How does a speaker work?

Loudspeaker

Bowers & Wilkins 683.

Modern home theatres may be light years ahead of early entertainment systems in terms of both audio and video quality, but little has changed over the years when it comes to the physics of audio reproduction. The basic design of most mainstream loudspeakers still revolves around a cabinet, speaker drivers, and its electronics -- yes, there's a circuit board hidden inside your boom box. To guide you through both the jargon and construction of this important home theater component, here's our quick guide on the anatomy of a conventional loudspeaker.

The subject of this article will be the forthcoming Bowers & Wilkins (B&W) 683 speaker illustrated on the right. It's a three-way, front-ported floorstander equipped with a 25mm dome tweeter, a 150mm midrange driver and another two 165mm bass units. Already overwhelmed by the technicalities? Fear not -- read on for more details.

Drivers
They are the heart and soul of any speaker system. In a nutshell, these convert an electric signal from the amplifier to audible sound via magnet-driven drivers. Most of these can be categorized into one of four main types based on their coverage within the overall audio spectrum.

High-frequency (HF) driver a.k.a tweeter

Midrange driver

Low-frequency (LF) driver a.k.a woofer

High-frequency drivers: Also known as tweeters or HF drivers, these generate sharp pitch sounds of musical instruments and effects such as shattering glass. They are usually one inch or smaller in size and are made from materials including silk, titanium and various forms of polymer. The 683 uses a proprietary Nautilus tube-loaded, aluminium dome tweeter which is designed to minimise reflections from the rear of the unit.

Midrange drivers: These cover the vocal range which is most readily picked up by our ears. Their sizes lie between a tweeter and woofer, though there are exceptions such as the woven Kevlar variant sported here. Other materials favored by the vendors can vary from inexpensive paper to exotic birch wood.

Low-frequency drivers: These are larger LF siblings of their midrange counterparts, tasked to deliver the extra oomph in rock albums and movie soundtracks. Their ability to go deep is somewhat related to the cone size, and thus the amount of air they move. While their performances are adequate for most music, don't expect them to simulate the deepest effects in movies. Most home theatre setups -- regardless of cost -- can benefit from the addition of a dedicated subwoofer.

Full-range drivers: These are high- and midrange drivers rolled into one compact package. Usually found in smaller satellite speakers of the home-theater-in-a-box fame, they have to be paired with a dedicated subwoofer for balanced audio reproduction. Speakers by KEF, for example, incorporate the tweeter into the center of the woofer for a better 'sweet spot' -- which theoretically means more people in the room will hear a stereo image.

The various combinations of drivers determine the design of the speaker. Two-way speakers are equipped with tweeters and bass-enhanced midrange drivers, while a three-way equivalent will have all three variants fitted onboard. This convention is measured regardless of how many drivers a speaker has of the same type -- for example, the dual 165mm woofers in the B&W DM683 do not constitute a four-way design.

Bass reflex port


To work around the performance bottleneck of a small speaker cabinet and drivers, a bass reflex port can enhance low-frequency delivery. This is installed either on the front or the rear, and comes in single- or multiple-port configuration.

A catch for such a design -- versus a sealed cabinet -- is the possibility of port noise. This results in a 'huffing'-type sound, but the B&W port shown here is dimpled in order to reduce this effect. Rear ported speakers can tend to complicate installation because they need to be placed at least a metre from the wall in order to supply nimble, tight bass.

Many speakers come supplied with foam bungs to plug the bass reflex port in smaller rooms, and while you lose absolute depth this can cause the bass to become 'tighter'.

Cabinet

A cabinet, or enclosure, houses all the various components of the speaker system, and its construction -- particularly the internal volume -- is secondary only in importance to the performance of the drivers themselves. Floorstanders and larger bookshelf speakers, with their larger cabinets, are renowned for their full-bodied sound and excellent low frequency delivery. Size aside, the material rigidity and wall thickness are other important considerations.

Many premium models typically favor thick, real, solid wood for their proven sonic characteristics and desirable vibration-damping quality. Medium-density fiberboard or MDF is another popular choice among vendors, while chipboard is commonly used throughout the budget series.

Spring clip/binding post

These connections are a rare sight on mini stereos and HTIBs which usually come with attached cables. But settle for nothing less than a spring clip attachment if you are looking to upgrade your speakers later. They also allow experimentation with third-party cables if you are still on stock black and red equivalents.

One step up the performance hierarchy are binding posts -- capable of accepting bare wires or plug- and spade-terminated cables. Even better are the biwire (refer to the image on the left) or triwire versions. These provide an option for dedicated amplification to each driver. Metal jumpers are also factory-installed to enable conventional amplification.

Crossover circuit

Short of elaborating on the science behind a crossover circuit, just think of it as a junction box for splitting and channeling various audio bands to the relevant drivers -- for example, low and high frequencies to the tweeters and bass unit, respectively.

Ideally, the supplied signal should be split without any overlapping or gaps between the various bands. In reality, this is almost impossible and can result in issues such as bloated bass or "black holes" in the sound range.

Accessories

There are quite a number of accessories available for speakers. Spikes, brackets and purpose-built stands are just some traditional addons. Do keep a lookout for speakers with integrated threads and wells for spikes and wall-mounted installations. The former is particularly useful for ensuring adequate damping for maximized speaker driver performance. After all, without a solid foundation, the entire speaker will be vibrating in tune with the drivers' movements. This is something you should avoid if you are serious about getting the best out of your investment.

Ideally, the speaker's tweeters should be sitting at ear height. For floorstanding speakers this is not usually a problem, but it's worth investing in a pair of good, damped speaker stands for bookshelf speakers. Don't put these straight on the floor -- not only will the sound suffer but the sensitive tweeters can suffer irrepairable damage from being kicked or knocked.

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Add Your Comment 6


Post comment as
 

tomo posted a comment   

I have a pair of Sonic Renagade speakers which have inbuilr amp but now find I can not get them to work.could anyone help with any info

 

cat posted a comment   

yes, but i need to know the PHYSICS of the speaker how it all works, like the conversion of the electric signal to virbration etc...

 

i am sam posted a comment   

next time leave blue prints

 

Genre 1 posted a comment   

I'm beginnning to think I was born in the wrong era , it's all fascinating & very explanitory . MAKES IT LOOK EASY

 

Fujistix posted a comment   

Very informative topic but i want to understand how the crossover actually works?

 

cjb78 posted a comment   
Australia

I thought this article would tell me how a speaker actually worked and developed sound, not just tell me about it's bits & peices. Good explanation of them though.




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