Speakers 101: The Crossover

No, not Crossing Over... sorry to disappoint I do not know any speakers that possess the talents of John Edward (what happened to him anyway?).

Now that I think of it that show hasnt been made for almost a decade... time to move on perhaps...

The crossover is an electronic circuit that in laymans terms separates the amplified signal going to the speaker, so the high frequencies go to the Tweeter, the mid frequencies go to the mid drivers, and the low frequencies head to the subwoofer. In the case of my two-way project, I am just splitting the signal between the tweeter and the mid/bass driver.

Not exactly an ideal representation, but you get the idea... I hope.

Why use a crossover?

Crossovers are used for two main reasons:

1) Drivers that are designed to work in a 2 or 3 way system are built with a sweet spot in mind. When producing sounds outside of this frequency range, some drivers can develop distortion and other unwanted 'colourations'. Using a crossover you can avoid these nasties.

and 2) Driving frequencies outside of the optimal frequency range of the speakers can not only add nasties, but can also reduce how well they produce the frequencies within their optimal range.

So how does it work?

Crossovers are in their simplest form are made up of capacitors and inductors.

Keeping this as simplistic and untechnical as possible... perhaps not as untechnical as possible but pretty close.... heck untechnical apparently isn't even a word..... 

When an Alternating Current(like an audio signal) passes through a capacitor in a crossover, as the frequency decreases(as the sound gets lower) the signal that is allowed to pass through the capacitor is decreased, this, in effect, creates what is known as a high pass filter, as it allows the high frequencies/sounds to pass, yet blocks the lower frequencies. This makes capacitors highly effective on tweeters.

Oppositely, when an Alternating Current(like an audio signal) passes through an Inductor in a crossover, as the frequency increases the signal that is allowed to pass through the inductor decreases, this, in effect, creates what is known as a low pass filter, this time round the inductor allows the lower frequencies/sounds to pass while blocking the higher frequencies. This makes inductors good for use on subs/bass drivers.

The values of the capacitor or inductor will dictate the frequencies at which the signals will decrease, and ultimately will be determined by what works best with the drivers themselves. More advanced crossovers add more circuitry to further improve on overall speaker performance.

Don’t worry. I will build upon this overly simplistic introduction to crossovers in later posts.

Speakers 101: The Cab

This is part two of Speakers 101. A series of posts looking at the basics. 

Yesterday I looked at drivers, but what do you put your drivers into? The cabinet ofcourse.

The design of the cab is just as important as the drivers themselves. The speaker enclosure has a much more vital role to play than to just provide a mount for the drivers. Commonly there are three types of cab.

Naturally the following diagrams are representative of the two-way cab I'm designing.

 

Open Baffle Speaker-  This is not much more than the driver being mounted onto a piece of timber. The rear of the speaker is open, hence the name. This is considered to be the least efficient design as a lot sound and energy is projected from the rear of the speaker. Despite this some discerning Audiophiles argue they create an ‘honest’ sound. A lot of guitar amps are still made with this construction concept.

 

Closed Box/Infinite Baffle- One of the more common designs of speaker cab, the closed box is where the drivers are mounted in a box that is completely sealed. The sealed nature of the enclosure means that the pressures that the driver produces in the backwards direction are contained, which changes the performance of the driver dramatically.

 

Ported Box/Bass Reflex- Much like a closed box, but this time the cab has an air vent or port cut into the enclosure. Ported boxes allow for a more efficient and bigger bottom end through releasing some of the presure contained within cab, hence why this design is very common in subwoofers, but this comes at the cost of bottom end clarity, and generally an increase in cab size.

The ports themselves have to be tuned, both in diameter, length and shape to provide good results. A good sounding cab with the best drivers money can buy can be completely comprimised through poor design of the port.


Selecting the cabinet type, size and dimensions is a bit of a scientific process, further complicated by driver positioning and port dimensions. Something I'll surely go through on later posts. Next up is the final part of Speakers 101: The Crossover.

Speakers 101: Drivers

So before I delve into any of the over the top technical stuff, that makes me wish that I paid more attention in high school physics, I should really go over the basics of what goes into a speaker.

For the speaker I'm building, there are three basic components. The Drivers, the Cabinet itself, and the Crossover. 

This is part one of Speakers 101.

Drivers

Arguably the most important part of a speaker, the driver is the speaker part of a speaker.  

...Huh?

Well, they’re the (usually) round thing that vibrates(usually using some kind of electromagnet) in such a way as to produce sound. There are a handful of different classifications of drivers. To name the most common-

Full Range Drivers are designed to produce sound across the full range of frequencies. The problem with full range drivers is that it is very difficult to produce a driver that works well across the entire frequency range. So more often than not two or more drivers are used.

Tweeters are drivers that use up to 140 odd characters to gossip about celebrities, troll, and #usehashtags. No, really, tweeters are drivers that are designed to best handle sounds in the upper end of the frequency range.Theyre the little ones usually at the top of a speaker.

Mid-range Drivers, as the name suggests they best produce sounds in the middle of the audible range.

Subwoofers (or suuuubwooooffffeeerrrssss!) give that low end growl that you can feel. They operate in very low frequencies. They're usually given a bad name by the noise coming from that lowered Daihatsu Charades with sports spoiler, low profile tyres and a matte black paint job that pulled up next to you at the traffic lights last friday night(true story).

Driver selection plays a huge role in designing a speaker cab and are constructed in a variety of different ways, using a vast array of different materials that not only have an effect on the sound produced, but also impacts on what kind of use a driver is best suited for.

Tune in next time for a look at Speaker Cabinets!

It all Begins...

Building a speaker... sounds easy right... buy a couple drivers, build a couple boxes, fit them out, plug them in... should be simple...

photo credit: *MarS via photopin cc 

If it was that easy to make a good sounding speaker, every speaker cabinet on the planet would sound great... people wouldn’t be spending thousand on hifi systems to get a great sounding system. But it turns out speaker design is truly a craft in its own right. Every little design modification can fundamentally change the sound the speaker produces.

So, keeping that in mind, for a first go I have decided to follow the long held KISS approach... Keep It Simple Stupid.

I’m going to build a pair of two-way ‘Bookshelf Style’ speakers. This design allows me both to explore the design of a speaker cabinet itself, without building something large and cumbersome, and become initiated with the electronic concepts behind crossovers.

Over the coming posts I’ll be exploring the concepts and practicalities behind designing, building and tuning speakers as I go through the process for the first time myself. I hope you enjoy the ride.