Loudspeakers Explained — Why Speaker Design Is a Battle with Physics

Up until the mid-1970s, any audiophile would tell you that loudspeakers were by far the most important part of a hi-fi system. After all, they are the things that convert electrical music signals into physical air movement, right? Speakers can sound wildly different, it was argued, much more so than any other parts of the system chain – so they were surely the most critical to a system’s performance.

No one questioned this idea, as it was thought to be one of hi-fi’s universal truths. Even electronics manufacturers like QUAD’s highly respected Peter Walker famously said that amplifiers were just “a piece of wire with gain”. As for source components, it was widely thought that turntables were just there to do a job and didn’t much influence the overall sound of the system. Things only changed when Linn’s Ivor Tiefenbrun began to contradict this received wisdom around 1975, and used the old computer industry adage of “garbage in, garbage out” to suggest that a hi-fi system cannot give its best if the source isn’t up to scratch.

In truth, any audio system is only as good as its weakest link – be it turntable, DAC, amp or whatever. But there’s no denying that loudspeakers do have an exceptionally difficult job, as there is so much that can go wrong for them. Even in 2025, with all our fancy computer-aided design tools and modelling, it’s fair to claim that they are further away from being perfect than any other part of the system chain.

This is because speakers go into battle with the laws of physics in a most intimate and brutal way. For example, no matter how clever you are, you simply cannot get truly strong and deep bass from small standmounters, due to the physical limitations on how air is moved.

Loudspeaker design is therefore all about compromise – it’s a puzzle about how best to get decent results from a pair of room-friendly, reasonably affordable transducers that do the least amount of damage to what they’re being fed. The joy of speakers is that there are so many different ways of solving this particular problem, so audio enthusiasts are spoiled for choice. Read on for a basic grounding on this incredibly complicated subject…

HISTORY

Enzo Ferrari – hero of twentieth-century motorsport and sports car manufacturer extraordinaire – was born in 1898. This was the same year that Oliver Lodge invented the first dynamic loudspeaker. It wasn’t successful, but drew a line under earlier, very basic electric or compressed air types that had been in development since the 1870s – mostly for telephone applications. From then on, the focus would be on dynamic (also called moving coil) designs that are nearly universal in today’s hi-fi world.

It began with what we now take largely for granted, namely, the accurate reproduction of music in the home. By 1915, Peter L. Jensen and Edwin Pridham’s Magnavox company was making drive units for radios and public address systems. Then Edward W. Kellogg and Chester W. Rice produced the first large moving coil driver in 1925, and the audio world never looked back.

Dynamic speakers really came good in the nineteen thirties and forties. Most initially used electromagnets rather than permanent magnets, which weren’t widely available until the end of World War II, when alnico types arrived. In 1932, Gilbert Arthur Briggs founded Wharfedale Wireless Works in Yorkshire, England, and went on to play a major part in speaker development. He popularised the 2-way speaker – which sported a tweeter and a mid/bass drive unit – and the use of ceramic magnets. T

ogether with his friend Peter Walker of QUAD, he held a series of ‘live versus recorded’ music demonstrations which popularised high fidelity music reproduction – these were held in many venues, including London’s Royal Festival Hall and New York’s Carnegie Hall.

Cinema sound got a huge boost in 1943, with Altec Lansing’s powerful 604 coaxial duplex driver, and then cabinet design and loading improved in leaps and bounds in the next two decades. By the mid-sixties – just in time for The Beatles and the Rolling Stones – dynamic speakers were really beginning to sound good. Yet they were still a long way away from perfect, as the launch of QUAD’s ESL-57 had shown at the 1956 British Audio Fair. This ingenious electrostatic design delivered a far less coloured listening experience compared to conventional dynamic designs.

For many audiophiles, the seventies were when hi-fi speakers became respectable. This was driven in no small part by the BBC's Research Department, which harnessed new drivers coming out of companies such as KEF to great effect. The LS3/5a mini-monitor was a game-changer, thanks to its evenness and delicacy of tone – it showed that you didn’t need a full-range speaker to reproduce music enjoyably.

This is because much of what’s really important in music happens in the midband, where this little speaker thrived. The design was licensed to a number of manufacturers and created a demand for compact speakers that continues to this day.

