Speakers are in every part of our lives, from the telephone and mobile phone, televisions, tablets and computers. They play such an important role, allowing us to communicate and to control what we hear and the way we hear it.
The speaker cone design we use today has been with us since the 1920s, and has changed very little from that original design. While many contenders have arrived to challenge along the way, none have been able to get near it for price and the faithfulness of its sound reproduction.
The mechanics of sound
A speaker's function is to convert an electrical AC signal into mechanical energy, which vibrates at various frequencies and pushes air. This multi frequency push of air (sound waves), is then interpreted by our eardrums as signals we can hear.
To do this, the electrical signal from the amplifier is connected to a coil, which is housed in the fixed magnetic field of a permanently fixed magnet. The constantly changing electrical signal from the AC signal wave causes the coil to move within that magnetic field, and the diaphragm or cone of the speaker is joined to this, so moves back and forth with the coil, creating sound waves through air movement.
Now this is fine for simple amplification or sound reproduction, as the frequency variations of most signals are not complex enough to require anything more than a single speaker driver. Guitar amplifiers are a good example of this, and often feature just a single speaker as the guitars frequency range is limited to a scale of 80hz to around 1200hz, dictated by its tuning and scale length.
If you were to compare this to say a Piano, which has a range of approximately 27hz - 4200hz, then you've more than tripled the frequency spread, and it's this spread, and the physical limitations of a speaker driver to quickly recreate such vastly different notes that dictates the need for a full range or multi speaker system to be used.
Taking the Piano example for instance, you are asking an electrical magnet and paper cone to move back and forward at 27 times per second, up to 4200 times per second, at the same time if you hit the lowest and highest keys together. Now it shouldn't take a genius to realise that's a pretty big ask from one device, and chances are it's going to either really struggle or just ignore one of the signals altogether.
The answer ?
The 2 way or 3 way speaker system gets around the limitations of any singular speaker driver by combining it in an enclosure with other units. These additional speakers will be of different design to the main driver, with their mechanical properties being designed to cater for a specific frequency range only and nothing outside of it. This gives your complex incoming signal the ability to be fully recreated under stable conditions, with each individual driver component not being stressed trying to cope with huge signal variations, so giving far far better definition and power handling, and clear sound reproduction.
How it works
For a full range or multi driver speaker system to work, the incoming AC signal is fed immediately into a crossover unit. This compact piece of circuitry is designed to filter the signal into high, middle and low frequencies which then can feed off to the appropriate driver. It does this by use of coils and resistors to either block or pass parts of the electrical signal. These units are carefully tuned to perform this separation with the minimum of loss to the dB level of the original signal.
The speakers then have a nice filtered and frequency banded signal to deal with instead of the raw original, which allows them to perform to their full potential.
This process, and the resulting sound output is also aided and enhanced greatly by the drivers location in the speaker cabinet, and the design of the cabinet itself, as speakers (woofers especially) produce just as much air pressure from the back as they do the front, so if the cabinet is sealed but internally open, that pressure is then pushing onto the rear of the midrange driver, and causing unwanted frequency cancellation. This is why you will see open ports or inlets on many speaker systems, as they are there to equalise and disperse that unwanted air mass from inside the cabinet, and often will actually enhance the clarity of the low end reproduction.
The three main players
The woofer, the mid and the tweeter. Most larger PA speakers these days are 3 way or ‘full range’, as this configuration gives you the best frequency and detail handling capabilities so lends itself to all musical types.
The main driver will be the woofer. On PA and live use speakers this will often be large, of 12 to 15 inch diameter in order to produce the larger SPL and low frequencies that are required of a party or professional environment, as the more air mass it can shift, the louder and more defined it will be.
Joined with a midrange driver, these will often be 2 to 4 inches diameter and are much more delicate than the woofer as they simply won't be required to deal with the larger electrical current or movement that the bass notes require. They will fill in everything from soft drum lines to a large part of the vocal spectrum, so play a hugely important role in the overall sound of a system, especially a larger live usage PA.
Topping things off, literally, is the tweeter, which is specifically designed to reproduce the high frequency parts of the incoming signal. It does so using the same electro-mechanical principles as the other drivers, though depending on the actual type and design of tweeter, the way in which it deals with the conversion can be done in several ways.
Though there are at least 8 proven commercial tweeter designs, most PA and live equipment will be found to use either the piezo ‘bullet’ type, or the larger horn type. The main reason for this is the dispersion characteristics, as both have a much larger ‘throw’ range than a conventional hi-fi style dome tweeter. Power handling is also a factor, as both have far more flexible loading capabilities compared to a dome type which is restricted by the dimensions and material construct of its driver.
Replace, repair or upgrade ?
Replacing damaged units, upgrading old systems, or completely building from scratch, the availability of individual speaker components has always allowed both easy refurbishment and self builds to suit all budgets and requirements, and there is a huge range of designs and brands on the market to suit your specific needs.
Most speaker components can be easily swapped out using similar or upgraded units, which means you don't have to completely replace a whole system just because of a damaged driver.
Upgrading cheaper systems with better quality woofer and tweeter units can give them a new lease of life for much less cost than buying new equipment.
Passive and active crossover units are available for both internal and external use, be it as replacements in a system, or as a new feature you are including as an upgrade.