 100Hz, then everything above it will have to be reproduced by the satellite speakers. And single drivers of 2" diameter cannot reach as low as 100Hz and deliver convincing outputs.
Therefore, most of these systems have subwoofers which are not subwoofers, but ordinary woofers, i.e. they reproduce a lot of the bass frequencies above 100Hz. In that case, their sound is localisable, i.e. the listener can position the location where the woofer is placed. At these frequencies, you need two woofers, one per channel. Combining two woofers into one messes up the soundstage (the auditory illusion that you are hearing instruments and singers on an invisible stage stretching from left to right in front of you). This is the key reason that good subwoofers refuse to reproduce frequencies above about 100Hz... they don't want to go higher, become localised, and then mess up the soundstage. See this article by Ken Rockwell titled "Stereo subwoofers: why every man needs two". He explains this matter well, and he's talking about pure subwoofers, not the small six-inch drivers which pass by that name in sat-sub systems.
The second problem with these so-called subwoofers is that they are not designed to do a convincing job with the low frequencies. In an attempt to be inexpensive and living-room-friendly, the enclosures are buit small, and they can hold only a 6" driver. A good subwoofer can be built with an 8" driver in rare cases, but is usually best built with a 10" or larger driver. A 6" driver has the same problems that we discussed about the 2" satellite speaker's driver and its peak-to-peak excursion. A smaller driver's cone has to move much more, peak-to-peak, to be able to generate the same sound with the same volume level as a larger speaker cone. This causes distortion with the smaller driver, or more typically, it causes much less loud bass sounds. This results in a "thin" or "airy" sound instead of a bass with depth and impact. (This "airy" sound has proudly been mentioned by one sat-sub speaker owner to me as a "feature". Strange, how proud owners of sub-standard products rationalise their choices.)
The third problem with these so-called subwoofers stems from their low power output and small driver cone excursion. In order to compensate this, some brands make subwoofer enclosures in the fourth-order bandpass alignment instead of the more common bass reflex or sealed alignments. What this fourth-order bandpass alignment means is that the frequency output of the subwoofer will be like that of a bandpass filter, i.e. it will reproduce one narrow range of frequencies quite loudly, but will not have a flat frequency response. Most non-technical customers won't know good bass with a flat frequency response because they have probably never heard good speakers. More well-educated customers will rarely want a bandpass subwoofer for their bass reproduction, knowing how uneven the frequence response is.
How to make a better subwoofer
This is not difficult, provided the rest of the system (i.e. the satellites) are designed to be used with a good subwoofer. For this, the satellite first must be designed to handle all frequencies down to 80-100Hz with sufficient accuracy and volume levels, leaving the subwoofer to do its job unhindered.
After that, any traditional subwoofer with a driver of 8" or larger diameter, in a bass reflex enclosure, will do a good job. Their quality may vary, but they will almost always do a better job than a puny 6" driver in a fourth-order bandpass enclosure.
Alternatives
It is easy to get better sound than these big-brand sat-sub systems by spending $500.
You must look for good two-way standmount speakers which have smallish size (anything between about 10" and 16" tall and sitting on stands). A two-way speaker is something which has two drivers, one handling the midrange and bass, and the other handling the high frequencies. There are plenty of good ones from many different brands; I will not list those brands here. And really good small standmount speakers can exceed $2000 in price, so you have the full range of price and quality to choose from.
And forget about subwoofers. You don't need them.
It is generally believed that subwoofers give you "good bass". Naive buyers therefore believe that in at least the bass department, a sat-sub system will give them better sound than something which just has small enclosures and no subwoofer. The truth is quite different. The popular trendy sat-sub speakers have such poor so-called subwoofers that a pair of well-made two-way standmount speakers will often give you better bass.
One mistake you must not make is try to look for floorstander speakers at a budget of $500. At that price, floorstanders are usually worse than standmounts. If you want good floorstander speakers, be prepared to spend much more.
In summary
It is really sad that uneducated customers make buying decisions based purely on their exposure to large advertising budgets of clever companies. If they had trusted their ears more, they would have been able to get better speakers for their money.
Maybe they do not want better sound as much as they want brand identification for their personal lives.