That decade saw materials technology progressing rapidly. Yamaha’s 1974 NS-1000 was a landmark product, being the first speaker to use vapour-deposited beryllium treble and midrange dome drivers, which had far lower mass than conventional plastic or paper cones of the day. Its lightning-fast transient attack showed the importance of the time domain in reproducing music, and inspired countless subsequent designs. It went on to influence speaker design of the eighties, with iconic products like Celestion’s metal dome tweeter-equipped SL6 standmounter following suit.

Many British speaker manufacturers were beginning to adopt polypropylene for their bass and midrange cones around this time. This had superior breakup characteristics to the Bextrene-coned KEF drivers seen in BBC designs. Mission’s first 770 from 1976 was the talisman for this technology, and many rivals followed. By the mid-eighties, polypropylene was near-ubiquitous in hi-fi speaker cones, and continues to be used by the likes of Spendor Audio today. Not long after this, fabric dome tweeters began to be widely replaced by stiffer metal dome designs.

By the early eighties, nearly all commercial loudspeakers were dynamic types with two (or more) moving coil drive units, and small was beautiful. Products such as the original Wharfedale Diamond and Acoustic Energy AE1 became iconic for this reason. As cabinet sizes decreased, reflex loading became more widespread. Closed boxes had dominated seventies speaker design, but the extra bass extension and/or efficiency that ported designs gave appealed to buyers.

Loudspeaker development carried on apace in the nineties. At the start of the decade, small boxes sitting on 24-inch frame stands were all the rage. But by the turn of the century, things looked very different – as floorstanders became all-conquering. Mission’s 1994 753 epitomised this new approach, being a slimline ‘tower’ design that stood over one metre tall, with a narrow front baffle housing multiple, small-diameter drivers. This was the shape of things to come in the following decades, and since then, arguably, little has changed in mainstream speaker design.

The reason this hit the spot is that floorstanders offer better, and/or deeper bass, and/or superior efficiency and power handling compared to standmounters that take up the same space when on stands. This is because the greater cabinet volume of floorstanders gives the designer more scope for tuning, and the narrow front baffle helps to solve diffraction problems too, which makes for better stereo imaging. Last but not least, slimline tower-type speakers seem to be more domestically acceptable to spouses.

As testament to the importance of Mission in the nineties, the 753’s little brother was arguably even more innovative, as its single mid/bass driver used High Definition Aerogel cones. These were lighter and stiffer than the 753’s polypropylene types, and sparked a fashion for more exotic cone materials. Companies like Focal and Audax ran with this type of material, while B&W launched its Kevlar cones in a blaze of publicity. Even carbon-fibre made a comeback, last seen in the mid-seventies with Sony’s ‘Carbocon’ drivers in its SS-5050.

By the new millennium, every speaker manufacturer seemed to have its preferred cone material – everything from wood to metal to fibreglass was available. Yet in cabinet design, so much of what was being sold was basically small-footprint, narrow baffle floorstanders with multiple drivers – Mission 753-style. Then again, tweeters were becoming more diverse, and the market greeted affordable ribbon types and the new BMR (Balanced Mode Radiators) technology with glee. Focal JM Lab paid homage to Yamaha by introducing beryllium dome tweeters to its premium products.

And the average budget fare was now increasingly adopting silk dome, instead of metal dome, high-frequency units. By this time, aluminium or titanium domes – so sexy in the late eighties – had become old hat.

Since the turn of the century, there have been few radical new technologies. Like so much in life, designers have looked back to the past and simply tried to implement it better. That’s why we’ve seen the reappearance of transmission line designs, from PMC and Kerr Acoustics among others, with a cabinet loading system originally popularised in the late seventies by IMF’s TLS80 and its siblings. Crossovers have improved thanks to better, audiophile-grade passive components, and permanent magnet technology has developed apace – in turn delivering greater efficiency and power handling.

Don’t forget behind-the-scenes advances too, such as dramatically better computer-aided design software, which simplifies simulations and modelling. Finite element analysis existed as far back as the seventies, but it is way more powerful now, and a better understanding of Thiele/Small parameters has helped to optimise the relationship between bass drivers and speaker cabinets. For example, Bowers & Wilkins' Andy Kerr recently explained to StereoNET how his company is now far better able to measure and model the behaviour of loudspeakers in real-life conditions – and how that is making big differences to the way its speakers are developed.

