I am sometimes amazed how good a portable radio can sound, with just a single speaker and an audio power of just 2 watts. I know, there is not much bass and certainly no deep bass, but the midrange, where all the vocals are, gets reproduced almost perfectly. It’s nice to have super low bass and super high treble, but the midrange is what matters most. That’s where most notes from most instruments are and also the human voices.
I do own a good pair of stereo speakers and I do enjoy listening to them. But it’s just not always necessary to get the full concert hall experience to enjoy music. So I sometimes listen to portable radios or PC speakers at relatively low volumes.
Wide-range Drivers
When you need relatively low power, full-range speakers can sound great. Think about half decent portable radios and Bluetooth speakers. Nearly all headphones use full range drivers, that’s perfectly fine at those low power levels.
You have simple speakers, that are in portable radios or in television sets and you have specially constructed full-range drivers to get more bass and more treble than normal speakers could output. Some have a tweeter dome and a tiny cone in the centre to get more treble output.
Intermodulation distortion is a problem in wide range speakers, especially at higher volumes.
Two-way Speakers
The next step up from a wide-range driver is a two-way system with a bass-midrange driver and a tweeter. These setups can be simple and sound very good.
A two-way speaker system can have a very simple crossover filter: a coil in series with the woofer and a capacitor in series with the tweeter. You might not even really need that coil: the woofer could take all the signal and the tweeter could take just the treble. If the crossover point between the woofer and the tweeter is above the speech range (for example at 5 kHz), you can have a very clean midrange. The tweeter is just for adding that extra spark of brilliance to the sound.
Many European tube radios of the 1950s and early 1960s had a big bass-midrange driver at the front plus two (electrostatic) tweeters on the sides. Amplifier power was often just 2 watts RMS and they sounded great.
Three-way Speakers
If you want deep bass or high-volume bass, you will need a dedicated woofer. Together with the midrange driver and the tweeter, you have a three-way system.
To get good bass, you need to pick a good design for your speaker enclosure. Two widely used solutions:
- A bass-reflex system (they have a port at the back of the speaker cabinet). These are relatively efficient but they do not have a very flat frequency response. If the system is well designed and the speaker cabinet is large, the can work well. This is the most widely used solution also for two-way systems.
- A completely sealed off speaker cabinet. The inside of the cabinet is padded with damping material. to prevent any sound inside the cabinet from bouncing around. As the enclosure is completely sealed, pushing the speaker cone inward or outward will cause a pressure difference, severely resisting the movement of the cone. In other words: you need excessive force to push the cone inward or outward, hence you need lots of amplifier power and the acoustic efficiency is very poor.
Some disadvantages of a three-way system are:
- Three way systems need a complex cross-over filter that should match the driver units (the actual speakers) and the enclosure design (the cabinet). Special care must be taken that the drivers are in-phase at the crossover points. This can all be done and good speaker brands get their act together, but some cheaper brands might not be so well designed.
- The crossover filters need some chunky capacitors and coils, especially at the lower crossover point. These parts need to handle some serious power. If there are resistors in the crossover network, they can get quite hot.
- If bipolar electrolytic capacitors are used in the crossover filter, they may change in value after a few years and go bad after a few decades. Nobody thinks about replacing these caps. People sometimes repair speaker cones or the rubber seals around them, but replacing capacitors?
- If there is a crossover point in the middle of the speech range, it affects sound quality where it matters most. There may not be an abrupt change in frequency response when the speaker is brand new, but their might be when components wear. It may be better to have crossover points <300 Hz and >3 kHz for this reason.\
You should probably never buy a speaker set from the catalogue alone, without listening to it. And if you do listen, do not just get carried away by the impressive bass and treble, but most importantly listen to midrange-heavy material, which should include vocals and preferably also speech. If you have a stereo recording of an on-stage dialogue, that should be perfect. If you play an instrument, listen to recordings of an instrument you know.
If you listen to other types of music, that are very heavy on bass and or treble, your priorities may differ of course.
Active Speakers
It helps if you put the power amplifiers inside the speaker cabinets and every single speaker gets its own power amplifier stage. When I talk about active speakers, I talk about a setup like this. Advantages of active speakers are:
- Each power amplifier can be coupled directly to a single driver unit, without long cables or passive crossover networks, therefore it can exercise good control over the speakers. Philips even had a transducer on the cone of the woofer, driving a closed loop control system to make the woofer behave itself. This was called MFB or Motional Feedback.
- As it now comes before the power stages, the crossover network can be an active filter with much tighter tolerances than a passive network. Components in the active filter do not have to handle any power.
- You can limit the drive strength of the tweeter amplifier so it will not burn the tweeter when there is clipping.
Of course, active speakers are expensive to build and complex to install. You need a power socket for each speaker and you still need cables for your signals and possibly for control. Of course you could go for wireless, but that it its own can of worms. Unless you have physical on-off switches on each separate speaker, they will draw standby current when not in use. When used with a generic preamp, those speakers will typically go into standby when there is silence for some time (for example 10 to 30 minutes) and they will wake up again when they get a strong enough signal. The need to wake them up before the music starts playing, can be annoying.
Surround Systems
In the early 2000s, the craze was surround sound. Suddenly everybody wanted to have a surround sound system to use with their DVD player and TV-set, turning the whole thing into a home cinema set.
I have seen some ultra cheap surround sets that made me laugh and cry at the same time. It came with 6 speakers: one so-called subwoofer that put out as much bass as a portable radio and five tiny speakers that sounded very tinny indeed. Their owners had tossed them all in the same corner, negating any surround effect they might provide. Needless to say: you are better off with a single soundbar or a pair of stereo speakers.
When done properly, surround sound can sound fantastic though. Good surround amplifiers come with measuring microphones to calibrate the signals to the speakers and adjust them for room acoustics and speaker placement. You will need good speakers in the front and centre positions and you do not want to rely on the subwoofer for all the bass.
For me it’s just not worth the expense (not just in terms of money but also in terms of speakers you need to place in your living room). SACD is dead now, so there are very few if any music releases on physical media that have surround sound. I seldom watch movies and when I do, a good stereo pair is all I need.