DESIGN BASICS

People want to hear as much of the audio spectrum as possible, from low church organ notes to the highest hi-hat cymbal harmonics – in frequency terms, this equates to around 20Hz in the bass, to 20kHz in the treble. But that’s not always possible, due to the physical size of a speaker. For example, smaller standmounting types cannot really go below 50Hz – so the bottom string on a bass guitar (the low E is 41.2Hz) is a hard ask. Likewise, older people’s hearing doesn’t go much above 10kHz, so designing tweeters that only bats can enjoy isn’t usually a priority.

In truth, most listeners get most of their enjoyment from the midrange ‘presence’ region, where the human ear is most sensitive. For this reason, speaker design is all about balancing listeners’ priorities between bass, mid and treble. Here are the main ways this is done…

Full range designs

Single-driver loudspeakers employ just one cone and magnet assembly to handle the full frequency spectrum of music. They’re not always successful at this job, because no drive unit has yet been designed that works evenly from 20Hz in the bass to 20kHz in the treble – the commonly accepted limits of human hearing. So full range speakers inevitably offer curtailed bass – Eclipse’s TD510Z being a case in point.

The upside of this approach is that because no electrical crossover is needed, the speaker tends to sound purer and more musical – at least in the middle part of the audio band where the human ear is most sensitive.This is because crossovers can introduce phase issues, and/or not properly marry different drivers to one another, and full-range speakers bypass this issue, as well as offering greater efficiency due to not having a power-sapping crossover.

2-way loudspeakers

Most modern speakers are essentially 2-way designs, with a tweeter handling treble frequencies (roughly above 2 to 3kHz), and a mid/bass driver taking care of everything below. This is because it is physically impossible for single drivers to work optimally at bass frequencies (like 100Hz) and at high frequencies (like 10kHz). The benefit of 2-ways is that they're relatively inexpensive to make, and not as easy as 3-ways to get wrong. Sometimes you see speakers with twin bass units, which are still technically 2-ways, because their bass drivers run in parallel to share the work – the tweeter crosses over with the twin bass units.

Alternatively, 2.5-way designs are becoming increasingly popular now, with both mid/bass drivers starting at the lowest frequency band and one rolling off around 100 to 200Hz, and the other going all the way up to meet the tweeter. This is because additional power handling is only needed in the lowest octaves, where our ears are less sensitive, and the imaging can be made more precise with the upper mid/bass driver, which is closest to the tweeter, delivering the midband. Surprisingly good results can be had from 2-way types if the designer knows what they're doing, but implementation is critical. In absolute terms, however, 2-way cannot compete with proper multi-driver designs…

3-way loudspeakers

This is a more complex way of designing a loudspeaker, and more expensive to manufacture because an additional driver and usually a larger cabinet are required. 3-ways split the signal very approximately around 500Hz and 5kHz – with a dedicated driver handling that middle range, a bass driver handling sub-500Hz and the tweeter handling over 5kHz.

The major benefit is that the crossover point between the drive units is out of the sensitive upper midband ‘presence’ region to which the human ear is highly attuned. It moves the bass-to-midband crossover point lower, and the midband-to-treble crossover higher. Some speaker designs are even 4-ways, with an additional super-tweeter working above 15kHz or so, but these are rare nowadays.

Subwoofers

Subs are purpose-designed bass speakers, often in medium or large cabinets and equipped with their own active amplification. They’re designed to cover so-called ‘subsonic’ (i.e. ‘below sound’) frequencies which humans feel more than hear – namely 15Hz to 20Hz, but most go further up (often to 120Hz) to where the response of conventional speakers begins to fall off. Subwoofers normally come with controls to select the crossover point (i.e. the frequency below which they start working) and also the steepness of the roll-off above that. They usually feature large (10, 12 or 15-inch) drivers and come in either sealed cabinets or ported ones.

The former gives a tighter, faster bass, and the latter can often deliver more bass from any given size of cabinet. Subs should be used sparingly in specialist hi-fi applications, because they often cause more problems than they solve, and careful set-up is needed. More advanced designs also include variable phase controls, allowing the user to further optimise the integration of the subwoofer with the loudspeakers.

ACTIVE vs. PASSIVE

Conventional loudspeakers are passive, which is to say that they have an electrical crossover built into the cabinet, which divides up the signal from the power amplifier between the respective drive units. Active speakers take a line-level signal from a preamplifier and divide this up electronically, which is then amplified by power amplifiers. These power amps are often built into the speakers themselves, but not always.

The active approach can give substantially better sound quality when done properly, but has been slow to catch on in domestic hi-fi because manufacturers and dealers alike prefer to sell conventional speakers and amplifiers. Active operation is normal in pro audio, though – not least because they are easier to tune within a given environment – and for subwoofers, of course.

Some loudspeaker manufacturers, such as ATC, offer both active and passive versions of their products. As with everything in hi-fi, although the consensus is that active operation is better than passive, some designers, such as Vivid Audio’s Laurence Dickie believe that passive drive units are easier to integrate – even in his huge statement Moya M1.

DRIVER TYPES

Dynamic

There’s no mystery about how loudspeakers work – a low-voltage AC electrical signal is fed in, and they turn this into physical air movement through compression and rarefaction. The challenge is how best to do this, and by far the most popular method is the use of dynamic drive units, mounted in a box-like cabinet. These use a so-called ‘voice coil’ attached to a permanent magnet and a cone, which moves the air when fed by an electrical current from the amplifier.

Also called moving coil drivers, they’re relatively inexpensive to produce and can be optimised for bass or midrange applications fairly easily. When implemented properly, they can sound superb and shift huge amounts of air, which explains their ubiquity. In the words of Wharfedale’s Gilbert Briggs back in 1948, “it is clear that the moving coil system has no serious rival”.

Electrostatic

The most popular alternative to moving coil speakers, electrostatics are large, thin frames housing electrostatic transducer panels, which are bolted into place. The latter are pieces of film stretched on a sub-frame, in the way that a drum skin is tensioned by its chassis. These are excited in time with the music to move the air. Electrostatics require very high voltages to work, which is why they need to be plugged into AC mains power.

Done well, they can sound more delicate and smoother than conventional dynamic types – with better imaging and a very taut, crisp bass. Yet they’re expensive to manufacture and fussy with placement – usually requiring a largish room to give of their best because they’re dipole designs with a figure-of-8 response pattern, rather like a ribbon microphone.

They’re also limited in power handling and lack the ability to deliver strong bass. That’s why some companies – such as MartinLogan – produce impressive sounding electrostatic/dynamic hybrids, with a large electrostatic panel handling the treble and midband, and a conventional 12” driver taking care of bass.

Ribbon

This type of speaker is similar to an electrostatic in some ways, but uses multiple ribbon transducers to move the air instead of charged plastic film panels. Ribbon drivers are super-light pieces of metal film that are excited by strong permanent magnets to shift air. As a single ribbon cannot move much air, multiple drivers are needed – and/or an additional dynamic bass driver, which is much better suited to moving large amounts of air.

That’s why most ribbon designs are hybrids, although some pure ribbon speakers are made by the likes of Magnepan and Apogee Acoustics. Pure ribbon speakers are rare and expensive, and not ideally suited to high listening levels or bass reproduction, but can deliver sublime sound in smaller listening rooms. Hybrids with ribbon tweeters and conventional dynamic drivers can be effective, and are more practical and affordable – as QUAD’s Revela 1 shows.

Balanced Mode Radiator

BMRs were invented in the nineties and have been slow to achieve popularity, but are getting more common now. They use special diaphragms which are moved by magnetic ‘exciters’ to create sound. They come in relatively small sizes, optimised for treble/midrange or full range performance. Most popular in space-limited applications, they have also been incorporated into full-size hi-fi speakers.

A niche technology, BMRs cannot match the bass of dynamic drivers, which is why they’re commonly seen in smaller consumer audio products or as midrange and/or treble units in hybrid designs such as Cambridge Audio’s Aeromax 6. When properly implemented, they give a fast, expansive and delicate sound with little of the colouration associated with dynamic drivers. They sound quite electrostatic-like, in fact.

Compression

The earliest type of drive unit, and still popular up to the nineteen sixties, many audiophiles are still fans of compression elements mated to horn waveguides – especially at the high end of the market. A small compression driver radiates sound straight into the open air via a flared horn, which acts as a kind of ‘acoustic transformer’. In effect, it impedance-matches the drive unit’s dense diaphragm material to less dense atmospheric air, which in turn amplifies the signal.

This setup tends to be far more efficient than other driver types, which is why they first became prominent in public address applications such as sports stadiums and cinemas. The downside is the lumpy frequency response, which can be far less smooth and even than standard dynamic drivers.

CABINET MATERIALS

All dynamic speakers require box-type cabinets to achieve realistic sound pressure levels, bass extension and/or efficiency. It’s easy to test how well a cabinet is doing its job – just knock it with your knuckles. If the sound it makes is bright, and/or takes time to decay, then it is sub-optimal; ideally, you should hear a dull, quiet ‘thud’ that decays quickly. Results vary depending on the speaker you test, but how ‘quiet’ the cabinet is depends largely on the type of material used.

Cheap types like plastic or MDF are naturally resonant, whereas more expensive ones, such as wood or advanced composites, are much quieter – and so contribute less to the speaker’s final sound. Here are the main types of cabinet materials…

Plastic

Any loudspeaker with a plastic cabinet should arguably not be regarded as serious hi-fi. It’s highly likely it will have been designed to a very low budget and is probably just a basic consumer audio product. This is because it’s very hard to get the strength and rigidity out of a plastic moulding that’s possible from, say, a wood cabinet. The sound will likely be diffuse, nasal and hard. In general terms, you should walk away from speakers with plastic cabinets unless your budget is very low.

MDF

Medium-density fibreboard is the staple of modern budget hi-fi loudspeakers, and even some mid-price ones. A cheap material that’s used in inexpensive furniture, MDF is basically a composite of hard or soft wood residuals, held together by a resin or wax binder. When used for speaker cabinets, it has a certain sound that can manifest as a ‘squawk’ in the midband, and/or it can sound muddy in the bass – this is the result of the cabinet ‘ringing’ at certain frequencies. MDF’s relative lack of rigidity makes it an imperfect cabinet solution, yet careful internal damping can certainly help to limit this. It is used primarily for cost reasons, as major savings can be made over real wood cabinets.

Wood

A versatile raw material which comes in many types, weights, densities, etc., wood is used in everything from ships and buildings, to aeroplanes and furniture. Speakers with real wood cabinets – such as hardened birch ply, for example – tend to be far stiffer and less resonant than MDF. This is why most high-end speakers use real wood of some type, both for the cabinet and internal bracing.

Designers have their own views on the optimal thickness of cabinet walls – some British brands like Harbeth use thin but stiff wooden cabs, whereas others go for thickness and mass. B&W’s premium 800 Series, for example, uses thick, multilayer wood cabinets, whereas its entry-level 600 Series uses MDF. Any speaker with wood cabinets is also likely to have a real wood veneer finish, which has little real impact on sound quality.

Composites

There are a number of other approaches to making a quiet cabinet beyond simple MDF and wood. Many manufacturers have experimented with all sorts of composite materials over the years, and some have had great success. Vivid Audio, for example, uses glass-reinforced balsa cored sandwich composites, which permit the use of far more exotic shapes than conventional boxes, which in turn can reduce internal resonances or ‘standing waves’.

Other companies use concrete, or concrete and resin mixes, and others use variations of fibreglass; there’s a multiplicity of different approaches at the high end of the speaker market. One of the most expensive solutions is carbon-fibre, as used by Wilson Benesch, which gives an extremely quiet, precise and neutral sound.

Metal

As speaker manufacturers grappled to make better cabinets in the late seventies, some began to use aluminium, especially on smaller loudspeakers. This metal is relatively light yet rigid, which is why it’s popular in aerospace applications – but is more resonant than wood and so needs careful internal damping. All the same, it has proven to be quite popular, especially in pro audio applications – and near-field hi-fi.

One of the best-selling small speakers in history, for example, was the tiny, all-aluminium Realistic Minimus 7, which was produced in large quantities in the nineteen-eighties. The downside is that aluminium needs careful damping and is not cheap to work with. These days, high-end brands like YG Acoustics and Magico are great advocates of metal cabinet technology.

CABINET LOADING

Not all loudspeakers have cabinets, of course. Electrostatics like QUAD’s ESL-57 are basically frames that house transducer panels which emit sound front and back. But conventional speakers with dynamic drivers require boxy cabinets to ensure that the sound radiates forward correctly, and also to manage rearward energy from the drive units with equal amplitude but opposite phase. Successful speaker cabinets mitigate cancellation and provide the most coherent wavefront across the widest possible bandwidth.

Cabinet loading generally has the greatest impact on the bass performance of a loudspeaker, which becomes increasingly omnidirectional as the frequency decreases. This directly impinges on the ‘workload’ that the loudspeaker presents to the amplifier, in terms of sensitivity and impedance. There are several options available to a speaker designer here, all of which have pros and cons. Here are the most common…

Bass reflex

This type of cabinet loading method has an aperture cut into the cabinet, known as a bass reflex port. This is linked to what is typically a short tube of a specified length and diameter to achieve a certain tuning frequency. It lets the air that the speaker's drive units move inside the cabinet escape out into the room in a controlled way. It means that any given speaker of any particular size can move air around the room more easily than a closed box (or infinite baffle) one.

This, in turn, gives better sensitivity figures and/or more extended bass. The downside is that the port can create its own problems and cause ‘chuffing’ as the air moves noisily out of the speaker. It can also slow the bass down, if poorly implemented. Typically very efficient over a narrow frequency band, bass reflex designs are by far the most common type of hi-fi speaker today.

Closed baffle

Also known as ‘sealed box’, ‘air spring’ or ‘acoustic suspension’, this type of speaker does not ‘breathe’ out into the room via a port. Instead, the box is carefully sealed so all the energy produced (theoretically) goes into the forward-radiating drive units. This system is also referred to as ‘infinite baffle’, but technically, the latter type of loading is where the ‘enclosure’ is the room itself, with the rearward energy from the driver exiting into an entirely different room.

With closed baffle loading, compression effects exist, and this means that any speaker of a given cabinet size and drivers will have a lower sensitivity than a bass reflex ported version, and/or poorer bass extension – so it will need a more powerful amplifier.The upside is that all the issues with a reflex port are bypassed, which makes for a tighter, firmer and more controlled bass. This approach was popularised by Acoustic Research in the nineteen sixties and seventies, and is still common in studio monitor loudspeakers.

Transmission line

You could call this “the thinking man’s bass port”! It’s basically a long and complex chamber inside the cabinet that permits the flow of air from inside the speaker to the atmosphere outside, but manages it very carefully. It is possible to tune the chamber in such a way that the bass unit has less of an effect on frequencies higher up than a bass reflex port would. It also generally results in a cleaner and more extended low bass, as phase issues are better resolved. The downside of TLs is that they can be power-hungry, making them harder to drive properly than a bass reflex design.

Horn

This once-popular cabinet loading technique has staged something of a comeback recently. A horn-shaped structure is used to improve efficiency and direct sound output from a drive unit by coupling it to the air more effectively. Effectively a waveguide, the horn acts as an acoustic transformer, matching the high impedance of the driver to the lower impedance of the surrounding air.

This increases the sound pressure level and allows more of the driver's energy to be converted into audible sound rather than being lost as heat. The horn's shape usually flares out from a narrow throat to a wider mouth, and its profile carefully controls the dispersion of sound waves.It improves the speaker’s ability to project sound over greater distances or into specific areas, which is why it’s used in public address systems. The horn is usually fitted to the front baffle of the speaker, but rear horn loading has become popular with single-driver specialist designs.

Auxiliary bass radiator

Often called a passive radiator, this is basically a speaker drive unit with a cone but without the motor or voice coil. Used to boost low-frequency sound, an ABR complements the conventional bass driver by moving in response to air pressure changes caused by it, pushing extra air around the sealed box as it is usually tuned with to resonate at specific frequencies within the sealed cabinet, rather like a drum skin vibrating to amplify the beat.

The advantage of this approach is that it’s cheaper than having an additional active bass driver, yet it is often more controlled than a bass reflex port design. It was popularised by Celestion’s Ditton 15 in the mid-1970s, then fell out of favour – but is now coming back.

Isobaric

This ‘equal pressure’ speaker loading system pairs two identical drivers, one behind the other, working together to produce bass in a smaller cabinet. Both drivers move in sync, driven by the same signal, but the inner driver’s output is hidden inside the box. This setup keeps the air pressure between them constant, effectively halving the cabinet size needed for deep bass. The outer driver radiates sound, while the inner one reinforces it, delivering powerful low frequencies with less distortion.

It is highly effective at what it seeks to do, but the downside is that it’s an expensive and complex system that isn’t easy to implement – hence its comparative rarity. It also requires a powerful amplifier that drives low impedance loads comfortably. Linn popularised this approach with its big late-seventies Isobarik floorstanding design, and more recently NEAT has got great results with compact standmounters like the Ministra.

SPECIFICATIONS

Humans already possess the best guide to the sound of a loudspeaker, namely our ears. But measured performance can provide useful additional information, particularly where amplifier matching is concerned. So it’s good to understand how to read specifications, whilst taking them with a small pinch of salt – they don’t always tell the whole story…

Power handling

Measured in watts (W), this figure is widely quoted by manufacturers, yet it is not absolutely mission-critical. A speaker with a rated maximum input power of 100W is unlikely to self-destruct if you run a 130W amplifier with it – unless you’re working it at full volume all the time with bass-heavy music. More important is the minimum input power. For example, if 50W is quoted as being the lowest powered amplifier you can use, then a 25W design is going to be trying very hard at normal listening levels and may even distort. It is usually distortion (also called ‘clipping’) that kills speaker drive units, so this must be avoided.

Impedance

The impedance, measured in ohms, of a dynamic drive unit varies with the frequency it is reproducing, so it is never fixed. That’s why manufacturers often quoted a ‘nominal impedance’ figure that shows the general operating range of the speaker when playing music. The average impedance of modern speakers is between 6 and 8 ohms, which tallies with today’s solid-state power amplifiers, which are optimised to work into these loads.

Some speakers, however, can drop much lower when asked to reproduce bass, down to 2.5 ohms in some cases. These are often smaller designs using infinite baffle loading, but not always. So care must be taken to use a suitably powerful amplifier that is stable into low loads, with speakers such as these.

Sensitivity

Measured in decibels (dB, normally at 1W at 1 metre), the sensitivity of a speaker is just as important as its power handling or nominal impedance. The figure tells you how loud the speaker will go for a given amount of power. The average figure is around 88dB, but is often 3dB lower for smaller standmount speakers, and can be much higher for speakers with large cabinets.

In extreme cases, petite infinite baffle mini monitors are as low as 82dB/1W/1m, or large horn speakers such as the Klipsch La Scala AL5 can be as high as 105dB. Generally, closed box loading either lowers a speaker’s sensitivity or its nominal impedance, or a bit of both – so higher powered amplifiers are recommended. Conversely, you should always try to match low-powered amplifiers to higher sensitivity speakers.

Frequency response

The frequency response of a loudspeaker, measured in Hertz (Hz), also known as cycles per second (cps), tells you how low and high it will go. 20Hz to 20kHz has traditionally been regarded as the maximum limits of lower and upper human hearing, respectively, although in practice, there is little information at these frequency extremes.

In reality, the smoothness of the speaker as it goes from low to high is more important, and designs which have peaks and troughs are to be avoided, as they’ll emphasise or obscure certain instruments or vocal ranges. The midrange (‘presence’) region is where the human ear is most sensitive, as that is the register of our own voices. So speakers with limited frequency responses – i.e. 60Hz to 15kHz – can still audition well if they measure smoothly between these points.

Sound pressure level

The maximum level of sound that a speaker can put out is measured in dB. Serious high-end speakers normally have a sound pressure level of around 120dB, lesser ones can be closer to 105dB, and it all depends on the type of drivers and cabinet loading – horn speakers do well here. Yet again, SPL can be a bit academic for most domestic hi-fi listeners who are unlikely to hit the maximum SPL of their speakers unless they’re deaf and/or enjoy very loud parties. Most musical listening goes on at around 95dB, or less, so the maximum sound pressure level of a speaker will not be a key consideration to most listeners.

THE VERDICT

What constitutes a great loudspeaker? That’s an easy question to ask, but a much harder one to answer! The immediate reply must be, “Great for whom?” At the drawing board stage, speaker designers need a clear idea of who it is being built for, how large their listening room is, what their favourite music is, what amplifier they’re likely to be using, and most importantly, what their budget is. When all the above is clear, it’s a case of using design best practices to meet those goals.

Loudspeaker designers then have to work within the rules of physics to get the job done. A rigid cabinet is needed to house the drive units, one that is as non-resonant as possible. High-quality drivers with light diaphragms for fast transient response and low distortion should be chosen. And these must be knitted together by a well-tailored crossover that uses good quality components. And from here on in, the devil is in the detail.

It’s all about getting a great sound in a practical package at a good price. That’s why there is no substitute for auditioning a loudspeaker with your own ears when seeking to buy, as there are so many variables involved. Good luck with your search!

Continue the discussion